Abstract: A field experiment was performed to explore the effects of N supplementation on nutrients (N, P, K), non-structural carbohydrate (NSC), structural carbohydrates (SC) and defensive compounds in leaves of dominant species Leymus secalinus in a salinized grassland of northern China, taking advantage of a field N addition gradients (0~32 g·m^-2·a^-1) experiment that has been established in the Loess Plateau in Youyu, Shanxi Province in 2017. The results showed that (1) Nitrogen input significantly increased the N and K contents, and N:K and N:P ratios, and decreased the P content and P:K ratios in leaves. (2) Nitrogen input decreased the foliar NSC and SC content. (3) Nitrogen input significantly increased total phenols, tannins and flavonoids contents in leaves. (4) By PCA analysis, it showed that there was a trade-off relationship between leaf traits under low and high N treatments (> 8 g·m^-2·a^-1);the soil inorganic N, ratios of soil available N:P and N:K significantly affected most leaf traits of the investigated species. These results indicated that plants would invest more newly synthesized carbon into its defensive components and reduce the allocation to NSC and SC under the background of high N deposition, that is, N input altered the trade-off among plant traits.

Key words: Nitrogen addition gradient, Leaf nutrient, Leaf carbon component, Leaf defensive compound, Allocation strategy

摘要： 本研究依托山西右玉黄土高原赖草（Leymus secalinus）草地2017年建立的氮（Nitrogen，N）添加梯度试验平台（0~32 g·m^-2·a^-1），探究N添加对优势植物赖草叶片养分[N、磷（Phosphorus，P）、钾（Potassium，K）]、非结构性碳水化合物、结构性碳水化合物和防御性化合物含量的影响。结果表明：N素输入显著提高叶片N，K含量和N：K和N：P比值，降低叶片P含量和P：K比值；N素输入显著降低叶片非结构性碳水化合物和结构性碳水化合物含量；N素输入显著增加叶片总酚、单宁和黄酮类化合物含量；PCA分析表明低N（≤ 8 g·m^-2·a^-1）和高N（>8 g·m^-2·a^-1）输入下赖草叶片性状存在显著差异，土壤无机N含量、土壤有效N：P和N：K是其主要影响因子。以上结果表明N素输入改变了盐渍化草地赖草叶片养分-碳组分-防御性化合物的分配策略。

关键词: 氮添加梯度, 叶片养分, 叶片碳组分, 防御性化合物, 分配策略