Responses of chlorophyll fluorescence and nitrogen level of Leymus chinensis seedling to changes of soil moisture and temperature.

Controlled experiment of Leymus chinensis seedlings grown in the environmental growth chambers at 3 soil moisture levels and 3 temperature levels was conducted in order to improve the understanding how leaf photosynthetic parameters will respond to climatic change. The results indicated that soil drought and high temperature decreased the photochemical efficiency of photosystem (Fv/Fm), the overall photochemical quantum yield of PSII(yield), the coefficient of photochemical fluorescence quenching(qP), but increased the coefficient of non-photochemical fluorescence quenching(qN). Severe soil drought would decrease Fv/Fm and yield by 3.12% and 37.04% under 26 degrees C condition, respectively, and 6.60% and 73.33% under 32 degrees C condition, respectively, suggesting that higher temperature may enhance the negative effects of soil drought. All the soil drought treatments resulted in the decline in leaf nitrogen content. There was no significant effect of temperature on leaf nitrogen level, but higher temperature significantly reduced the root nitrogen content and the ratio of root nitrogen to leaf nitrogen, indicating the different strategies of adaptation to soil drought and temperature. It was also implied that higher temperature would enhance the effect of soil drought on leaf photosynthetic capacity, decrease the adaptability of Leymus chinensis to drought.