MCA: Characterizing Rhizosphere Decomposition with Novel Techniques in Contrasting Salt Marshes

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Salt marshes provide several important ecosystem services to coastal communities. One of the most valuable services is buffering coasts from damage due to rising sea levels and coastal storms. Marshes provide this service by building soils and growing vertically. Marsh soils are mostly made of minerals delivered by rivers and organic matter from marsh grasses. Delivery of these materials can be put at risk by human activities. This places additional importance on efficient burial and long-term preservation of organic matter in maintaining marsh elevation. This research examines the small-scale mechanisms controlling soil organic matter preservation. Laboratory and field experiments are testing how three preservation mechanisms operate under controlled and natural conditions. Results help explain spatial variability in soil carbon stocks and may inform models predicting salt marsh survival with sea-level rise. The expertise gained through this project provides both career development and advances in coastal carbon science. High school students and undergraduate students are also gaining exposure to this science project through an outreach program in Georgia. Three mechanisms affecting decomposition — oxygen availability, mineral protection, and root exudate priming — are being investigated using novel geochemical and isotope tracing and imaging techniques. The experiments are based at two Long-Term Ecological Research sites – Georgia Coastal Ecosystems and Plum Island Ecosystems – which have similar tidal ranges, marsh grasses, and production rates but different carbon storage rates. In the lab, mineral and organic rhizosphere soils are maintained under oxic or anoxic conditions to test how soil carbon is preserved. A field experiment is being deployed at both sites, to manipulate tidally-driven redox conditions. The research is adding knowledge about how redox conditions affect carbon transformations. The fate of root exudates through microbial incorporation or soil particle stabilization helps discover what makes both mineral and organic salt marshes resilient to changing coastal conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.