Photosynthetic characteristics and growth of Populus euphratica seedlings with water stress.

The effects of water stress on the photosynthesis and growth characteristics of Populus euphratica seedlings were studied by pot experiment in Aksu Water Balance Station,CAS.The results indicated that the daily curve of the net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci) and transpiration rate(Tr) were hardly influenced by water stress.All of the daily change curve of Pn,Gs,Ci and Tr showed single-peak,and the peak time of Pn,Gs,Ci and Tr of the daily curve were at 12:00.As soil water content was in the range of 21.6%～24.0%,the water use efficiency(WUE) of seedlings was not obvious double-peak curve,the peak time of WUE of the daily change curve was at 8:00 and 18:00,respectively.Others showed single-peak type,while the peak times were different.The daily average value of Pn,Gs,Ci and Tr of seedlings decreased with the soil water content decreasing.As soil water content was in the range of 12.0%～19.2%,the daily average value of the WUE was the highest.The height,stem diameter,biomass accumulations of different organs and the total biomass of seedlings reduced significantly with the decreasing of soil water content.As soil water content was in the range of 12.0%～19.2%,the decreased degree of aboveground biomass of seedlings was higher than the underground biomass,and the root-shoot ratio(R/T) was increased obviously.The photosynthetic and growth were effected obviously by different water treatments.When the soil water content was higher than 12.0%,the seedling drought tolerance was increased with the increasing of WUE and the changing of root-shoot ratio.In the condition of the soil water content lower than 9.6%,the regulating ability of seedlings was decreased,therefore the growth of seedlings was inhibited.