Physiological Response To Double CO₂ Concentration, Elevated Temperature And Nitrogen In Quercus Mongolica

In this study, the dominant species Quercus mongolica seedlings in northeast forest was studied on the responses to double CO₂ concentration and elevated temperature. We used portable photosynthetic analysis system Li-6400 to measure photosynthesis and dark respiration of Quercus mongolica. We also measured pigment content, carbonhydrate content, biomass and their seasonal variation. The results were as fowllowing:1. Three nitrogen levels had increased maximum photosynthesis of Quercus mongalica seedlings slightly under interaction of double CO₂ concentration and elevated temperature. Only high nitrogen increased maximum photosynthesis under elevated temperature. Maximum photosynthesis was also obviously affected by nitrogen. In all the treatments, maximum photosynthesis of high nitrogen level was obviously higher than that of low nitrogen and no nitrogen added levels.2. Three nitrogen levels had increased dark respiration of Quercus mongalica seedlings under interaction of double CO2 concentration and elevated temperature. Respiration was high in July. This was relative to the high temperature in this month.3. Seasonal variation and different nitrogen levels had obviously affected chlorophyll content. Chlorophyll content of high nitrogen increased with seasonal variation, conversely low nitrogen and no nitrogen added levels decreased with seasonal variation. CO2 concentration, temperature and their cooperation with high nitrogen had increased chlophyll content synthesis in August. In all the treatments, chlorophyll a/b had significantly increased in July. It was because of high temperature in July which resulted in decreasing chlorophyll b content.4. Leaf carbon and nitrogen ratio increased with the decrease of nitrogen level. No nitrogen added level of elevated temperature only and its interaction with double CO2 concentration was obviously higher than control. But it was affected by carbon and nitrogen content diffently. The former was affected by the increase of carbon content, while the latter was affected by nitrogen content decreasing.5. Organ carbonhydrate contents of Quercus mongalica seedlings were not obviously affected by different treatments, but obviously affected by seasonal variation. The contents were also diffetent with organs: soluble sugar: leaf> taproot> stem> lateral root> fine root. Starch contents were obviously affected by seasonal variatinon, in June: stem> taproot> leaf> lateral root> fine root;in July: leaf> taproot> stem> lateral root> fine root;in August: taproot> leaf> lateral root> stem> fine root.6. Biomass of high nitrogen obviously increased, especially under elevated temperature.Below-ground biomass of high nitrogen increased more obviously under elevated temperature in result of root and shoot ratio increased. The interaction of double CO2 concentration and elevated temperature on biomass and allocation were not very obvious. This indicated double CO2 concentration was not positive to the growth of Quercus mongalica seedlings or the interaction of double CO2 concentration and elevated temperature did not affect Quercus mongalica seedlings obviously, or both. In conclusion, global climate change will not significantly affect the productivity of Quercus mongalica seedlings.