Diversity Of Light Energy Utilization And Community Stability Of Dominant Species In Quercus Liaotungensis Forest

The paper mainly took Quercus liaotungensis's natural secondary forests in semi-arid region of the Loess Plateau as research object. To confirm the community stability of Quercus liaotungensis forest in this area, fixed sample plots was chose in Moutain forests area around Yan'an road. LI-6400 portable photosynthesis system was used to measure the diurnal course of net photosynthetic rate of dominant species in Quercus liaotungensis forest in different periods of the growing season and of inside and outside Quercus liaotungensis forest. The related mathematical models about the response characteristics of photosynthesis to the light was established and photosynthetic parameters was analyzed; the relationship of photosynthesis and impact factor was analyzed by multiple linear regression analysis; photosynthetic adaptive functional group in different periods of the growing season was divided by cluster analysis. The main results are as follows:1. The diurnal courses of available photosynthetic radiation of 16 dominant species inside and outside the Quercus liaotungensis forest were single-peak type in different periods of the growing season of their vegetal environment. Diurnal courses of carbon dioxide concentration inside and outside the Quercus liaotungensis forest showed"U"shape plot and had remarkable change in their prosperous growth period, instead slight change in early growth period. The diurnal courses of temperature inside and outside the Quercus liaotungensis forest increased slightly first and decreased later which showed a gentle single-peak curve; The relative humidity inside and outside the Quercus liaotungensis forest showed changes of an inverted"parabolic curve"change; The soil moisture showed little difference between inside and outside the Quercus liaotungensis forest, while showed remarkable difference among different seasons because of different climate condition.2. The diurnal course of net photosynthetic rate of 6 dominant species outside Quercus liaotungensis forest were double-peaked curves during growing season, and there were remarkable midday depression. The photosynthesis diurnal courses of dominant species inside forest were mainly single-peaked curves. But double-peaked curves were also found because of different species, growing season, weather condition and canopy. In contrast, Quercus liaotungensis showed a distinct"noon-break"after reaching a peak. 3. Multiple linear regression analysis show: the stomatal conductivity and intercellular CO2 concentration were the main factors, which influenced the net photosynthetic rate, the effects of available photosynthetic radiation, air temperature, relative humidity and vapor pressure deficit on the net photosynthetic rate, rate were depend on different species, different periods and different inhabitats. The ecological factors had indirect effect on the net photosynthetic rate of these species by influencing stomatal conductivity and intercellular CO2 concentration. The annual average photosynthetic ability was: tree layer>shrub layer>grass layer.4. Dominant species inside and outside Quercus liaotungensis forest have different adaptive characteristics and abundant light energy utilization. There were large differences between the same species in different and different species in the same inhabit. The light saturation points and light compensation points between three months and the two habitats had significant difference while dark respiration rate and apparent quantum yield only had a significant difference in different habitats.5. The 16 dominant species inside Quercus liaotungensis forest were divided into different functional groups in different months during growing season by hierarchical cluster analysis which identified significant patterns with 5 photosynthetic parameters,including maximum net photosynthetic rate,light saturation point,light compensation point,dark respiration rate and apparent quantum yield. Different species were divided into the same functional group in different months, each of the functional group has a distinct photosynthetic survival strategies parameter adjusting pattern in order to make the utmost utilization of light energy and maintain the Quercus liaotungensis forest to be stable.