Relating Water Use to Tree Vitality of Populus euphratica Oliv. in the Lower Tarim River, NW China

This study aimed to compare the hydraulic characteristics of different vitalities of Populus euphratica to reveal the differences in their water use strategies and water consumption to provide useful data to scale water use of riparian poplar forests in the lower reaches of the Tarim River, Northwestern China. Our results showed that the sapwood area of P. euphratica could be estimated based on its correlation with tree biometric parameters. The sapwood area of vital poplars tended to be larger than the senesced poplar despite both having the same diameter at breast height. This indicates that poplar vitality should be taken into account when estimating its sapwood area. Therefore, we established two different sapwood area estimation models for vital and senesced poplar (sapwood area = 1.452 x DBH1.553, R-2 = 0.891; sapwood area = 0.915 x DBH1.618, R-2 = 0.718; DBH: diameter at breast height). The sap flow process of vital and senesced poplar had certain differences and similarities; the average diurnal sap flow velocity and water consumption of vital poplar were 15.85 cm/h and 45.95 L, respectively; for the senesced poplar, it was 9.64 cm/h and 18.17 L, respectively, which were smaller than that of vital poplars. The influence of environmental factors on the sap flow velocity of two different P. euphratica was similar; the sap flow of both vital and senesced poplar had positive correlation with air temperature (R-2 = 0.800 and 0.851), solar radiation (R-2 = 0.732 and 0.778), vapor pressure deficit (R-2 = 0.508 and 0.643) and groundwater depth (R-2 = 0.301 and 0.171), while negative correlation with air humidity (R-2 = -0.313 and -0.478).