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; 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.

由于化石燃料燃烧，氮固定农作物的种植以及氮肥的产生，在过去100年中，人类在过去100年中显着增加了生物可获得的氮（所谓的反应性氮）。 释放的大部分反应性氮都在雨水和雪中结束，因此无意中施肥了森林和草原土壤。 这种氮肥对土壤中碳的储存以及从土壤回到大气中释放的碳的影响尚不清楚。 这项研究的目的是检查氮输入升高对微生物衰减土壤有机物衰减的影响，该过程将二氧化碳释放到大气中。该研究将使用正在进行的氮添加实验（营养网络）的全球网络来测试氮沉积增加对草原土壤的影响。此信息对于为全球生态系统模型提供了信息，以及关于土壤中碳的长期存储的预测。该项目还包括该项目调查人员从事的教育，外展和培训活动计划。他们将通过Cedar Creek校园的长期生态研究计划以及Cedar Creek的年度开放日将结果传播给公众。此外，调查人员将继续指导明尼苏达大学本科研究机会计划和Macalester College的研究实习计划的独立研究中的本科生。土壤碳（C）的循环池（C）被微生物分解的土壤碳（C），很容易被微生物分解，而循环池则稳定在Microbobial Decogen上，均具有不同的循环量，以响应Microbial Decogen，以供应NIT（NIT）。初步数据表明，n添加增加了快速土壤C池的分解速率（平均停留时间1年），并降低了慢土C池的分解速率（平均停留时间1 - 10年）。这些结果与叶子垃圾分解研究和许多生物学和化学机制的结果相似，以解释该模式。评估机制对于预测氮对土壤c固存的影响是必要的。这项研究的目的是检查控制土壤有机物分解对N添加的反应的化学和生物学机制。这项研究改善了正在进行的论文研究，该研究研究了n富集对多个土壤有机物池的影响，包括未划分，骨料叠加和矿物质的土壤有机物。具体而言，这项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原地点进行了复制，以量化N富集对底物化学的影响，微生物酶活性和微生物的生长效率以及对增长的增长添加的n的生长的生长，从而增长了N. n。水解酶和植物组织（底物）N含量的活性，导致快速土壤C池的分解增加； 2）n添加降低了氧化酶的活性并提高微生物的生长效率，从而导致慢土库的分解减少； 3）与立即添加的n添加长期n后，对微生物过程（酶活性和生长效率）的添加影响将更大。