Responses of Transpiration Characteristics and Water Use Efficiency of Pinus Elliottii Leaf to Elevated CO_2 Concentration

To determine how transpiration characteristics and water use efficiency of Pinus elliottii respond to elevated CO_2 concentrations,LI-6400 Portable Photosynthesis System was used to examine the changes of the net photosynthesis rate(Pn),transpiration rate(Tr),intercellular CO_2 concentration(Ci),stomatal conductance(Gs) and vapor deficit at the leaf surface(Vpdl) of 1-year-old leaf and 0-year-old leaf with light intensity under different CO_2 concentration.The results showed that with enhanced light intensity,Ci and Vpdl decreased;Gs,Pn and Tr increased first,then Gs and Pn gradually decreased after leaf got to light saturation point;WUE also increased first,but it gradually decreased after it reach max value.With elevated CO_2 concentration,Ci and Vpdl increased;Gs and Tr decreased;Pn and WUE increased when CO_2 concentration elevated from 400 to 1 200 μmol/mol,but Pn and WUE decreased when CO_2 concentration elevated to 1 600 μmol/mol;at the same time,the light saturation point of 1-year-old leaf elevated.