Investigating interactions between mineral-associated and dissolved soil organic matter to improve understanding of soil carbon retention under intermittent flooding

我的研究计划的长期目标是了解在全球变化和土地利用管理下，土壤有机质（SOM）如何受到土壤微生物群落和植物的相互作用的影响。SOM管理着关键的生态系统服务，如通过SOM中储存的碳(C)调节气候变化。维持和增加全球SOM储量是全球的优先事项，但由于气候变化的压力因素往往会加速SOM的矿化，这也是一个持续的挑战。普遍的想法是，SOM通过将有机质附着在土壤矿物质上的强烈化学相互作用来保护微生物不矿化，从而限制了微生物的进入。因此，矿物伴生有机质库（MAOM）被认为是SOM最相关的部分，有助于理解长期的SOM保留和碳封存。然而，这忽略了新出现的证据，即MAOM池很容易丢失，很容易从矿物质中分离成溶解的有机物（DOM），然后被微生物浸出或呼吸。这通常发生在洪水期间，当氧气耗尽将MAOM从其化学保护键释放到DOM中时。在加拿大东部，随着气候变化，洪水强度和持续时间预计会增加，因此需要更全面地了解洪水事件后SOM的脆弱性和保留情况。需要一个更准确的框架，考虑洪水事件中MAOM和DOM之间交换的复杂生物物理控制，以了解控制土壤C储存的机制。在接下来的五年里，我的目标是深入了解间歇性洪水下生物物理控制如何影响MAOM和DOM之间的交换，并应用所获得的知识来更好地理解洪水对持续性SOM净平衡的影响。为了解决这个问题，我将整合来自三个短期目标的见解：确定洪水期间土壤结构如何影响土壤有机质的吸收和溶解，从而影响土壤有机质的净平衡。2. 评估微生物生长对洪水的响应及其后续结果对DOM-MAOM交换和C损失的影响。3. 探讨根际过程如何抵消或放大洪水对DOM-MAOM交换的影响。我的计划将产生非常需要的MAOM和DOM交换以及SOM保留的基础知识，为间歇性洪水和农业管理情景下的SOM提供更完整的图片，加拿大政府和土地资源管理者的优先目标，包括农业食品部门。该项目的新成果将解释植物根系、土壤微生物群落和土壤物理环境如何影响MAOM对洪水的脆弱性。我的项目将培养7名HQP，他们将在分子化学和微生物技术、同位素生物地球化学以及实验设计和实施方面获得专业知识，使他们成为土壤生物地球化学领域的领导者。

The long-term goal of my research program is to understand how soil organic matter (SOM) is impacted by the interactions of soil microbial communities and plants under global change and land-use management. SOM governs key ecosystem services such as regulating climate change through carbon (C) stored within SOM. Maintaining and increasing global SOM stocks is a global priority yet also a consistent challenge due to climate change stressors that often accelerate SOM mineralization. The prevailing thinking is that SOM is protected from microbial mineralization via strong chemical interactions that attached organic matter to soil minerals, limiting microbial access. Thus, the mineral-associated organic matter pool (MAOM) is considered the most relevant fraction of SOM for understanding long-term SOM retention and C sequestration. However, this overlooks emerging evidence that this MAOM pool is vulnerable to loss, easily disassociating from minerals into dissolved organic matter (DOM) where it can then be leached or respired by microbes. This often occurs during flood events when oxygen depletion releases MAOM from its chemical protective bonds into DOM. In Eastern Canada, increases in flood intensity and duration are expected with climate change, necessitating a more complete understanding of SOM vulnerability and retention following flood events. A more accurate framework that considers the complex biophysical controls on the exchanges between MAOM and DOM during flood events is needed to understand the mechanisms controlling soil C storage. Over the next five years my goal is to gain insights into how biophysical controls affect the exchanges between MAOM and DOM under intermittent flooding and to apply the knowledge gained to better understand flooding impacts on the net balance of persistent SOM. To address this, I will integrate insight from across three short-term objectives: 1. Determine how soil structure impacts sorption and solubilization of SOM during flood events and consequently the net balance of MAOM. 2. Evaluate the influence of microbial growth responses to flooding and the subsequent outcomes on DOM-MAOM exchanges and C loss. 3. Explore how rhizosphere processes counter-act or amplify flooding effects on DOM-MAOM exchange. My program will generate much needed fundamental knowledge of MAOM and DOM exchange and SOM retention, providing a more complete picture of SOM under intermittent flooding and agricultural management scenarios, priority goals for Canadian governments and land resource managers, including the agri-food sector. Novel outcomes from this program will explain how plant roots, soil microbial communities, and the soil physical environment impact MAOM vulnerability to flooding. My program will train 7 HQP who will gain expertise in molecular chemical and microbial techniques, isotope biogeochemistry, and designing and implementing experiments, positioning them to become leaders in the field of soil biogeochemistry.