The Photosynthetic Response Of Phoebe Bournei To Doubled CO₂ Concenteraion In Atmosphere

We studied the photosynthetic response of Phoebe bournei to be doubledCO2 concentraion in atmosphere under light of lOOMmol.m-2 . s-1 . The results showed that chlorophyll content of per unit fresh weight of leaves under 700ppm CC>2 concentraion in atmosphere were decreased compared with the control: total chlorophyll content decreased 28.7%, of which chlorophyll a decreased 28.6%, and chlorophyll b decreased 19.8%. Chlorophyll a/b decreased from 1.952 to 1.547. In contract the content of contenoid of per unit fresh weight of leaves increased 2.8%. After treating with 700ppm CO2 for three months, in the leaves of Phoebe boumeijhe amount of closed PSII center increased, both the rate of photosynthetic electron transport and efficiency of the photosynthetic energy' conversion decreased. Under light of lOOMmol.m-2. s-1 and 700ppm CO2 concentraion the coefficent of potochemical quenching of PSII center went down, meanwhile the coefficent of nonpotochemical quenching of PSII center went up. Thus it enabled that the PSII center dissipated more energy by non-radiantion, and it led to the lower energy conversion efficency. Protein and solvable sugar per unit fresh weight in the leaves were decreased by 53.91 and 2.45 respectively in the plants which grown under 700ppm CO2 after three months, and the fresh biomass decreasing 8.8%. The ture photosynthetic rate of Phoebe bournei enhanced over 21.7% after treating with 700ppm CO2 for short time, but decreased about 89% after treating with 700ppm CO2 for three months. In comparision with the control, the dark respiration and potorespiration per unit leaf area decreased by 95.6% and 43.7% respectively. Thus, the results indicated that because of the effects of the C02 as reactant and drop of dark respiration and potorespiration, the ture photosynthetic rate enhanced after treating with 700ppm C02 for short time. When treating with 700ppm C02 for long time, both of the dark respiration and potorespiration were restrained seriously , the abilities providing carbon and energy by PPP path and TCA path to the anabolism to protein,nucleic acid,fat,and so on were dropped. Therefore it result in the foul-up,and limited the potosynthesis apparently, and led to the photosynthetic acclimation. Because of the metabolism failed down after treating with 700ppm COi for long time, the power of the plants to resist disease were dropped finally.