Diurnal variation and effective factors of photosynthesis on the canopy layer of young Pinus elliottii forest

Diurnal variation of photosynthesis , leaf temperature , air temperature , relative humidity , light intensity and CO2 concentration on the canopy layer of young Pinus elliottii forest in the low hilly area of northern Sichuan basin and their chlorophyll content of leaf were measured .The results showed that the net photosynthesis rate of 1-year-old leaf and 0-year-old leaf increased with the enhanced light intensity ;the phenomenon of midday depression of photosynthetic rate wasn't found .The leaf temperature was lower than air temperature all the time except between 12 :00 -14 :00 .The variation regularity of stomatal conductance and transpiration rate was similar , their max value both emerged at 14 :00 .The diurnal variation of air relative humidity was in a U curve .The CO2 concentration was gradually decreased from 8 :00 to 16 :00 , and it started to increase at 18 :00 .The net photosynthesis rate of 1-year-old leaf was always lower than that of 0-year-old leaf , however , chlorophyll content of the former was higher than the latter .Through the correlation analysis , we found the main factors causing the diurnal variation of photosynthesis included leaf temperature , air relative humidity , light intensity and stomatal conductance .[ Ch , 3 fig .1 tab .17 ref .]