The Photosynthetic Characteristic And Its Responses To The Environment Of Major Trees In Hunan Province

The photosynthetic characteristics of six typical tree species in subtropical evergreen broadleaf forest area, i.e. Cinnamomum camphora, Cyclobanalopsis glaber, Castanopsis eyrei, Quercus fabri, liquidambar formosana, Pinus massoniana, and their response to environmental factors were investigated using LI-COR6400 portable photosynthesis system. The study of the photosynthetic characteristics included the seasonal and diurnal change in photosynthetic rate, relationships between photosynthetic rate and the physiological and environmental factors, relationships between photosynthetic rate and the concentration of chlorophyll, nitrogen, phosphor in the corresponding leaves. The main results were as follows.Different season had the different diurnal curves of net photosynthetic rate (Pn) in different trees. The diurnal net photosynthetic rate of Quercus fabri, liquidambar formosana in sunny day varied with double peak curves in summer and single peak curve in autumn. The diurnal net photosynthetic rate of Pinus massoniana, Cyclobanalopsis glaber,Castanopsis eyrei in sunny day varied with single peak curves in both summer and autumn. Among the three primary succession tree species, Quercus fabric ranked the highest of daily average Pn, Liquidambar formosana was the second, Pinus massoniana was the lowest. Among the climax succession tree species, the Pn value of Cyclobanalopsis glaber was higher than that of Castanopsis eyrei.Except for the Pinus massoniana, the diurnal Pn changes of other five experimental trees showed significant midday depression. The outcome resulted from different exterior and interior factors.The interior factors contributed more to the Pn than the exterior ones. Based on the ANOVA, the primary factors that affecting the Pn were intercellular CO2 concentration (Ci), stomatal conductance (Cond), transpirational rate. The environmental factors such as photosynthetic active radiation (PAR), air temperature (Ta), relative humidity (RH) had the different influence to different trees. The ecological and physiological factors that affecting the photosynthetic characteristics were not single each other but interactive.In the four trees, Cinnamomum camphora, Quercus fabri, liquidambar formosana, Pinus massoniana, the relative correlation between Pn and chlorophyll, nitrogen contents of leaves showed the high values which are positive. The relationship between chlorophyll and nitrogen contents of leaves was positive too. But the correlation value between Pn and phosphor contents of leaves was negative.Under the same light intensity, The Pn value of Pinus massoniana under present CO2 conc-entration(360/rniol-mol-1) was larger than the Pn were measured under 800,1200 mol.mol-1 .in which the light compensate point (LCP) increased by 6 and 4 mol-m-2-s-1, respectively, the lightsaturate point decreased by 200junol-m~ -s" . The effect of the leaves of PZHMS massoniana to the CO2 enrichment decreased the E and Cond, but increased the water use efficiency (WUE).When the CO2 concentration increased to 700, the light saturate point and light compensate point(LCP) of Quercus fabric decreased by 300, 80/imol-m"2-s"1.The E and Cond showed the same result too. Under the same light intensity, the Pn and Ci of Liquidambar formosana had increased with the elevating CO2 concentrations.The light compensation point and light saturation point of Cinnamomum camphora leaves at the ambient CO2 concentration were 40.6 jtmol-m'V1 and 1 250 /miol-m'V1. When light intensity reached 1 000 /miol-m'V1 and ambient CO2 concentration, its CO2 compensation point and CO2 saturation point were 50 /unol-mol"1 and 1 200 /unol-mol"', respectively. Under different CO2 treatment, the maximal WUE of Cinnamomum camphora leaves was always appeared to antique light intensity:750 /unol-m'V. With the increasing of CO2 concentration, Pn and WUE of Cinnamomum camphora , Pn , WUE and Ci of Cyclobanalopsis glaber, Castanopsis eyrei havd increased . When the CO2 concentration doubled, the WUE of Cyclobanalopsis glaber was lower than Castanops...