Stomatal Conductance Characteristics of Populus euphratica Leaves and Response to Environmental Factors in the Extreme Arid Region

According to the observed data of Populus euphratica which growing in extreme arid environment in 2005,the gas exchange characteristics of P.euphratica were studied under natural condition by using a portable Li-6400 photosynthesis system.The results showed that:the oscillations of stomatal conductance in P.euphratica leaves took place in the diurnal course in hot and bright sunny day with an oscillation periodicity of about 2 h,and disappeared after 20:00.The assimilation and transpiration,associated with stomatal conductance,exhibited and sustained oscillations in the diurnal course simultaneously.Stomatal conductance is higher in leaves of sunny positions than that of shade positions of P.euphratica.Stomatal conductance of P.euphratica has significant correlation with temperature,relative humidity and leaf water potential.When CO2 concentration is lower,the stomatal conductance of P.euphratica increment with the CO2 concentration rises.However,when CO2 concentration attained a certain value,the stomatal conductance was no longer increase.If CO2 concentration continued to goes up,the stomatal conductance would significantly reduces with the CO2 concentration rising.It was feedback manner that mechanism of stomatal adjustment of P.euphratica adapting habit of extreme arid region,namely to fall leaf water potential cause stomatal conductance to decrease,which reduced water consumption from transpiration to save water and adapt drought.Water utilization efficiency(WUE) of P.euphratica increased with stomatal limitation value decreasing,vice versa,it will increase.These results provided scientific basic for understanding drought resistan t mechanism and improving water utilization efficiency of P.euphratica.