黑河流域植被水分利用效率时空分异及其对降水和气温的响应

植被水分利用效率(WUE)是衡量植被生态系统碳水耦合关系的重要指标,研究其时空分异特征对区域水资源合理利用及配置有重要意义。基于改进的光能利用率模型CASA,模拟估算了黑河流域2000—2013年植被净初级生产力(NPP),结合ETWatch模型估算的黑河流域2000—2013年蒸散数据ET,进一步估算了黑河流域植被水分利用效率WUE。分析了黑河流域NPP、ET和WUE空间格局和时间变化特征,探讨了WUE变化对降水和气温的相关性。结果表明:1)黑河流域空间上植被NPP在2000—2013年多年平均值为81.05 gC m~(-2) a~(-1),ET平均值为133.38 mm,植被WUE平均值为0.448 gC mm~(-1) m~(-2)。植被NPP、ET与WUE的空间格局基本上类似,均呈现出自上游至下游逐渐减少的分布格局。2)黑河流域2000—2013年间植被平均NPP与平均WUE均呈现显著上升趋势(P0.05),而ET平均值变化不显著。WUE年际变化斜率与其平均值在空间分布上存在一定的对应关系,空间上植被WUE的高值区同时是其呈增长趋势的主要区域,植被WUE平均值较低的区域其年际变化也趋于稳定。3)不同植被类型的WUE差异较为显著,植被自身受环境影响形成的生理生态参数是其WUE差异的主要原因,不同植被类型WUE平均值关系为:灌丛草地森林农田沼泽荒漠。中游绿洲区栽培植被平均WUE仅为0.90 gC mm~(-1) m~(-2),因此应当重视提高其对水资源的利用效率。4)整体上黑河流域植被WUE年际变化主要受降水的影响,植被WUE与降水呈负相关的区域主要分布在中游绿洲灌溉区,表明人为活动干扰会削弱气候因素对植被WUE的影响。

Temporal and spatial variability of water use efficiency of vegetation and its response to precipitation and temperature in Heihe River Basin

Water use efficiency (WUE) is an important index to measure the coupling relationship between water and carbon in vegetation ecosystem. Research on the WUE spatial and temporal variability is of great significance to rational utilization and allocation of regional water resources. In this study, the net primary productivity (NPP) was estimated by improved Carnegie-Ames-Stanford Approach (CASA) model. Combined with the evapotranspiration data (ET) estimated by the ETWatch model, we studied the spatial pattern and temporal variations of the NPP, ET and WUE in Heihe River Basin from 2000 to 2013, and discussed the response of WUE to precipitation and air temperature. The results showed that:1) the annual average value of NPP was 81.05 gC m^-2 a^-1 in Heihe River Basin in 2000-2013. Meanwhile, the annual ET averaged 133.38 mm and WUE was 0.448 gC mm^-1 m^-2. The spatial pattern of the NPP, ET and WUE were gradually decreasing from upstream and middle to downstream. 2) The average annual NPP and WUE showed an obvious upward trend from 2000 to 2013, while the ET showed a slightly upward trend. There is a corresponding relationship between slope of WUE of vegetation and its average value in spatial distribution. The high-value area of WUE is also the main area for its growth in spatial distribution. By contrast, the inter-annual variation of WUE tends to be stable in the area with lower average WUE value. 3) There were significant differences in WUE among different vegetation types. The main reason for the difference in WUE was the physiological and ecological parameters of vegetation which formed by the influence of the environment. The annual average WUE was listed in order of shrub > grassland > forest > farmland > swamp > desert. The average WUE of cultivated vegetation in the oasis area in the middle reaches is only 0.90 gC mm^-1 m^-2. We should to pay more attention to improving its utilization efficiency of water resources. 4) The inter-annual change of WUE is mainly affected by precipitation, but there showed a negative correlation between WUE change and precipitation in the middle reaches of oasis area, which indicating that human activity will weaken the influence of climatic factors on WUE of vegetation.