The influence of trigger events on bursts of soil microbial metabolism and N2O production and consumption

气候驱动土壤中发生的生物过程，但在农业氮管理中却很少被描述和考虑。这是由于土壤氮循环过程的数量和复杂性。在这一建议中，我们研究了气候触发因素（冻土融化和干土湿润）在刺激微生物活动爆发和造成土壤N损失中的作用。具体而言，本工作侧重于基质有效性对无机氮过程的影响，无机氮过程控制硝化和反硝化在产生N2O排放中的时间和相对重要性。我的假设是，环境事件通过微生物细胞裂解和土壤有机质的溶解而释放底物来触发微生物代谢。此外，受土壤温度和含水量影响的微生物代谢作用于这些基质的速率，以及碳和氮分布的结构，决定了反硝化的位置、强度和产物，从而决定了N2O的排放。我的研究目标是了解气候和气候变化对土壤N转化和氮损失的影响。该提案的具体目标是首先（博士1）研究受控环境条件下融化和润湿触发导致N2O爆发的机制，其次（博士2）研究在野外条件下融化和润湿触发下土壤剖面中N2O的产生和消耗。***这项研究利用了最近的技术发展，可以对N2O排放物的同位素组成进行高频测量，以确定触发事件期间N2O的来源。N2O产量的测量将与土壤水分和温度的连续测量相结合，以提供触发事件的物理效应如何转化为微生物代谢变化的动态图像。***本研究的创新之处在于使用N2O浓度和同位素组成的高频测量来研究与环境事件相关的微生物代谢性质。使用N2O的15N位点偏好将区分在这些事件中作为N2O来源的硝化和反硝化以及通过反硝化消耗的N2O。***这项研究将深入了解气候变化对土壤微生物过程的潜在影响。更好地了解农业管理如何影响与解冻和湿润事件相关的N2O排放。这对于制定维持土壤肥力和减少农业温室气体排放、减少对水质的影响以及提高农业的盈利能力和可持续性的战略至关重要。

Climate drives the biological processes occurring in soil yet is a poorly described and seldom considered part of nitrogen management in agriculture. This is due to the number and complexity of processes involved in the soil N cycle. In this proposal we examine the role of climatic triggers (thawing of frozen soil and wetting of dry soil) in stimulating bursts of microbial activity and causing soil N losses. Specifically this work focuses on the influence substrate availability on inorganic nitrogen processes that control the timing and relative importance of nitrification and denitrification in producing N2O emissions. My hypothesis is that environmental events trigger microbial metabolism through the release of substrates as a result of microbial cell-lysis and solubilization of soil organic matter. Further, it is the rate at which microbial metabolism acts on these substrates, as influenced by soil temperature and water content, and the architecture of carbon and nitrogen distribution which determines the location, intensity, and products of denitrification and therefore N2O emissions.***The goal of my research is to understand the impacts of climate and climate change on soil N transformations and nitrogen losses. The specific objective of this proposal is firstly (PhD1) to examine the mechanisms resulting in N2O bursts in response to thawing and wetting triggers under controlled environment conditions and secondly (PhD 2) to examine the production and consumption of N2O in soil profiles in response to thawing and wetting triggers under field conditions.***This research takes advantage of recent technological developments that allow high frequency measurement of the isotopomeric composition of N2O emissions to determine the source of N2O during trigger events. Measurements of N2O production will be coupled with continuous measurement of soil water and temperature to provide a dynamic picture of how the physical effects of trigger events are translated into shifts in microbial metabolism. ***This research is innovative in that it uses high frequency measurement of concentration and isotopomeric composition of N2O to study the nature of microbial metabolism associated with environmental events. The use of 15N site preference of N2O will distinguish between nitrification and denitrification as sources of N2O during these events as well as the consumption of N2O by denitrification. ***This research will provide insight into the potential impacts of climate change on soil microbial processes. A better understanding of how agricultural management impacts N2O emissions associated with thawing and wetting events. This is important for developing strategies to sustain soil fertility and reduce greenhouse gas emissions from agriculture, reduce impacts on water quality and increase the profitability and sustainability of agriculture.