Growth and physiological responses of Picea asperata seedlings to elevated temperature and to nitrogen fertilization

Picea asperata is a dominant species in the subalpine coniferous forests distributed in eastern edges of Tibetan Plateau and upper reaches of the Yangtze River. The paper mainly identified the short-term influences of experimental warming, nitrogen fertilization, and their combination on growth and physiological performances of Picea asperata seedlings. These seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0; 25 g m(-2) a(-1) N) for 6 months. We used a free air temperature increase of overhead infrared heater to raise both air and soil temperature by 2.1 and 2.6A degrees C, respectively. The temperature increment induced an obvious enhancement in biomass accumulation and the maximum net photosynthetic rate, and decreased AOS and MDA level under ambient nitrogen conditions. Whereas, negative effects of experimental warming on growth and physiology was observed under nitrogen fertilization condition. On the other hand, nitrogen fertilization significantly improved plant growth in unwarmed plots, by stimulating total biomass, maximum net photosynthetic rate (A (max)), antioxidant compounds, as well as reducing the content of AOS and MDA. However, in warmed plots, nitrogen addition clearly decreased A (max), antioxidant compounds, and induced higher accumulation of AOS and MDA. Obviously, the beneficial effects of sole nitrogen on growth and physiology of Picea asperata seedlings could not be magnified by artificial warming.