DISSERTATION RESEARCH: Effects of nitrogen enrichment on multiple soil organic matter pools

论文研究：氮富集对多个土壤有机质库的影响

• 批准号: 1401082
• 负责人: Sarah Hobbie
• 金额: $ 1.98万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-06-01 至 2016-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1401082&HistoricalAwards=false
• 关键词: DISSERTATION; RESEARCH; Effects; nitrogen; enrichment

Humans have significantly increased the amount of biologically available nitrogen (so-called reactive nitrogen) over the past 100 years due to fossil fuel combustion, cultivation of nitrogen-fixing crops, and creation of nitrogen fertilizers. Much of the reactive nitrogen that has been released ends up in rain and snow, thus inadvertently fertilizing forest and grassland soils. The effects of this nitrogen fertilization on storage of carbon in soils, and release of carbon from soils back to the atmosphere, are unclear. The objective of this research is to examine the effects of elevated nitrogen inputs on the decay of soil organic matter by microbes, a process that releases carbon dioxide to the atmosphere. The research will use a global network of ongoing nitrogen addition experiments (the Nutrient Network) to test the effects of increased nitrogen deposition on grassland soils. This information is necessary to inform global ecosystem models, as well as make predictions about the long-term storage of carbon in soils. The project also includes a program of education, outreach, and training activities pursued by the project's investigators. They will disseminate their results to the general public through the Cedar Creek Schoolyard Long-Term Ecological Research program, as well as Cedar Creek's Annual Open House. Furthermore, the investigators will continue to mentor undergraduates in independent research in the University of Minnesota Undergraduate Research Opportunity program and Macalester College's Research Intern Program.Rapidly cycling pools of soil carbon (C) that are readily decomposed by microbes, and more slowly cycling pools that are stabilized against microbial decomposition, likely respond differently to nitrogen (N) enrichment. Preliminary data shows that N addition increases the rate of decomposition of the fast soil C pool (mean residence time 1 year) and decreases the rate of decomposition of the slow soil C pool (mean residence time 1-10 years). These results parallel those from leaf litter decomposition studies and a number of biological and chemical mechanisms have been proposed to explain the pattern. Evaluating mechanism is necessary to make predictions about the effects of N addition on soil C sequestration. The objective of this research is to examine chemical and biological mechanisms controlling the response of soil organic matter decomposition to N addition. This research improves upon ongoing dissertation research that examines the effects of N enrichment on multiple soil organic matter pools, including unoccluded, aggregate-occluded, and mineral-occluded soil organic matter. Specifically, the research will use a network of ongoing N addition experiments, replicated in six grassland sites across the Central Great Plains, USA, to quantify the effects of N enrichment on substrate chemistry, microbial enzyme activity, and microbial growth efficiency towards elucidating the mechanisms underlying the response of soil organic matter decomposition to added N. The research will test the hypotheses that: 1) N addition increases microbial growth, the activity of hydrolytic enzymes, and plant tissue (substrate) N content, contributing to increased decomposition of the fast soil C pool; 2) N addition decreases activity of oxidative enzymes and increases microbial growth efficiency, contributing to decreased decomposition of the slow soil C pool; and 3) N addition effects on microbial processes (enzyme activity and growth efficiency) will be larger following long-term N addition compared to an immediate, one-time N addition.

在过去的100年里，由于化石燃料的燃烧、固氮作物的种植和氮肥的创造，人类显著增加了生物可利用氮（所谓的活性氮）的数量。释放出来的大部分活性氮最终都进入了雨雪中，从而不经意地给森林和草地土壤施肥。这种氮肥对土壤中碳的储存以及从土壤中释放回大气的碳的影响尚不清楚。这项研究的目的是检验氮输入增加对微生物对土壤有机质腐烂的影响，这一过程将二氧化碳释放到大气中。这项研究将使用一个正在进行的氮添加实验的全球网络（营养网络）来测试增加的氮沉积对草地土壤的影响。这些信息对于全球生态系统模型以及对土壤中碳的长期储存进行预测是必要的。该项目还包括由项目调查人员开展的教育、推广和培训活动计划。他们将通过雪松溪校园长期生态研究项目以及雪松溪年度开放日向公众传播他们的研究结果。此外，研究人员将继续指导本科生在明尼苏达大学的本科生研究机会项目和麦卡莱斯特学院的研究实习生项目中进行独立研究。土壤碳(C)的快速循环池容易被微生物分解，而土壤碳(C)的缓慢循环池则稳定不受微生物分解，它们对氮(N)富集的反应可能不同。初步数据表明，施氮增加了快速土壤C库（平均停留时间为1年）的分解速率，降低了缓慢土壤C库（平均停留时间为1 ~ 10年）的分解速率。这些结果与凋落叶分解研究的结果相似，并提出了一些生物和化学机制来解释这种模式。评价机制是预测施氮对土壤固碳影响的必要条件。本研究的目的是研究控制土壤有机质分解对N添加响应的化学和生物机制。本研究改进了正在进行的论文研究，该研究考察了氮富集对多种土壤有机质库的影响，包括未封闭，团聚体封闭和矿物封闭的土壤有机质。具体而言，该研究将使用正在进行的N添加实验网络，在美国中部大平原的六个草地上复制，量化N富集对底物化学，微生物酶活性和微生物生长效率的影响，以阐明土壤有机质分解对添加N的响应机制。研究将验证以下假设：1)施氮增加了微生物生长、水解酶活性和植物组织（底物）氮含量，促进了快速土壤C库分解；2)氮素添加降低了土壤氧化酶活性，提高了微生物生长效率，减缓了土壤碳库的分解；3)长期施氮对微生物过程（酶活性和生长效率）的影响大于一次性施氮。