Growth and photosynthetic responses of two coniferous species to experimental warming and nitrogen fertilization

The paper studied the short-term effects of experimental warming, nitrogen fertilization, and their combination on growth and photosynthetic performances of Picea asperata Mast. and Pinus tabulaeformis Carr. seedlings. These seedlings were subjected to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (0 and 25 g N·m-2·year-1) for 6 months. Warming alone and fertilization alone significantly increased biomass accumulation and photosynthetic performances of both two species. The combination of warming and fertilization stimulated greater accumulation of stem, root, and total biomass and further increased chlorophyll content and net photosynthesis rate (A) in Pinus tabulaeformis seedlings. However, for Picea asperata seedlings, the interaction induced less increment in plant height, total biomass, chlorophyll contents, A, and the efficiency of photosystem than nitrogen treatment alone. These results implied that both climate warming and nitrogen addition were favorable for the early growth of both coniferous species; the interaction of these two factors caused adding or multiplying single-factor effects in the case of Pinus tabulaeformis seedlings but dampening them in the case of Picea asperata seedlings, at least in short time.