Photosynthetic Characteristics Of Quercus Variabilis And Robinia Pseudoacacia Under Different Light Conditions

Photosynthesis of the plants can reflect the responses to environments.In this paper,fluorescence parameters of shadedand sunlit leaves?the light-response curves of electron transport rate?and 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.The results showed that the Fv'/Fm' and qP of the shaded leaves were higher than that of the sunlit leaves,and the ETR of the sunlit leaves were higher than that of the shaded leaves.The temperature was significantly positively correlated with the Fv/Fm,NPQ and ETR of the Robinia pseudoacacia leaves,and extremely significant withFv'/Fm'.Humidity was significantly positively correlated with Fv/Fm of Q.variabilis and R.pseudoacacia leaves;Fi,/Fm,ETR and Chl of R.pseudoacacia leaves were significantly positively correlated.Study on the J-I curve of shadedand sunlit leaves showed that the determination coefficient of the J-I curves fitted by three models were more than 0.96.Compared with the rectangular hyperbola and nonrectangular hyperbola,the determination coefficient of the Ye model was highest(>0.99).The Jmax values of the shaded leaves for Q.variabilis and R.pseudoacaciawere 25.0%and 18.0%lower than the sunlit leaves,respectively The Isat values of the sunlit leaves of Q.variabilis and R.p.seudoacacia were 26.0%and 10.1%higher than those of the shaded leaves.Jmaxof Q.variabilis and R.pseudoacaciawas correlated with temperature.Isat of R.pseudoacacia was correlated with temperature,soil water content and net photosynthetic rate.The initial slope(a)values ofthe J-I curves for Q.variabilis and R pseudoacaciahad significant negativerelationships with net photosynthetic rate.Net photosynthetic rates(Pn)of Q.variabilis in the forest inner was higher than that in the forest margin,and initial light efficiency(a)was 12.4%more than that in the forest margin in July and August when photosynthetically active radiation was less than 200 ?mol·m-2·s-1.It is indicated that the ability to capture and utilize weak light of Q.variabilis leaves in the forest inner was obviously higher than that in the forest margin.When photosynthetically active radiation was more than 200 ?mol·m-2·s-1,Pn of Q variabilis leaves in the forest margin was larger than that in the forest inner.Under weak light conditions(0?200 ?mol·m-2·s-1),Pn of R.pseudoacacia in the forest inner was higher than that in the forest margin.Pn of R.pseudoacacia in the forest inner was less than that in the forest margin when light intensity was more than 200 ?mol·m-2·s-1.The dark respiration rate(Rd)and light compensation point(Ic)in the forest inner were 50.0%and 42.8%lower than those in the forest margin.The less Rd and Ic of the forest inner could reduce carbon loss and adapt to low photosynthetic rate.The stomatal conductance light-response of R.pseudoacacia in the forest inner significantly differed from that in the forest margin.The leaves of Q.variabilis and R.pseudoacacia had strong adaptability to the change of light conditions.The values of maximum net photosynthetic rate(Pn max)and a of Q.variabilis leaves were mainly controlled by gs,and Rd and Ic were primarily affected by air temperature.Pn max and a ofR.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.