Greenhouse Gas Fluxes in Agroecosystems: Towards an Integrated Understanding on Source-Processes and Spatio-Temporal Variation

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Greenhouse gas emissions derived from land-use systems are significant contributors (14%) to climate change, with croplands accounting for two-thirds of these emissions. Greenhouse gas emissions result from biophysical processes driven by soil temperature, oxygen concentration, and water content as well as the availability of nitrogen and carbon substrates for microbial activity. Processes such as denitrification and nitrification generate nitrous oxide, while plant root growth and microbial respirations produce carbon dioxide. The complexity of these processes results in large variability of greenhouse gas emissions both in space and time. Moreover, the additions of nitrogen from fertilizers and manure, and carbon from plant roots further increase this complexity. Collectively, these interacting factors lead to significant uncertainties in the quantification of greenhouse gas fluxes and sources across the landscape. My long-term research objective is to understand the triggers and drivers of nitrous oxide and carbon dioxide generation in soils. This knowledge is critical for identifying effective emission reduction options in Canadian agroecosystems, hence contributing to climate change mitigation. To achieve this objective, the proposed research will: 1. Distinguish and quantify nitrous oxide that is produced through nitrification versus denitrification processes in soils, and investigate which process is the main flux source following nitrogen additions such as manure and fertilizer. 2. Differentiate between sources of carbon dioxide from soils (organic matter breakdown versus root-derived respiration), and identify the effects of root growth on both carbon dioxide flux and turnover of organic matter across gradients of root carbon environments. 3. Quantify the response of nitrous oxide and carbon dioxide production resulting from cyclic fluctuations of soil oxygen concentration, wetting-drying, and temperature. 4. Use this gained understanding to identify causes and explain spatio-temporal variations in field fluxes with focus on peak emissions within varying field topography. In the next 5 years, I will train two MSc, two PhD, and four undergraduate students throughout this program. This research will create critical scientific foundations for improved management of greenhouse gas emissions, and support innovative strategies for emission reductions that are adaptable to Canadian agroecosystems under a changing environment.