Study On Photosynthetic Eco-physiology In Semi-natural Vegetation Communities In New Jiangwan Shanghai

The semi-natural vegetation communities was studied in new jiangwan conservation Shanghai.The main forest-forming species is totally 7,Sophora japonica L.,Broussonetia papyrifera L.,Celtis sinensis Pers.,Ligustrum Lucidum Ait.,Cinnamomum camphora L., Elaeagnus pungens Thunb.,Castanopsis sclerophylla.The six main species and their seedings in diffirent habitats were selected to measure the parameters,the basic photosynthetic characteristics and fluorescence characteristics,such as the temporal dynamics in photosynthetic rate,transpiration rate,water use efficiency.This paper analysis the effect between the internal factors(stomatal conductance,intercellular CO₂ concentration,water use efficiency)and external factors(photosynthetically active radiation,atmospheric CO₂ concentration)and photosynthetic rate.The LMA,leaf weight ratio,the total N,the total P in their leaves were also measured,and the relation was compared between these physiological factors and their basic photosynthetic characteristics and fluorescence characteristics,which could give some scientifically rational suggestion for urban vegetation construction.The field observations of the photosynthetic characteristics and fluorescence characteristics were conducted by using Li-6400 Portable Photosynthesis System in typical weather conditions in July,2007.Our results are as followed:(1)The photosynthetic characteristics of the main species in different habitatsThe dynamic of daily photosynthesis of the main species in different habitats show three patterns,bell-shape curve,bimodal curve,or irregular curve.Diurnal changes of photosynthesis in canopy species is showing bimodal curves,species in forest gap bell-shape curves,and understory species irregular curves.Daily average net photosynthesis in deciduous tree is higher than that in the evergreen tree in canopy and forest gap,and there are no significant differences of daily average net photosynthesis among youngtree and seedings in understory.Under saturated light intensity, photosynthetic rate is correlated with photosynthetically active radiation obviously (P＜0.05),according to natural logarithm.There are midday depression of photosynthesis in canopy and forest gap.The tendency of the change in stomatal conductance was similar to that of net photosynthetic rate in these tissues.Intercellular CO₂ concentration shows a inverted u shape,the maximum value appears in 15∶00.Diurnal variation of transpiration rate is bell-shape curve,the maximum value appears in 9∶00.Species of transpiration rate in understory is much lower than that in canopy and forest gap,seedings of Broussonetia papyrifera L.and Sophora japonica L..have higher transpiration rate.Based on principal component analysis between net photosynthesis and physio-ecological factors,in canopy the first principal component is photosynthetically active radiation and the second is intercellular CO₂ concentration,while in understory the first principal component is stomatal conductance,photosynthetically active radiation is the second one.(2)Light response curve of the main species in different habitatsIn three habitats,the difference of maximum net photosynthetic rate was significant (P＜0.01),the apparent quantum efficiency was no significant difference,and dark respiration rate decreases as the light intensity decreases.In canopy and forest gap, deciduous trees of Sophora japonica L.,Celtis sinensis Pers.and Broussonetia papyrifera L.have higher light saturation points and light compensation points than evergreen ones of Cinnamomum camphora L.and Ligustrum Lucidum Ait..(3)Physiological factors of the main species in different habitatsIn canopy,total content of chlorophyâ…¡has a significant difference,the maximum content is Sophora japonica L.,the content of chlorophyâ…¡in understory is lower than that in canopy.The leaf nitrogen contents were gradually increased with the light intensity.In canopy The leaf nitrogen contents have a significant difference(P＜0.05).Sophora japonica L.and Broussonetia papyrifera L.have high leaf nitrogen contents and low photosynthetic nitrogen use efficiency.(4)Chlorophyâ…¡fluorescence of the main species in different habitatsIn canopy,qP of Sophora japonica L..,Broussonetia papyrifera L.and Celtis sinensis Pets.were gradually increased with the induction time,and then became steady,while Cinnamomum camphora L.,Ligustrum Lucidum Ait.and Castanopsis sclerophylla have wave processes.The NPQ of all trees have a high level initially,and then decrease with the induction time,finally tend to be stable.Fv′/Fm′,ΦPSâ…¡and rETR increased with the induction time,and then became steady.The range of maximal photochemical efficiency Fv/Fm was between 0.79-0.84,and that ofΦPSâ…¡0.63-0.71.In understory,Fv/Fm of the seedings has no obvious difference,0.80-0.84;Fv′/Fm′has a little change with the induction time,0.73-0.77;ΦPSâ…¡and qP are gradually increased with the induction time,and finally tend to be stable;There are higher NPQ in the seedings of Sophora japonica L..and Broussonetia papyrifera L.than that of others, they increase with the induction time slowly,and then decrease and stabilize in a level, while the NPQ of the other seedings increase with time and finally stabilize.