短期氮、水添加对放牧背景下荒漠草原短花针茅叶片属性的影响

叶片属性是反映植物对环境变化敏感程度的重要特征，可在一定程度上预测植物对放牧干扰后的恢复能力。短花针茅（Stipa breviflora）是内蒙古荒漠草原的主要建群种。在不同放牧强度背景下的短花针茅草原开展了围封模拟放牧持续利用的实验，同时进行添加氮素和水分的恢复措施，测定了7月和9月中旬建群种短花针茅叶片的比叶面积、叶干物质含量，以及叶片全氮、叶片全磷和叶片全碳含量，分析水分和氮素添加对建群种短花针茅叶片的影响，探讨不同放牧强度下短花针茅可持续利用的氮水调控机制。结果显示，氮素和水分添加显著地增加了短花针茅叶片氮含量，降低了叶片碳氮比；放牧强度也显著地增加了叶片氮含量，且轻度放牧下的叶片氮含量（20.36 g/kg）显著高于对照（18.80 g/kg）；生长末期短花针茅的比叶面积、叶片碳含量、叶片碳氮比和叶片碳磷比显著高于生长盛期，叶片氮含量和磷含量显著低于生长盛期；在生长盛期和生长末期，不同放牧强度背景下对短花针茅所采取的氮素和水分的供给措施也不同。研究结果表明在放牧背景下短期氮、水添加提高了短花针茅的叶片氮含量，特别是在生长季后期水分添加增加了叶片氮和磷含量，可进一步促进短花针茅的生长。我们的结果也表明了资源供给水平的改善有助于短花针茅的迅速恢复。

Influence of short-term nitrogen and water addition on the leaf traits of Stipa breviflora in a desert steppe under different grazing intensities

Leaf functional traits can most reflect the sensitivity of plant growth to the environmental changes, and can thus be used to predict the recovery ability of plants after grazing disturbance to some extent. In this study, we explored the effects of water and nitrogen (N) addition on changes of several leaf functional traits of the dominant species, Stipa breviflora, in a desert steppe at a grazing experimental site with control of grazing intensity. Our objectives are to uncover the adjustment of increasing water and N supply to some functional traits of S. breviflora under different grazing intensities. The results showed that N and water addition significantly increased foliar N concentrations and decreased leaf carbon to N ratio (C/N) of S. breviflora. The grazing intensity also significantly increased foliar N concentrations. The foliar N concentration under light grazing (20.36 g/kg) was significantly higher than that under control (18.80 g/kg). The specific leaf area, leaf C concentration, C/N ratio, and C/phosphorus (P) ratio of S. breviflora at the end of growing season were significantly higher than those at the peak of growing season, while the leaf N and P concentrations at the end of growing season were significantly lower than those at the peak of growing season. The addition of N and water, either alone or combined, was also different under different grazing intensities at the peak and end of growing. Our study showed that the leaf N concentration of S. breviflora increased with N and water addition under different grazing intensities, especially increased the leaf N and P concentration at the end of growing season, which can further promoted the growth of S. breviflora. The results also indicate that the improvement of resource supply is helpful to rapid recovery of S. breviflora under different grazing intensities.