Abstract: To investigate the effects of nitrogen fertilization on the photosynthetic capacity and growth of three-year old potted-plants of I . delavayi , an alpine herb , the effects of nitrogen supply on the foliage traits, gas exchange response curves, leaf nitrogen partitioning , chlorophyll fluorescence parameters and growth parameters were examined . The results showed
that when the nitrogen supply was 0 g􊄯kg, severe photoinhibition occurred though the leaf nitrogen allocation to light harvesting system complex decreased in I . delavayi . In addition , the leaf nitrogen content allocated to the photosynthetic components was smallest among all treatments, which resulted in the worst photosynthetic capacity and slowest relative growth
rate of whote plant (RGR). With nitrogen supply increased, the leaf nitrogen content (N) , chlorophyll content (Chl ), leaf nitrogen content allocated to the photosynthetic components (NR 、NB and NL ) and light utility efficiency increased correspondingly, and it contributed to photosynthetic capacity enhancing . Because the leaf nitrogen content allocated to bioenergetics
was more than to Rubisco , after offering nitrogen fertilizer , Jmax􊄯Vcmax increased , which helped I. delavayi adapt to the alpine environment , such as lower temperature and higher irradiance. With nitrogen supply increasing, the speed of growth of I . delavayi was accelerated , which was benefit to the reproduction and next-year growth .When nitrogen supply was more than 0 .2 g􊄯kg, N, Chl and the thickness of mesophyll tissue, photosynthetic rate and RGR did not increase statistically. In a word, the optimum amount of nitrogen needed by the I. delavayi was about 220 - 230 mg/kg soil.

Key words: Incarvillea delavayi