关键词: 长序榆, 氮添加, C、N、P养分, 非结构性碳水化合物

Abstract:

Objective: Under the background of increasing nitrogen deposition,the effects of nitrogen deposition on carbon,nitrogen and phosphorus accumulation of endangered Ulmus elongata and their quantitative relationship and non-structural carbohydrate content were studied by adding exogenous nitrogen,so as to provide reference for the protection of this minimal population. Method: The accumulations of total carbon,nitrogen and phosphorus in roots,stems and leaves of U. elongata and their quantitative relationships between those nutrients and changes of non-structural carbohydrate contents were analyzed by applying different concentrations of nitrogen to the annual seedlings of U. elongata. Result: The leaf biomass was significantly reduced with the addition of high nitrogen (N:262.3 mg·L^-1),but the root or stem biomass was not significantly affected. Both low nitrogen (N:52.46 mg·L^-1) and high nitrogen treatment increased the total carbon content in roots,but significantly decreased the total carbon content in leaves. Under high nitrogen treatment,the total nitrogen content in roots,stems and leaves increased significantly,while the total phosphorus content decreased significantly with the increase of nitrogen application level. Both low and high nitrogen treatments reduced the C:N value in the plant,however C:P and N:P were the highest under high nitrogen treatment. The soluble polysaccharides and starch contents in roots and stems were increased under both low and high nitrogen treatments. The content of soluble polysaccharide and starch in leaves was significantly decreased by high nitrogen treatment. The content of non-structural carbohydrates (NSC) first decreased and then increased in roots and stems,and in leaves NSC was contrary to roots and stems with the increase of nitrogen application level. High nitrogen treatment led to the decrease of P_n,G_s,Tr,WUE and L_s in varying degrees,but the increase of C_i concentration. Conclusion: High nitrogen treatment increases N content in Ulmus elongates,and however inhibits the leaf photosynthesis,reduces the carbon accumulation and increases the phosphorus limitation,which increases the risk of endangerment. At the same time,U. elongata copes with the adverse effects of high nitrogen by accumulating more NSC in roots.

Key words: Ulmus elongata, nitrogen addition, C, N, P nutrients, non-structural carbohydrates