| For study of photosynthesis characteristic of Quercus aquifolioides under the nature environment. The comparisons of photosynthesis characteristic in normal and controlled situations have been taken. The main elements as photosynthesis active radiation(PAR), concentration (CO2), air temperature(Ta), leaf temperature(Tl), (HR) et have been Measured and logged by Li-6400 portable photosynthesis system. While the photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (Cond), in tercellar CO2 concentration (Ci), vapor pressure deficit (VPD) et. have been logged as well. Samples are taken every hour to determine the diurnal characters of them. During sunrise and sunset, the intervals are less than one hour. Keep the leaf temperature at about 22℃, and then set the photosynthesis active radiation and change the CO2 concentration can get the photosynthesis curve. Another content of the experiment is tracking the nature condition. The results: (1) variation of photosynthesis rate is midday depression pattern; the two peaks have nearly the same width. The peak occurred in morning lasts higher than the one in the afternoon. (2)The stomatal conductance is related to photosynthesis closely, and keep same change trend. The Cond also affects the intercellar CO2 concentration and transpiration rate to some degree. The vapor pressure deficit is attributes to PAR and air temperature. The diurnal variation curves of photosynthesis rate, stomatal conductance and transpiration all are two peak pattern and show similar trend during the same time .(3) Under the controlled situations, VPD changes very little, so CO2 concentration is the main factor affecting the stomatal conductance. When CO2 concentration is change between 300-750ppm, stomatal conductance, photosynthesis rate and light compensation point (LCP) keep same trend with CO2 concentration. With the CO2 concentration keeping increasing beyond 1000ppm, stomatal conductance and photosynthesis rate will drop,...
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