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

农业部门的日益全球化和生物能源部门的增长为加拿大农民生产更多的粮食、纤维和原料创造了激励因素。必须以可持续的方式做到这一点，使农产品达到加工者和公众的高质量标准，使我们的农村社区保持经济利润和就业机会，使农业活动符合农业环境目标。可持续的农业生态系统被设想为保护土壤有机碳（C），并更多地依赖于内部土壤氮（N）的循环，从而有助于C的固存和避免氮肥的低效使用。在加拿大的潮湿温带地区，养分保护尤为重要，因为在降水量高的地区，土壤更容易受到养分流失的影响，50%的加拿大农场位于这些地区。“活土壤”的概念是一个可能的解决方案，因为它依赖于自然发生的土壤微生物和动物群同时分解和合成有机碳和氮，但由于这些过程发生迅速，在微观水平，在土壤孔隙内，我们不知道土壤食物网如何在农场操作水平上对作物生产做出贡献。在这里，我们将在三个不同的尺度上解决这个问题：（i）从孔隙尺度，采用稳定同位素探测方法和高分辨率图像分析，（ii）考虑土壤食物网内发生的能量学和营养转移，（iii）在田间尺度，使用优化模型确定通过土壤生物群落的有机和无机肥料投入的时间转换，与作物营养需求有关。这项研究计划的新奇在于它对控制农业生态系统中C和N循环的生物过程的基本研究问题的贡献，该生物过程被整合到一个应用决策模型中，为加拿大农业社区提供了实际的答案。主要研究者在过去的6年中为许多HQP的培训做出了贡献，其中包括10名硕士和16名博士。在此期间，在国际期刊上发表了90多篇同行评审论文，其中大部分以HQP为第一作者。该提案将通过一个个性化的培训方案为12名受训人员提供支持，该方案包括同行指导，并侧重于出色的科学交流、网络联系和专业技能的获得。这为他们未来担任科学领导者的角色提供了出色的准备，这一点从需要高级技术技能和管理能力的学术、政府和工业工作对这些受训人员的需求中可以看出。

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.