Effects of Water Stress on Photosynthetic Characteristics of Six Sorts of Seedlings

Gas exchange,chlorophyll relative content and leaf water potential were measured and compared in leaves of 6 broadleaved tree species under soil water control conditions,the 6 species are Populus simonii Carr.,Ulmus pumila var.sabulosa,Ulmus glaucescens Franch.,Ulmus pumila L.,Salix matsudana Koidz.,Amorpha fruticosa L..The results showed that the six tree species had different decreased magnitude in net photosynthetic rate,transpiration rate,Intercellular CO_2 concentration,stomatal conductance and water use efficiency under stronger drought stress.The decrease range ranked as Ulmus pumila L,Populus simonii Carr,Salix matsudana Koidz,Amorpha fruticosa L,Ulmus glaucescens Franch,Ulmus pumila var.sabulosa,indicating that there were some differences in photosynthetic capacity and water use efficiency among different tree species under drought stress.Chlorophyll relative content were also different among six tree species,under severe drought stress condition,biggest decrease of chlorophyll relative content was observed in Ulmus pumila L,and smallest decrease occurred in Ulmus pumila var sabulosa.The results indicated that damage degree of photosynthetic apparatus of the six tree species were different under drought stress conditions.The results of leaf water potential indicated that Ulmus pumila L and Populus simonii Carrwere more sensitive to drought stress and easily being hurt.Ulmus pumila var.sabulosa and Ulmus glaucescens Franch had the stronger drought tolerance of dehydration and slower response to drought stress, the leaves of them were not easily damaged by drought stress.