Coupling the water use of Populus euphratica and Tamarix ramosissima and evapotranspiration partitioning in a desert riparian forest ecosystem

Abstract

Evapotranspiration (ET) partitioning involves determining how the flux of water is mediated by abiotic and biotic pathways. Previous studies have shown the average transpiration fraction (T/ET) from sites to global scales. However, few studies couple plant water use with ET partitioning to understanding how changes in plant community structure affect the seasonal to interannual variability in ET partitioning in desert riparian forest ecosystem. In this study, we used an isotope tracer coupled to a ''multi-source'' model to estimate the ET and its components, such as soil evaporation (E) and plant transpiration (T). The total T was further partitioned into the transpiration of Populus euphratica (Tp) and Tamarix ramosissima (Tt). The consistency of R2 (0.78 and 0.74) between the simulated and total ET measured by eddy covariance and Tp by sap flow illustrated that this model can reconstruct the water exchange in desert riparian forest ecosystem. The fraction Tp/ET was slightly higher than Tt/ET, but less than E/ET, and their ratios were 0.16, 0.14 and 0.70, respectively, from 2014 to 2017. The fractions of Tp/T and Tt/T were almost equal values of 52% and 48%. The different water use strategies and stomatal conductance sensitivities between P. euphratica and T. ramosissima demonstrated that their different responses to the changes of vapor pressure deficit (VPD) and groundwater depth. In drought period, Tp was greater than Tt, indicating that P. euphratica had a competitive advantage because of its deep groundwater utilization strategy and high sensitivity to stomatal conductance. The change of community structure indicated by increase coverage of P. euphratica in desert riparian forest ecosystem had significant enhance on T/ET than total ET. This study emphasizes that considering the different water uses among various species to optimize the ecological water demand will improve the management of desert riparian forest ecosystems.