Studies on Diurnal Variation of Photosynthesis on Five Species of Poplars

Photosynthetic physiological characteristics of Populus ×canadensis ‘zhongliao1’, PopulusבLiaoninensis’,DM-9-18, P.pseudosimonii and P.simonii were compared in this study. The results showed that：The order of daily average net photosynthetic rate from high to low was P.בLiaoninensis’,DM-9-18,P. simonii, Populus×canadensis‘zhongliao1’ and P. pseudosimonii. The P.pseudosimonii was the lowest in overall level of net photosynthetic rate. The diurnal course of Populus×canadensis‘zhongliao1’ had bimodal curve, showing obvious “midday depression” phenomenon, which mainly caused by stomatal limitation. The others were single peak curve. Stomatal conductance and intercellular CO2 concentration on five species of poplars reduced in the period from 10:00 to 14:00. Reduction of net photosynthetic rate was mainly due to stomatal limitation. Net photosynthetic rate decreased mainly due to nonstomatal limitation from 14：00 to 18：00. Net photosynthetic rate on five species of poplars had significantly and extremely significantly positive correlation with transpiration rate and stomatal conductance.PAR of environmental factors had great influence upon on net photosynthesis rate, and showed significant positive correlation.