Abstract: In order to investigate the effects of grazing and nitrogen addition on plant-soil carbon and nitrogen cycling in Inner Mongolian desert grasslands, nitrogen addition treatments were carried out in forbidden (UG, 0 sheep unit·hm^-2) and heavily grazed (HG, 1.74 sheep unit·hm^-2) sample plots at the following levels:control (CK, 0 g·m^-2·a^-1), low nitrogen (LN, 5 g·m^-2·a^-1), medium nitrogen (MN, 10 g·m^-2·a^-1) and high nitrogen (HN, 20 g·m^-2·a^-1), total nitrogen (TN), stable carbon isotopes (δ¹³C), stable nitrogen isotopes (δ¹⁵N), soil organic carbon (SOC) and available nitrogen (AN) were measured and analyzed, and the results showed that:Grazing significantly increased the content of TC, TN and AN in the soil (P<0.05);Grazing significantly reduced the values of δ¹³C and δ¹⁵N of the leaves of Stipa breviflora needlegrass (P<0.05);grazing significantly reduced the δ¹³C and δ¹⁵N values of Stipa breviflora leaves (P<0.05). To a certain extent, both grazing and nitrogen addition accelerated the nutrient cycling of fagus sylvatica and soil, and at the same time, nitrogen addition had a certain effect on nitrogen uptake and fractionation of fagus sylvatica, which is important for the recovery of degraded grassland.

Key words: Desert grassland, Nitrogen addition, Plants and soil, Carbon and nitrogen content, Stable isotopes

摘要： 为了探究放牧和氮添加对内蒙古荒漠草原植物-土壤碳、氮循环的影响，在禁牧（UG，0只羊单位·hm^-2）和重度放牧（HG，1.74只羊单位·hm^-2）样地进行氮添加处理，各处理水平为：对照（CK，0 g·m^-2·a^-1）、低氮（LN，5 g·m^-2·a^-1）、中氮（MN，10 g·m^-2·a^-1）和高氮（HN，20 g·m^-2·a^-1）。通过对短花针茅（Stipa breviflora）叶片和土壤全碳（Total carbon，TC）、全氮（Total nitrogen，TN）、稳定碳同位素（Stable carbon isotopes，δ¹³C）、稳定氮同位素（Stable nitrogen isotopes，δ¹⁵N）及土壤有机碳（Soil organic carbon，SOC）、速效氮（Available nitrogen，AN）的测定分析，结果表明：放牧显著增加土壤TC、TN和AN含量（P<0.05）；放牧使短花针茅叶片δ¹³C，δ¹⁵N值显著减小（P<0.05）；氮添加使短花针茅叶片δ¹⁵N值显著减小（P<0.05）。放牧和氮添加在一定程度上均加速了短花针茅和土壤的养分循环，同时氮添加对短花针茅的氮吸收及分馏效应有一定影响，对退化草地恢复起重要作用。

关键词: 荒漠草原, 氮添加, 植物和土壤, 碳氮含量, 稳定同位素