Effects Of Nitrogen And Phosphorus Supply On Growth And Photosynthesis Of Larch Seedlings

Larch (Larix gmelini) is the most important industrial timber species in northeastern China, and considered to have important ecological significance in boreal forest ecosystem. However, the growth of larch is often limited by nitrogen and phosphorus shortage because slow decomposition rate of litter results by low temperature and long winter in boreal forest. Therefore, studied the adaptive mechanisms of growth and photosynthesis of larch to different nitrogen and phosphorus supply level have important practice and theory significance to improve productivity of larch forest and enrich silviculture theory. In this study, we use sand culture method and design nitrogen and phosphorus supply level. Growth, nutrition absorption and photosynthetic characteristic of one-year-old larch seedlings under different nitrogen and phosphorus supply level were studied. The results show:1. Deficient nitrogen and phosphorus supply significant restrain shoot growth of larch seedling, but have no effect on root growth. Increased nitrogen and phosphorus supply have obvious improve effect on shoot growth. 16 mmol.L-1 may be have arrived or approached the optimum nitrogen concentration for growth of larch seedling. The optimum phosphorus supply level is 1 mmol.L-1, excessive phosphorus supply (2 mmol.L-1) has restraining effect on growth of seedling.When seedlings were supplied with deficient nitrogen and phosphorus, partitioning of biomass to roots was more in order to increase root growth and enlarge absorption surface to nutrition. This may be a adaptive strategy of larch seedling to low nutrition supply.2. Additional nitrogen supply significant increased needle, stem and root nitrogen concentration in larch seedling. Thereinto, needle nitrogen concentration is highest and have the most change extent with the increase of nitrogen supply. These suggest increase nitrogen supply may enhance plant absorb more nitrogen nutrition, and needle nitrogen concentration is more sensitive to variety of nitrogen supply level.Phosphorus supply level has no effect on the nitrogen absorption of larch seedling. Low phosphorus supply didn't decrease the needle phosphorus concentration, but it did induce a decline of stem and root phosphorus concentration, these suggest insufficient phosphorus supply decreased the phosphorus absorption of seedling. Increase phosphorus supply may increase stem and root phosphorus concentration, but when phosphorus supply arrive 2 mmol.L-1, phosphorus concentration in organ is no longer increase, and both nitrogen and phosphorus contents of whole plant have show decrease tendency, these farther prove that 2 mmol.L-1 phosphorus supply concentration is excess, and have restrained larch seedling root system nutrition absorption.3. There is a strong correlation between nitrogen supply and photosynthesis of larch seedling. Nitrogen supply deficiency reduce chlorophyll content, carotenoid content, total soluble protein content of needle of larch seedling and result in light-saturated net photosynthetic rate (Pmax) which reflect plant photosynthetic ability decreased. Low photosynthetic ability of larch seedling is mainly due to the declineof Rubisco contents and activity under low nitrogen supply level.When nitrogen supply deficiency, larch seedling is more sensitive to photoinhibition, these can be seen from the decrease of Fv/Fm and PSII. Whereas increase nitrogen supply can significant improve photochemistry efficiency and alleviate photoinhibition. In addition, with the decease of nitrogen supply level, qP of larch seedling also decrease, and this change was accompanied by a increase of NPQ, these suggest that under nitrogen deficiency, the light energy which have been captured by plant can't be used effectively, but more of them is dissipated in heat.Compare with the effect of nitrogen, phosphorus have little effect on photosynthesis of larch seedling. Phosphorus deficiency didn't induce in deceased of photosynthetic pigment content and total soluble protein content, and Pmax only decrease 18.1%. On the ot...