摘要:作为对全球变化响应最敏感的生态系统类型之一，草原生态系统植被氮含量的季节、年际变化及其对气候变化（氮沉降、降水格局改变）的响应研究相对匮乏。基于内蒙古温带典型草原5年的氮添加（10 g N m^-2 a^-1）和水添加（添加量80 mm，分2 mm×40 次、5 mm×16 次、10 mm×8 次、20 mm×4 次、40 mm×2 次5种处理）控制试验分析了水氮添加后植被氮含量在生态系统和物种两个水平的季节和年际变化。结果表明，高强度水添加处理有降低（10 mm/次和40 mm/次）生态系统氮含量的趋势，但不显著，小强度水添加处理（2 mm/次、5 mm/次）在不同年份之间无一致的升高或降低趋势，但所有水添加处理有降低两种优势物种整个生长季氮含量的趋势。氮添加促进生态系统和两种优势物种整个生长季的氮含量，但该促进作用可被水添加抵消，且这种抵消作用随水氮添加年限的延长而加剧。水氮添加均增加了生态系统氮含量的年际变异，但对特定物种季节内变异的影响在湿润和干旱年份存在一定差异。本研究将为预测草原生态系统对未来氮沉降增加和降水格局改变的响应及模型改进提供科学依据。



Abstract:As a key factor that affects various ecosystem processes, plant nitrogen (N) concentration is very important to forecast the responses of ecosystem to global climate change, e.g., altered precipitation regime and enhanced N deposition. Grassland, one of the most sensitive ecosystems to climate change, has been paid insufficient attentions in terms of the intra- and inter-annual dynamics of plant N concentration. In this study, a five-year manipulative field experiment was conducted by employing N addition (10 g N m^-2 a^-1) and water addition (80 mm a^-1 in terms of five intensities, i.e., 2 mm×40 times, 5 mm×16 times, 10 mm×8 times, 20 mm×4 times, and 40 mm×2 times) in a typical steppe in Inner Mongolia temperate grassland. We analyzed the effects of water and nitrogen additions on the intra- and inter-annual dynamics of plant nitrogen concentration. We found that water addition of 10 mm×8 times and 40 mm×2 times decreased ecosystem plant N concentration in the dry years, while that of 20 mm×4 times increased ecosystem plant N concentration, but these increases or decreases were not significant statistically. Under water additions of other lower intensity (2 mm×40 times and 5 mm×16 times), neither increase nor decrease patterns were clearly observed across years. Plant N concentration of two dominant species, Stipa krylovii and Artemisia frigida, was both lower in the early and late growing season, while it was higher in the middle of the growing season. Water addition decreased plant N concentration of these two dominant species throughout the growing season, but without significance. The N addition enhanced ecosystem N concentration and plant N concentration of two dominant species across the growing season. However, this enhancement could be down regulated by water addition, and this down regulation due to water addition increased with the duration of experiments. The N and water additions both increased inter-annual variability of ecosystem N concentration, while the effects they exerted on intra-annual variability of plant N concentration of two dominant species dependent on the annual precipitation amount. Our work has important implications for model improvement and an advanced understanding of grassland-response to N deposition and the altered precipitation regime.





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