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.，Ulrnus pumila var. sabulosa，Ulmus glaucescens Franch.，Ulmus pumila L.，Salia matsudana Koidz.，Amorpha fruticosa L.. The results showed that the six tree species had different decreased magnitude in net photosynthetic rate

transpiration rate

Intercellular CO2 concentration

stomatal conductance and water use efficiency under stronger drought stress. The decrease range ranked as Ulmus pumila L

Populus simonii Carr

Sali.r matsudana Koidz

Amorpha fruticosa L

Ulmus glaucescens Franch，Ulmus pumilavar

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 indiGated 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 Ulrnus 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.