Irrigation in lowland rice production systems in Sub-Saharan Africa (SSA) is mainly based on traditional surface irrigation methods with continuous flooding practices. This irrigation method ends up using a lot more w...Irrigation in lowland rice production systems in Sub-Saharan Africa (SSA) is mainly based on traditional surface irrigation methods with continuous flooding practices. This irrigation method ends up using a lot more water that would have otherwise been used to open more land and be used in other water-requiring sectors. Various studies suggest Alternate Wetting and Drying (AWD) as an alternative practice for water management that reduces water use without significantly affecting yield. However, this practice has not been well adopted by the farmers despite its significant benefits of reduced total water use. Improving the adoption of AWD using irrigation Decision Support Systems (DSSs) helps the farmer on two fronts;to know “how much water to apply” and “when to irrigate”, which is very critical in maximizing productivity. This paper reviews the applicability of DSSs using AWD in lowland rice production systems in Sub-Saharan Africa.展开更多
Climate change-induced heat stress combines two challenges:high day-and nighttime temperatures,and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit.It is one of the m...Climate change-induced heat stress combines two challenges:high day-and nighttime temperatures,and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit.It is one of the major factors in low productivity of maize in rainfed stress-prone environments in South Asia,affecting a large population of smallholder farmers who depend on maize for their sustenance and livelihoods.The International Maize and Wheat Improvement Center(CIMMYT)maize program in Asia,in partnership with public-sector maize research institutes and private-sector seed companies in South Asian countries,is implementing an intensive initiative for developing and deploying heat-tolerant maize that combines high yield potential with resilience to heat and drought stresses.With the integration of novel breeding tools and methods,including genomics-assisted breeding,doubled haploidy,fieldbased precision phenotyping,and trait-based selection,new maize germplasm with increased tolerance to heat stress is being developed for the South Asian tropics.Over a decade of concerted effort has resulted in the successful development and release of 20 high-yielding heat-tolerant maize hybrids in CIMMYT genetic backgrounds.Via public–private partnerships,eight hybrids are presently being deployed on over 50,000 ha in South Asian countries,including Bangladesh,Bhutan,India,Nepal,and Pakistan.展开更多
Climate change caused by past,current,and future greenhouse gas emissions has become a major concern for scientists in the field in many countries and regions of the world.This study modelled future precipitation chan...Climate change caused by past,current,and future greenhouse gas emissions has become a major concern for scientists in the field in many countries and regions of the world.This study modelled future precipitation change by downscaling a set of large-scale climate predictor variables(predictors)from the second generation Canadian Earth System Model(CanESM2)under two Representative Concentration Pathway(RCP)emission scenarios(RCP4.5 and RCP8.5)in the semi-arid Borana lowland,southern Ethiopia.The Statistical DownScaling Model(SDSM)4.2.9 was employed to downscale and project future precipitation change in the middle(2036-2065;2050s)and far(2066-2095;2080s)future at the local scale.Historical precipitation observations from eight meteorological stations stretching from 1981 to 1995 and 1996 to 2005 were used for the model calibration and validation,respectively,and the time period of 1981-2018 was considered and used as the baseline period to analyze future precipitation change.The results revealed that the surface-specific humidity and the geopotential height at 500 hPa were the preferred large-scale predictors.Compared to the middle future(2050s),precipitation showed a much greater increase in the far future(2080s)under both RCP4.5 and RCP8.5 scenarios at all meteorological stations(except Teletele and Dillo stations).At Teltele station,the projected annual precipitation will decrease by 26.53%(2050s)and 39.45%(2080s)under RCP4.5 scenario,and 34.99%(2050s)and 60.62%(2080s)under RCP8.5 scenario.Seasonally,the main rainy period would shift from spring(March to May)to autumn(September to November)at Dehas,Dire,Moyale,and Teltele stations,but for Arero and Yabelo stations,spring would consistently receive more precipitation than autumn.It can be concluded that future precipitation in the semi-arid Borana lowland is predicted to differ under the two climate scenarios(RCP4.5 and RCP8.5),showing an increasing trend at most meteorological stations.This information could be helpful for policymakers to design adaptation plans in water resources management,and we suggest that the government should give more attention to improve early warning systems in drought-prone areas by providing dependable climate forecast information as early as possible.展开更多
Mountains are paramount for exploring biodiversity patterns due to the mosaic of topographies and climates encompassed over short distances.Biodiversity research has traditionally focused on taxonomic diversity when i...Mountains are paramount for exploring biodiversity patterns due to the mosaic of topographies and climates encompassed over short distances.Biodiversity research has traditionally focused on taxonomic diversity when investigating changes along elevational gradients,but other facets should be considered.For first time,we simultaneously assessed elevational trends in taxonomic,functional,and phylogenetic diversity of woody plants in Andean tropical montane forests and explored their underlying ecological and evolutionary causes.This investigation covered four transects(traversing ca.2200 m a.s.l.) encompassing 114 plots of 0.1 ha across a broad latitudinal range(ca.10°).Using Hill numbers to quantify abundance-based diversity among 37,869 individuals we observed a consistent decrease in taxonomic,functional,and phylogenetic diversity as elevation increased,although the decrease was less pronounced for higher Hill orders.The exception was a slight increase in phylogenetic diversity when dominant species were over-weighted.The decrease in taxonomic and functional diversity might be attributed to an environmental filtering process towards highlands,where the increasingly harsher conditions exclude species and functional strategies.Besides,the differences in steepness decrease between Hill orders suggest that rare species disproportionately contribute to functional diversity.For phylogenetic diversity the shifting elevational trend between Hill orders indicates a greater than previously considered influence in central Andean highlands of tropical lowlands originated species with strong niche conservatism relative to distantly related temperate lineages.This could be explained by a decreasing presence and abundance of temperate,extratropical taxa towards the central Andes relative to northern or southern Andes,where they are more prevalent.展开更多
Heat-tolerant varieties, such as N22 and Dular, which were used in this study, usually have low yield potential and undesirable plant characteristics but combining them with high yielding and improved rice varieties, ...Heat-tolerant varieties, such as N22 and Dular, which were used in this study, usually have low yield potential and undesirable plant characteristics but combining them with high yielding and improved rice varieties, new heat-tolerant rice genotypes with high yield potential can be achieved. In this study, phenotyping and selecting desirable materials from various crosses were performed under high temperature conditions during the reproductive stage. Screening was performed in the field and glasshouse to select individuals with heat tolerance and high yield potential. Several advanced breeding lines from Gayabyeo/N22 cross produced desirable individuals with heat tolerance, resistance to pests and diseases, and high yield potential. The genetic variation in percent sterility among the selected backcross populations grown in high temperature environments showed that large number of plants can be identified and selected with lower percent sterility.展开更多
The lowland rainforests of Meghalaya, India represent the westernmost limit of the rainforests north of the Tropic of Cancer. These forests, on the Shillong plateau, are akin to Whitmore's ‘tropical lowland everg...The lowland rainforests of Meghalaya, India represent the westernmost limit of the rainforests north of the Tropic of Cancer. These forests, on the Shillong plateau, are akin to Whitmore's ‘tropical lowland evergreen rainforest' formation and exhibit striking similarities and conspicuous differences with the equatorial rainforests in Asia-Pacific as well as tropical seasonal rainforests in southwestern China near the Tropic of Cancer. We found these common attributes of the rainforests in Meghalaya: familial composition with predominance of Euphorbiaceae, Lauraceae, Meliaceae, Moraceae, Myrsiticaceae,Myrtaceae and Rubiaceae; deciduousness in evergreen physiognomy; dominance of mega-and mesophanerophytic life-forms; abundance of species with low frequency of occurrence(rare and aggregated species); low proportional abundance of the abundant species; and truncated lognormal abundance distribution. The levels of stand density and stand basal area were comparable with seasonal rainforests in southwestern China, but were lower than equatorial rainforests. Tropical Asian species predominated flora, commanding 95% of the abundance. The differences include overall low stature(height) of the forest, inconspicuous stratification in canopy, fewer species and individuals of liana, thicker understory,higher proportion of rare species, absence of locally endemic species and relatively greater dominance of Fagaceae and Theaceae. The richness of species per hectare(S) was considerably lower at higher latitudes in Meghalaya than in equatorial rainforests, but was comparable with seasonal rainforests. Shannon's diversity index(H’=4.40 nats for ≥10 cm gbh and 4.25 nats for ≥30 cm gbh) was lower on higher latitudes in Meghalaya in comparison to species-rich equatorial rainforests, but it was the highest among all lowland rainforests near the Tropic of Cancer.展开更多
Tropical forests play a critical role in mitigating climate change because they account for large amount o terrestrial carbon storage and productivity.However,there are many uncertainties associated with the estimatio...Tropical forests play a critical role in mitigating climate change because they account for large amount o terrestrial carbon storage and productivity.However,there are many uncertainties associated with the estimation o carbon dynamics.We estimated forest structure and carbon dynamics along a slope（17.3°–42.8°）and to assess the relations between forest structures,carbon dynamics,and slopes in an intact lowland mixed dipterocarp forest,in Kuala Belalong,Brunei Darussalam.Living biomass,basa area,stand density,crown properties,and tree family composition were measured for forest structure.Growth rate,litter production,and litter decomposition rates were also measured for carbon dynamics.The crown form index and the crown position index were used to assess crown properties,which we categorized into five stages,from very poor to perfect.The living biomass,basal area and stand density were 261.5–940.7 Mg ha-1,43.6–63.6 m2ha-1and 6,675–8400 tree ha-1,respectively.The average crown form and position index were 4,which means that the crown are mostly symmetrical and sufficiently exposed for photosynthesis.The mean biomass growth rate,litter production,litter decomposition rate were estimated as11.9,11.6 Mg ha-1a-1,and 7.2 g a-1,respectively.Biomass growth rate was significantly correlated with living biomass,basal area,and crown form.Crown form appeared to strongly influence living biomass,basal area and biomass growth rate in terms of light acquisition.However,basal area,stand density,crown properties,and biomass growth rate did not vary by slope or tree family composition.The results indicate that carbon accumulation by tree growth in an intact lowland mixed dipterocarp forest depends on crown properties.Absence of any effect of tree family composition on carbon accumulation suggests that the main driver of biomass accumulation in old-growth forests of Borneo is not species-specific characteristics of tree species.展开更多
Genetic diversity of rice landraces from lowland and upland accessions of China was investigated using 66 polymorphic simple sequence repeat （SSR） markers. The total number of alleles detected from all 324 tested ac...Genetic diversity of rice landraces from lowland and upland accessions of China was investigated using 66 polymorphic simple sequence repeat （SSR） markers. The total number of alleles detected from all 324 tested accessions was 555 with an average allele number （Na） of 8.409 per locus, the average effective number of alleles （Ne） of 3.574 and the average Shannon＇s information index （I） of 1.378. The genetic diversity was higher for the indica landraces compared to the japonica landraces, and the upland landraces were more genetically diverse than the lowland landraces. The SSR markers, RM72, RM232, RM219, RM241, RM224 and RM3 showed the highest rates of polymorphism and these SSR markers were suitable to assess the genetic diversity of rice germplasm resources. A dendrogram of 324 accessions of lowland and upland landraces showed that all rice accessions were mainly subdivided into two groups, japonica and indica, with some being intermediate. The distribution of lowland and upland landraces among the japonica and indica rice groups was distinct, with obvious differentiation between the lowland and upland landraces in japonica rice, but no such clear distinction in indica rice.展开更多
Background:Peatlands form one of the largest carbon pools in the terrestrial ecosystems,representing approximately one-third of the world’s soil carbon.The aim of this study was to evaluate C:N:P stoichiometry as an ...Background:Peatlands form one of the largest carbon pools in the terrestrial ecosystems,representing approximately one-third of the world’s soil carbon.The aim of this study was to evaluate C:N:P stoichiometry as an indicator of changes initialized by dehydration in Histosols of varied origins.Four types of Histosols from lowland and mountain areas were investigated:fibric Histosols,hemic Histosols,sapric Histosols and Histosols drainic.Results:We established the concentration and stoichiometry of carbon,nitrogen and phosphorous in the Histosols,and found marked differences in C:N:P stoichiometry between the different types–especially the dehydrated samples.The mean C:N:P ratio of dehydrated soil was narrower than the C:N:P ratio of soil under the influence of water,which demonstrates that dehydrating Histosols leads to a narrower C:N:P stoichiometry.This is directly related to the intensification of the organic matter mineralisation process and the resulting loss of organic carbon.We recorded a 50%lower carbon stock in the case of Histosols drainic compared to the other types of Histosols.Conclusions:The narrower C:N:P stoichiometry in Histosols drainic is the result of an decrease in the ratio of N and P to the C content.Thus,this study demonstrates that C:N:P stoichiometry is a useful indicator of the changes that occur in Histosols as a result of dehydration.展开更多
Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction a...Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.展开更多
Livelihood assets are a matter of high concern for secured survival.Drought-prone Gamo lowland households have differential access to livelihood resources which indicates the varying capacity of resisting to shocks.Th...Livelihood assets are a matter of high concern for secured survival.Drought-prone Gamo lowland households have differential access to livelihood resources which indicates the varying capacity of resisting to shocks.The main objective of this study is to explore the impacts of livelihood assets on livelihood security in the drought-prone Gamo lowlands.Multistage sampling procedures were employed to select the study sites and sample respondents.Primary data of households’capital assets and livelihood security status were produced from 285 survey households,agricultural experts,key informants,focus group discussants,and field observation through transect walks.Descriptive and inferential statistics were used to analyze quantitative data,whereas discussions and annotations were employed for analyzing qualitative data.The Sustainable Livelihoods Framework is used with modifications to schematize the study conceptually.The findings indicated that the study households possessed combinations of livelihood resources differentially.Financial and natural capitals were found to be the most deficient and better-accessed capitals,respectively.The study also showed that lowland residents’access to assets has significant indications of livelihood security.Households’poor access to assets such as financial,information,and social capital demands raised attention of the concerned stakeholders and policy debates in the drought-prone rural setup.Hence,it has been concluded that the more assets are accessed,the stronger the capacity of the households to resist shocks,and better the livelihood security.Accordingly,enhancing people’s access to multiple livelihood assets is suggested to sustainably secure livelihoods.展开更多
The coastal lowlands in northern Jiangsu Province, China, is characterized by low relief and low water surface gradient in streams. The flooding stages are commonly lower than the high-tide level and the tidal range i...The coastal lowlands in northern Jiangsu Province, China, is characterized by low relief and low water surface gradient in streams. The flooding stages are commonly lower than the high-tide level and the tidal range is relatively small. All these factors prohibit rapid discharge of floodwater and make the flood regimes here extremely sensitive to the sea level rise. The 1991 Plum Rain was examined, when precipitation was significantly higher than normal. The one-dimensional open-channel non-conservative flow model was used to simulate the stream flow in the channel network of studied area. GIS technology was used to delineate the maximum in undated area by analyzing the DEMs.展开更多
Silicon(Si) is known as a beneficial nutrient in the cultivation of rice, playing a key role in photosynthesis enhancement, lodging resistance and tolerance to various environmental stress. The present study aimed to ...Silicon(Si) is known as a beneficial nutrient in the cultivation of rice, playing a key role in photosynthesis enhancement, lodging resistance and tolerance to various environmental stress. The present study aimed to examine available Si content in both lowland soils(n = 29) and neighboring upland soils(n = 21) collected from Benin and Nigeria and to evaluate the validity of the assessment results through a pot experiment. Our results revealed that the acetate-buffer method predicted Si concentration in rice straw at the harvest stage(R^2 = 0.68, P < 0.01) better than the anaerobic-incubation method(R2 = 0.31, P > 0.05), and 76% of the uplands and 38% of the lowlands were deficient(< 50 mg/kg) in acetate-buffer soluble Si. These findings suggest that the Si-deficiency soils prevail across the study area, making rice plants starved for Si and prone to environmental stress.展开更多
The aim of this paper is to discuss the reasonable method to set up the man-made ecosystem where the high productivity, high economic effects and ecological efficiencies, continual resources and suitable environment c...The aim of this paper is to discuss the reasonable method to set up the man-made ecosystem where the high productivity, high economic effects and ecological efficiencies, continual resources and suitable environment could be obtained.展开更多
The difference in protein content, MDH,POD and COD isozymes have been seenbetween lowland rice roots and upland rice roots during root growth and development. High pro-tein content has been examined in upland rice roo...The difference in protein content, MDH,POD and COD isozymes have been seenbetween lowland rice roots and upland rice roots during root growth and development. High pro-tein content has been examined in upland rice roots,but isozyme bands in lowland rice roots aremore than that in upland rice roots.Total area of POD isozyme bands at seedling and tilleringstages of upland rice is larger than that of lowland rice.The POD isozymes zymogram in the rootof upland rice is more stable compared with that of lowland rice.More COD isozyme numbershave been showed in roots of upland rice,but the relative activity of COD isozyme in roots of up-land rice at the seedling and tillering stages is lower than that of lowland rice.COD<sub>7</sub> band can beshown in upland rice root at flowering stage,but it is absent in lowland rice.Therefore,COD<sub>7</sub>,band can be taken as an index for resistance of the upland rice to drought environment.展开更多
Development pressure has led to serious deforestation on the Indochina Peninsula. Particularly rapid defor-estation has occurred in easily accessible lowland areas, and it is thus important to accumulate knowledge abo...Development pressure has led to serious deforestation on the Indochina Peninsula. Particularly rapid defor-estation has occurred in easily accessible lowland areas, and it is thus important to accumulate knowledge about these forests immediately. We measured evapotranspiration rates for a lowland dry evergreen forest in Kampong Thom Province, central Cambodia, using the energy balance Bowen ratio (EBBR) method based on meteorological data collected from a 60-m-high observation tower. Daily evapotranspiration was higher during the dry season than during the rainy season of the Asian monsoon climate. The seasonal variation in evapotranspiration generally corresponded to the seasonal difference in the vapor pressure deficit. A multi-layer model was used to simulate the seasonal variation in evapotranspiration. The multilayer model also reproduced the larger evapotranspiration rate in the dry season than in the rainy season. However, observed values substantially exceeded model-calculated results during certain periods at the beginning of the dry season and in the late dry season. Moreover, during the rainy season, the model tended to overestimate evapotranspiration. The differences between these observed and simulated values may have been caused by seasonal characteristics of photosynthesis and transpiration in the lowland dry evergreen forest that were not considered in the model simulation.展开更多
We investigated the effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation. We selected a study village in Khammouane province, central Laos, and set up non-puddling and puddling plots...We investigated the effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation. We selected a study village in Khammouane province, central Laos, and set up non-puddling and puddling plots from high to low positions. Even when puddling was conducted carefully, the ponding water in the plots disappeared in the case of little rainfall. Further, percolatifons during the later periods of rice growth increased drastically. Therefore, it is difficult to overcome drought stresses only by conducting puddling. We also compared the water conditions in the non-puddling and puddling plots. In the puddling plots at high position and low position along a stream, the number of days without ponding water in the puddling plots was less than that in the non-puddling field in July, suggesting the possibility of a different transplanting date. We tried to estimate the effects of transplanting date on the rice yields and found that transplanting 15 days earlier leads to an increase of 0.5 t/ha in the rice yields. Moreover, the profits from the increased yields exceed the puddling costs considerably, leading to a definite increase in income. Because the transplanting date has no effects in the fields with high ground water, puddling is effective in paddy fields where ponding does not occur to a significant degree.展开更多
Field surveys indicate lateral variation in peat humification levels （von Post） in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of...Field surveys indicate lateral variation in peat humification levels （von Post） in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers （silt,clays and fine sands） obtained from Quaternary floodplain deposits and residual soil （weathered schist）.The unconfined compressive strength （UCS） of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength （UCS） in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages （due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome）.展开更多
Lowland water resources management represents a challenge of the future that calls any community. Irrigated crops are grown in some areas of Burkina Faso, others are limited by a lack of irrigation infrastructure. Due...Lowland water resources management represents a challenge of the future that calls any community. Irrigated crops are grown in some areas of Burkina Faso, others are limited by a lack of irrigation infrastructure. Due to limited crop irrigation, crops and the associated populations dependent on them, depend on rain and on climatic factors. Thus, there is a need to understand and implement traditional mechanisms for managing lowland water in Dano, where climatic and geological conditions provide a sustained source of water. Here, I use a literature review combined with field work and interviews/questionnaires to estimate the potential exploitable plains to 16,056 ha or 24% of the communal area. Management mechanisms and traditional operating systems of lowland waters were clear, which helped to set the technological level of farmers, in partial control of water management.展开更多
文摘Irrigation in lowland rice production systems in Sub-Saharan Africa (SSA) is mainly based on traditional surface irrigation methods with continuous flooding practices. This irrigation method ends up using a lot more water that would have otherwise been used to open more land and be used in other water-requiring sectors. Various studies suggest Alternate Wetting and Drying (AWD) as an alternative practice for water management that reduces water use without significantly affecting yield. However, this practice has not been well adopted by the farmers despite its significant benefits of reduced total water use. Improving the adoption of AWD using irrigation Decision Support Systems (DSSs) helps the farmer on two fronts;to know “how much water to apply” and “when to irrigate”, which is very critical in maximizing productivity. This paper reviews the applicability of DSSs using AWD in lowland rice production systems in Sub-Saharan Africa.
基金the support of USAID under the Feed the Future Initiative of the U.S.government through the project Heat Tolerant Maize for Asia(Grant No.:CGIAR Trust Fund MTO No.069033)/CIMMYT)Financial support received earlier from the CGIAR Research Program MAIZEthe CGIAR Initiatives on Accelerated Breeding and SeEdQUAL。
文摘Climate change-induced heat stress combines two challenges:high day-and nighttime temperatures,and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit.It is one of the major factors in low productivity of maize in rainfed stress-prone environments in South Asia,affecting a large population of smallholder farmers who depend on maize for their sustenance and livelihoods.The International Maize and Wheat Improvement Center(CIMMYT)maize program in Asia,in partnership with public-sector maize research institutes and private-sector seed companies in South Asian countries,is implementing an intensive initiative for developing and deploying heat-tolerant maize that combines high yield potential with resilience to heat and drought stresses.With the integration of novel breeding tools and methods,including genomics-assisted breeding,doubled haploidy,fieldbased precision phenotyping,and trait-based selection,new maize germplasm with increased tolerance to heat stress is being developed for the South Asian tropics.Over a decade of concerted effort has resulted in the successful development and release of 20 high-yielding heat-tolerant maize hybrids in CIMMYT genetic backgrounds.Via public–private partnerships,eight hybrids are presently being deployed on over 50,000 ha in South Asian countries,including Bangladesh,Bhutan,India,Nepal,and Pakistan.
文摘Climate change caused by past,current,and future greenhouse gas emissions has become a major concern for scientists in the field in many countries and regions of the world.This study modelled future precipitation change by downscaling a set of large-scale climate predictor variables(predictors)from the second generation Canadian Earth System Model(CanESM2)under two Representative Concentration Pathway(RCP)emission scenarios(RCP4.5 and RCP8.5)in the semi-arid Borana lowland,southern Ethiopia.The Statistical DownScaling Model(SDSM)4.2.9 was employed to downscale and project future precipitation change in the middle(2036-2065;2050s)and far(2066-2095;2080s)future at the local scale.Historical precipitation observations from eight meteorological stations stretching from 1981 to 1995 and 1996 to 2005 were used for the model calibration and validation,respectively,and the time period of 1981-2018 was considered and used as the baseline period to analyze future precipitation change.The results revealed that the surface-specific humidity and the geopotential height at 500 hPa were the preferred large-scale predictors.Compared to the middle future(2050s),precipitation showed a much greater increase in the far future(2080s)under both RCP4.5 and RCP8.5 scenarios at all meteorological stations(except Teletele and Dillo stations).At Teltele station,the projected annual precipitation will decrease by 26.53%(2050s)and 39.45%(2080s)under RCP4.5 scenario,and 34.99%(2050s)and 60.62%(2080s)under RCP8.5 scenario.Seasonally,the main rainy period would shift from spring(March to May)to autumn(September to November)at Dehas,Dire,Moyale,and Teltele stations,but for Arero and Yabelo stations,spring would consistently receive more precipitation than autumn.It can be concluded that future precipitation in the semi-arid Borana lowland is predicted to differ under the two climate scenarios(RCP4.5 and RCP8.5),showing an increasing trend at most meteorological stations.This information could be helpful for policymakers to design adaptation plans in water resources management,and we suggest that the government should give more attention to improve early warning systems in drought-prone areas by providing dependable climate forecast information as early as possible.
基金Guillermo Bañares was funded through grants from the Spanish Ministry of Education (FPU14/05303),Escuela Internacional de Doctorado-Universidad Rey Juan Carlos (Doctor Internacional 2017)and the Education and Research Department of Madrid Autonomous Region Government (REMEDINAL TE,S2018/EMT-4338)supported through three grants from the Spanish Ministries of Economy and Competitiveness and Science and Technology (CGL2013-45634-P,CGL2016-75414-P,and PID2019-105064 GB-I00)a grant from Centro de Estudios de América Latina (CEAL)at Universidad Autónoma de Madrid and Banco Santander.
文摘Mountains are paramount for exploring biodiversity patterns due to the mosaic of topographies and climates encompassed over short distances.Biodiversity research has traditionally focused on taxonomic diversity when investigating changes along elevational gradients,but other facets should be considered.For first time,we simultaneously assessed elevational trends in taxonomic,functional,and phylogenetic diversity of woody plants in Andean tropical montane forests and explored their underlying ecological and evolutionary causes.This investigation covered four transects(traversing ca.2200 m a.s.l.) encompassing 114 plots of 0.1 ha across a broad latitudinal range(ca.10°).Using Hill numbers to quantify abundance-based diversity among 37,869 individuals we observed a consistent decrease in taxonomic,functional,and phylogenetic diversity as elevation increased,although the decrease was less pronounced for higher Hill orders.The exception was a slight increase in phylogenetic diversity when dominant species were over-weighted.The decrease in taxonomic and functional diversity might be attributed to an environmental filtering process towards highlands,where the increasingly harsher conditions exclude species and functional strategies.Besides,the differences in steepness decrease between Hill orders suggest that rare species disproportionately contribute to functional diversity.For phylogenetic diversity the shifting elevational trend between Hill orders indicates a greater than previously considered influence in central Andean highlands of tropical lowlands originated species with strong niche conservatism relative to distantly related temperate lineages.This could be explained by a decreasing presence and abundance of temperate,extratropical taxa towards the central Andes relative to northern or southern Andes,where they are more prevalent.
基金supported by the ASEAN-Korea Economic Cooperation Fundthe Ministry of Foreign Affairs and Trade, South Koreathe Rural Development Administration, Republic of Korea
文摘Heat-tolerant varieties, such as N22 and Dular, which were used in this study, usually have low yield potential and undesirable plant characteristics but combining them with high yielding and improved rice varieties, new heat-tolerant rice genotypes with high yield potential can be achieved. In this study, phenotyping and selecting desirable materials from various crosses were performed under high temperature conditions during the reproductive stage. Screening was performed in the field and glasshouse to select individuals with heat tolerance and high yield potential. Several advanced breeding lines from Gayabyeo/N22 cross produced desirable individuals with heat tolerance, resistance to pests and diseases, and high yield potential. The genetic variation in percent sterility among the selected backcross populations grown in high temperature environments showed that large number of plants can be identified and selected with lower percent sterility.
基金The Department of Biotechnology,New Delhi provided principal funding through a grant to US(BT/PR7928/NDB/52/9/2006)
文摘The lowland rainforests of Meghalaya, India represent the westernmost limit of the rainforests north of the Tropic of Cancer. These forests, on the Shillong plateau, are akin to Whitmore's ‘tropical lowland evergreen rainforest' formation and exhibit striking similarities and conspicuous differences with the equatorial rainforests in Asia-Pacific as well as tropical seasonal rainforests in southwestern China near the Tropic of Cancer. We found these common attributes of the rainforests in Meghalaya: familial composition with predominance of Euphorbiaceae, Lauraceae, Meliaceae, Moraceae, Myrsiticaceae,Myrtaceae and Rubiaceae; deciduousness in evergreen physiognomy; dominance of mega-and mesophanerophytic life-forms; abundance of species with low frequency of occurrence(rare and aggregated species); low proportional abundance of the abundant species; and truncated lognormal abundance distribution. The levels of stand density and stand basal area were comparable with seasonal rainforests in southwestern China, but were lower than equatorial rainforests. Tropical Asian species predominated flora, commanding 95% of the abundance. The differences include overall low stature(height) of the forest, inconspicuous stratification in canopy, fewer species and individuals of liana, thicker understory,higher proportion of rare species, absence of locally endemic species and relatively greater dominance of Fagaceae and Theaceae. The richness of species per hectare(S) was considerably lower at higher latitudes in Meghalaya than in equatorial rainforests, but was comparable with seasonal rainforests. Shannon's diversity index(H’=4.40 nats for ≥10 cm gbh and 4.25 nats for ≥30 cm gbh) was lower on higher latitudes in Meghalaya in comparison to species-rich equatorial rainforests, but it was the highest among all lowland rainforests near the Tropic of Cancer.
基金supported by research grants from the Korea Forest Service(S121314L130100)
文摘Tropical forests play a critical role in mitigating climate change because they account for large amount o terrestrial carbon storage and productivity.However,there are many uncertainties associated with the estimation o carbon dynamics.We estimated forest structure and carbon dynamics along a slope（17.3°–42.8°）and to assess the relations between forest structures,carbon dynamics,and slopes in an intact lowland mixed dipterocarp forest,in Kuala Belalong,Brunei Darussalam.Living biomass,basa area,stand density,crown properties,and tree family composition were measured for forest structure.Growth rate,litter production,and litter decomposition rates were also measured for carbon dynamics.The crown form index and the crown position index were used to assess crown properties,which we categorized into five stages,from very poor to perfect.The living biomass,basal area and stand density were 261.5–940.7 Mg ha-1,43.6–63.6 m2ha-1and 6,675–8400 tree ha-1,respectively.The average crown form and position index were 4,which means that the crown are mostly symmetrical and sufficiently exposed for photosynthesis.The mean biomass growth rate,litter production,litter decomposition rate were estimated as11.9,11.6 Mg ha-1a-1,and 7.2 g a-1,respectively.Biomass growth rate was significantly correlated with living biomass,basal area,and crown form.Crown form appeared to strongly influence living biomass,basal area and biomass growth rate in terms of light acquisition.However,basal area,stand density,crown properties,and biomass growth rate did not vary by slope or tree family composition.The results indicate that carbon accumulation by tree growth in an intact lowland mixed dipterocarp forest depends on crown properties.Absence of any effect of tree family composition on carbon accumulation suggests that the main driver of biomass accumulation in old-growth forests of Borneo is not species-specific characteristics of tree species.
基金supported by the National Basic Research Program of China(Grant No.2010CB125904-5)the National Key Technology Research and Development Program of China(Grant No.2013BAD01B02-2)the Protective Program of Crop Germpalsm of China(Grant No.NB2012-2130135-25-01)
文摘Genetic diversity of rice landraces from lowland and upland accessions of China was investigated using 66 polymorphic simple sequence repeat （SSR） markers. The total number of alleles detected from all 324 tested accessions was 555 with an average allele number （Na） of 8.409 per locus, the average effective number of alleles （Ne） of 3.574 and the average Shannon＇s information index （I） of 1.378. The genetic diversity was higher for the indica landraces compared to the japonica landraces, and the upland landraces were more genetically diverse than the lowland landraces. The SSR markers, RM72, RM232, RM219, RM241, RM224 and RM3 showed the highest rates of polymorphism and these SSR markers were suitable to assess the genetic diversity of rice germplasm resources. A dendrogram of 324 accessions of lowland and upland landraces showed that all rice accessions were mainly subdivided into two groups, japonica and indica, with some being intermediate. The distribution of lowland and upland landraces among the japonica and indica rice groups was distinct, with obvious differentiation between the lowland and upland landraces in japonica rice, but no such clear distinction in indica rice.
基金supported by the Ministry of Science and Higher Education of the Republic of Poland(SUB/040012/D019A425,A428).
文摘Background:Peatlands form one of the largest carbon pools in the terrestrial ecosystems,representing approximately one-third of the world’s soil carbon.The aim of this study was to evaluate C:N:P stoichiometry as an indicator of changes initialized by dehydration in Histosols of varied origins.Four types of Histosols from lowland and mountain areas were investigated:fibric Histosols,hemic Histosols,sapric Histosols and Histosols drainic.Results:We established the concentration and stoichiometry of carbon,nitrogen and phosphorous in the Histosols,and found marked differences in C:N:P stoichiometry between the different types–especially the dehydrated samples.The mean C:N:P ratio of dehydrated soil was narrower than the C:N:P ratio of soil under the influence of water,which demonstrates that dehydrating Histosols leads to a narrower C:N:P stoichiometry.This is directly related to the intensification of the organic matter mineralisation process and the resulting loss of organic carbon.We recorded a 50%lower carbon stock in the case of Histosols drainic compared to the other types of Histosols.Conclusions:The narrower C:N:P stoichiometry in Histosols drainic is the result of an decrease in the ratio of N and P to the C content.Thus,this study demonstrates that C:N:P stoichiometry is a useful indicator of the changes that occur in Histosols as a result of dehydration.
基金Supported by the China Geological Survey(No.121201006000182401)the National Natural Science Foundation of China(Nos.41476074,41372173)
文摘Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.
文摘Livelihood assets are a matter of high concern for secured survival.Drought-prone Gamo lowland households have differential access to livelihood resources which indicates the varying capacity of resisting to shocks.The main objective of this study is to explore the impacts of livelihood assets on livelihood security in the drought-prone Gamo lowlands.Multistage sampling procedures were employed to select the study sites and sample respondents.Primary data of households’capital assets and livelihood security status were produced from 285 survey households,agricultural experts,key informants,focus group discussants,and field observation through transect walks.Descriptive and inferential statistics were used to analyze quantitative data,whereas discussions and annotations were employed for analyzing qualitative data.The Sustainable Livelihoods Framework is used with modifications to schematize the study conceptually.The findings indicated that the study households possessed combinations of livelihood resources differentially.Financial and natural capitals were found to be the most deficient and better-accessed capitals,respectively.The study also showed that lowland residents’access to assets has significant indications of livelihood security.Households’poor access to assets such as financial,information,and social capital demands raised attention of the concerned stakeholders and policy debates in the drought-prone rural setup.Hence,it has been concluded that the more assets are accessed,the stronger the capacity of the households to resist shocks,and better the livelihood security.Accordingly,enhancing people’s access to multiple livelihood assets is suggested to sustainably secure livelihoods.
基金Project supported by the SUS-DSD Cooperative Foundation between the Netherlands and China
文摘The coastal lowlands in northern Jiangsu Province, China, is characterized by low relief and low water surface gradient in streams. The flooding stages are commonly lower than the high-tide level and the tidal range is relatively small. All these factors prohibit rapid discharge of floodwater and make the flood regimes here extremely sensitive to the sea level rise. The 1991 Plum Rain was examined, when precipitation was significantly higher than normal. The one-dimensional open-channel non-conservative flow model was used to simulate the stream flow in the channel network of studied area. GIS technology was used to delineate the maximum in undated area by analyzing the DEMs.
基金financial support by the Japan Society for the Promotion of Science (Grant No. 19002001)the Ministry of Agriculture, Forestry and Fisheries and the Ministry of Foreign Affairs, Japan
文摘Silicon(Si) is known as a beneficial nutrient in the cultivation of rice, playing a key role in photosynthesis enhancement, lodging resistance and tolerance to various environmental stress. The present study aimed to examine available Si content in both lowland soils(n = 29) and neighboring upland soils(n = 21) collected from Benin and Nigeria and to evaluate the validity of the assessment results through a pot experiment. Our results revealed that the acetate-buffer method predicted Si concentration in rice straw at the harvest stage(R^2 = 0.68, P < 0.01) better than the anaerobic-incubation method(R2 = 0.31, P > 0.05), and 76% of the uplands and 38% of the lowlands were deficient(< 50 mg/kg) in acetate-buffer soluble Si. These findings suggest that the Si-deficiency soils prevail across the study area, making rice plants starved for Si and prone to environmental stress.
文摘The aim of this paper is to discuss the reasonable method to set up the man-made ecosystem where the high productivity, high economic effects and ecological efficiencies, continual resources and suitable environment could be obtained.
文摘The difference in protein content, MDH,POD and COD isozymes have been seenbetween lowland rice roots and upland rice roots during root growth and development. High pro-tein content has been examined in upland rice roots,but isozyme bands in lowland rice roots aremore than that in upland rice roots.Total area of POD isozyme bands at seedling and tilleringstages of upland rice is larger than that of lowland rice.The POD isozymes zymogram in the rootof upland rice is more stable compared with that of lowland rice.More COD isozyme numbershave been showed in roots of upland rice,but the relative activity of COD isozyme in roots of up-land rice at the seedling and tillering stages is lower than that of lowland rice.COD<sub>7</sub> band can beshown in upland rice root at flowering stage,but it is absent in lowland rice.Therefore,COD<sub>7</sub>,band can be taken as an index for resistance of the upland rice to drought environment.
文摘Development pressure has led to serious deforestation on the Indochina Peninsula. Particularly rapid defor-estation has occurred in easily accessible lowland areas, and it is thus important to accumulate knowledge about these forests immediately. We measured evapotranspiration rates for a lowland dry evergreen forest in Kampong Thom Province, central Cambodia, using the energy balance Bowen ratio (EBBR) method based on meteorological data collected from a 60-m-high observation tower. Daily evapotranspiration was higher during the dry season than during the rainy season of the Asian monsoon climate. The seasonal variation in evapotranspiration generally corresponded to the seasonal difference in the vapor pressure deficit. A multi-layer model was used to simulate the seasonal variation in evapotranspiration. The multilayer model also reproduced the larger evapotranspiration rate in the dry season than in the rainy season. However, observed values substantially exceeded model-calculated results during certain periods at the beginning of the dry season and in the late dry season. Moreover, during the rainy season, the model tended to overestimate evapotranspiration. The differences between these observed and simulated values may have been caused by seasonal characteristics of photosynthesis and transpiration in the lowland dry evergreen forest that were not considered in the model simulation.
文摘We investigated the effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation. We selected a study village in Khammouane province, central Laos, and set up non-puddling and puddling plots from high to low positions. Even when puddling was conducted carefully, the ponding water in the plots disappeared in the case of little rainfall. Further, percolatifons during the later periods of rice growth increased drastically. Therefore, it is difficult to overcome drought stresses only by conducting puddling. We also compared the water conditions in the non-puddling and puddling plots. In the puddling plots at high position and low position along a stream, the number of days without ponding water in the puddling plots was less than that in the non-puddling field in July, suggesting the possibility of a different transplanting date. We tried to estimate the effects of transplanting date on the rice yields and found that transplanting 15 days earlier leads to an increase of 0.5 t/ha in the rice yields. Moreover, the profits from the increased yields exceed the puddling costs considerably, leading to a definite increase in income. Because the transplanting date has no effects in the fields with high ground water, puddling is effective in paddy fields where ponding does not occur to a significant degree.
基金the IPPP grant PV018-2011A for financial support from the University of Malaya
文摘Field surveys indicate lateral variation in peat humification levels （von Post） in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers （silt,clays and fine sands） obtained from Quaternary floodplain deposits and residual soil （weathered schist）.The unconfined compressive strength （UCS） of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength （UCS） in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages （due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome）.
文摘Lowland water resources management represents a challenge of the future that calls any community. Irrigated crops are grown in some areas of Burkina Faso, others are limited by a lack of irrigation infrastructure. Due to limited crop irrigation, crops and the associated populations dependent on them, depend on rain and on climatic factors. Thus, there is a need to understand and implement traditional mechanisms for managing lowland water in Dano, where climatic and geological conditions provide a sustained source of water. Here, I use a literature review combined with field work and interviews/questionnaires to estimate the potential exploitable plains to 16,056 ha or 24% of the communal area. Management mechanisms and traditional operating systems of lowland waters were clear, which helped to set the technological level of farmers, in partial control of water management.
