Desert riparian plants experience high variability in water availability due to hydrological fluctuations. How riparian plants can survive with low water availability has been well studied, however, little is known ab...Desert riparian plants experience high variability in water availability due to hydrological fluctuations. How riparian plants can survive with low water availability has been well studied, however, little is known about the effects of high water availability on plant community structuring. We conducted a mesocosm experiment to test whether seedling competition under simulated high groundwater availability can explain the shift of co-dominance of Populus euphratica and Tamarix ramosissima in early communities to P. euphratica dominance in mature ones along the Tarim River in northwestern China. Seedlings of these two plant species were grown in monoculture and mixture pools with high groundwater availability. Results indicated that the above-ground biomass and relative yield of T. ramosissima were higher than those of P. euphratica. The competitive advantages of T. ramosissima included its rapid response in growth to groundwater enrichment and its water spender strategy, as evidenced by the increased leaf biomass proportion and the inert stomatal response to leaf-to-air vapor pressure deficit （VPD）. In comparison, P. euphratica showed a conservative strategy in water use, with a sensitive response to leaf-to-air VPD. Result of the short-term competition was inconsistent with the long-term competition in fields, suggesting that competition exclusion is not the mechanism structuring the desert riparian plant communities. Thus, our research highlights the importance of mediation by environmental fluctuations （such as lessening competition induced by disturbance） in structuring plant communities along the Tarim riparian zones.展开更多
近几十年来新疆气候变化显著,“暖湿化”转型与“湿干转折”先后出现,势必对地区植被生产力、大气干旱状况以及二者间的响应关系产生影响。以植被总初级生产力(GPP)和大气水分亏缺(VPD)作为评价指标,分析了1982—2018年新疆地区植被GPP...近几十年来新疆气候变化显著,“暖湿化”转型与“湿干转折”先后出现,势必对地区植被生产力、大气干旱状况以及二者间的响应关系产生影响。以植被总初级生产力(GPP)和大气水分亏缺(VPD)作为评价指标,分析了1982—2018年新疆地区植被GPP、VPD的时空分布与演变规律,并揭示了大气水分胁迫对植被GPP的影响。结果表明:(1)新疆植被GPP整体具有北高南低的分布特征,年均值为256.6 g C·m^(-2)·a^(-1),呈显著上升趋势。GPP增加趋势占植被总面积的82.00%,其中增加显著区约占42.81%,多分布于南疆绿洲和北疆山前农业区;GPP下降趋势占比较小且分布零散。(2)新疆地区VPD具有“山区低、平原/盆地高”的鲜明格局,年均值为0.66 kPa,呈不显著波动上升趋势。全疆大部地区表现出VPD显著性上升,下降趋势零星出现在昆仑山脉高海拔山区。(3)新疆植被GPP对VPD的响应“正负共存”,并具有明显空间异质性。GPP与VPD的负相关占植被区总面积的54.52%,主要出现在山前草地地带;正相关则主要分布在塔里木盆地边缘和天山北坡及其东段,以栽培作物和灌木类型为主。VPD对GPP的影响在不同植被类型间差异鲜明,而在同一植被类型内正、负响应共存。分析认为,虽然大气水分胁迫尚未成为地区植被生产力变化的主导驱动力,但在新疆干旱化急剧增加背景下,仍需加强对GPP与VPD响应关系的跟踪。展开更多
在干旱地区,降水中的氢氧稳定同位素组成常受到雨滴云下二次蒸发作用的影响而发生改变。基于全球降水同位素网(GNIP)在我国西北东部站点的数据并结合气象数据,分析雨滴二次蒸发作用发生的条件、季节特征、影响因素以及对降水氢氧稳定同...在干旱地区,降水中的氢氧稳定同位素组成常受到雨滴云下二次蒸发作用的影响而发生改变。基于全球降水同位素网(GNIP)在我国西北东部站点的数据并结合气象数据,分析雨滴二次蒸发作用发生的条件、季节特征、影响因素以及对降水氢氧稳定同位素组成的影响规律。研究表明:在我国西北东部,当近地表水汽压差(VPD)等于0.52 k Pa时,降水中氢氧稳定同位素组成规律发生显著改变。当VPD>0.52 k Pa时,地区降水线(LMWL)的斜率和截距与全球降水线(GMWL)无显著差别,且氘剩余(d-excess)也与VPD不存在显著相关关系。然而,当VPD>0.52 k Pa时,LMWL的斜率和截距显著地小于GMWL,d-excess与VPD存在显著的负相关关系。表明当VPD<0.52 k Pa时,保留了云层中热力学平衡分馏特征,而当VPD>0.52 k Pa时,降水氢氧稳定同位素经历了动力学非平衡分馏过程——云下雨滴在降落过程中二次蒸发作用。根据Tetens公式,当气温(t)<7.0℃时,空气饱和水汽压不可能超过0.52 k Pa,所以,当t<7.0℃时不可能发生雨滴二次蒸发过程。这样,在温带干旱地区,在t较低的冬半年降水中的δ18O只存在显著的温度效应,而在t较高的夏半年降水中的δ18O同时存在温度和降水效应。展开更多
植被物候直接影响其生物量,调控生态系统碳循环过程。目前,气候变化(尤其干旱)对中国中高纬度植被物候的影响依然不清楚。因此,文章基于GIMMS NDVI3g数据集,提取中国30°N以北地区中多种植被类型生长季的开始日期(Start of the Seas...植被物候直接影响其生物量,调控生态系统碳循环过程。目前,气候变化(尤其干旱)对中国中高纬度植被物候的影响依然不清楚。因此,文章基于GIMMS NDVI3g数据集,提取中国30°N以北地区中多种植被类型生长季的开始日期(Start of the Season,SOS)与结束日期(End of the Season,EOS)两物候参数。然后结合野外观测数据,验证提取物候参数结果可靠性,并结合饱和水汽压差(Vapor Pressure Deficit,VPD)与改进后的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)探究植被物候对干旱的响应特征规律。结果表明:(1)不同地区的植被物候变化呈现明显的差异性,单季植被与双季植被第1个生长季的SOS集中在每年的第30~180天,而双季植被第2个生长季的SOS集中在每年的第200~220天。单季植被与双季植被第1个生长季的EOS主要集中在每年的第180~300天,双季植被第2个生长季的EOS主要集中在每年的第260~300天。(2)森林季前VPD的上升导致植被的SOS提前及EOS延迟;草地季前VPD上升导致植被的SOS滞后以及EOS提前。(3)研究区内大部分地区的SPEI与植被的SOS、EOS均呈正相关,即干旱促使该地区植被的SOS、EOS提前。展开更多
基金funded by the National Basic Research Program of China(2013CB429903)the National Natural Science Foundation of China(4117103741171095)
文摘Desert riparian plants experience high variability in water availability due to hydrological fluctuations. How riparian plants can survive with low water availability has been well studied, however, little is known about the effects of high water availability on plant community structuring. We conducted a mesocosm experiment to test whether seedling competition under simulated high groundwater availability can explain the shift of co-dominance of Populus euphratica and Tamarix ramosissima in early communities to P. euphratica dominance in mature ones along the Tarim River in northwestern China. Seedlings of these two plant species were grown in monoculture and mixture pools with high groundwater availability. Results indicated that the above-ground biomass and relative yield of T. ramosissima were higher than those of P. euphratica. The competitive advantages of T. ramosissima included its rapid response in growth to groundwater enrichment and its water spender strategy, as evidenced by the increased leaf biomass proportion and the inert stomatal response to leaf-to-air vapor pressure deficit （VPD）. In comparison, P. euphratica showed a conservative strategy in water use, with a sensitive response to leaf-to-air VPD. Result of the short-term competition was inconsistent with the long-term competition in fields, suggesting that competition exclusion is not the mechanism structuring the desert riparian plant communities. Thus, our research highlights the importance of mediation by environmental fluctuations （such as lessening competition induced by disturbance） in structuring plant communities along the Tarim riparian zones.
文摘近几十年来新疆气候变化显著,“暖湿化”转型与“湿干转折”先后出现,势必对地区植被生产力、大气干旱状况以及二者间的响应关系产生影响。以植被总初级生产力(GPP)和大气水分亏缺(VPD)作为评价指标,分析了1982—2018年新疆地区植被GPP、VPD的时空分布与演变规律,并揭示了大气水分胁迫对植被GPP的影响。结果表明:(1)新疆植被GPP整体具有北高南低的分布特征,年均值为256.6 g C·m^(-2)·a^(-1),呈显著上升趋势。GPP增加趋势占植被总面积的82.00%,其中增加显著区约占42.81%,多分布于南疆绿洲和北疆山前农业区;GPP下降趋势占比较小且分布零散。(2)新疆地区VPD具有“山区低、平原/盆地高”的鲜明格局,年均值为0.66 kPa,呈不显著波动上升趋势。全疆大部地区表现出VPD显著性上升,下降趋势零星出现在昆仑山脉高海拔山区。(3)新疆植被GPP对VPD的响应“正负共存”,并具有明显空间异质性。GPP与VPD的负相关占植被区总面积的54.52%,主要出现在山前草地地带;正相关则主要分布在塔里木盆地边缘和天山北坡及其东段,以栽培作物和灌木类型为主。VPD对GPP的影响在不同植被类型间差异鲜明,而在同一植被类型内正、负响应共存。分析认为,虽然大气水分胁迫尚未成为地区植被生产力变化的主导驱动力,但在新疆干旱化急剧增加背景下,仍需加强对GPP与VPD响应关系的跟踪。
文摘在干旱地区,降水中的氢氧稳定同位素组成常受到雨滴云下二次蒸发作用的影响而发生改变。基于全球降水同位素网(GNIP)在我国西北东部站点的数据并结合气象数据,分析雨滴二次蒸发作用发生的条件、季节特征、影响因素以及对降水氢氧稳定同位素组成的影响规律。研究表明:在我国西北东部,当近地表水汽压差(VPD)等于0.52 k Pa时,降水中氢氧稳定同位素组成规律发生显著改变。当VPD>0.52 k Pa时,地区降水线(LMWL)的斜率和截距与全球降水线(GMWL)无显著差别,且氘剩余(d-excess)也与VPD不存在显著相关关系。然而,当VPD>0.52 k Pa时,LMWL的斜率和截距显著地小于GMWL,d-excess与VPD存在显著的负相关关系。表明当VPD<0.52 k Pa时,保留了云层中热力学平衡分馏特征,而当VPD>0.52 k Pa时,降水氢氧稳定同位素经历了动力学非平衡分馏过程——云下雨滴在降落过程中二次蒸发作用。根据Tetens公式,当气温(t)<7.0℃时,空气饱和水汽压不可能超过0.52 k Pa,所以,当t<7.0℃时不可能发生雨滴二次蒸发过程。这样,在温带干旱地区,在t较低的冬半年降水中的δ18O只存在显著的温度效应,而在t较高的夏半年降水中的δ18O同时存在温度和降水效应。
文摘植被物候直接影响其生物量,调控生态系统碳循环过程。目前,气候变化(尤其干旱)对中国中高纬度植被物候的影响依然不清楚。因此,文章基于GIMMS NDVI3g数据集,提取中国30°N以北地区中多种植被类型生长季的开始日期(Start of the Season,SOS)与结束日期(End of the Season,EOS)两物候参数。然后结合野外观测数据,验证提取物候参数结果可靠性,并结合饱和水汽压差(Vapor Pressure Deficit,VPD)与改进后的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)探究植被物候对干旱的响应特征规律。结果表明:(1)不同地区的植被物候变化呈现明显的差异性,单季植被与双季植被第1个生长季的SOS集中在每年的第30~180天,而双季植被第2个生长季的SOS集中在每年的第200~220天。单季植被与双季植被第1个生长季的EOS主要集中在每年的第180~300天,双季植被第2个生长季的EOS主要集中在每年的第260~300天。(2)森林季前VPD的上升导致植被的SOS提前及EOS延迟;草地季前VPD上升导致植被的SOS滞后以及EOS提前。(3)研究区内大部分地区的SPEI与植被的SOS、EOS均呈正相关,即干旱促使该地区植被的SOS、EOS提前。
