Abstract:The photosynthetic characteristics of different life forms of mainly dominant species under different habitats during summer were studied in New Jiangwan Conservation which is located in Yangpu district of Shanghai.The process and characteristic of plant community in urban abandoned district were analyzed from the view of photosynthetic ecology.Meanwhile,the dynamic changes of plant community structure were forecasted with the analysis of the mainly environmental factors.The results shows that：(1)Diurnal changes of photosynthesis in canopy species was showing bimodal curves,species in forest gap bell shape curves,and understory species irregular curves.This indicated the midday depression of photosynthesis of subtropical trees under typical climate in summer.The habitat characteristics also influenced the photosynthetic capacity.(2)The daily average net photosynthetic rates of deciduous trees，such as Robinia pseudoacacia and Celtis sinensis were higher than that of other adult trees in canopy.And deciduous trees had higher light saturation point.Elaeagnus pungens,one of the shade-tolerant shrubs had the highest daily average net photosynthetic rate in understory,next were the young trees and seedlings of Cinnamomum camphora and Ligustrum lucidum,while deciduous trees in understory had low daily average net photosynthetic rate.(3)Based on principal component analysis between net photosynthesis and physio ecological factors,in canopy the first principal component was ecological factors,while in gap the first principal component was physiological factors.High photosynthetic efficiency of deciduous trees made them rapidly occupy the upper space.Pioneer tree species with high dispersal ability dominated in early succession stage in new Jiangwan conservation.When the tree community formed，understory seedlings were mainly the species such as C.camphora and L.lucidum with wide range of light adaption.Upper deciduous trees large-scale decline makes C.camphora and L.lucidum gradually replace deciduous trees.