氮沉降增加对宁夏荒漠草原植物－土壤碳氮磷化学计量特征的影响机制

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...

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。

大气N沉降增加会引起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。在全国大部分区域N沉降趋于平稳甚至下降的背景下，西北地区煤炭行业的快速发展使得N沉降速率加快。本项目基于2015-2017年在宁夏荒漠草原设置的环境变化的野外原位试验，主要开展了植物-微生物-土壤C:N:P生态化学计量学特征、植被-土壤系统地上和地下间养分传递规律和驱动机制、C:N:P平衡关系与植物群落特征和生态系统C交换的内在联系等三个方面的研究。重要结果包括，1）N添加提高了植物全N和N:P，降低了C:N，对全C、全P和C:P的影响存在物种差异性。N添加对微生物各指标的影响与对植物的影响相似，且其效应在降水量增加条件下尤为明显。N添加对土壤C:N:P生态化学计量学特征的影响较小，但在一定程度上提高了土壤N供给水平、缓解了土壤P限制。植物全N、N:P以及微生物生物量N内稳性较低，可较好地反映土壤N供给水平以及养分受限类型；2）降水量变化及N添加下，植物和微生物C:N:P平衡特征主要受其他土壤因子的调控，而非土壤元素平衡关系；3）N添加下，植物群落组成与微生物生物量N、C:N、N:P、土壤硝态N、铵态N以及全P有较强的相关关系，意味着微生物C:N:P生态化学计量特征对植物群落组成的影响与其他土壤因子高度相关；4）降水量变化及N添加下，减少降水量降低了土壤水分和养分有效性、抑制了植物生长，从而降低了生态系统C交换。适量增加降水量则通过提高土壤含水量、刺激土壤酶活性、调节土壤C:N:P平衡特征等途径，促进了植物生长和物种多样性，从而提高了生态系统C汇功能。短期N添加亦促进了生态系统C交换，但其与降水的交互作用尚不明显；5）少量N添加下，适量P添加可通过提高土壤P有效性、增加凋落物归还量和刺激微生物P释放等途径，调节土壤P供给和植物P需求间压力，从而缓解N添加引起的植物群落多样性降低。项目研究结果为充分认识全球变化下草原生态系统C汇潜力、植物和土壤相互作用的养分平衡制约关系提供了数据支撑。