Both the attribution of historical change and future projections of droughts rely heavily on climate modeling. However,reasonable drought simulations have remained a challenge, and the related performances of the curr...Both the attribution of historical change and future projections of droughts rely heavily on climate modeling. However,reasonable drought simulations have remained a challenge, and the related performances of the current state-of-the-art Coupled Model Intercomparison Project phase 6(CMIP6) models remain unknown. Here, both the strengths and weaknesses of CMIP6 models in simulating droughts and corresponding hydrothermal conditions in drylands are assessed.While the general patterns of simulated meteorological elements in drylands resemble the observations, the annual precipitation is overestimated by ~33%(with a model spread of 2.3%–77.2%), along with an underestimation of potential evapotranspiration(PET) by ~32%(17.5%–47.2%). The water deficit condition, measured by the difference between precipitation and PET, is 50%(29.1%–71.7%) weaker than observations. The CMIP6 models show weaknesses in capturing the climate mean drought characteristics in drylands, particularly with the occurrence and duration largely underestimated in the hyperarid Afro-Asian areas. Nonetheless, the drought-associated meteorological anomalies, including reduced precipitation, warmer temperatures, higher evaporative demand, and increased water deficit conditions, are reasonably reproduced. The simulated magnitude of precipitation(water deficit) associated with dryland droughts is overestimated by 28%(24%) compared to observations. The observed increasing trends in drought fractional area,occurrence, and corresponding meteorological anomalies during 1980–2014 are reasonably reproduced. Still, the increase in drought characteristics, associated precipitation and water deficit are obviously underestimated after the late 1990s,especially for mild and moderate droughts, indicative of a weaker response of dryland drought changes to global warming in CMIP6 models. Our results suggest that it is imperative to employ bias correction approaches in drought-related studies over drylands by using CMIP6 outputs.展开更多
Livestock grazing is the most extensive land use in global drylands and one of the most extensive stressors of biological soil crusts(biocrusts).Despite widespread concern about the importance of biocrusts for global ...Livestock grazing is the most extensive land use in global drylands and one of the most extensive stressors of biological soil crusts(biocrusts).Despite widespread concern about the importance of biocrusts for global carbon(C)cycling,little is known about whether and how long-term grazing alters soil organic carbon(SOC)stability and stock in the biocrust layer.To assess the responses of SOC stability and stock in the biocrust layer to grazing,from June to September 2020,we carried out a large scale field survey in the restored grasslands under long-term grazing with different grazing intensities(represented by the number of goat dung per square meter)and in the grasslands strictly excluded from grazing in four regions(Dingbian County,Shenmu City,Guyuan City and Ansai District)along precipitation gradient in the hilly Loess Plateau,China.In total,51 representative grassland sites were identified as the study sampling sites in this study,including 11 sites in Guyuan City,16 sites in Dingbian County,15 sites in Shenmu City and 9 sites in Ansai District.Combined with extensive laboratory analysis and statistical analysis,at each sampling site,we obtained data on biocrust attributes(cover,community structure,biomass and thickness),soil physical-chemical properties(soil porosity and soil carbon-to-nitrogen ratio(C/N ratio)),and environmental factors(mean annual precipitation,mean annual temperature,altitude,plant cover,litter cover,soil particle-size distribution(the ratio of soil clay and silt content to sand content)),SOC stability index(SI)and SOC stock(SOCS)in the biocrust layer,to conduct this study.Our results revealed that grazing did not change total biocrust cover but markedly altered biocrust community structure by reducing plant cover,with a considerable increase in the relative cover of cyanobacteria(23.1%)while a decrease in the relative cover of mosses(42.2%).Soil porosity and soil C/N ratio in the biocrust layer under grazing decreased significantly by 4.1%–7.2%and 7.2%–13.3%,respectively,compared with those under grazing exclusion.The shifted biocrust community structure ultimately resulted in an average reduction of 15.5%in SOCS in the biocrust layer under grazing.However,compared with higher grazing(intensity of more than 10.00 goat dung/m2),light grazing(intensity of 0.00–10.00 goat dung/m2 or approximately 1.20–2.60 goat/(hm2•a))had no adverse effect on SOCS.SOC stability in the biocrust layer remained unchanged under long-term grazing due to the offset between the positive effect of the decreased soil porosity and the negative effect of the decreased soil C/N ratio on the SOC resistance to decomposition.Mean annual precipitation and soil particle-size distribution also regulated SOC stability indirectly by influencing soil porosity through plant cover and biocrust community structure.These findings suggest that proper grazing might not increase the CO_(2) release potential or adversely affect SOCS in the biocrust layer.This research provides some guidance for proper grazing management in the sustainable utilization of grassland resources and C sequestration in biocrusts in the hilly regions of drylands.展开更多
Drylands are among those regions most sensitive to climate and environmental changes and human-induced perturbations.The most widely accepted definition of the term dryland is a ratio,called the Surface Wetness Index(...Drylands are among those regions most sensitive to climate and environmental changes and human-induced perturbations.The most widely accepted definition of the term dryland is a ratio,called the Surface Wetness Index(SWI),of annual precipitation to potential evapotranspiration(PET)being below 0.65.PET is commonly estimated using the Thornthwaite(PET Th)and Penman–Monteith equations(PET PM).The present study compared spatiotemporal characteristics of global drylands based on the SWI with PET Th and PET PM.Results showed vast differences between PET Th and PET PM;however,the SWI derived from the two kinds of PET showed broadly similar characteristics in the interdecadal variability of global and continental drylands,except in North America,with high correlation coefficients ranging from 0.58 to 0.89.It was found that,during 1901–2014,global hyper-arid and semi-arid regions expanded,arid and dry sub-humid regions contracted,and drylands underwent interdecadal fluctuation.This was because precipitation variations made major contributions,whereas PET changes contributed to a much lesser degree.However,distinct differences in the interdecadal variability of semi-arid and dry sub-humid regions were found.This indicated that the influence of PET changes was comparable to that of precipitation variations in the global dry–wet transition zone.Additionally,the contribution of PET changes to the variations in global and continental drylands gradually enhanced with global warming,and the Thornthwaite method was found to be increasingly less applicable under climate change.展开更多
Drylands refer to regions with an aridity index lower than 0.65,and billions of people depend on services provided by the critically important ecosystems in these areas.How ecosystem carbon exchange in global drylands...Drylands refer to regions with an aridity index lower than 0.65,and billions of people depend on services provided by the critically important ecosystems in these areas.How ecosystem carbon exchange in global drylands(CED)occurs and how climate change affects CED are critical to the global carbon cycle.Here,we performed a comprehensive bibliometric study on the fields of annual publications,marked journals,marked institutions,marked countries,popular keywords,and their temporal evolution to understand the temporal trends of CED research over the past 30 a(1991-2020).We found that the annual scientific publications on CED research increased significantly at an average growth rate of 7.93%.Agricultural Water Management ranked first among all journals and had the most citations.The ten most productive institutions were centered on drylands in America,China,and Australia that had the largest number and most citations of publications on CED research."Climate change"and climate-related(such as"drought","precipitation","temperature",and"rainfall")research were found to be the most popular study areas.Keywords were classified into five clusters,indicating the five main research focuses on CED studies:hydrological cycle,effects of climate change,carbon and water balance,productivity,and carbon-nitrogen-phosphorous coupling cycles.The temporal evolution of keywords further showed that the areas of focus on CED studies were transformed from classical pedology and agricultural research to applied ecology and then to global change ecological research over the past 30 a.In future CED studies,basic themes(such as"water","yield",and"salinity")and motor themes(such as"climate change","sustainability",and"remote sensing")will be the focus of research on CED.In particular,multiple integrated methods to understand climate change and ecosystem sustainability are potential new research trends and hotspots.展开更多
Drylands are highly vulnerable to climate change and human activities.The drylands of China account for approximately 10.8%of global drylands,and China is the country most severely affected by aridity in Asia.Therefor...Drylands are highly vulnerable to climate change and human activities.The drylands of China account for approximately 10.8%of global drylands,and China is the country most severely affected by aridity in Asia.Therefore,studying the spatial variation characteristics in soil multifunctionality(SMF)and investigating the driving factors are critical for elucidating and managing the functions of dryland ecosystems in China.Based on the environmental factors(mean annual precipitation(MAP),mean annual temperature(MAT),solar radiation(Srad),soil acidity(pH),enhanced vegetation index(EVI),and cation exchange capacity(CEC))and aridity from the“dataset of soil properties for land surface modeling over China”,we used non-linear regression,ordinary least square(OLS)regression,structural equation model(SEM),and other analytical methods to investigate the relationships of SMF with environmental factors across different aridity levels in China.SMF in different dryland regions varied significantly and showed a patchy distribution,with SMF index values ranging from–1.21 to 2.42.Regions with SMF index values from–0.20 to 0.51 accounting for 63.0%of dryland area in China.OLS regression results revealed that environmental factors like MAP,MAT,Srad,pH,EVI,and CEC were significantly related to SMF(P<0.05).MAP and MAT were correlated to SMF at the whole aridity level(P<0.05).SEM results showed that the driving factors of SMF differed depending on the aridity level.Soil pH was the strongest driving factor of SMF when the aridity was less than 0.80(P<0.001).Both soil CEC and EVI had a positive effect on SMF when aridity was greater than 0.80(P<0.01),with soil CEC being the strongest driving factor.The importance ranking revealed that the relative importance contribution of soil pH to SMF was greatest when aridity was less than 0.80(66.9%).When aridity was set to greater than 0.80,the relative importance contributions of CEC and EVI to SMF increased(45.1%and 31.9%,respectively).Our findings indicated that SMF had high spatial heterogeneity in drylands of China.The aridity threshold controlled the impact of environmental factors on SMF.展开更多
Carbon sequestration is one of the important ecosystem services provided by forested landscapes. Dry forests have high potential for carbon storage. However, their potential to store and sequester carbon is poorly und...Carbon sequestration is one of the important ecosystem services provided by forested landscapes. Dry forests have high potential for carbon storage. However, their potential to store and sequester carbon is poorly understood in Kenya. Moreover, past attempts to estimate carbon stock have ignored drylands ecosystem heterogeneity. This study assessed the potential of Mukogodo dryland forest-landscape in offsetting carbon dioxide through carbon sequestration and storage. Four carbon pools (above and below ground biomass, soil, dead wood and litter) were analyzed. A total of 51<span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">(400</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">m<sup>2</sup>) sample plots were established using stratified-random sampling technique to estimate biomass across six vegetation classes in three landscape types (forest reserve, ranches and conservancies) using nested-plot design. Above ground biomass was determined using generalized multispecies model with diameter at breast height, height and wood density as variables. Below ground, soil, litter and dead wood biomass;carbon stocks and carbon dioxide equivalents (CO<sub>2eq</sub>) were estimated using secondary information. The CO<sub>2eq</sub> was multiplied by current prices of carbon trade to compute carbon sequestration value. Mean ± SE of biomass and carbon was determined across vegetation and landscape types and mean differences tested by one-way Analysis of Variance. Mean biomass and carbon was about 79.15 ± 40.22</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TB</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha</span></span></span><span style="font-size:10px;"><span style="vertical-align:super;">-</span></span><span><span><span style="font-family:;" "=""><sup>1</sup> and 37.25 ± 18.89</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;">-</span>1</sup> respectively. Cumulative carbon stock was estimated at 682.08</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;">-</span>1</sup>;forest reserve (251.57</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup>-1</sup>) had significantly high levels of carbon stocks compared to ranches (209.78</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;white-space:normal;">-</span>1</sup>) and conservancies (220.73</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;white-space:normal;">-</span>1</sup>, <i>P</i> = 0.000). Further, closed forest significantly contributed to the overall biomass and carbon stock (58%). The carbon sequestration potential was about 19.9MTCO<sub>2eq</sub> with most conservative worth of KES 39.9B (US$40M) per annum. The high carbon stock in the landscape shows the potential of dryland ecosystems as carbon sink for climate change mitigation. However, for communities to benefit from bio-carbon funds in future, sustainable landscape management and restorative measures should be practiced to enhance carbon storage and provision of other ecosystem services.</span></span></span>展开更多
Droughts are one of the climate extremes that occur frequently in drylands,constraining the terrestrial carbon uptake and water cycle processes.Studies about the long-term changes in the effect of drought stress on dr...Droughts are one of the climate extremes that occur frequently in drylands,constraining the terrestrial carbon uptake and water cycle processes.Studies about the long-term changes in the effect of drought stress on dryland ecosystems under global warming are still insufficient so far.Here we comprehensively investigate long-term changes in droughts and the effect of drought stresses on ecosystems across global drylands for 1982–2015,and further reveal changes in the configurations of the key meteorological and ecological factors of droughts,by using observation and reanalysis datasets.Climatically,the spatial patterns of intensity,occurrence,duration and severity of all drought categories across global drylands are highly consistent with each other.Associated with severe droughts,drylands witness insufficient precipitation(-12.4 mm mon^(-1)area-averaged over global drylands),warmer temperature(0.6℃),water deficit(-19.0 mm mon^(-1)),higher atmospheric aridity(0.06 k Pa),lower soil moisture(-0.03 m^(3)m^(-3)),suppressed vegetation growth and declined carbon uptake(-0.13 g C m^(-2)d^(-1)).The affected area,occurrence,duration and severity for mild to severe droughts in drylands and the anomalies of meteorological and ecological factors for all drought categories have increased significantly during 1982-2015.Specifically,when droughts occur,the precipitation deficit is weakened at a rate of 3.7–9.6 mm mon^(-1)(30 yr)^(-1),the higher temperature(atmospheric aridity)is further intensified at 0.71–0.87-1(30 yr)^(-1)(39–47 Pa(30 yr)^(-1)),the water(soil moisture)deficit is relieved at 1.7–5.1 mm mon^(-1)(30yr)^(-1)(4.1×10^(-3)–7.4×10^(-3)m^(3)m^(-3)(30 yr)^(-1)),and the suppressed vegetation growth is generally alleviated at 0.98×10^(-2)–1.2×10^(-2)(30 yr)^(-1).Since the 2000s,the increasing trend in the suppressed vegetation growth during droughts tends to stagnate over about 50%of the dryland area.By checking the probability density function,the configurations of the key meteorological and ecological factors of droughts show significant differences between the periods before and after 2000.The probability of drought stress caused by precipitation and soil moisture deficit has decreased by 20%and 10%,respectively,while that caused by higher temperature and atmospheric aridity has been doubled,and increased by 26%and 15%,respectively.Thus,the impact of drought stress on dryland ecosystems caused by atmospheric aridity are increasing under global warming.展开更多
Since Shi et al.proposed that the climate in the drylands of Northwest China experienced a significant transition from a“warming and drying”trend to a“warming and wetting”trend in the 1980s,researchers have conduc...Since Shi et al.proposed that the climate in the drylands of Northwest China experienced a significant transition from a“warming and drying”trend to a“warming and wetting”trend in the 1980s,researchers have conducted numerous studies on the variations in precipitation and humidity in the region and even in arid Central Asia.In particular,the process of the“warming and wetting”trend by using obtained measurement data received much attention.However,there remain uncertainties about whether the“warming and wetting”trend has paused and what its future variations may be.In this study,we examined the spatiotemporal variations in temperature,precipitation,the aridity index(AI),vegetation,and runoff during 1950-2019.The results showed that the climate in the drylands of Northwest China and the northern Tibetan Plateau is persistently warming and wetting since the 1980s,with an acceleration since the 1990s.The precipitation/humidity variations in North China,which are mainly influenced by summer monsoon,are generally opposite to those in the drylands of Northwest China.This reverse change is mainly controlled by an anomalous anticyclone over Mongolia,which leads to an anomalous easterly wind,reduced water vapor output,and increased precipitation in the drylands of Northwest China.While it also causes an anomalous descending motion,increased water vapor divergence,and decreased precipitation in North China.Precipitation is the primary controlling factor of humidity,which ultimately forms the spatiotemporal pattern of the“westerlies-dominated climatic regime”of antiphase precipitation/humidity variations between the drylands of Northwest China and monsoonal region of North China.The primary reasons behind the debate of the“warming and wetting”trend in Northwest China were due to the use of different time series lengths,regional ranges,and humidity indices in previous analyses.Since the EC-Earth3 has a good performance for simulating precipitation and humidity in Northwest and North China.By using its simulated results,we found a wetting trend in the drylands of Northwest China under low emission scenarios,but the climate will gradually transition to a“warming and drying”trend as emissions increase.This study suggests that moderate warming can be beneficial for improving the ecological environment in the drylands of Northwest China,while precipitation and humidity in monsoon-dominated North China will persistently increase under scenarios of increased emissions.展开更多
Much of drylands has been hit by land degradation during the recent decades.But whether and how desertification is related to climate change is poorly understood.Here,using the Normalized Difference Vegetation Index(N...Much of drylands has been hit by land degradation during the recent decades.But whether and how desertification is related to climate change is poorly understood.Here,using the Normalized Difference Vegetation Index(NDVI)time series and climatic variables,we assessed the desertification dynamics over China's drylands from 1982 to 2016 and explored the climate change impacts,with a particular focus on the influence of the 2015/2016 El Niño event.We found a fluctuant downward trend of barren land area from 1982 to the early 2010s,but followed by a sharp increase afterwards.Decrease in precipitation combined with high temperature are major contributors to the barren land expansion.During the 2015/2016 El Niño,the concurrence of severe drought and heat stress gave rise to the most serious land desertification in the record.Hyper-arid and arid drylands are the predominant contributors to the abrupt barren land area increase during 2015/2016.Our findings,therefore,highlight the climate change impacts on dryland desertification processes.Future dryland expansion and accompanying drought stress may exacerbate the risk of land degradation in these regions.展开更多
Drylands account for approximately 41% of the global total land area. Significant warming and rare precipitation in drylands result in a fragile ecology and deterioration of the living environment, making it more sens...Drylands account for approximately 41% of the global total land area. Significant warming and rare precipitation in drylands result in a fragile ecology and deterioration of the living environment, making it more sensitive to global climate change. As an important regulator of the Earth's climate system, the oceans play a vital role in the process of climate change in drylands. In modern climate change in particular, the impact of marine activities on climate change in drylands cannot be neglected. This paper reviews the characteristics of climate change in drylands over the past 100 years, and summarizes the researches conducted on the impact of marine activities on these changes. The review focuses on the impact of the Pacific Decadal Oscillation(PDO), Atlantic Multidecadal Oscillation(AMO), El Ni?o and La Ni?a on climate change in drylands, and introduces the mechanisms by which different oceanic oscillation factors synergistically affect climate change in drylands.Studies have shown that global drylands have experienced a significant intensification in warming in the past 100 years, which shows obvious characteristics of interdecadal dry/wet variations. The characteristics of these changes are closely related to the oscillatory factors of the oceanic interdecadal scale. Different phase combinations of oceanic oscillation factors significantly change the land-sea thermal contrast, which in turn affects the westerly jet, planetary wave and blocking frequency, resulting in changes in the temperature and dry/wet characteristics of drylands. With the intensification of climate change in drylands, the impact of marine activities on these regions will reveal new characteristics in the future, which will increase the uncertainty of future climate change in drylands and intensify the impact of these drylands on global climate.展开更多
Upland rice shows dryland adaptation in the form of a deeper and denser root system and greater drought resistance than its counterpart,irrigated rice.Our previous study revealed a difference in the frequency of the O...Upland rice shows dryland adaptation in the form of a deeper and denser root system and greater drought resistance than its counterpart,irrigated rice.Our previous study revealed a difference in the frequency of the OsNCED2 gene between upland and irrigated populations.A nonsynonymous mutation(C to T,from irrigated to upland rice)may have led to functional variation fixed by artificial selection,but the exact biological function in dryland adaptation is unclear.In this study,transgenic and association analysis indicated that the domesticated fixed mutation caused functional variation in OsNCED2,increasing ABA levels,root development,and drought tolerance in upland rice under dryland conditions.OsNCED2-overexpressing rice showed increased reactive oxygen species-scavenging abilities and transcription levels of many genes functioning in stress response and development that may regulate root development and drought tolerance.OsNCED2^(T)-NILs showed a denser root system and drought resistance,promoting the yield of rice under dryland conditions.OsNCED2^(T)may confer dryland adaptation in upland rice and may find use in breeding dryland-adapted,water-saving rice.展开更多
Water is the key factor limiting dryland wheat grain yield.Mulching affects crop yield and yield components by affecting soil moisture.Further research is needed to determine the relationships between yield components...Water is the key factor limiting dryland wheat grain yield.Mulching affects crop yield and yield components by affecting soil moisture.Further research is needed to determine the relationships between yield components and soil moisture with yield,and to identify the most important factor affecting grain yield under various mulching measures.A long-term 9-yearifeld experiment in the Loess Plateau of Northwest China was carried out with three treatments:no mulch (CK),plastic mulch (M_(P)) and straw mulch (M_(S)).Yield factors and soil moisture were measured,and the relationships between them were explored by correlation analysis,structural equation modeling and significance analysis.The results showed that compared with CK,the average grain yields of M_(P) and M_(S) increased by 13.0and 10.6%,respectively.The average annual grain yield of the M_(P) treatment was 134 kg ha^(–1) higher than the M_(S) treatment.There were no significant differences in yield components among the three treatments (P<0.05).Soil water storage of the M_(S) treatment was greater than the M_(P) treatment,although the differences were not statistically signifiant.Soil water storage during the summer fallow period (SWSSF) and soil water storage before sowing (SWSS) of M_(S) were significantly higher than in CK,which increased by 38.5 and 13.6%,respectively.The relationship between M_(P) and CK was not statistically significant for SWSSF,but the SWSS in M_(P) was significantly higher than in CK.In terms of soil water storage after harvest (SWSH) and water consumption in the growth period(ET),there were no signi?cant differences among the three treatments.Based on the three analysis methods,we found that spike number and ET were positively correlated with grain yield.However,the relative importance of spike number to yield was the greatest in the M_(P )and M_(S) treatments,while that of ET was the greatest in CK.Suifcient SWSSF could indirectly increase spike number and ET in the three treatments.Based on these results,mulch can improve yield and soil water storage.The most important factor affecting the grain yield of dryland wheat was spike number under mulching,and ET with CK.These findings may help us to understand the main factors influencing dryland wheat grain yield under mulching conditions compared to CK.展开更多
Tillage practices during the fallow period benefit water storage and yield in dryland wheat crops.However,there is currently no clarity on the responses of soil organic carbon(SOC),total nitrogen(TN),and available nut...Tillage practices during the fallow period benefit water storage and yield in dryland wheat crops.However,there is currently no clarity on the responses of soil organic carbon(SOC),total nitrogen(TN),and available nutrients to tillage practices within the growing season.This study evaluated the effects of three tillage practices(NT,no tillage;SS,subsoil tillage;DT,deep tillage)over five years on soil physicochemical properties.Soil samples at harvest stage from the fifth year were analyzed to determine the soil aggregate and aggregate-associated C and N fractions.The results indicated that SS and DT improved grain yield,straw biomass and straw carbon return of wheat compared with NT.In contrast to DT and NT,SS favored SOC and TN concentrations and stocks by increasing the soil organic carbon sequestration rate(SOCSR)and soil nitrogen sequestration rate(TNSR)in the 0-40 cm layer.Higher SOC levels under SS and NT were associated with greater aggregate-associated C fractions,while TN was positively associated with soluble organic nitrogen(SON).Compared with DT,the NT and SS treatments improved soil available nutrients in the 0-20 cm layer.These findings suggest that SS is an excellent practice for increasing soil carbon,nitrogen and nutrient availability in dryland wheat fields in North China.展开更多
Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to ...Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to dry land degradation in the southwestern United States is reported.The local NPP scaling(LNS)approach was applied to map the extent and magnitude of degrada tion.LNS seeks to identifty reference sites in which there is no degradation that can be used as a standard for comparison with other sites that share the same environment,except for degradation.Twelve years were analyzed(2000--2011),using Normalized Difference Vegetation Index(NDVI)data(250 m)from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite-borne multispectral sensor.The results indicated that the total NPP reductions in the study area were about35.9±4.7Tg C/yr,which equates to 0.31±0.04 Mg C·ha^(-1)· yr^(-1).The NPP reductions in grassland-savanna and livestock grazing areas were large and mostly consistent between years in spite of large variations in overall NPP caused by differences in land-use,interannual variations in rainfall,and other aspects of weather.In comparison with other cover types,forested land generally had higher NPP reduction per unit area.The maps also enable attribution of degradation from the finest management units to entire agencies,such as the Bureau of Land Management,which had 50%less production per unit area than the U.S.Forest Service.The degradation within Native American land was low with total NPP reduction of about 2.41±0.24 Tg C/yr and unit area reduction of productivity of just 0.21±0.02 Mg C·ha^(-1)·yr^(-1),yet the percent reduction from potential was in equivalence with other land management agencies.展开更多
Water resource availability is the major limiting factor for sustainable development in drylands.Climate change intensifies the conflicting water demands between people and the environment and highlights the importanc...Water resource availability is the major limiting factor for sustainable development in drylands.Climate change intensifies the conflicting water demands between people and the environment and highlights the importance of effective water resource management for achieving a balance between economic development and environmental protection.In 2008,Inner Mongolia,typical dryland in northern China,proposed strict regulations on water exploitation and utilization aimed at achieving sustainable development.Our study is the first to investigate the effectiveness and performance of these long-standing water conservation regulations.Our analyses found that the regulations drove industrial transformation,evidenced by the decreasing proportion of environmentally harmful industries such as coal and steel,and the increasing proportion of tertiary industries(especially tourism).Following industrial transformation,economic development decoupled from industrial water consumption and subsequently led to reduced negative environmental impacts.Based on these results,adaptive strategies were developed for 12 cities by revealing and integrating their development pathways and relative status in achieving sustainable development.Integration and cooperation between cities were proposed,e.g.,a water trade agreement between eastern Inner Mongolia(an economically underdeveloped region with relatively abundant water resources)and central Inner Mongolia(an economically developed region with high water stress).Such an agreement may enable the holistic achievement of sustainable development across regions.By integrating the findings of our research,our study presents a reproducible framework for water-management-based sustainable development strategies in drylands.展开更多
Climate change has a significant impact on agriculture.However,the impact investigation is currently limited to the analysis of meteorological data,and there is a dearth of long-term monitoring of crop phenology and s...Climate change has a significant impact on agriculture.However,the impact investigation is currently limited to the analysis of meteorological data,and there is a dearth of long-term monitoring of crop phenology and soil moisture associated with climate change.In this study,temperature and precipitation(1957-2020)were recorded,crop growth(1981-2019)data were collected,and field experiments were conducted at central and eastern Gansu and southern Ningxia,China.The mean temperature increased by 0.36°C,and precipitation decreased by 11.17 mm per decade.The average evapotranspiration(ET)of winter wheat in 39 years from 1981 to 2019 was 362.1 mm,demonstrating a 22.1-mm decrease every 10 years.However,the ET of spring maize was 405.5 mm over 35 years(1985-2019),which did not show a downward trend.Every 10 years,growth periods were shortened by 5.19 and 6.47 d,sowing dates were delayed by 3.56 and 1.68 d,and maturity dates advanced by 1.76 and 5.51 d,respectively,for wheat and maize.A film fully-mulched ridge-furrow(FMRF)system with a rain-harvesting efficiency of 65.7‒92.7%promotes deep rainwater infiltration into the soil.This leads to double the soil moisture in-furrow,increasing the water satisfaction rate by 110‒160%.A 15-year grain yield of maize increased by 19.87%with the FMRF compared with that of half-mulched flat planting.Grain yield and water use efficiency of maize increased by 20.6 and 17.4%when the density grew from 4.5×10^(4)to 6.75×10^(4)plants ha-1 and improved by 12.0 and 12.7%when the density increased from 6.75×10^(4)to 9.0×10^(4)plants ha-1,respectively.Moreover,responses of maize yield to density and the corresponding density of the maximum yield varied highly in different rainfall areas.The density parameter suitable for water planting was 174 maize plants ha-1 with 10 mm rainfall.Therefore,management strategies should focus on adjusting crop planting structure,FMRF water harvesting system,and water-suitable planting to mitigate the adverse effects of climate change and enhance sustainable production of maize in the drylands.展开更多
Otindag Sandy Land in China is an important ecological barrier to Beijing;the changes in its ecological quality are major concerns for sustainable development and planning of this area.Based on principal component ana...Otindag Sandy Land in China is an important ecological barrier to Beijing;the changes in its ecological quality are major concerns for sustainable development and planning of this area.Based on principal component analysis and path analysis,we first generated a modified remote sensing ecological index(MRSEI)coupled with satellite and ground observational data during 2001–2020 that integrated four local indicators(greenness,wetness,and heatness that reflect vegetation status,water,and heat conditions,respectively,as well as soil erosion).Then,we assessed the ecological quality in Otindag Sandy Land during 2001–2020 based on the MRSEI at different time scales(i.e.,the whole year,growing season,and non-growing season).MRSEI generally increased with an upward rate of 0.006/a during 2001–2020,with clear seasonal and spatial variations.Ecological quality was significantly improved in most regions of Otindag Sandy Land but degraded in the southern part.Regions with ecological degradation expanded to 18.64%of the total area in the non-growing season.The area with the worst grade of MRSEI shrunk by 15.83%of the total area from 2001 to 2020,while the area with the best grade of MRSEI increased by 9.77%of the total area.The temporal heterogeneity of ecological conditions indicated that the improvement process of ecological quality in the growing season may be interrupted or deteriorated in the following non-growing season.The implementation of ecological restoration measures in Otindag Sandy Land should not ignore the seasonal characteristics and spatial heterogeneity of local ecological quality.The results can explore the effectiveness of ecological restoration and provide scientific guides on sustainable development measures for drylands.展开更多
Rangelands of Central Asia(referring to Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan in this study), the largest contiguous area of grazed land in the world, serve as an important source of liveliho...Rangelands of Central Asia(referring to Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan in this study), the largest contiguous area of grazed land in the world, serve as an important source of livelihood for pastoral and agro-pastoral communities in this region. They also play an important role in absorbing CO2 as a global carbon sink. However, unsustainable management of rangelands has led to their degradation hugely by downgrading their potential agro-ecological, environmental and socio-economical roles. This paper reviewed the rangeland degradation in Central Asia, a topic which so far has received only scant coverage in the international scientific literature. It also provided examples of successful experiences and outlined possible options that land managers can adopt to enhance the sustainable management of these vast degraded rangelands. The experiences and lessons described in this paper may also be relevant for other degraded rangeland areas, especially in the developing countries. The causes of rangeland degradation within the Central Asian region are numerous, complex and inter-related. Therefore, while addressing the factors associated with improper rangeland management may shed some light on the causes of rangeland degradation, the scope of this paper would not be all-encompassing for the major causes of degradation. There is a need to develop and widely apply the viable and locally accepted and adapted packages of technical, institutional and policy options for sustainable rangeland management. Incentivizing the collective action of small-scale pastoralists who group together to facilitate access to remote pastures can reduce the degree of overgrazing within community pastures, such as those near the settlements. We also found that migratory grazing through pooling of resources among small-scale pastoralists can increase household income. After their independence, most Central Asian countries adopted various rangeland tenure arrangements. However, the building of enhanced capacities of pasture management and effective local rangeland governance structures can increase the likelihood, which will be sustainable and equitable. Finally, this paper presented several promising technical options, aiming at reversing the trend of rangeland degradation in Central Asia.展开更多
Countries in the Middle Eastern and North African(MENA) region are among the most water-scarce regions in the world, and their dryland soils are usually poor in organic carbon content(<0.5%). In this study, we summ...Countries in the Middle Eastern and North African(MENA) region are among the most water-scarce regions in the world, and their dryland soils are usually poor in organic carbon content(<0.5%). In this study, we summarize examples of how people in the few oases of the MENA region overcome environmental challenges by sustainably managing economically important date production. On the basis of the limited studies found in the existing literature, this mini-review focuses on the role of traditional soil organic matter amendments beneath the soil surface as a key tool in land restoration. We conclude that soil organic matter amendments can be very successful in restoring soil water and preventing the soil from salinization.展开更多
The combined effects of climate change and human pressure have led to the progressive degradation of natural resources in semi-arid regions. Woody taxa in these regions play an important role in the functioning and se...The combined effects of climate change and human pressure have led to the progressive degradation of natural resources in semi-arid regions. Woody taxa in these regions play an important role in the functioning and services provided by semi-arid savannah by serving as forage for both domestic and non-domestic grazers. Maintaining the functioning of semi-arid savannas thus requires understanding the dynamics of these communities of woody taxa and their responses to exogenous forces, such as climate. To better understand the dynamics of woody taxa in semi-arid environments we collected dendrometric characteristics from five field sites along an environmental gradient in the Ferlo region of central Senegal. Density and basal area were found to be greater in the northern part of the zone, contrasted with the distance between individuals and crown cover, which is greater in the southern part of the zone. Stand structure estimated from the distribution according to height and diameter at breast height shows a preponderance of individuals in the shrub layer, although with a significant representation of the tree layer in southern Ferlo. Stand regeneration was better in the south and less effective in the north. There was a trend towards the rejuvenation of populations belonging to the dominant species. There were only three species for which degradation was not apparent (Balanites aegyptiaca, Acacia raddiana and Dalbergia melanoxylon), all of which have important ethnobotanical uses, suggesting that human use of taxa can play an important role in preventing degradation. Three distinct groups of woody taxa were found to correspond to gradients of precipitation, topography, and human land use pressure. Our results suggest an important role in the management and reintroduction of woody species in the Sahel and the regulation of pastoral techniques necessary for the rehabilitation of the agro-pastoral zone of Senegal.展开更多
基金supported by Ministry of Science and Technology of China (Grant No. 2018YFA0606501)National Natural Science Foundation of China (Grant No. 42075037)+1 种基金Key Laboratory Open Research Program of Xinjiang Science and Technology Department (Grant No. 2022D04009)the National Key Scientific and Technological Infrastructure project “Earth System Numerical Simulation Facility” (EarthLab)。
文摘Both the attribution of historical change and future projections of droughts rely heavily on climate modeling. However,reasonable drought simulations have remained a challenge, and the related performances of the current state-of-the-art Coupled Model Intercomparison Project phase 6(CMIP6) models remain unknown. Here, both the strengths and weaknesses of CMIP6 models in simulating droughts and corresponding hydrothermal conditions in drylands are assessed.While the general patterns of simulated meteorological elements in drylands resemble the observations, the annual precipitation is overestimated by ~33%(with a model spread of 2.3%–77.2%), along with an underestimation of potential evapotranspiration(PET) by ~32%(17.5%–47.2%). The water deficit condition, measured by the difference between precipitation and PET, is 50%(29.1%–71.7%) weaker than observations. The CMIP6 models show weaknesses in capturing the climate mean drought characteristics in drylands, particularly with the occurrence and duration largely underestimated in the hyperarid Afro-Asian areas. Nonetheless, the drought-associated meteorological anomalies, including reduced precipitation, warmer temperatures, higher evaporative demand, and increased water deficit conditions, are reasonably reproduced. The simulated magnitude of precipitation(water deficit) associated with dryland droughts is overestimated by 28%(24%) compared to observations. The observed increasing trends in drought fractional area,occurrence, and corresponding meteorological anomalies during 1980–2014 are reasonably reproduced. Still, the increase in drought characteristics, associated precipitation and water deficit are obviously underestimated after the late 1990s,especially for mild and moderate droughts, indicative of a weaker response of dryland drought changes to global warming in CMIP6 models. Our results suggest that it is imperative to employ bias correction approaches in drought-related studies over drylands by using CMIP6 outputs.
基金supported by the National Natural Science Foundation of China (41830758)the "Light of the West" Cross Team-Key Laboratory Cooperative Research Project of the Chinese Academy of Sciences
文摘Livestock grazing is the most extensive land use in global drylands and one of the most extensive stressors of biological soil crusts(biocrusts).Despite widespread concern about the importance of biocrusts for global carbon(C)cycling,little is known about whether and how long-term grazing alters soil organic carbon(SOC)stability and stock in the biocrust layer.To assess the responses of SOC stability and stock in the biocrust layer to grazing,from June to September 2020,we carried out a large scale field survey in the restored grasslands under long-term grazing with different grazing intensities(represented by the number of goat dung per square meter)and in the grasslands strictly excluded from grazing in four regions(Dingbian County,Shenmu City,Guyuan City and Ansai District)along precipitation gradient in the hilly Loess Plateau,China.In total,51 representative grassland sites were identified as the study sampling sites in this study,including 11 sites in Guyuan City,16 sites in Dingbian County,15 sites in Shenmu City and 9 sites in Ansai District.Combined with extensive laboratory analysis and statistical analysis,at each sampling site,we obtained data on biocrust attributes(cover,community structure,biomass and thickness),soil physical-chemical properties(soil porosity and soil carbon-to-nitrogen ratio(C/N ratio)),and environmental factors(mean annual precipitation,mean annual temperature,altitude,plant cover,litter cover,soil particle-size distribution(the ratio of soil clay and silt content to sand content)),SOC stability index(SI)and SOC stock(SOCS)in the biocrust layer,to conduct this study.Our results revealed that grazing did not change total biocrust cover but markedly altered biocrust community structure by reducing plant cover,with a considerable increase in the relative cover of cyanobacteria(23.1%)while a decrease in the relative cover of mosses(42.2%).Soil porosity and soil C/N ratio in the biocrust layer under grazing decreased significantly by 4.1%–7.2%and 7.2%–13.3%,respectively,compared with those under grazing exclusion.The shifted biocrust community structure ultimately resulted in an average reduction of 15.5%in SOCS in the biocrust layer under grazing.However,compared with higher grazing(intensity of more than 10.00 goat dung/m2),light grazing(intensity of 0.00–10.00 goat dung/m2 or approximately 1.20–2.60 goat/(hm2•a))had no adverse effect on SOCS.SOC stability in the biocrust layer remained unchanged under long-term grazing due to the offset between the positive effect of the decreased soil porosity and the negative effect of the decreased soil C/N ratio on the SOC resistance to decomposition.Mean annual precipitation and soil particle-size distribution also regulated SOC stability indirectly by influencing soil porosity through plant cover and biocrust community structure.These findings suggest that proper grazing might not increase the CO_(2) release potential or adversely affect SOCS in the biocrust layer.This research provides some guidance for proper grazing management in the sustainable utilization of grassland resources and C sequestration in biocrusts in the hilly regions of drylands.
基金sponsored by the National K&D Program of China (Grant No. 2016YFA0600404)the China Special Fund for Meteorological Research in the Public Interest (Grant No. GYHY201106028 and GYHY2015060011)+1 种基金the National Natural Science Foundation of China (Grant No. 41530532)the Jiangsu Collaborative Innovation Center for Climate Change
文摘Drylands are among those regions most sensitive to climate and environmental changes and human-induced perturbations.The most widely accepted definition of the term dryland is a ratio,called the Surface Wetness Index(SWI),of annual precipitation to potential evapotranspiration(PET)being below 0.65.PET is commonly estimated using the Thornthwaite(PET Th)and Penman–Monteith equations(PET PM).The present study compared spatiotemporal characteristics of global drylands based on the SWI with PET Th and PET PM.Results showed vast differences between PET Th and PET PM;however,the SWI derived from the two kinds of PET showed broadly similar characteristics in the interdecadal variability of global and continental drylands,except in North America,with high correlation coefficients ranging from 0.58 to 0.89.It was found that,during 1901–2014,global hyper-arid and semi-arid regions expanded,arid and dry sub-humid regions contracted,and drylands underwent interdecadal fluctuation.This was because precipitation variations made major contributions,whereas PET changes contributed to a much lesser degree.However,distinct differences in the interdecadal variability of semi-arid and dry sub-humid regions were found.This indicated that the influence of PET changes was comparable to that of precipitation variations in the global dry–wet transition zone.Additionally,the contribution of PET changes to the variations in global and continental drylands gradually enhanced with global warming,and the Thornthwaite method was found to be increasingly less applicable under climate change.
基金This study was supported by the National Key Research and Development Program of China(2016YFA0600104)the National Natural Science Foundation of China(41991234,31800406)the International Partnership Program of Chinese Academy of Sciences(121311KYSB20170004).
文摘Drylands refer to regions with an aridity index lower than 0.65,and billions of people depend on services provided by the critically important ecosystems in these areas.How ecosystem carbon exchange in global drylands(CED)occurs and how climate change affects CED are critical to the global carbon cycle.Here,we performed a comprehensive bibliometric study on the fields of annual publications,marked journals,marked institutions,marked countries,popular keywords,and their temporal evolution to understand the temporal trends of CED research over the past 30 a(1991-2020).We found that the annual scientific publications on CED research increased significantly at an average growth rate of 7.93%.Agricultural Water Management ranked first among all journals and had the most citations.The ten most productive institutions were centered on drylands in America,China,and Australia that had the largest number and most citations of publications on CED research."Climate change"and climate-related(such as"drought","precipitation","temperature",and"rainfall")research were found to be the most popular study areas.Keywords were classified into five clusters,indicating the five main research focuses on CED studies:hydrological cycle,effects of climate change,carbon and water balance,productivity,and carbon-nitrogen-phosphorous coupling cycles.The temporal evolution of keywords further showed that the areas of focus on CED studies were transformed from classical pedology and agricultural research to applied ecology and then to global change ecological research over the past 30 a.In future CED studies,basic themes(such as"water","yield",and"salinity")and motor themes(such as"climate change","sustainability",and"remote sensing")will be the focus of research on CED.In particular,multiple integrated methods to understand climate change and ecosystem sustainability are potential new research trends and hotspots.
基金supported by the Xinjiang Outstanding Youth fund(2021D01E03)the National Natural Science Foundation of China(U2003214 and 41977099).
文摘Drylands are highly vulnerable to climate change and human activities.The drylands of China account for approximately 10.8%of global drylands,and China is the country most severely affected by aridity in Asia.Therefore,studying the spatial variation characteristics in soil multifunctionality(SMF)and investigating the driving factors are critical for elucidating and managing the functions of dryland ecosystems in China.Based on the environmental factors(mean annual precipitation(MAP),mean annual temperature(MAT),solar radiation(Srad),soil acidity(pH),enhanced vegetation index(EVI),and cation exchange capacity(CEC))and aridity from the“dataset of soil properties for land surface modeling over China”,we used non-linear regression,ordinary least square(OLS)regression,structural equation model(SEM),and other analytical methods to investigate the relationships of SMF with environmental factors across different aridity levels in China.SMF in different dryland regions varied significantly and showed a patchy distribution,with SMF index values ranging from–1.21 to 2.42.Regions with SMF index values from–0.20 to 0.51 accounting for 63.0%of dryland area in China.OLS regression results revealed that environmental factors like MAP,MAT,Srad,pH,EVI,and CEC were significantly related to SMF(P<0.05).MAP and MAT were correlated to SMF at the whole aridity level(P<0.05).SEM results showed that the driving factors of SMF differed depending on the aridity level.Soil pH was the strongest driving factor of SMF when the aridity was less than 0.80(P<0.001).Both soil CEC and EVI had a positive effect on SMF when aridity was greater than 0.80(P<0.01),with soil CEC being the strongest driving factor.The importance ranking revealed that the relative importance contribution of soil pH to SMF was greatest when aridity was less than 0.80(66.9%).When aridity was set to greater than 0.80,the relative importance contributions of CEC and EVI to SMF increased(45.1%and 31.9%,respectively).Our findings indicated that SMF had high spatial heterogeneity in drylands of China.The aridity threshold controlled the impact of environmental factors on SMF.
文摘Carbon sequestration is one of the important ecosystem services provided by forested landscapes. Dry forests have high potential for carbon storage. However, their potential to store and sequester carbon is poorly understood in Kenya. Moreover, past attempts to estimate carbon stock have ignored drylands ecosystem heterogeneity. This study assessed the potential of Mukogodo dryland forest-landscape in offsetting carbon dioxide through carbon sequestration and storage. Four carbon pools (above and below ground biomass, soil, dead wood and litter) were analyzed. A total of 51<span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">(400</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">m<sup>2</sup>) sample plots were established using stratified-random sampling technique to estimate biomass across six vegetation classes in three landscape types (forest reserve, ranches and conservancies) using nested-plot design. Above ground biomass was determined using generalized multispecies model with diameter at breast height, height and wood density as variables. Below ground, soil, litter and dead wood biomass;carbon stocks and carbon dioxide equivalents (CO<sub>2eq</sub>) were estimated using secondary information. The CO<sub>2eq</sub> was multiplied by current prices of carbon trade to compute carbon sequestration value. Mean ± SE of biomass and carbon was determined across vegetation and landscape types and mean differences tested by one-way Analysis of Variance. Mean biomass and carbon was about 79.15 ± 40.22</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TB</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha</span></span></span><span style="font-size:10px;"><span style="vertical-align:super;">-</span></span><span><span><span style="font-family:;" "=""><sup>1</sup> and 37.25 ± 18.89</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;">-</span>1</sup> respectively. Cumulative carbon stock was estimated at 682.08</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;">-</span>1</sup>;forest reserve (251.57</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup>-1</sup>) had significantly high levels of carbon stocks compared to ranches (209.78</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;white-space:normal;">-</span>1</sup>) and conservancies (220.73</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">TC</span></span></span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span style="font-family:;" "="">ha<sup><span style="font-size:10px;white-space:normal;">-</span>1</sup>, <i>P</i> = 0.000). Further, closed forest significantly contributed to the overall biomass and carbon stock (58%). The carbon sequestration potential was about 19.9MTCO<sub>2eq</sub> with most conservative worth of KES 39.9B (US$40M) per annum. The high carbon stock in the landscape shows the potential of dryland ecosystems as carbon sink for climate change mitigation. However, for communities to benefit from bio-carbon funds in future, sustainable landscape management and restorative measures should be practiced to enhance carbon storage and provision of other ecosystem services.</span></span></span>
基金supported by the Ministry of Science and Technology of China(Grant No.2018YFA0606501)the National Natural Science Foundation of China(Grant No.42075037)。
文摘Droughts are one of the climate extremes that occur frequently in drylands,constraining the terrestrial carbon uptake and water cycle processes.Studies about the long-term changes in the effect of drought stress on dryland ecosystems under global warming are still insufficient so far.Here we comprehensively investigate long-term changes in droughts and the effect of drought stresses on ecosystems across global drylands for 1982–2015,and further reveal changes in the configurations of the key meteorological and ecological factors of droughts,by using observation and reanalysis datasets.Climatically,the spatial patterns of intensity,occurrence,duration and severity of all drought categories across global drylands are highly consistent with each other.Associated with severe droughts,drylands witness insufficient precipitation(-12.4 mm mon^(-1)area-averaged over global drylands),warmer temperature(0.6℃),water deficit(-19.0 mm mon^(-1)),higher atmospheric aridity(0.06 k Pa),lower soil moisture(-0.03 m^(3)m^(-3)),suppressed vegetation growth and declined carbon uptake(-0.13 g C m^(-2)d^(-1)).The affected area,occurrence,duration and severity for mild to severe droughts in drylands and the anomalies of meteorological and ecological factors for all drought categories have increased significantly during 1982-2015.Specifically,when droughts occur,the precipitation deficit is weakened at a rate of 3.7–9.6 mm mon^(-1)(30 yr)^(-1),the higher temperature(atmospheric aridity)is further intensified at 0.71–0.87-1(30 yr)^(-1)(39–47 Pa(30 yr)^(-1)),the water(soil moisture)deficit is relieved at 1.7–5.1 mm mon^(-1)(30yr)^(-1)(4.1×10^(-3)–7.4×10^(-3)m^(3)m^(-3)(30 yr)^(-1)),and the suppressed vegetation growth is generally alleviated at 0.98×10^(-2)–1.2×10^(-2)(30 yr)^(-1).Since the 2000s,the increasing trend in the suppressed vegetation growth during droughts tends to stagnate over about 50%of the dryland area.By checking the probability density function,the configurations of the key meteorological and ecological factors of droughts show significant differences between the periods before and after 2000.The probability of drought stress caused by precipitation and soil moisture deficit has decreased by 20%and 10%,respectively,while that caused by higher temperature and atmospheric aridity has been doubled,and increased by 26%and 15%,respectively.Thus,the impact of drought stress on dryland ecosystems caused by atmospheric aridity are increasing under global warming.
基金supported by the National Natural Science Foundation of China(Grant Nos.41988101&42101149)the National Key Research and Development Program of China(Grant No.2018YFA0606404).
文摘Since Shi et al.proposed that the climate in the drylands of Northwest China experienced a significant transition from a“warming and drying”trend to a“warming and wetting”trend in the 1980s,researchers have conducted numerous studies on the variations in precipitation and humidity in the region and even in arid Central Asia.In particular,the process of the“warming and wetting”trend by using obtained measurement data received much attention.However,there remain uncertainties about whether the“warming and wetting”trend has paused and what its future variations may be.In this study,we examined the spatiotemporal variations in temperature,precipitation,the aridity index(AI),vegetation,and runoff during 1950-2019.The results showed that the climate in the drylands of Northwest China and the northern Tibetan Plateau is persistently warming and wetting since the 1980s,with an acceleration since the 1990s.The precipitation/humidity variations in North China,which are mainly influenced by summer monsoon,are generally opposite to those in the drylands of Northwest China.This reverse change is mainly controlled by an anomalous anticyclone over Mongolia,which leads to an anomalous easterly wind,reduced water vapor output,and increased precipitation in the drylands of Northwest China.While it also causes an anomalous descending motion,increased water vapor divergence,and decreased precipitation in North China.Precipitation is the primary controlling factor of humidity,which ultimately forms the spatiotemporal pattern of the“westerlies-dominated climatic regime”of antiphase precipitation/humidity variations between the drylands of Northwest China and monsoonal region of North China.The primary reasons behind the debate of the“warming and wetting”trend in Northwest China were due to the use of different time series lengths,regional ranges,and humidity indices in previous analyses.Since the EC-Earth3 has a good performance for simulating precipitation and humidity in Northwest and North China.By using its simulated results,we found a wetting trend in the drylands of Northwest China under low emission scenarios,but the climate will gradually transition to a“warming and drying”trend as emissions increase.This study suggests that moderate warming can be beneficial for improving the ecological environment in the drylands of Northwest China,while precipitation and humidity in monsoon-dominated North China will persistently increase under scenarios of increased emissions.
基金This study was supported by the National Natural Science Foundation of China(42105160)the Basic Research to Operation Funds of the Chinese Academy of Meteorological Sciences(2020Y004).
文摘Much of drylands has been hit by land degradation during the recent decades.But whether and how desertification is related to climate change is poorly understood.Here,using the Normalized Difference Vegetation Index(NDVI)time series and climatic variables,we assessed the desertification dynamics over China's drylands from 1982 to 2016 and explored the climate change impacts,with a particular focus on the influence of the 2015/2016 El Niño event.We found a fluctuant downward trend of barren land area from 1982 to the early 2010s,but followed by a sharp increase afterwards.Decrease in precipitation combined with high temperature are major contributors to the barren land expansion.During the 2015/2016 El Niño,the concurrence of severe drought and heat stress gave rise to the most serious land desertification in the record.Hyper-arid and arid drylands are the predominant contributors to the abrupt barren land area increase during 2015/2016.Our findings,therefore,highlight the climate change impacts on dryland desertification processes.Future dryland expansion and accompanying drought stress may exacerbate the risk of land degradation in these regions.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41722502, 41521004, 41575006 & 91637312)the China Overseas Expertise Introduction Project for Discipline Innovation (111 Project) (Grant No. B13045)
文摘Drylands account for approximately 41% of the global total land area. Significant warming and rare precipitation in drylands result in a fragile ecology and deterioration of the living environment, making it more sensitive to global climate change. As an important regulator of the Earth's climate system, the oceans play a vital role in the process of climate change in drylands. In modern climate change in particular, the impact of marine activities on climate change in drylands cannot be neglected. This paper reviews the characteristics of climate change in drylands over the past 100 years, and summarizes the researches conducted on the impact of marine activities on these changes. The review focuses on the impact of the Pacific Decadal Oscillation(PDO), Atlantic Multidecadal Oscillation(AMO), El Ni?o and La Ni?a on climate change in drylands, and introduces the mechanisms by which different oceanic oscillation factors synergistically affect climate change in drylands.Studies have shown that global drylands have experienced a significant intensification in warming in the past 100 years, which shows obvious characteristics of interdecadal dry/wet variations. The characteristics of these changes are closely related to the oscillatory factors of the oceanic interdecadal scale. Different phase combinations of oceanic oscillation factors significantly change the land-sea thermal contrast, which in turn affects the westerly jet, planetary wave and blocking frequency, resulting in changes in the temperature and dry/wet characteristics of drylands. With the intensification of climate change in drylands, the impact of marine activities on these regions will reveal new characteristics in the future, which will increase the uncertainty of future climate change in drylands and intensify the impact of these drylands on global climate.
基金This work was supported by the National Natural Science Foundation of China(U1602266,32060474,and 31601274)grants from the Yunnan Provincial Science and Technology Department(202005AF150009 and 202101AS070001).
文摘Upland rice shows dryland adaptation in the form of a deeper and denser root system and greater drought resistance than its counterpart,irrigated rice.Our previous study revealed a difference in the frequency of the OsNCED2 gene between upland and irrigated populations.A nonsynonymous mutation(C to T,from irrigated to upland rice)may have led to functional variation fixed by artificial selection,but the exact biological function in dryland adaptation is unclear.In this study,transgenic and association analysis indicated that the domesticated fixed mutation caused functional variation in OsNCED2,increasing ABA levels,root development,and drought tolerance in upland rice under dryland conditions.OsNCED2-overexpressing rice showed increased reactive oxygen species-scavenging abilities and transcription levels of many genes functioning in stress response and development that may regulate root development and drought tolerance.OsNCED2^(T)-NILs showed a denser root system and drought resistance,promoting the yield of rice under dryland conditions.OsNCED2^(T)may confer dryland adaptation in upland rice and may find use in breeding dryland-adapted,water-saving rice.
基金supported financially by the National Key Research and Development Program of China(2021YFD1900703)the National Natural Science Foundation of China(31272250)。
文摘Water is the key factor limiting dryland wheat grain yield.Mulching affects crop yield and yield components by affecting soil moisture.Further research is needed to determine the relationships between yield components and soil moisture with yield,and to identify the most important factor affecting grain yield under various mulching measures.A long-term 9-yearifeld experiment in the Loess Plateau of Northwest China was carried out with three treatments:no mulch (CK),plastic mulch (M_(P)) and straw mulch (M_(S)).Yield factors and soil moisture were measured,and the relationships between them were explored by correlation analysis,structural equation modeling and significance analysis.The results showed that compared with CK,the average grain yields of M_(P) and M_(S) increased by 13.0and 10.6%,respectively.The average annual grain yield of the M_(P) treatment was 134 kg ha^(–1) higher than the M_(S) treatment.There were no significant differences in yield components among the three treatments (P<0.05).Soil water storage of the M_(S) treatment was greater than the M_(P) treatment,although the differences were not statistically signifiant.Soil water storage during the summer fallow period (SWSSF) and soil water storage before sowing (SWSS) of M_(S) were significantly higher than in CK,which increased by 38.5 and 13.6%,respectively.The relationship between M_(P) and CK was not statistically significant for SWSSF,but the SWSS in M_(P) was significantly higher than in CK.In terms of soil water storage after harvest (SWSH) and water consumption in the growth period(ET),there were no signi?cant differences among the three treatments.Based on the three analysis methods,we found that spike number and ET were positively correlated with grain yield.However,the relative importance of spike number to yield was the greatest in the M_(P )and M_(S) treatments,while that of ET was the greatest in CK.Suifcient SWSSF could indirectly increase spike number and ET in the three treatments.Based on these results,mulch can improve yield and soil water storage.The most important factor affecting the grain yield of dryland wheat was spike number under mulching,and ET with CK.These findings may help us to understand the main factors influencing dryland wheat grain yield under mulching conditions compared to CK.
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(U22A20609)the National Key Research and Development Program of China(2021YFD1901102-4)+2 种基金the State Key Laboratory of Integrative Sustainable Dryland Agriculture(in preparation)the Shanxi Agricultural University,China(202003-3)the Open Fund from the State Key Laboratory of Soil Environment and Nutrient Resources of Shanxi Province,China(2020002)。
文摘Tillage practices during the fallow period benefit water storage and yield in dryland wheat crops.However,there is currently no clarity on the responses of soil organic carbon(SOC),total nitrogen(TN),and available nutrients to tillage practices within the growing season.This study evaluated the effects of three tillage practices(NT,no tillage;SS,subsoil tillage;DT,deep tillage)over five years on soil physicochemical properties.Soil samples at harvest stage from the fifth year were analyzed to determine the soil aggregate and aggregate-associated C and N fractions.The results indicated that SS and DT improved grain yield,straw biomass and straw carbon return of wheat compared with NT.In contrast to DT and NT,SS favored SOC and TN concentrations and stocks by increasing the soil organic carbon sequestration rate(SOCSR)and soil nitrogen sequestration rate(TNSR)in the 0-40 cm layer.Higher SOC levels under SS and NT were associated with greater aggregate-associated C fractions,while TN was positively associated with soluble organic nitrogen(SON).Compared with DT,the NT and SS treatments improved soil available nutrients in the 0-20 cm layer.These findings suggest that SS is an excellent practice for increasing soil carbon,nitrogen and nutrient availability in dryland wheat fields in North China.
文摘Dryland degradation has long been recognized at regional,national,and global scales,yet there are no objective assessments of its location and severity.An assessment of reductions in net primary production(NPP)due to dry land degradation in the southwestern United States is reported.The local NPP scaling(LNS)approach was applied to map the extent and magnitude of degrada tion.LNS seeks to identifty reference sites in which there is no degradation that can be used as a standard for comparison with other sites that share the same environment,except for degradation.Twelve years were analyzed(2000--2011),using Normalized Difference Vegetation Index(NDVI)data(250 m)from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite-borne multispectral sensor.The results indicated that the total NPP reductions in the study area were about35.9±4.7Tg C/yr,which equates to 0.31±0.04 Mg C·ha^(-1)· yr^(-1).The NPP reductions in grassland-savanna and livestock grazing areas were large and mostly consistent between years in spite of large variations in overall NPP caused by differences in land-use,interannual variations in rainfall,and other aspects of weather.In comparison with other cover types,forested land generally had higher NPP reduction per unit area.The maps also enable attribution of degradation from the finest management units to entire agencies,such as the Bureau of Land Management,which had 50%less production per unit area than the U.S.Forest Service.The degradation within Native American land was low with total NPP reduction of about 2.41±0.24 Tg C/yr and unit area reduction of productivity of just 0.21±0.02 Mg C·ha^(-1)·yr^(-1),yet the percent reduction from potential was in equivalence with other land management agencies.
基金supported by the CAS Strategic Priority Research Programme(No.XDA20050103)the International Partnership Program of Chinese Academy of Sciences(No.121311KYSB20170004-04)and the National Natural Science Foundation of China(Grant No.42001267).
文摘Water resource availability is the major limiting factor for sustainable development in drylands.Climate change intensifies the conflicting water demands between people and the environment and highlights the importance of effective water resource management for achieving a balance between economic development and environmental protection.In 2008,Inner Mongolia,typical dryland in northern China,proposed strict regulations on water exploitation and utilization aimed at achieving sustainable development.Our study is the first to investigate the effectiveness and performance of these long-standing water conservation regulations.Our analyses found that the regulations drove industrial transformation,evidenced by the decreasing proportion of environmentally harmful industries such as coal and steel,and the increasing proportion of tertiary industries(especially tourism).Following industrial transformation,economic development decoupled from industrial water consumption and subsequently led to reduced negative environmental impacts.Based on these results,adaptive strategies were developed for 12 cities by revealing and integrating their development pathways and relative status in achieving sustainable development.Integration and cooperation between cities were proposed,e.g.,a water trade agreement between eastern Inner Mongolia(an economically underdeveloped region with relatively abundant water resources)and central Inner Mongolia(an economically developed region with high water stress).Such an agreement may enable the holistic achievement of sustainable development across regions.By integrating the findings of our research,our study presents a reproducible framework for water-management-based sustainable development strategies in drylands.
基金We gratefully acknowledge the funding support from the National Key Research and Development Program of China(2012BAD0903 and 2018YFD0100200)the China Agriculture Research System(CARS-02-77).
文摘Climate change has a significant impact on agriculture.However,the impact investigation is currently limited to the analysis of meteorological data,and there is a dearth of long-term monitoring of crop phenology and soil moisture associated with climate change.In this study,temperature and precipitation(1957-2020)were recorded,crop growth(1981-2019)data were collected,and field experiments were conducted at central and eastern Gansu and southern Ningxia,China.The mean temperature increased by 0.36°C,and precipitation decreased by 11.17 mm per decade.The average evapotranspiration(ET)of winter wheat in 39 years from 1981 to 2019 was 362.1 mm,demonstrating a 22.1-mm decrease every 10 years.However,the ET of spring maize was 405.5 mm over 35 years(1985-2019),which did not show a downward trend.Every 10 years,growth periods were shortened by 5.19 and 6.47 d,sowing dates were delayed by 3.56 and 1.68 d,and maturity dates advanced by 1.76 and 5.51 d,respectively,for wheat and maize.A film fully-mulched ridge-furrow(FMRF)system with a rain-harvesting efficiency of 65.7‒92.7%promotes deep rainwater infiltration into the soil.This leads to double the soil moisture in-furrow,increasing the water satisfaction rate by 110‒160%.A 15-year grain yield of maize increased by 19.87%with the FMRF compared with that of half-mulched flat planting.Grain yield and water use efficiency of maize increased by 20.6 and 17.4%when the density grew from 4.5×10^(4)to 6.75×10^(4)plants ha-1 and improved by 12.0 and 12.7%when the density increased from 6.75×10^(4)to 9.0×10^(4)plants ha-1,respectively.Moreover,responses of maize yield to density and the corresponding density of the maximum yield varied highly in different rainfall areas.The density parameter suitable for water planting was 174 maize plants ha-1 with 10 mm rainfall.Therefore,management strategies should focus on adjusting crop planting structure,FMRF water harvesting system,and water-suitable planting to mitigate the adverse effects of climate change and enhance sustainable production of maize in the drylands.
基金the financial support given by the Special Funds for Science and Technology Innovation on Carbon Peak Carbon Neutral of Jiangsu Province,China(BK20220017)the Innovation Development Project of China Meteorological Administration(CXFZ2023J073)the National Key R&D Program of China(2018YFC1506606).
文摘Otindag Sandy Land in China is an important ecological barrier to Beijing;the changes in its ecological quality are major concerns for sustainable development and planning of this area.Based on principal component analysis and path analysis,we first generated a modified remote sensing ecological index(MRSEI)coupled with satellite and ground observational data during 2001–2020 that integrated four local indicators(greenness,wetness,and heatness that reflect vegetation status,water,and heat conditions,respectively,as well as soil erosion).Then,we assessed the ecological quality in Otindag Sandy Land during 2001–2020 based on the MRSEI at different time scales(i.e.,the whole year,growing season,and non-growing season).MRSEI generally increased with an upward rate of 0.006/a during 2001–2020,with clear seasonal and spatial variations.Ecological quality was significantly improved in most regions of Otindag Sandy Land but degraded in the southern part.Regions with ecological degradation expanded to 18.64%of the total area in the non-growing season.The area with the worst grade of MRSEI shrunk by 15.83%of the total area from 2001 to 2020,while the area with the best grade of MRSEI increased by 9.77%of the total area.The temporal heterogeneity of ecological conditions indicated that the improvement process of ecological quality in the growing season may be interrupted or deteriorated in the following non-growing season.The implementation of ecological restoration measures in Otindag Sandy Land should not ignore the seasonal characteristics and spatial heterogeneity of local ecological quality.The results can explore the effectiveness of ecological restoration and provide scientific guides on sustainable development measures for drylands.
基金the Asian Development Bank,the International Center for Agricultural Research in the Dry Areas,Russian Scientific Fund(14-38-00023)the CGIAR Research Program on Dryland Systems for their support and funding
文摘Rangelands of Central Asia(referring to Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan in this study), the largest contiguous area of grazed land in the world, serve as an important source of livelihood for pastoral and agro-pastoral communities in this region. They also play an important role in absorbing CO2 as a global carbon sink. However, unsustainable management of rangelands has led to their degradation hugely by downgrading their potential agro-ecological, environmental and socio-economical roles. This paper reviewed the rangeland degradation in Central Asia, a topic which so far has received only scant coverage in the international scientific literature. It also provided examples of successful experiences and outlined possible options that land managers can adopt to enhance the sustainable management of these vast degraded rangelands. The experiences and lessons described in this paper may also be relevant for other degraded rangeland areas, especially in the developing countries. The causes of rangeland degradation within the Central Asian region are numerous, complex and inter-related. Therefore, while addressing the factors associated with improper rangeland management may shed some light on the causes of rangeland degradation, the scope of this paper would not be all-encompassing for the major causes of degradation. There is a need to develop and widely apply the viable and locally accepted and adapted packages of technical, institutional and policy options for sustainable rangeland management. Incentivizing the collective action of small-scale pastoralists who group together to facilitate access to remote pastures can reduce the degree of overgrazing within community pastures, such as those near the settlements. We also found that migratory grazing through pooling of resources among small-scale pastoralists can increase household income. After their independence, most Central Asian countries adopted various rangeland tenure arrangements. However, the building of enhanced capacities of pasture management and effective local rangeland governance structures can increase the likelihood, which will be sustainable and equitable. Finally, this paper presented several promising technical options, aiming at reversing the trend of rangeland degradation in Central Asia.
基金supported by the Exploratory Grant(STC_TUNGER-006/INTOASES)as part of the Bilateral Scientific and Technological Cooperation between the Republic of Tunisia and the Federal Republic of Germany
文摘Countries in the Middle Eastern and North African(MENA) region are among the most water-scarce regions in the world, and their dryland soils are usually poor in organic carbon content(<0.5%). In this study, we summarize examples of how people in the few oases of the MENA region overcome environmental challenges by sustainably managing economically important date production. On the basis of the limited studies found in the existing literature, this mini-review focuses on the role of traditional soil organic matter amendments beneath the soil surface as a key tool in land restoration. We conclude that soil organic matter amendments can be very successful in restoring soil water and preventing the soil from salinization.
文摘The combined effects of climate change and human pressure have led to the progressive degradation of natural resources in semi-arid regions. Woody taxa in these regions play an important role in the functioning and services provided by semi-arid savannah by serving as forage for both domestic and non-domestic grazers. Maintaining the functioning of semi-arid savannas thus requires understanding the dynamics of these communities of woody taxa and their responses to exogenous forces, such as climate. To better understand the dynamics of woody taxa in semi-arid environments we collected dendrometric characteristics from five field sites along an environmental gradient in the Ferlo region of central Senegal. Density and basal area were found to be greater in the northern part of the zone, contrasted with the distance between individuals and crown cover, which is greater in the southern part of the zone. Stand structure estimated from the distribution according to height and diameter at breast height shows a preponderance of individuals in the shrub layer, although with a significant representation of the tree layer in southern Ferlo. Stand regeneration was better in the south and less effective in the north. There was a trend towards the rejuvenation of populations belonging to the dominant species. There were only three species for which degradation was not apparent (Balanites aegyptiaca, Acacia raddiana and Dalbergia melanoxylon), all of which have important ethnobotanical uses, suggesting that human use of taxa can play an important role in preventing degradation. Three distinct groups of woody taxa were found to correspond to gradients of precipitation, topography, and human land use pressure. Our results suggest an important role in the management and reintroduction of woody species in the Sahel and the regulation of pastoral techniques necessary for the rehabilitation of the agro-pastoral zone of Senegal.
