Abstract:

An opentop chamber (OTC) system was used on the dominant species 〖WTBX〗Phragmites australis〖WTBZ〗 in reclaimed marsh in Eastern Chongming island to study the effects of elevated temperature(ET) on the photosynthesis of leaves in rapid growth season.Photosynthetic parameters containing maximum net photosynthetic rate (〖WTBX〗P〖WTBZ〗max),dark respiration rate(〖WTBX〗Rd〖WTBZ〗),apparent quantum yield〖WTBX〗(AQY〖WTBZ〗),light compensation point(〖WTBX〗LCP〖WTBZ〗),light saturation point (〖WTBX〗LSP〖WTBZ〗) and light response processes of leaves of 〖WTBX〗Phragmites australis〖WTBZ〗  were measured after one and twoyear treatment.The results showed that these physical characteristics were diverse under different ET time.Comparing with the control(CK),the OTC manipulation showed positive effects,〖WTBX〗P〖WTBZ〗max and〖WTBX〗 LSP〖WTBZ〗 increased significantly,〖WTBX〗Rd〖WTBZ〗 and 〖WTBX〗LCP〖WTBZ〗 decreased significantly after oneyear treatment(1aET).The opposite results happened to twoyear treatment (2aET).No significant differences happened to 〖WTBX〗AQY〖WTBZ〗 between years.The net photosynthetic rate light intensity (〖WTBX〗PnPAR〖WTBZ〗) curves which were nonlinear (〖WTBX〗R2〖WTBZ〗>098) fitted moved up and jumped down after 1aET and 2aET respectively.Furthermore,the effect of ET on transpiration rate (〖WTBX〗Tr〖WTBZ〗) was enhanced significantly,which served as a selfprotection response for dissipating heat.The responses of stomatal conductance (〖Gs)and intercellular CO2 concentration(Ci〖WTBZ〗) were correlated with photosynthetic active radiation(PAR).All results implied that photosynthetic acclimatization occurred due to nonstomatal factors limited under longer time scale