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

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.