在中国科学院内蒙古草原生态系统定位研究站的羊草样地，采用15N同位素示踪技术研究了羊草（Leymus chinensis）群落标记氮素的去向。结果表明：在我国典型草原羊草群落，植物对标记氮素的回收率为31.61%，氮素添加显著影响植物对标记氮素的回收，随着氮素添加量的增加，地上和地下植物器官对标记氮素的回收量均显著提高。标记氮素被凋落物的回收率为2.92%，地下凋落物的回收率显著高于地上凋落物。标记氮素的土壤存留率为36.16%，主要分布在地表0～40 cm的土层范围内；各土层存留的标记氮素量均随着氮素添加量的增加而显著提高。标记氮素的当季损失率为21.77%～43.38%。风险/收益比分析表明，在该试验条件下，添加5.25 g N•m-2与28 g N•m-2的处理风险大于收益，添加17.5 g N•m-2的处理风险最低，收益最高，在草原生态系统的管理中可供参考。
An important grassland ecosystem management strategy is the application of nitrogen fertilizer; however, the fate of applied nitrogen is highly correlated with risks and benefits associated with the fertilization of grasslands. The fate of nitrogen tracers applied to a typical Inner Mongolia steppe ecosystem has not been studied previously. We examined the fate of 15N-labelled fertilizer in a Leymus chinensis site at the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. The results showed that after one growing season an average of 31.61% (range from 25.33% to 38.65%) of the applied 15N was recovered in the plant pool. 15N recovered by aboveground and belowground organs significantly increased with increasing nitrogen rates suggesting that nitrogen fertilizer significantly affected the recovery of 15N by plants. About 2.92% (range from 2.58% to 3.16%) of the applied 15N was recovered in the litter, with the percent 15N in the belowground litter significantly higher than in the aboveground litter pool. About 36.16% of the labelled nitrogen was retained in the soil pool, mostly in the 0-40 cm soil layer. 15N retained by the soil increased significantly with increases in the nitrogen application rate. The loss of 15N was about 21.77%-43.38% of the labelled nitrogen. Risk/benefit analysis showed that, under the climatic and soil conditions prevailing during this experiment, fertilizer application rates of 5.25 g N•m-2 and 28 g N•m-2 were associated with high risk/benefit ratios, whereas the 17.5 g N•m-2 fertilizer treatment achieved the lowest risk/benefit ratio among the nitrogen rate treatments. These results provide a reference for future grassland ecosystem management strategies.