Spatial And Temporal Characteristics Of Ecosystem Water Use Efficiency And Its Influencing Factors In The Loess Plateau

As a proportional relationship between carbon and water cycles,ecosystem water use efficiency represents the association between photosynthetic carbon assimilation and water consumption of plants.It is a key factor in the coupling of two major processes:carbon and water cycle.The study of the spatial and temporal variation patterns of WUE and its influencing factors in the Chinese Loess Plateau is helpful to understand the characteristics of the carbon and water cycle in the arid region,and also contributes to the sustainable development of the ecosystem and water resources management in the region.Therefore,in this thesis,the spatial and temporal variation characteristics of WUE in the CLP are explored based on GPP and ET remote sensing products,meteorological stations and carbon and water flux observation data using the linear regression analysis.Meanwhile,the correlation between WUE and precipitation,temperature,vapor pressure difference,sunshine hours and leaf area index are analyzed by using partial correlation analysis.Finally,the impact and relative contribution rate of each influencing factor on the trend of WUE are calculated based on the decomposition method of homogeneity factor and the two-step method of quantification based on statistical model.The results show that:（1）The variability of WUE during the month shows a typical single-peaked state,with the peak of the single-peak occurring in August at 1.69 g C·m^-2·mm^-1 from 2000 to2018.The regional GPP growth rate is significantly greater than the ET growth rate,resulting in an overall increasing WUE trend of 0.024 g C·m^-2·mm^-1·a^-1.There is a high degree of consistency in the interannual rates of change in WUE for all vegetation,showing an increasing trend,with the rates of change in the order of cropland>forests>grassland>shrubs.（2）From 2000 to 2018,the interannual WUE values of the Chinese Loess Plateau range from 1.20 to 1.69 g C·m^-2·mm^-1 with a mean value of 1.24 g C·m^-2·mm^-1.Spatially,the distribution pattern of WUE is generally high in the southeast and low in the northwest at CLP.There are large differences in the multi-year mean values of WUE for different vegetation.Specifically,the forest WUE has the highest multi-year mean(2.20 g C·m^-2·mm^-1)and the shrub WUE has the lowest multi-year mean(0.66 g C·m^-2·mm^-1),while the others are agricultural land(1.45 g C·m^-2·mm^-1)and grassland(1.21 g C·m^-2·mm^-1)in that order.（3）The trend of WUE is controlled by GPP in 87.37%of the CLP,while only 8.94%of the area is controlled by ET,mainly in the western and northwestern regions of the CLP.To summarize,the fluctuation of WUE is determined mainly by the change of GPP in the region.（4）The impact and relative contribution rate of LAI,which is the main factor dominating the change in WUE trend,is 0.014 g C·m^-2·mm^-1·a^-1 and 39.97%,respectively.The impact of meteorological elements including P,Temp,VPD and SD are 0.001 g C·m^-2·mm^-1·a^-1,-0.001 g C·m^-2·mm^-1·a^-1,0.001 g C·m^-2·mm^-1·a^-1 and 0.001 g C·m^-2·mm^-1·a^-1,respectively,with relative contribution rates of 7.41%,13.06%,5.71%and 4.77%,respectively.The influence of other elements is 0.008 g C·m^-2·mm^-1·a^-1,with a relative contribution rate of 29.18%.In this thesis,33 pictures,6 table,126 references.