水分利用效率(Water Use Efficiency,WUE)是表征生态系统碳水耦合的重要指标,研究退化草地WUE的时空变化,对探明草地退化的环境效应具有重要意义。选择草地退化严重的伊犁河谷为研究区,基于MODIS NDVI(Normalized Difference Vegetation Index)、GPP(Gross Primary Productivity)、ET(Evapotranspiration)以及气象数据,并借助于GIS空间分析技术及趋势分析等方法,对2000—2014年伊犁河谷草地生态系统WUE时空变化和其影响因素进行了研究。结果 表明:(1)伊犁河谷草地WUE,ET及GPP均呈现明显的海拔分异,但WUE高值区域并未出现在干旱的荒漠区,而是主要分布在GPP为高值(GPP>650 g C/m2)且ET相对较高(300～500 mm)的区域;(2)近15年伊犁河谷草地ET及GPP总体呈降低趋势,WUE则总体呈增加趋势; 空间上,全区79.20%区域WUE有所增加,ET和GPP发生减少的比例则分别为92.31%和78.10%;(3)研究区WUE增加主要是由于ET减少程度高于GPP,但ET变化与GPP关系紧密,WUE的变化并不由单一的GPP或ET变化所主导,而是两者变化综合作用的结果;(4)近15年伊犁河谷降水的减少导致植被覆盖降低和ET减少,进而影响WUE的变化。WUE变化具有明显的空间异质性,15年内全区平均WUE增加6.61%,降水的减少是导致伊犁河谷WUE增加的主要气候因子。
Water use efficiency(WUE)is an important index indicating the coupling of carbon and water in the ecosystem. Study on the spatiotemporal variation of WUE in degraded grassland is of great significance for verifying the environmental effects of grassland degradation. Ili River Valley, labeled with serious grassland degradation, was selected as the study area. Based on data of MODIS NDVI(Normalized Difference Vegetation Index), GPP(Gross Primary Productivity), ET(Evapotranspiration)and meteorological factors, and with the help of GIS technology and the method of trend analysis, the spatiotemporal variation of WUE in the grassland ecosystem of Ili River Valley in 2000—2014 and its influencing factors were studied. The results showed that:(1)WUE, ET and GPP in the grassland of Ili River Valley all showed obvious differentiation along the altitude; areas with high WUE did not appear in arid desert area, but mainly distributed in area with high GPP(GPP>650 g C/m2)and relatively high ET(300～500 mm);(2)in the past 15 years, ET and GPP in the grassland of Ili River Valley decreased, while WUE increased; spatially, WUE increased in 79.20% of the grassland; the proportions of areas with decreased ET and GPP were 92.31% and 78.10%, respectively;(3)the increase of WUE in the study area was mainly due to the fact that the decrease of ET was higher than that of GPP; however, the change of ET was closely related to that of GPP; the change of WUE was not resulted from the single change in GPP or ET, but from the comprehensive interaction of changes in the both;(4)in the past 15 years, the decrease of precipitation in Ili River Valley was the main reason for the decrease of vegetation coverage, which affected the variations of WUE further. Variations of WUE in the grassland of Ili River Valley showed obvious regional characteristics. WUE increased by 6.61% on average within 15 years. The decrease of precipitation was the main climate factor that leaded to the increase of WUE in Ili River Valley.
