Abstract: Pinus massoniana, a pioneer species, plays an important role in restoration of degraded ecosystem and controlling soil erosion in south China. Most P. massoniana plantations are sparse and dwarfish, with low quality and poor natural regeneration. To test whether light is a limiting factor for seedling emergence and growth of P. massoniana, the effects of five light intensities (5%, 15%, 40%, 60%, 100% of full sun light) on seedling emergence, survival, growth, and morphological plasticity were investigated. The results showed that seedling emergency, germination index, and vitality index were significantly affected by light intensity (P<0.05). Seedling emergency, germination index, and vitality index reached the maximum at 40% light intensity. With increasing light intensity, stem length decreased, while root collar diameter and root length increased. The highest total biomass, root biomass, stem biomass, leaf biomass, and robustness of seedlings were observed under 100% light intensity. With increasing light intensity,the ratio of root to shoot and root biomass allocation increased, while the stem and leaf biomass allocation declined. The results suggested that seedling emergence was inhibited under high and low light intensity while low light intensity inhibited seedling growth. Our results provided experimental evidence that light is a key ecological factor affecting seedling emergence and growth of P. massoniana.

Key words: nitrogen and phosphorus., nitrogen deposition, soil pH, carbon, temperate steppe