大气N沉降增加不但会加速N循环，而且可能引起N:P失衡和系统P限制增加，造成生物多样性降低和生态系统退化。开展长期N添加下荒漠草原植物－土壤C、N、P化学计量关系的研究，有助于更好地理解N沉降增加对脆弱生态系统结构、功能和稳定性的影响。本项目基于2012年在宁夏荒漠草原设置的N沉降增加的野外模拟试验，通过测定不同发育阶段植物叶片/地下部分、微生物和土壤C、N、P含量，同时监测生长季旺盛期植被群落组成、叶片生理生态特征、土壤pH、交换性阳离子、微生物群落结构和酶活性，研究长期N添加下植物地上/地下、微生物和土壤C:N:P化学计量特征及相互关系，探讨植被－土壤系统地上和地下间养分的传递和调节，揭示元素化学计量关系与植被生产力和生物多样性的内在联系，阐明N沉降增加对荒漠草原植物和土壤相互作用的元素计量平衡关系的影响机制，为全球气候变化背景下脆弱生态系统恢复和适应性管理提供科学指导。

Increasing atmospheric N deposition could not only accelerate N cycling, but also cause N:P imbalance and P limitation increase, resulting in the decrease in species biodiversity and the degeneration of ecosystems. The study on the effects of long-term N deposition increase on stoichiometric relationships between C, N, and P in plants, microbes, and soils in desert steppe, based on the theory and method of ecological stoichiometry, could provide a better understanding of how increasing N deposition affects the structure, function, and stability of ecosystems. In this project, based on a simulated field experiment of increasing atmospheric N deposition conducted in a desert steppe of Ningxia in 2012, through measuring C, N, and P contents in plants (both leaves and roots or rhizomes), microbes, and soils during different growth seasons, investigating plant community structure and leaf eco-physiological characteristics in peak growth period, monitoring soil pH, exchangeable metal, hydrolytic enzyme activities and microbial structure in peak growth period as well, we mainly aim at 1) studying the relationships of C:N:P ecological stoichiometry between plant leaves, plant roots/ rhizomes, microbes, and soils under over 7-year N addition, 2) analyzing the patterns of C, N, and P dynamics between plants, microbes, and soils, 3) exploring the characteristics of nutrient transmitting and regulating within plant aboveground parts, plant belowground parts, microbes, and soils, 4) making clear the inherent relationships between C:N:P ratio and vegetation productivity and biodiversity, respectively. Based on the analyses above, the effects and driven mechanisms of over 7-year of simulated N deposition increase on stoichiometric balances between C, N, and P within plants, microbes, and soils in the desert steppe of Ningxia will be evaluated synthetically. This project could provide a scientific guidance for the restoration and adaptation management of fragile ecosystem in North China under global climate change...