Biotic controls on the residence time of soil carbon and nitrogen: new understanding from stable isotope probing and optimization modeling

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Increasing globalization of the agricultural sector and growth of the bioenergy sector creates incentives for Canadian farmers to produce more food, fiber and feedstock. This must be done sustainably, so agricultural products meet the high quality standards of processors and the general public, economic profits and jobs remain in our rural communities and farming activities are aligned with agro-environmental objectives. Sustainable agroecosystems are envisioned to conserve soil organic carbon (C) and rely more on internal soil nitrogen (N) recycling, thus contributing to C sequestration and avoiding inefficient N fertilizer use. Nutrient conservation is especially important in humid temperate regions of Canada because soils are more vulnerable to nutrient loss in areas with high precipitation regimes and 50% of Canadian farms are located in these regions. The living soil' concept is a possible solution since it relies upon the naturally-occurring soil microorganisms and fauna to simultaneous decompose and synthesize organic C and N, but since these processes occur rapidly, at a microscopic level, within soil pores, we do not know how the soil foodweb contributes to crop production at an farm operations level. Here, we will tackle the problem at three different scales: (i) from the pore-scale with stable isotope probing methods and high-resolution image analysis, (ii) considering energetics and trophic transfers that occur within the soil foodweb, and (iii) at the field scale, using an optimization modelling to determine the temporal transformations of organic and inorganic fertilizer inputs through the soil biotic community, in relation to crop nutrient demands. The novelty of this research program is its contribution to fundamental research questions regarding the biological processes that control C and N cycling in agroecosystems, which is integrated into an applied decision-making model that provides practical answers for the Canadian farming community. The principal investigator contributed to the training of many HQP in the past 6 years, including 10 M.Sc. and 16 Ph.D. graduates, More than 90 peer-reviewed papers were published in international journals during this period, most of which had HQP as first author. This proposal will support 12 trainees through an individualized training program that includes peer-to-peer mentoring and focuses on excellent scientific communication, networking and professional skills acquisition. This provides outstanding preparation for their future role as scientific leaders, as evidenced by the demand for these trainees in academic, government and industry jobs that require advanced technical skills and managerial abilities.