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

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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.