毛乌素沙地植被水分利用效率的时空格局

水分利用效率（WUE）是衡量生态系统碳水循环耦合程度的重要指标，明晰其动态变化规律有助于判断区域植被生态建设是否与当地的自然条件相适应。利用基于CASA（Carnegie-Ames-Stanford Approach）模型得到的植被净初级生产力（NPP）数据和MODIS系列产品中的蒸散发（ET）数据，估算了2001—2016年毛乌素沙地植被的WUE，并探讨了其时空演变特征及与气象因子的关系。结果显示：（1）WUE的多年平均值为0.62 gC·mm^-1·m^-2，空间上自东向西递减，在不同植被类型间表现为栽培植物>灌丛>草甸>草原>荒漠；（2）WUE以0.009 gC·mm^-1·m^-2·a^-1的速率上升，东部地区变化尤为显著，NPP的快速增长是WUE呈增加趋势的主要原因；（3）WUE与各气象因子的相关程度由大至小依次为太阳辐射、降水量、风速和气温，分布在西部地区的荒漠植被WUE受气象因子影响最小。经过一系列生态建设工程的治理，毛乌素沙地大部分地区自2001年以来NPP和WUE均呈增加趋势，即生态系统在变“绿”的同时还实现了水分的高效利用，有利于当地生态环境的健康发展；但在水热条件较差的中西部地区，新建设的植被生长缓慢且导致蒸散发产生强烈变化，使WUE呈减少趋势，暴露出植被建设规模与水资源承载能力不匹配的问题，需引起格外重视。

Spatial-temporal patterns of vegetation water use efficiency in the Mu Us Desert

Water use efficiency （WUE） is a key proxy for linking carbon and water exchange processes in terrestrial ecosystems. Understanding the spatial-temporal variations in WUE helps to evaluate the adaptability of vegetation to local environmental conditions. This study estimated the vegetation WUE in the Mu Us Desert during 2001-2016 using remote-sensing data and meteorological observations. Carbon sequestration （i.e.， net primary productivity， NPP） was estimated based on the Carnegie-Ames-Stanford Approach （CASA） model， while water consumption （i.e.， evapotranspiration， ET） was obtained from the MODIS product. The spatial-temporal patterns of WUE and their responses to meteorological factors were investigated by trend analysis and correlation analysis， respectively. The results showed that： （1） the mean annual WUE across the Mu Us Desert was 0.62 gC·mm^-1·m^-2 with a trend of decrease from the east to the west， and among different vegetation types， the values of WUE ranked in the order of cultivated vegetation>shrub>meadow>steppe>desert； （2） WUE increased at the rate of 0.009 gC·mm^-1·m^-2·yr^-1 during the study period， especially significantly in eastern， and the increase in WUE mainly attributed to the rapid rise in NPP； and （3） the relationships between WUE and meteorological factors followed a sequence of solar radiation， precipitation， wind speed， and air temperature from strong to weak， and there were relatively insignificant relationships between WUE and meteorological factors in the western part of the Mu Us Desert. The study highlight that the revegetation programs implemented in the Mu Us Desert have achieved good outputs that both NPP and WUE have increased since 2001， which contributed to the improvement of local ecological environment； however， in the central and western part of the Mu Us Desert with poor condition of water and heat， the mismatch between revegetation magnitude and water should be paid more attention.