Water relations of Alhagi sparsifolia Shap. at the transition zone between oases and sandy desert were studied in the southern fringe of Taklamakan Desert. Results showed that A. sparsifolia maintained the positive tu...Water relations of Alhagi sparsifolia Shap. at the transition zone between oases and sandy desert were studied in the southern fringe of Taklamakan Desert. Results showed that A. sparsifolia maintained the positive turgor during the summer. The steady high predawn water potential (psi(P)) indicated A. sparsifolia had sufficient hydration and water supply in growing season. In July, water deficit caused by drought stress had no effect on the transpiration of A. sparsifolia. Therefore, drought stress is not a main factor affecting the survival of plants. The physiological adaptation to drought of A. sparsifolia was shown mainly at the leaf level by significant difference (DeltaII) and relative water content (RWC) between the osmotic pressure at full turgor and at turgor loss, by occurring of osmotic adjustment, by high percentage of dry mass-related water content ( WCsat), by RWC at turgor loss point ( RWCp) in stable level and low RWC of the saturated symplast (RWCsym). However, the morphological features of transpiring surface reduction and deep root system seem to be the main way for the plant to adapt to the extreme drought environment. Result also suggests that one time of irregular irrigation in summer will not be helpful to recover water status of A. sparsifolia in location where the water table is very low.展开更多
Drought is one of the extreme events that can be caused by internal climate variability （ICV） and external forcing （EF）. Here, the authors investigate the relative contributions of ICY and EF to meteorological dro...Drought is one of the extreme events that can be caused by internal climate variability （ICV） and external forcing （EF）. Here, the authors investigate the relative contributions of ICY and EF to meteorological drought changes in China using 40 members from the Community Earth System Model Large Ensemble （CESE_LE） project for historical simulations （in response to greenhouse gases and other EF） and future simulations under the RCP8.5 scenario. The authors use the Standardized Precipitation Index （SPI） to represent meteorological drought, and then define and analyze four drought parameters （frequency, severity, duration, and maximum duration） over eight regions of China. For historical periods, the ICV plays a dominant role in drought variation, while with global warming under the RCP8.5 scenario the EF becomes the prominent factor for drought characteristics. With the global warming signal, the effect of ICV varies with the drought parameters. This study suggests that the ICV should be taken into account when climate model simulations are used to investigate drought--in particular, for historical periods.展开更多
Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China(ARNC)...Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China(ARNC),the change trends,abrupt change points,and their significance of runoff and 0℃ level height(FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall(MK) nonparametric test,and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods.The results are indicated as follows:(1) in recent 50 years,there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature.The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains(NSQM) compared to that of the northern slope of the Kunlun Mountains(NSKM).Likewise,the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains(NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains(SSTM).However,the FLH on NSKM has been decreasing with the speed of 2.33 m every year.(2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions,and even in same region.(3) There is a positive significant relation between the summer runoff and FLH in ARNC(NSQM P <0.05;other three regions P <0.01).Therefore,the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC.(4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM,NSTM,NSQM,and SSTM are 7.19,3.80,2.79,and 6.63,respectively,which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC.The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.展开更多
Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteor...Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.展开更多
Precipitation(PPT)is the primary climatic determinant of plant growth and aboveground net primary productivity(ANPP)for many of the world’s major terrestrial ecosystems.Thus,relationships between PPT and productivity...Precipitation(PPT)is the primary climatic determinant of plant growth and aboveground net primary productivity(ANPP)for many of the world’s major terrestrial ecosystems.Thus,relationships between PPT and productivity can provide insight into how changes in climate may alter ecosystem functions globally.Spatial PPT–ANPP relationships for grasslands are found remarkably similar around the world,but whether and how they change during periods of extended climatic anomalies remain unknown.Here,we quantifed how regional-scale PPTANPP relationships vary between an extended wet and a dry period by taking advantage of a 35-year record of PPT and NDVI(as a surrogate for ANPP)at 1700 sites in the temperate grasslands of northern China.We found a sharp decrease in the strength of the spatial PPT–ANPP relationship during an 11-year period of below average PPT.We attributed the collapse of this relationship to asynchrony in the responses of different grassland types to this decadal period of increased aridity.Our results challenge the robustness of regional PPT–productivity if aridity in grasslands is increased globally by climate change.展开更多
文摘Water relations of Alhagi sparsifolia Shap. at the transition zone between oases and sandy desert were studied in the southern fringe of Taklamakan Desert. Results showed that A. sparsifolia maintained the positive turgor during the summer. The steady high predawn water potential (psi(P)) indicated A. sparsifolia had sufficient hydration and water supply in growing season. In July, water deficit caused by drought stress had no effect on the transpiration of A. sparsifolia. Therefore, drought stress is not a main factor affecting the survival of plants. The physiological adaptation to drought of A. sparsifolia was shown mainly at the leaf level by significant difference (DeltaII) and relative water content (RWC) between the osmotic pressure at full turgor and at turgor loss, by occurring of osmotic adjustment, by high percentage of dry mass-related water content ( WCsat), by RWC at turgor loss point ( RWCp) in stable level and low RWC of the saturated symplast (RWCsym). However, the morphological features of transpiring surface reduction and deep root system seem to be the main way for the plant to adapt to the extreme drought environment. Result also suggests that one time of irregular irrigation in summer will not be helpful to recover water status of A. sparsifolia in location where the water table is very low.
基金supported by the Key Project of the Ministry of Science and Technology of China[grant number2016YFA0602401]the National Natural Science Foundation of China[grant number 41275110]supported by the National Science Foundation[grant number AGS-0944101]
文摘Drought is one of the extreme events that can be caused by internal climate variability （ICV） and external forcing （EF）. Here, the authors investigate the relative contributions of ICY and EF to meteorological drought changes in China using 40 members from the Community Earth System Model Large Ensemble （CESE_LE） project for historical simulations （in response to greenhouse gases and other EF） and future simulations under the RCP8.5 scenario. The authors use the Standardized Precipitation Index （SPI） to represent meteorological drought, and then define and analyze four drought parameters （frequency, severity, duration, and maximum duration） over eight regions of China. For historical periods, the ICV plays a dominant role in drought variation, while with global warming under the RCP8.5 scenario the EF becomes the prominent factor for drought characteristics. With the global warming signal, the effect of ICV varies with the drought parameters. This study suggests that the ICV should be taken into account when climate model simulations are used to investigate drought--in particular, for historical periods.
基金supported by National Basic Research Program of China(Grant No. 2010CB951003)
文摘Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China(ARNC),the change trends,abrupt change points,and their significance of runoff and 0℃ level height(FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall(MK) nonparametric test,and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods.The results are indicated as follows:(1) in recent 50 years,there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature.The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains(NSQM) compared to that of the northern slope of the Kunlun Mountains(NSKM).Likewise,the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains(NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains(SSTM).However,the FLH on NSKM has been decreasing with the speed of 2.33 m every year.(2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions,and even in same region.(3) There is a positive significant relation between the summer runoff and FLH in ARNC(NSQM P <0.05;other three regions P <0.01).Therefore,the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC.(4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM,NSTM,NSQM,and SSTM are 7.19,3.80,2.79,and 6.63,respectively,which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC.The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.
基金supported by the National Basic Research Program of China (Grant Nos. 2010CB951801 and 2006CB400500)
文摘Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.
基金supported by the National Natural Science Foundation of China(31922053)the start-up fund of Hainan University(Grant No.KYQD(ZR)21096)the National Key R&D Program of China(2017YFA0604801).
文摘Precipitation(PPT)is the primary climatic determinant of plant growth and aboveground net primary productivity(ANPP)for many of the world’s major terrestrial ecosystems.Thus,relationships between PPT and productivity can provide insight into how changes in climate may alter ecosystem functions globally.Spatial PPT–ANPP relationships for grasslands are found remarkably similar around the world,but whether and how they change during periods of extended climatic anomalies remain unknown.Here,we quantifed how regional-scale PPTANPP relationships vary between an extended wet and a dry period by taking advantage of a 35-year record of PPT and NDVI(as a surrogate for ANPP)at 1700 sites in the temperate grasslands of northern China.We found a sharp decrease in the strength of the spatial PPT–ANPP relationship during an 11-year period of below average PPT.We attributed the collapse of this relationship to asynchrony in the responses of different grassland types to this decadal period of increased aridity.Our results challenge the robustness of regional PPT–productivity if aridity in grasslands is increased globally by climate change.
