中文摘要：

为了解氮素沉降对草地群落的影响,通过人工氮肥添加模拟试验,研究了黄土高原天然草地优势植物长芒草（Stipa bungeana）在不同施氮水平下叶片和立枯物碳（C）、氮（N）、磷（P）元素含量的变化特征,探讨了N素增加对N、P重吸收率和C：N：P化学计量比的影响及其内在联系。结果表明：氮素添加显著增加了长芒草叶片的C、N和立枯物的N、P含量,对叶片P和立枯物C含量无显著影响;氮素添加显著降低了长芒草的N、P重吸收率,对照处理的N、P重吸收率最高,分别为60.35%和71.75%,并且,在相同氮素处理条件下P的重吸收率显著大于N重吸收率;随着氮素添加量的增大,叶片的C：N降低,N：P和C：P增加,N：P为18.25–29.01。研究表明,黄土高原天然草地群落主要受P限制,随氮素沉降增加,P限制进一步加剧;长芒草较高的N、P重吸收率是保证其在贫瘠的土壤中生存的重要机制。

英文摘要：

Aims Our purpose was to study the effects of deposition of nitrogen （N） on plant carbon （C）, N, phosphorus （P）, N and P nutrient resorption efficiencies, C：N：P stoichiometry and their internal relations on Stipa bungeana of Loess Plateau natural grassland. Methods Deposition of N was simulated by N fertilization at four levels. Changes of C, N and P contents were detected, and C：N ：P and the N and P nutrient resorption efficiencies were estimated for S. bungeana. Important findings The C and N contents of leaves and N and P contents of standing litter increased signifi-cantly with N addition. However, the P content of leaves and C content of standing litter did not response to N addition. The N and P resorption efficiencies of S. bungeana decreased significantly with N addition. When there was no N addition, N and P resorption efficiencies were highest （60.35% and 71.75%, respectively）. Meanwhile, the P resorption efficiency was greater than that of N in same treatment. The C：N of S. bungeana decreased gradually with N addition, but the N：P and C：P increased with N addition. Values of the N：P were 18.25–29.01. The results showed the Loess Plateau natural grassland was mainly limited by P, and the strength of P limitation was enhanced with N deposition. Higher N and P resorption efficiencies were an important strategy for S. bungeana to survive soil infertility.