Soil seed banks play an important role in the distribution and composition of plant communities in semiarid grassland ecosystems. However, information on how spatial scale influences the spatial heterogeneity of soil ...Soil seed banks play an important role in the distribution and composition of plant communities in semiarid grassland ecosystems. However, information on how spatial scale influences the spatial heterogeneity of soil seed banks in a grassland under grazing disturbance is still lacking. Based on field sampling and greenhouse germination, we measured the species composition and seed density of soil seed banks at different spatial scales （30 mx30 m, 30 mx60 m and 30 mx90 m） along a topographical gradient in a sandy grassland in Horqin Sand Land, Northern China. By applying geostatistical methods, we examined how spatial scale and topography affected the spatial distribution of soil seed banks in the study area. Our results showed that the total number of species in soil seed banks, as well as the number of dominant annuals, increased with the increase of spatial scales. Seed density in soil seed banks decreased with the increase of spatial scales due to an increase in the slopes and relative heights of the sampling points. Geostatistical analysis showed that the relative structural variance （C/（C0＋C）） of seed density and species richness were over 65% for all spatial scales, indicating that these variables had an ob- vious spatial autocorrelation and the spatial structured variance accounted for the largest proportion of the total sample variance. Spatial autocorrelation of seed density in soil seed banks increased with the increase of measured scales, while that of species richness showed a reverse trend. These results suggest that the total number of spe- cies in soil seed banks is spatial scale dependent and lower topography may accommodate more seeds. Spatial distribution of seed density in soil seed banks is also scale dependent due to topographic variation. Grassland management, therefore, needs to consider local grazing disturbance regime, spatial scale and topography.展开更多
The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known abo...The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—′Returning Grazing Lands to Grasslands(RGLG)′ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.展开更多
The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG), degraded grassland (DG),and improved grassland (IG),in Horqin Sandy Land,Inner Mongolia,Northeast China...The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG), degraded grassland (DG),and improved grassland (IG),in Horqin Sandy Land,Inner Mongolia,Northeast China.Soil samples were collected at depths of 0-10,10-20,and 20-30 cm.Total organic carbon (TOC) and total nitrogen (TN) exhibited positive effects on the total number of nematodes and trophic groups.Significant treatment effects were found in the total number of nematodes,plant parasites,and omnivores-predators.Measures taken in the improved grassland could improve the number of omnivore-predators,especially in the deeper soil layers.Nematode richness was lower in the DG treatment than in the IG and UG treatments.The food web structure index (SI) was significantly higher in the UG and IG treatments than in the DG treatment.A higher SI suggested a food web with more trophic linkages and relatively healthy ecosystems.展开更多
Mowing is an important land management practice for natural semi-arid regions. A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems. However, the resp...Mowing is an important land management practice for natural semi-arid regions. A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems. However, the responses of plant functional traits to long-term mowing and their allometric scaling under long-term mowing are poorly understood. For a better understanding of the effects of mowing on grassland ecosystems, we analyzed the allometric traits of leaves and stems of Leymus chinensis （Trin.） Tzvel., a dominant grass species in eastern Eurasian temperate grassland, at different mowing intensities （no clipping, clipping once every two years, once a year and twice a year）. Experiments were conducted on plots established over a decade ago in a typical steppe of Xilinhot, Inner Mongolia, China. Results showed that most of the functional traits of L. chinensis decreased with the increased mowing intensity. The responses of leaves and stems to long-term mowing were asymmetric, in which leaf traits were more stable than stem traits. Also significant allometric relationships were found among most of the plant functional traits under the four mowing treatments. Sensitive traits of L. chinensis （e.g. leaf length and stem length） were primary indicators associated with aboveground biomass decline under high mowing intensity. In conclusion, the allometric growth of different functional traits of L. chinensis varies with different long-term mowing practices, which is likely to be a strategy used by the plant to adapt to the mowing disturbances.展开更多
How species diversityroductivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover...How species diversityroductivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and above- ground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northem China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use （grazing and exclosure）. These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and bio- mass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species rich- ness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which fur- tiler affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of tem- poral dynamics and land use in understanding the relationship between species richness and ecosystem fianction.展开更多
Sandy grassland in northern China is a fragile ecosystem with poor soil fertility.Exploring how plant species regulate growth and nutrient absorption under the background of nitrogen(N)deposition is crucial for the ma...Sandy grassland in northern China is a fragile ecosystem with poor soil fertility.Exploring how plant species regulate growth and nutrient absorption under the background of nitrogen(N)deposition is crucial for the management of the sandy grassland ecosystem.We carried out a field experiment with six N levels in the Hulunbuir Sandy Land of China from 2014 to 2016 and explored the Agropyron michnoi Roshev.responses of both aboveground and belowground biomasses and carbon(C),N and phosphorus(P)concentrations in the plant tissues and soil.With increasing N addition,both aboveground and belowground biomasses and C,N and P concentrations in the plant tissues increased and exhibited a single-peak curve.C:N and C:P ratios of the plant tissues first decreased but then increased,while the trend for N:P ratio was opposite.The peak values of aboveground biomass,belowground biomass and C concentration in the plant tissues occurred at the level of 20 g N/(m2•a),while those of N and P concentrations in the plant tissues occurred at the level of 15 g N/(m2•a).The maximum growth percentages of aboveground and belowground biomasses were 324.2%and 75.9%,respectively,and the root to shoot ratio(RSR)decreased with the addition of N.N and P concentrations in the plant tissues were ranked in the order of leaves>roots>stems,while C concentration was ranked as roots>leaves>stems.The increase in N concentration in the plant tissues was the largest(from 34%to 162%),followed by the increase in P(from 10%to 33%)and C(from 8%to 24%)concentrations.The aboveground biomass was positively and linearly correlated with leaf C,N and P,and soil C and N concentrations,while the belowground biomass was positively and linearly correlated with leaf N and soil C concentrations.These results showed that the accumulation of N and P in the leaves caused the increase in the aboveground biomass,while the accumulation of leaf N resulted in the increase in the belowground biomass.N deposition can alter the allocation of C,N and P stoichiometry in the plant tissues and has a high potential for increasing plant biomass,which is conducive to the restoration of sandy grassland.展开更多
To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northem China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land...To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northem China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land, Inner Mongolia. The results showed that sustained heavy grazing resulted in serious degradation of the vegetation; moderate grazing can maintain vegetation stabilization; and light grazing can promote rapid restoration of degraded vegetation. The livestock productivity was the highest in the moderate grazing grassland, and sustained heavy grazing resulted in rapid decrease of the livestock productivity. Heavy grazing can cause a retrogressive succession of grassland vegetation, whereas moderate and light grazing may promote progressive succession of plant species. The effects of changing climate on succession processes were not significant in the short term; a warm-humid climate is favorable to restoration of degraded vegetation, whereas a sustained warm-drought climate may result in degradation of grassland vegetation. Heavy livestock grazing should be stopped for the sustainable use of grassland; the proper grazing intensity for sandy grassland is two to three sheep or sheep equivalents per hectare in Inner Mongolia.展开更多
The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances...The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.展开更多
To understand the effects of animal grazing activities and climate change on sandy grassland vegetation in northern China, a field grazing and protected enclosure experiment was conducted from 1992 through 2006 in Hor...To understand the effects of animal grazing activities and climate change on sandy grassland vegetation in northern China, a field grazing and protected enclosure experiment was conducted from 1992 through 2006 in Horqin Sand Land, Inner Mongolia. The results showed that (1) the grazing was primary responsible for changes of the vegetation richness and diversity in the grazing grassland and that changing climate was the main reason for changes in the species richness and diversity in the grassland protected from grazing; (2) light and moderate grazing can promote restoration of the richness and the diversity in the degraded grassland, and heavy grazing could result in a decrease of the richness and diversity; (3) heavy grazing can result in significant decrease of the perennial diversity, and moderate and light grazing promotes increase of the perennial diversity; the grazing, whether heavy or moderate and light grazing, was beneficial to increase of the annual diversity; (4) heavy grazing was not beneficial to diversity of Graminean and Chenopodiaceae, and moderate and light grazing was favorable the diversity of Compositae and Chenopodiaceae; (5) the warm-humid climate was favorable to increase of the richness and the diversity, and the warm-drought climate could result in decease of the richness and the diversity; (6) increased precipitation was favorable to perennial diversity and the diversity of Graminean, Leguminosae, and Compositae, and decreased precipitation had few effects on the annual diversity and Chenopodiaceae diversity.展开更多
Soil erosion can cause considerable effect on global natural resources and eco-environment. In the paper, the CENTURY model has been used to simulate soil erosion in Xilin Gol Grassland of Inner Mongolia. The results ...Soil erosion can cause considerable effect on global natural resources and eco-environment. In the paper, the CENTURY model has been used to simulate soil erosion in Xilin Gol Grassland of Inner Mongolia. The results showed before the 1960s, the soil erosion amount was over 2 kg /m2.a in grassland ecosystem in the study area because no trees had been planted. But after the 1960s the mean annual accumulator C lost from soil organic matter due to soil erosion was only 0.3 kg /m2.a in forest ecosystem. So afforestation has exerted notable effect on decreasing soil erosion amount in Xilin Gol Grassland.展开更多
Water was a key factor restricting the plantation in sandy areas. Foliar δ^(13)C value regarded as an indicator of longterm water use efficiency(WUE) of plants was generally used to evaluate the adaptability of plant...Water was a key factor restricting the plantation in sandy areas. Foliar δ^(13)C value regarded as an indicator of longterm water use efficiency(WUE) of plants was generally used to evaluate the adaptability of plants to arid and semi-arid environment. In Horqin sandy land of China, the foliar δ^(13)C values of 114 species in 35 families naturally growing in the area, and 15 species of sand-fixing trees and shrubs were measured and analyzed in 2012. The results showed that 97 species in all 114 species were C_3 plants and only 17 species were C_4 plants. Most C_4 plants belonged to Gramineae family. The foliar δ^(13)C value of C_3 plants was between -25.000 and -31.075‰ with an average of-28.226‰, while those of C_4 plants between -12.578 and -16.334‰, with an average of -13.678‰. The δ^(13)C values of mature leaves collected in August were averagely 0.85‰ less than that of juvenile leaves collected in June. The foliar δ^(13)C values and WUE of 15 sand-fixing tree species in Horqin sandy land ranked in the order as: S.vulgaris >H.rhamnoides >C.ovata >P.mongolica >T.chinensis >R.typhina >S.matsudana >E.angustifolia >U.pumila >S.gordejevii >X.sorbifolia >C.microphylla >H.fruticosum >C.korshinskii >E.bungeanus.展开更多
Construction of artificial grassland is a key factor to solve the shortage of grass and forage balance in cold and semi-arid areas of high plateau,and it is the key measure to ensure the sustainable development of gra...Construction of artificial grassland is a key factor to solve the shortage of grass and forage balance in cold and semi-arid areas of high plateau,and it is the key measure to ensure the sustainable development of grassland animal husbandry in this area. At present,the artificial grassland construction is neither reasonable nor scientific,which restricts the healthy and rapid development of artificial grassland in the cold and semi-arid areas of high plateau. In this research,with Naqu Area in Tibet as a case,problems and current status in construction process of artificial grassland are analyzed in cold and semi-arid areas of high plateau. Suitable artificial forage species in Nagqu are elaborated,and recommendations for the construction and development of artificial grassland are discussed.展开更多
Caragana microphylla Lam., a pioneer leguminous shrub species for vegetation re-establishment, is widely distributed in the semi-fixed and fixed sandy lands of the Horqin region. Some soil chemical and physical proper...Caragana microphylla Lam., a pioneer leguminous shrub species for vegetation re-establishment, is widely distributed in the semi-fixed and fixed sandy lands of the Horqin region. Some soil chemical and physical properties were measured under the canopy of C. microphylla and in the adjacent open areas to determine the effects of individual shrubs on soil properties. The influence of isolated C. microphylla on chemical and physical properties of the topsoil was significantly different between plots under the shrub canopy and in the shrub interspaces. Beneath the shrub canopy greater amounts of fine particle fractions, a higher water-holding capacity, and a lower bulk density, as well as higher aboveground and belowground litter biomass were found. Soil organic C and total N concentrations were 23%-31.6% and 14%-27.2% higher under the shrub canopies than in the shrub interspaces, respectively, giving rise to 'islands of fertility'. In a desertified sandy grassland ecosystem, C. microphylla was believed to play a major role in organic C sequestration, N accumulation, and the hydrologic cycle. Additionally, it has been found to be of ecological importance for vegetative restoration and reversal of desertification.展开更多
Changes in the distribution of soil aggregate sizes and concentrations of aggregate-associated organic carbon （OC） and nitrogen （N） in response to the fertilization of grasslands are not well understood. Understan...Changes in the distribution of soil aggregate sizes and concentrations of aggregate-associated organic carbon （OC） and nitrogen （N） in response to the fertilization of grasslands are not well understood. Understanding these changes is essential to the sustainable development of artificial grasslands. For understanding these changes, we collected soil samples at 0-20 and 20-40 cm depths from a semi-arid artificial alfalfa grassland after 27 years of applications of phosphorus （P） and nitrogen＋phosphorus＋manure （NPM） fertilizers on the Loess Pla- teau of China. The distribution of aggregate sizes and the concentrations and stocks of OC and N in total soils were determined. The results showed that NPM treatment significantly increased the proportions of 〉2.0 mm and 2.0-0.25 mm size fractions, the mean geometric diameter （MGD） and the mean weight diameter （MWD） in the 0-20 cm layer. Phosphorous fertilizer significantly increased the proportion of 〉2.0 mm size fractions, the MGD and the MWD in the 0-20 cm layer. Long-term application of fertilization （P and NPM） resulted in the accumulation of OC and N in soil aggregates. The largest changes in aggregate-associated OC and N in the 0-20 cm layer were found at the NPM treatment, whereas the largest changes in the 20-40 cm layer were found at the P treatment. The results suggest that long-term fertilization in the grassland leads to the accumulation of OC and N in the coarse size fractions and the redistribution of OC and N from fine size fractions to coarse size fractions.展开更多
Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposit...Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposition and,ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels（low N with 50 kg N/（hm2？a）（LN）, medium N with 100 kg N/（hm2？a）（MN）, and high N with 200 kg N/（hm2？a）（HN）） and three N addition forms（ammonium-N-based with 100 kg N/（hm2？a） as ammonium sulfate（AS）, nitrate-N-based with 100 kg N/（hm2？a） as sodium nitrate（SN）, and mixed-N-based with 100 kg N/（hm2？a） as calcium ammonium nitrate（CAN）） compared to control with no N addition（CK）. The results indicated that the litter mass remaining in all N treatments exhibited a similar decomposition pattern： fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period（120–1,200 days）. The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I（〈398 days） and a linear decay function in phase II（≥398 days）. The three N addition levels exerted insignificant effects on litter decomposition in the early stages（〈398 days, phase I; P〉0.05）. However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively（P〈0.05）. AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period（P〉0.05）. The effects of these two N addition forms differed greatly from those of CAN after 746 and 1,053 days, respectively（P〈0.05）. During the decomposition period, N concentrations in the decomposing litter increased whereas C concentrations decreased, which also led to an exponential decrease in litter C：N ratios in all treatments. No significant effects were induced by N addition levels and forms on litter C and N concentrations（P〉0.05）. Our results indicated that exogenous N additions could exhibit neutral or inhibitory effects on litter decomposition, and the inhibitory effects of N additions on litter decomposition in the final decay stages are not caused by the changes in the chemical qualities of the litter, such as endogenous N and C concentrations. These results will provide an important data basis for the simulation and prediction of C cycle processes in future N-deposition scenarios.展开更多
The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carrie...The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carried out at 60%WHC(water holding capacity)and 25℃to evaluate the gross N transformation rates and N_(2)O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province,China.The results showed that the gross rates of N mineralization,immobilization,and nitrification were 3.60,1.90,and 5.63 mg N/(kg·d)in silt loam soil,respectively,which were 3.62,4.26,and 3.13 times those in sandy loam soil,respectively.The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia)in sandy loam soil and silt loam soil were all higher than 1.00,whereas the n/ia in sandy loam soil(4.36)was significantly higher than that in silt loam soil(3.08).This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil,and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_(3)–leaching.Under aerobic conditions,both nitrification and denitrification made contributions to N_(2)O emissions.Nitrification was the dominant pathway leading to N_(2)O production in soils and was responsible for 82.0%of the total emitted N_(2)O in sandy loam soil,which was significantly higher than that in silt loam soil(71.7%).However,the average contribution of denitrification to total N_(2)O production in sandy loam soil was 17.9%,which was significantly lower than that in silt loam soil(28.3%).These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.展开更多
The main purpose of this study was to explore the dynamic changes of greenhouse gas（GHG）from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China.Grassland degradation is...The main purpose of this study was to explore the dynamic changes of greenhouse gas（GHG）from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China.Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2,CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63–386.36 mg/（m·h）, CH4 uptake fluxes of 0.113–0.023 mg/（m·h） and N2O fluxes of –1.68–19.90 μg/（m·h）. Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes.Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.展开更多
Vegetation near-soil-surface factors can protect topsoil from erosion,however,their contributions to the reduction of soil erosion,especially under natural rainfall events,have not been systematically recognized.This ...Vegetation near-soil-surface factors can protect topsoil from erosion,however,their contributions to the reduction of soil erosion,especially under natural rainfall events,have not been systematically recognized.This study was performed to quantify the effects of near-soil-surface factors on runoff and sediment under natural rainfall events on grasslands dominated by Bothriochloa ischaemum(Linn.)Keng(BI grassland)and Artemisia gmelinii Thunb.(AG grassland)in two typical watersheds on the Loess Plateau,China in 2018.By successive removal of the plant canopy,litter,biological soil crusts(BSCs)and plant roots,we established five treatments including plant roots,plant roots+BSCs,plant roots+BSCs+litter,intact grassland and bare land in each grassland type.In total,twenty runoff plots(5 m×3 m)with similar slopes and aspects were constructed in the two types of grasslands.Results showed that plant canopy,litter and roots reduced runoff,while BSCs,which swelled in the presence of water,increased runoff.In contrast,all of these factors reduced sediment yield.In addition,the reductions in runoff and sediment yield increased with I30(maximum 30-min rainfall intensity)for each vegetation near-soil-surface factor except for BSCs.Among these factors,plant canopy had the largest contribution to runoff reduction,accounting for 48.8% and 39.9% in the BI and AG grasslands,respectively.The contributions of these vegetation near-soil-surface factors to sediment yield reduction were similar(21.3%-29.9%)in the two types of grasslands except for BSCs in the AG grassland(10.3%).The total reduction in runoff in the BI grassland(70.8%)was greater than that in the AG grassland(53.1%),while the reduction in sediment yield was almost the same in both grasslands(97.4%and 96.7%).In conclusion,according to the effects of different vegetation near-soil-surface factors on runoff and sediment production,our results may provide more complete insight and scientific basis into the effects of various vegetation related factors in controlling soil erosion.展开更多
The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others rev...The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years （1973-2007）. The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed： （1） woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and （2） an increase in undesirable woody species, livestock population and cultivated area had a significant （P〈0.05） negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.展开更多
基金funded by the National Natural Science Foundation of China(41171414)the Knowledge Innovation Program of Chinese Academy of Sciences(KZCX2-EW-QN313)+2 种基金the National Science and Technology Support Program (2011BAC07B02)the National Basic Research Program of China(2009CB421303)the West Light Foundation of the Chinese Academy of Sciences(0928711001)
文摘Soil seed banks play an important role in the distribution and composition of plant communities in semiarid grassland ecosystems. However, information on how spatial scale influences the spatial heterogeneity of soil seed banks in a grassland under grazing disturbance is still lacking. Based on field sampling and greenhouse germination, we measured the species composition and seed density of soil seed banks at different spatial scales （30 mx30 m, 30 mx60 m and 30 mx90 m） along a topographical gradient in a sandy grassland in Horqin Sand Land, Northern China. By applying geostatistical methods, we examined how spatial scale and topography affected the spatial distribution of soil seed banks in the study area. Our results showed that the total number of species in soil seed banks, as well as the number of dominant annuals, increased with the increase of spatial scales. Seed density in soil seed banks decreased with the increase of spatial scales due to an increase in the slopes and relative heights of the sampling points. Geostatistical analysis showed that the relative structural variance （C/（C0＋C）） of seed density and species richness were over 65% for all spatial scales, indicating that these variables had an ob- vious spatial autocorrelation and the spatial structured variance accounted for the largest proportion of the total sample variance. Spatial autocorrelation of seed density in soil seed banks increased with the increase of measured scales, while that of species richness showed a reverse trend. These results suggest that the total number of spe- cies in soil seed banks is spatial scale dependent and lower topography may accommodate more seeds. Spatial distribution of seed density in soil seed banks is also scale dependent due to topographic variation. Grassland management, therefore, needs to consider local grazing disturbance regime, spatial scale and topography.
基金Under the auspices of Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA05060103)National Natural Science Foundation of China(No.41105117)State Key Laboratory of Forest and Soil Ecology(No.LFSE2013-06)
文摘The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—′Returning Grazing Lands to Grasslands(RGLG)′ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.
基金Project supported by the National Key Technologies R & D Program of China (No.2005BA517A-8).
文摘The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG), degraded grassland (DG),and improved grassland (IG),in Horqin Sandy Land,Inner Mongolia,Northeast China.Soil samples were collected at depths of 0-10,10-20,and 20-30 cm.Total organic carbon (TOC) and total nitrogen (TN) exhibited positive effects on the total number of nematodes and trophic groups.Significant treatment effects were found in the total number of nematodes,plant parasites,and omnivores-predators.Measures taken in the improved grassland could improve the number of omnivore-predators,especially in the deeper soil layers.Nematode richness was lower in the DG treatment than in the IG and UG treatments.The food web structure index (SI) was significantly higher in the UG and IG treatments than in the DG treatment.A higher SI suggested a food web with more trophic linkages and relatively healthy ecosystems.
基金financially supported by the National Basic Research Program of China(2014CB138806)the Natural Science Fund Project of Inner Mongolia(2015ZD02)+2 种基金the International Science and Technology Cooperation Program of China(2013DFR30760)the National Scientific and Technical Support Program of China(2012BAD12B02)the Special Fund for Agro-scientific Research in the Public Interest(201303060)
文摘Mowing is an important land management practice for natural semi-arid regions. A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems. However, the responses of plant functional traits to long-term mowing and their allometric scaling under long-term mowing are poorly understood. For a better understanding of the effects of mowing on grassland ecosystems, we analyzed the allometric traits of leaves and stems of Leymus chinensis （Trin.） Tzvel., a dominant grass species in eastern Eurasian temperate grassland, at different mowing intensities （no clipping, clipping once every two years, once a year and twice a year）. Experiments were conducted on plots established over a decade ago in a typical steppe of Xilinhot, Inner Mongolia, China. Results showed that most of the functional traits of L. chinensis decreased with the increased mowing intensity. The responses of leaves and stems to long-term mowing were asymmetric, in which leaf traits were more stable than stem traits. Also significant allometric relationships were found among most of the plant functional traits under the four mowing treatments. Sensitive traits of L. chinensis （e.g. leaf length and stem length） were primary indicators associated with aboveground biomass decline under high mowing intensity. In conclusion, the allometric growth of different functional traits of L. chinensis varies with different long-term mowing practices, which is likely to be a strategy used by the plant to adapt to the mowing disturbances.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KZCX2-EW-QN313)the National Natural Science Foundation of China(No.41171414,41071185)+1 种基金the Key Project of Scientific and Technical Supporting Programs(No.2011BAC07B02-09)the West Light Foundation of the Chinese Academy of Sciences(No.O928711001)
文摘How species diversityroductivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and above- ground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northem China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use （grazing and exclosure）. These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and bio- mass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species rich- ness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which fur- tiler affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of tem- poral dynamics and land use in understanding the relationship between species richness and ecosystem fianction.
基金the National Natural Science Foundation of China(31560657)the Natural Science Foundation of Inner Mongolia Autonomous Region,China(2018MS03079)。
文摘Sandy grassland in northern China is a fragile ecosystem with poor soil fertility.Exploring how plant species regulate growth and nutrient absorption under the background of nitrogen(N)deposition is crucial for the management of the sandy grassland ecosystem.We carried out a field experiment with six N levels in the Hulunbuir Sandy Land of China from 2014 to 2016 and explored the Agropyron michnoi Roshev.responses of both aboveground and belowground biomasses and carbon(C),N and phosphorus(P)concentrations in the plant tissues and soil.With increasing N addition,both aboveground and belowground biomasses and C,N and P concentrations in the plant tissues increased and exhibited a single-peak curve.C:N and C:P ratios of the plant tissues first decreased but then increased,while the trend for N:P ratio was opposite.The peak values of aboveground biomass,belowground biomass and C concentration in the plant tissues occurred at the level of 20 g N/(m2•a),while those of N and P concentrations in the plant tissues occurred at the level of 15 g N/(m2•a).The maximum growth percentages of aboveground and belowground biomasses were 324.2%and 75.9%,respectively,and the root to shoot ratio(RSR)decreased with the addition of N.N and P concentrations in the plant tissues were ranked in the order of leaves>roots>stems,while C concentration was ranked as roots>leaves>stems.The increase in N concentration in the plant tissues was the largest(from 34%to 162%),followed by the increase in P(from 10%to 33%)and C(from 8%to 24%)concentrations.The aboveground biomass was positively and linearly correlated with leaf C,N and P,and soil C and N concentrations,while the belowground biomass was positively and linearly correlated with leaf N and soil C concentrations.These results showed that the accumulation of N and P in the leaves caused the increase in the aboveground biomass,while the accumulation of leaf N resulted in the increase in the belowground biomass.N deposition can alter the allocation of C,N and P stoichiometry in the plant tissues and has a high potential for increasing plant biomass,which is conducive to the restoration of sandy grassland.
基金funded by a Chinese National Key Project for Basic Scientific Research (2009CB421303)a Chinese National Fund Project (30972422)
文摘To understand the effects of grazing activities and climate change on sandy grassland ecosystems in northem China, a livestock field grazing and enclosure experiment was conducted from 1992 to 2006 in Horqin Sand Land, Inner Mongolia. The results showed that sustained heavy grazing resulted in serious degradation of the vegetation; moderate grazing can maintain vegetation stabilization; and light grazing can promote rapid restoration of degraded vegetation. The livestock productivity was the highest in the moderate grazing grassland, and sustained heavy grazing resulted in rapid decrease of the livestock productivity. Heavy grazing can cause a retrogressive succession of grassland vegetation, whereas moderate and light grazing may promote progressive succession of plant species. The effects of changing climate on succession processes were not significant in the short term; a warm-humid climate is favorable to restoration of degraded vegetation, whereas a sustained warm-drought climate may result in degradation of grassland vegetation. Heavy livestock grazing should be stopped for the sustainable use of grassland; the proper grazing intensity for sandy grassland is two to three sheep or sheep equivalents per hectare in Inner Mongolia.
基金supported by the National Key Basic Research and Development Program of China (2016YFC0500703)the National Natural Science Foundation of China (31572452, 41573063, 31870438)
文摘The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.
基金funded by one of the 973 Projects (2009CB421303)
文摘To understand the effects of animal grazing activities and climate change on sandy grassland vegetation in northern China, a field grazing and protected enclosure experiment was conducted from 1992 through 2006 in Horqin Sand Land, Inner Mongolia. The results showed that (1) the grazing was primary responsible for changes of the vegetation richness and diversity in the grazing grassland and that changing climate was the main reason for changes in the species richness and diversity in the grassland protected from grazing; (2) light and moderate grazing can promote restoration of the richness and the diversity in the degraded grassland, and heavy grazing could result in a decrease of the richness and diversity; (3) heavy grazing can result in significant decrease of the perennial diversity, and moderate and light grazing promotes increase of the perennial diversity; the grazing, whether heavy or moderate and light grazing, was beneficial to increase of the annual diversity; (4) heavy grazing was not beneficial to diversity of Graminean and Chenopodiaceae, and moderate and light grazing was favorable the diversity of Compositae and Chenopodiaceae; (5) the warm-humid climate was favorable to increase of the richness and the diversity, and the warm-drought climate could result in decease of the richness and the diversity; (6) increased precipitation was favorable to perennial diversity and the diversity of Graminean, Leguminosae, and Compositae, and decreased precipitation had few effects on the annual diversity and Chenopodiaceae diversity.
基金Partly supported by Postdoctoral Foundation of China (No.24) and the National Natural Science Foundation of China (No. 39900084)
文摘Soil erosion can cause considerable effect on global natural resources and eco-environment. In the paper, the CENTURY model has been used to simulate soil erosion in Xilin Gol Grassland of Inner Mongolia. The results showed before the 1960s, the soil erosion amount was over 2 kg /m2.a in grassland ecosystem in the study area because no trees had been planted. But after the 1960s the mean annual accumulator C lost from soil organic matter due to soil erosion was only 0.3 kg /m2.a in forest ecosystem. So afforestation has exerted notable effect on decreasing soil erosion amount in Xilin Gol Grassland.
基金Supported by the Scientific Research Project of Hebei Higher Education(QN2015306)National Key Technology Research and Development Program of China during the 12th Five-Year Plan(2012BAD16B0302)
文摘Water was a key factor restricting the plantation in sandy areas. Foliar δ^(13)C value regarded as an indicator of longterm water use efficiency(WUE) of plants was generally used to evaluate the adaptability of plants to arid and semi-arid environment. In Horqin sandy land of China, the foliar δ^(13)C values of 114 species in 35 families naturally growing in the area, and 15 species of sand-fixing trees and shrubs were measured and analyzed in 2012. The results showed that 97 species in all 114 species were C_3 plants and only 17 species were C_4 plants. Most C_4 plants belonged to Gramineae family. The foliar δ^(13)C value of C_3 plants was between -25.000 and -31.075‰ with an average of-28.226‰, while those of C_4 plants between -12.578 and -16.334‰, with an average of -13.678‰. The δ^(13)C values of mature leaves collected in August were averagely 0.85‰ less than that of juvenile leaves collected in June. The foliar δ^(13)C values and WUE of 15 sand-fixing tree species in Horqin sandy land ranked in the order as: S.vulgaris >H.rhamnoides >C.ovata >P.mongolica >T.chinensis >R.typhina >S.matsudana >E.angustifolia >U.pumila >S.gordejevii >X.sorbifolia >C.microphylla >H.fruticosum >C.korshinskii >E.bungeanus.
基金Supported by Spark Project of the Ministry of Science and Technology(2015GA840007)National Forage Industry Technology System Fund Project of the Ministry of Agriculture for Tibet Experiment Station(CARS-35)National Nonprofit Industry Research Project(201203006)
文摘Construction of artificial grassland is a key factor to solve the shortage of grass and forage balance in cold and semi-arid areas of high plateau,and it is the key measure to ensure the sustainable development of grassland animal husbandry in this area. At present,the artificial grassland construction is neither reasonable nor scientific,which restricts the healthy and rapid development of artificial grassland in the cold and semi-arid areas of high plateau. In this research,with Naqu Area in Tibet as a case,problems and current status in construction process of artificial grassland are analyzed in cold and semi-arid areas of high plateau. Suitable artificial forage species in Nagqu are elaborated,and recommendations for the construction and development of artificial grassland are discussed.
基金Project supported by the National Natural Science Foundation of China (Nos. 40471004 and 40471083)the Innovation Foundation from the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (No. 2004110)
文摘Caragana microphylla Lam., a pioneer leguminous shrub species for vegetation re-establishment, is widely distributed in the semi-fixed and fixed sandy lands of the Horqin region. Some soil chemical and physical properties were measured under the canopy of C. microphylla and in the adjacent open areas to determine the effects of individual shrubs on soil properties. The influence of isolated C. microphylla on chemical and physical properties of the topsoil was significantly different between plots under the shrub canopy and in the shrub interspaces. Beneath the shrub canopy greater amounts of fine particle fractions, a higher water-holding capacity, and a lower bulk density, as well as higher aboveground and belowground litter biomass were found. Soil organic C and total N concentrations were 23%-31.6% and 14%-27.2% higher under the shrub canopies than in the shrub interspaces, respectively, giving rise to 'islands of fertility'. In a desertified sandy grassland ecosystem, C. microphylla was believed to play a major role in organic C sequestration, N accumulation, and the hydrologic cycle. Additionally, it has been found to be of ecological importance for vegetative restoration and reversal of desertification.
基金funded by the Program for New Century Excellent Talents in University (NCET-13-0487)the Program from Northwest A&F University (2014YQ007)+4 种基金the National Basic Research Program of China (2009CB118604)the National Science and Technology Support for Major Projects of China (2011BAD31B01)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-JC408)Science and Technology Generalized Program for the Overall Development of Agriculture in Ningxia (NTKJ-2014-01)the Scientific Research Program from Education Department of Shaanxi Province (11JK0650).
文摘Changes in the distribution of soil aggregate sizes and concentrations of aggregate-associated organic carbon （OC） and nitrogen （N） in response to the fertilization of grasslands are not well understood. Understanding these changes is essential to the sustainable development of artificial grasslands. For understanding these changes, we collected soil samples at 0-20 and 20-40 cm depths from a semi-arid artificial alfalfa grassland after 27 years of applications of phosphorus （P） and nitrogen＋phosphorus＋manure （NPM） fertilizers on the Loess Pla- teau of China. The distribution of aggregate sizes and the concentrations and stocks of OC and N in total soils were determined. The results showed that NPM treatment significantly increased the proportions of 〉2.0 mm and 2.0-0.25 mm size fractions, the mean geometric diameter （MGD） and the mean weight diameter （MWD） in the 0-20 cm layer. Phosphorous fertilizer significantly increased the proportion of 〉2.0 mm size fractions, the MGD and the MWD in the 0-20 cm layer. Long-term application of fertilization （P and NPM） resulted in the accumulation of OC and N in soil aggregates. The largest changes in aggregate-associated OC and N in the 0-20 cm layer were found at the NPM treatment, whereas the largest changes in the 20-40 cm layer were found at the P treatment. The results suggest that long-term fertilization in the grassland leads to the accumulation of OC and N in the coarse size fractions and the redistribution of OC and N from fine size fractions to coarse size fractions.
基金funded by the National Natural Science Foundation of China (41073061, 41203054, 40730105, 40973057)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-EW-302)
文摘Litter decomposition is the fundamental process in nutrient cycling and soil carbon（C） sequestration in terrestrial ecosystems. The global-wide increase in nitrogen（N） inputs is expected to alter litter decomposition and,ultimately, affect ecosystem C storage and nutrient status. Temperate grassland ecosystems in China are usually N-deficient and particularly sensitive to the changes in exogenous N additions. In this paper, we conducted a 1,200-day in situ experiment in a typical semi-arid temperate steppe in Inner Mongolia to investigate the litter decomposition as well as the dynamics of litter C and N concentrations under three N addition levels（low N with 50 kg N/（hm2？a）（LN）, medium N with 100 kg N/（hm2？a）（MN）, and high N with 200 kg N/（hm2？a）（HN）） and three N addition forms（ammonium-N-based with 100 kg N/（hm2？a） as ammonium sulfate（AS）, nitrate-N-based with 100 kg N/（hm2？a） as sodium nitrate（SN）, and mixed-N-based with 100 kg N/（hm2？a） as calcium ammonium nitrate（CAN）） compared to control with no N addition（CK）. The results indicated that the litter mass remaining in all N treatments exhibited a similar decomposition pattern： fast decomposition within the initial 120 days, followed by a relatively slow decomposition in the remaining observation period（120–1,200 days）. The decomposition pattern in each treatment was fitted well in two split-phase models, namely, a single exponential decay model in phase I（〈398 days） and a linear decay function in phase II（≥398 days）. The three N addition levels exerted insignificant effects on litter decomposition in the early stages（〈398 days, phase I; P〉0.05）. However, MN and HN treatments inhibited litter mass loss after 398 and 746 days, respectively（P〈0.05）. AS and SN treatments exerted similar effects on litter mass remaining during the entire decomposition period（P〉0.05）. The effects of these two N addition forms differed greatly from those of CAN after 746 and 1,053 days, respectively（P〈0.05）. During the decomposition period, N concentrations in the decomposing litter increased whereas C concentrations decreased, which also led to an exponential decrease in litter C：N ratios in all treatments. No significant effects were induced by N addition levels and forms on litter C and N concentrations（P〉0.05）. Our results indicated that exogenous N additions could exhibit neutral or inhibitory effects on litter decomposition, and the inhibitory effects of N additions on litter decomposition in the final decay stages are not caused by the changes in the chemical qualities of the litter, such as endogenous N and C concentrations. These results will provide an important data basis for the simulation and prediction of C cycle processes in future N-deposition scenarios.
基金financed by the National Natural Science Foundation of China(41301345,41101284)。
文摘The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carried out at 60%WHC(water holding capacity)and 25℃to evaluate the gross N transformation rates and N_(2)O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province,China.The results showed that the gross rates of N mineralization,immobilization,and nitrification were 3.60,1.90,and 5.63 mg N/(kg·d)in silt loam soil,respectively,which were 3.62,4.26,and 3.13 times those in sandy loam soil,respectively.The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia)in sandy loam soil and silt loam soil were all higher than 1.00,whereas the n/ia in sandy loam soil(4.36)was significantly higher than that in silt loam soil(3.08).This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil,and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_(3)–leaching.Under aerobic conditions,both nitrification and denitrification made contributions to N_(2)O emissions.Nitrification was the dominant pathway leading to N_(2)O production in soils and was responsible for 82.0%of the total emitted N_(2)O in sandy loam soil,which was significantly higher than that in silt loam soil(71.7%).However,the average contribution of denitrification to total N_(2)O production in sandy loam soil was 17.9%,which was significantly lower than that in silt loam soil(28.3%).These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.
基金financially supported by the National Key Basic Research Program of China (2014CB138803,2016YFC0500502)the Natural Science Foundation of China (31570451)the Program for Changjiang Scholars and Innovative Research Team in University (IRT_15R06)
文摘The main purpose of this study was to explore the dynamic changes of greenhouse gas（GHG）from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China.Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2,CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63–386.36 mg/（m·h）, CH4 uptake fluxes of 0.113–0.023 mg/（m·h） and N2O fluxes of –1.68–19.90 μg/（m·h）. Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes.Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.
基金funded by the Chinese Academy of Sciences(CAS)"Youth Scholar of West China"Program(XAB2019A04)the National Natural Science Foundation of China(42130717).
文摘Vegetation near-soil-surface factors can protect topsoil from erosion,however,their contributions to the reduction of soil erosion,especially under natural rainfall events,have not been systematically recognized.This study was performed to quantify the effects of near-soil-surface factors on runoff and sediment under natural rainfall events on grasslands dominated by Bothriochloa ischaemum(Linn.)Keng(BI grassland)and Artemisia gmelinii Thunb.(AG grassland)in two typical watersheds on the Loess Plateau,China in 2018.By successive removal of the plant canopy,litter,biological soil crusts(BSCs)and plant roots,we established five treatments including plant roots,plant roots+BSCs,plant roots+BSCs+litter,intact grassland and bare land in each grassland type.In total,twenty runoff plots(5 m×3 m)with similar slopes and aspects were constructed in the two types of grasslands.Results showed that plant canopy,litter and roots reduced runoff,while BSCs,which swelled in the presence of water,increased runoff.In contrast,all of these factors reduced sediment yield.In addition,the reductions in runoff and sediment yield increased with I30(maximum 30-min rainfall intensity)for each vegetation near-soil-surface factor except for BSCs.Among these factors,plant canopy had the largest contribution to runoff reduction,accounting for 48.8% and 39.9% in the BI and AG grasslands,respectively.The contributions of these vegetation near-soil-surface factors to sediment yield reduction were similar(21.3%-29.9%)in the two types of grasslands except for BSCs in the AG grassland(10.3%).The total reduction in runoff in the BI grassland(70.8%)was greater than that in the AG grassland(53.1%),while the reduction in sediment yield was almost the same in both grasslands(97.4%and 96.7%).In conclusion,according to the effects of different vegetation near-soil-surface factors on runoff and sediment production,our results may provide more complete insight and scientific basis into the effects of various vegetation related factors in controlling soil erosion.
基金funded by the European Commission under the Agricultural Innovations for Drylands Africa (AIDA),Grant Number 043863-SSA Africa (2006)
文摘The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years （1973-2007）. The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed： （1） woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and （2） an increase in undesirable woody species, livestock population and cultivated area had a significant （P〈0.05） negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.
