Abstract: Climate warming and nitrogen deposition significantly impact grassland ecosystem functions. However,the way precipitation modulates the response of the desert steppe’s productive function response to climate warming and nitrogen deposition remains unclear. This study was conducted on Stipa breviflora desert steppe in Inner Mongolia,using a long-term experimental platform for warming and nitrogen addition. The productivity and ecosystem carbon exchange response to warming and nitrogen addition were analyzed over two consecutive years with substantial differences in precipitation. The results show that:(1) Aboveground biomass of the plant community was significantly different between dry and wet years. Nitrogen addition significantly reduced the aboveground biomass of C₃ species by 10.50% in the dry year but increased that of plant community and C₃ species by 11.69% and 8.06%,respectively,in the wet year. (2) In the dry year,nitrogen addition significantly promoted net ecosystem carbon fixation,while warming significantly reduced gross ecosystem productivity. In the wet year,neither warming nor nitrogen addition had significant effects on ecosystem carbon exchange. Therefore,the effects of warming and nitrogen addition on the productive function of the desert steppe were greatly affected by precipitation change. Therefore,long-term field monitoring combined with interannual precipitation fluctuations is necessary to explore the effects of global change on grassland ecosystem functions.

Key words: C₃ plant, C₄ plant, Desert steppe, Ecosystem carbon exchange, Global change

摘要： 气候变暖和大气氮沉降对草地生态系统功能有重要影响。然而，降水变化如何调节荒漠草原生态系统生产功能对气候变暖和氮沉降的响应还不清楚。本研究基于内蒙古短花针茅(Stipa breviflora Griseb.)荒漠草原长期增温和氮添加试验平台，分析两个连续降水差异较大年份中植物生产力和生态系统碳交换对增温和氮添加响应的不同。结果表明：(1)植物群落地上生物量在干旱和湿润年份有显著差异。在干旱年份，氮添加使得C₃植物地上生物量显著降低了10.50%；在湿润年份，氮添加使得植物群落地上生物量和C₃植物地上生物量分别显著增加了11.69%和8.06%。(2)在干旱年份，氮添加显著促进了净生态系统碳固定，而增温显著降低了总生态系统生产力；在湿润年份，增温和氮添加对生态系统碳交换均没有显著影响。因此，野外长期监测结合年际间降水波动对分析全球变化影响草原生态系统功能十分必要。

关键词: C₃植物, C₄植物, 荒漠草原, 生态系统CO₂交换, 全球变化