Simulation on photosynthetic light-responses of leaves of Quercus variabilis and Robinia pseudoacacia under different light conditions.

Abstract

Photosynthesis can reflect the responses of plants to environmental changes. In this study, photosynthetic light-response curves were measured by the Li-6400XT photosynthetic system in Quercus variabilis and Robinia pseudoacacia plantations in Xiaolangdi Forest Ecosystem Research Station. Photosynthetic light-response curves were fitted by Ye model. The differences of photosynthetic parameters between inner and margin forests were examined. Stomatal conductance (gs) light-response curve were fitted using the mechanism model of gs coupled with a modified model of light-response of photosynthesis. The light-response characteristics of gs were investigated. Net photosynthetic rates (Pn) of Q. variabilis in the inner forest was higher than that in the margin. The initial light efficiency (Α) was 12.4% more in the inner forest than that in the margin in July and August when photosynthetically active radiation was less than 200 Μmol·m-2·s-1. The ability to capture and utilize weak light of Q. variabilis leaves in the inner forest was obviously higher than that in the margin. When photosynthetically active radiation was higher than 200 Μmol·m-2·s-1, Pn of Q. variabilis leaves in the margin forest was larger than that in the inner. Under weak light conditions (0-200 Μmol·m-2·s-1), Pn of R. pseudoacacia in the inner forest was higher than that in the margin. Pn of R. pseudoacacia in the inner forest was less than that in the margin when light intensity was higher than 200 Μmol·m-2·s-1. The dark respiration rate (Rd) and light compensation point (Ic) in the inner forest were 50.0% and 42.8% lower than those in the margin. The less Rd and Ic of the inner forest could reduce carbon loss and adapt to low photosynthetic rate. The stomatal conductance light-response of R. pseudoacacia in the inner forest significantly differed from that in the margin. The leaves of Q. variabilis and R. pseudoacacia had strong adaptability to the changes of light condition. The values of maximum net photosynthetic rate (Pn max) and Α of Q. variabilis leaves were mainly controlled by gs, and Rd and Ic were primarily affected by air temperature. Pn max and Α of R. pseudoacacia leaves had significant positive correlation with air temperature. The Ic and the light saturation point (Is) were remarkably correlated with leaf saturation vapor pressure deficit.