Plant Physioecological Research In Photosynthesis Of Predominant Trees In Different Succession Stages Of Evergreen Broad-leaved Forest

Using portable photosynthesis system HCM-1000, main physioecological indices of 4 predominant trees (Schima superba, Castanopsis fargessi, Lithocarpus glaber, Castanopsis sclerophylla) in evergreen broad-leaved forest of Tiantong National Forest Park, Zhejiang Province were mensurated in controlled situations of the lab as: light compensation point (LCP), light saturation point (LSP), CO2 compensation point (F), and in natural environment of 6 plots representing different succession stages (from "secondary shrub plot" to "Pinus massoniana plot", "Pinus massoniana + Schima superba plot", "Schima superba + Pinus massoniana plot", "Schima superba + Castanopsis fargessi plot", and "Castanopsis fargessi plot") as: daily variations of net photosynthetic rate (Pn), photosynthetic active radiation (PAR), CO2 concentration (CC>2-abs), leaf temperature (Tleaf), relative humidity (RH), evaporation (E), leaf to air vapor pressure deficit (VPD), intercellular CO2 concentration (Ci), stomatal conductance (Gj). Multi-linear regression equations of Pn to ecological and physiological factors (PAR, CO2-abs, Tleaf, RH, E, VPD, Ci, Gi) were set up. Importances of the factors were arrayed according to partial coefficients in corresponding equations. Variations of those physioecological indices were analyzed for 3 aspects: between species, between succession stage, and between seasons. Using canopy structure analyzer and WinScanopy software, canopy structure parameters as: Photosynthetic active photon flux density (PPFD), gap fraction (GF), leaf area index (LAI), mean leaf angle (MLA) and clumping factors (CF) were analyzed. Variances of canopy structure and its radiation environment in different succession stages were summarized. Results of the integrating research were as follows:For photosynthetic characters: Pn of the four dominant species is accordingly highin evergreen broad-leaved trees, which Schima superba (S.su) > Lithocarpus glaber (L.gl) > Castanopsis fargessi (C.fa)> Castanopsis sclerophylla (C.sc). And for LCP: C.sc > L.gl > S.su > C.fa. For LSP: S.su > L.gl > C.sc > C.fa. For photoinhibition point: S.su > C.sc > L.gl > C.fa. So the tolerance of shading: C.fa>S.su>L.gl>C.sc. For @: L.gl>C.sc>S.su>C.ca. The traits of daily Pn-PFD curve were that the maximum Pn appear between 8:00-10:00, and the "midday depression" phenomenon may occur universally. Generally speaking, S.su, L.gl, and C.sc have double climax during the day. And C.ca has only one in the morning. In different developmental stages, the sorted order of Pn is mature trees, juvenile trees, and germinal trees. In different seasons, Pn is higher in summer and autumn than spring and winter. The sorted order of importance for all factors is: Q> E> VPD > PAR > Gi > CO2.abs> RH > Tleaf. So physiological factors may have more direct and significant affects on photosynthetic courses.With succession of evergreen broad-leaved forest, factors affecting photosynthesis many change systematically. Pn, LCP, LSP, Rd, Gi, Ci and Chl concentration have a trend of decrease. Canopy structure parameters as: PPFD, GF, CF decrease accordingly. LAI has a trend of increase. And MLA has a trend of increase at first and decrease subsequently.According to physioecological characters of photosynthesis, the composition of species in different succession stages also changed significantly. S.su can exist in all 6 plots. L.gl and C.sc adult trees appear from Pinus massoniana+ Schima superba forest, while C.ca adult trees appear latest from Schima superba + Pinus massoniana forest.