Effects of Different Ratios of Nitrogen Forms on Gas Exchange of Saussurea katochaete Maxim and Total Biomass of the Community Under the Experimental Warming
The Qinghai-Tibet Plateau is the region where is sensitive to the global warming. The climate changes affect all aspects of plants in the region and thus affect the productivity of alpine meadow. The open-top chambers were used to simulate the increasing temperature, and the fertilizers with different ratios of nitrate to ammonium were applied in the plots. The gas exchange and chlorophyll fluorescence of Saussurea katochaete Maxim and total biomass of the community were determined. The results showed that net photosynthetic rate of S. katochaete decreased as the ratios of nitrate to ammonium increased, but stomatal conductance increased. Other parameters of gas exchange showed irregular changes. PhiPsⅡ reached the peak when the ratio of nitrate to ammonium was 0%. Non-photosynthesis quenching increased as the ratios of nitrate to ammonium increased. In the community containing S. katochaete,the total biomass reached the peak when nitrate and ammonium was equal. All the results suggested that nitrogen fertilizers of different ratios of nitrate to ammonium might affect net photosynthetic rate of S. katochaete and the community biomass. Nitrogen fertilizer application is of significance to increase productivity of alpine meadow in Qinghai-Tibet Plateau.