Effects of Drought Stress on Photosynthesis and Chlorophyll Fluorescence Parameters of Populus euphratica

Populus euphratica is an important tree species of desert riparian forest.This paper studied the response of leaf water potential,soil water suction,photosynthesis and chlorophyll fluorescence parameters of one-year-old seedlings of P.euphratica treated by different water-retaining agent contents,as well as their physiological adaptive mechanisms to drought stress.The results showed that the soil water content decreased,and soil water suction increased with the decreased of water-retaining agent content,then the drought stress increased.With the water stress increased,leaf water potential,Pnmax,AQY,LSP,Pn,WUE,Gs and Tr reduced and the Ci increased,which showed that the declined Pn caused by non stomatal limitation.Water stress was noneffective to the Chl(a+b),LCP and Rd.With the photons flux density enhanced,the Pn,WUE,Gs and Tr increased,but the Ci reduced.With the drought stress decreased,Fv/Fm,Fv/Fo,ΦPSⅡ,ETR and qP increased,but the NPQ reduced,which indicated that with the drought stress decreased,the efficiency of light energy capture,activity of electron transport and photochemical quantum efficiency increased.With the water stress increased,the photo-inhibition appeared,the increased NPQ illuminated the counteracted photo-inhibition and protected structures by improving thermal dissipation.