| The forth assessment report of IPCC predicted that atmospheric CO2 concentration will be above 700μmol·mol-1, and the temperature of the earth's surface would rise 1 to 3.5 degrees centigrade in the next 50 to 100 years. Subalpine forest community in eastern Sichuan is at the east edge of the Qinghai-Tibet plateau, its plant community is very sensitive to global climate change. In the paper,the plant-growth chamber system for climate modeling is used to study the response of gas exchange, photosynthetic pigment concentration, specific leaf area, leaf nutrient content and sugar and soluble protein content of Fargesia denudata in subalpine in eastern Sichuan to elevated atmospheric CO2 concentration (about 700μmol·mol-1,EC),elevated temperature (2(±0.5)℃increased, ET),and both increased (ECT) (the background environment where the growth chamber system located is the control treatment,CON).The research is to provide basic datas for panda protecting biology and a theoretical basis for ptotecting and recovering subalpine vegetation in eastern Sichuan under the trend of global warming. The main results are as follows.1) In the saturated light intensity, compared with the control treatment, the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E) of F. denudata increased while the water use efficiency (WUE) reduced under the EC and ECT treatment. The net photosynthetic rate, stomatal conductance and transpiration rate decreased significantly while the water use efficiency increased when elevate the temperature.The study of curves the net photosynthetic rate of F. denudata responsed to light and intercellular CO2 concentration show that there had a photosynthetic down regulation of phenomenon under the EC,ET and ECT treatment,but the intensity of down regulation was not significant compared to the control treatment.The apparent quantum yield (AQY) expressed for EC> ECT> CON> ET.The initial rate of carboxylation (CE), dark respiration (Rd) and photorespiration Rate (Rp) increased compared to the control treatment, and the accommodative range of light and intercellular CO2 concentration had expanded.2) The impact of EC, ET and ECT treatments on photosynthetic pigment concentration of F. denudata was significant.The chlorophyll a (Chla), chlorophyll b (Chlb), chlorophyll (a+b) (Chl(a+b)) and carotenoid concentrations were all increased significantly under the EC treatment;the chlorophyll a concentration increased when rising the temperature while the chlorophyll b, chlorophyll (a+b) and carotenoid concentration decreased; under the ECT treatment, the chlorophyll a concentration of F. denudata had no significant change, and the other three concentrations decreased. The ratio of chlorophyll a and chlorophyll b (Chla/b) increased by 5.94%,19.48% and 4.03% seperately under EC, ET and ECT treatments.3) Comparing with the control treatment, the influence of EC,ET and ECT treatment on specific leaf area (SLA), leaf dry matter content (LDMC) and nutrient content of leaves of F. denudata were not consistent. The specific leaf area, leaf nitrogen and leaf phosphorus concentration increased under the EC treatment, and the leaf dry matter content and total carbon content decreased; the specific leaf area, leaf dry matter content and leaf nitrogen, phosphorus concentrations increased under ET and ECT treatments, and the total carbon content increased significantly and showed no significant change respectively.4) The three different rising treatments make soluble sugar, starch, cellulose, glucose, fructose and sucrose contents in leaves of F. denudata all increased significantly, while the increasing amount of starch was the most, followed by sucrose. This is because the assimilation capability of carbon increased under EC and ECT treatments, and it promoted the accumulation of a variety of photosynthetic products; the soluble protein content increased while heighten the CO2 concentration, but the difference was not significant; it was lower than the control treatment under both ET and ECT treatments and the difference was significant.In conclusion, long-term growth of F. denudata in elevated CO2 concentration and temperature adapted to light and CO2 concentration in a larger range, and with a significant increasing of specific leaf area and various carbohydrates content, but there were some differences among its gas exchange, nutrient content, photosynthetic pigment concentration and soluble protein content in response to different treatments. The impact mechanisms of the photosynthetic characteristics of F. denudata are not entirely consistent under elevated CO2 concentration and temperature treatments, the mechanism of action is more complex when the CO2 concentration and temperature are both elevated. |
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