PARENT SESSION
Contributed Oral Session 133: Biogeochemistry of Streams and Wetlands
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal
Plant-mediated control of wetland soil microbial respiration.
Megonigal, J.*,1, Neubauer, Scott1, 2, Givler, Kimberly1, Valentine, Sarah1, 1 Smithsonian Environmental Research Center, Edgewater, MD, USA2 Baruch Marine Field Laboratory, Georgetown, SC, USA
ABSTRACT- Spatial and temporal variability in microbial metabolic pathways influences ecosystem-level processes including soil carbon storage, the regeneration of inorganic nutrients, and the production of atmospherically-important trace gases. We measured seasonal changes in rates of microbial Fe(III) reduction, sulfate reduction, and methanogenesis in tidal freshwater and brackish marshes on the Patuxent River, Maryland, USA, and assessed the ability of plant roots to influence these processes by regenerating electron acceptors and supplying electron donors. In both marshes, microbial Fe(III) reduction was a dominant respiration pathway early in the growing season (>50% of anaerobic metabolism), but it decreased in importance over the course of the summer. Coincident with the seasonal decline in Fe(III) reduction, methanogenesis (freshwater marsh) or sulfate reduction (brackish site) increased in importance. At the brackish marsh, there were no rhizosphere-related changes in the partitioning between Fe(III) reduction and sulfate reduction, suggesting that plants did not control anaerobic metabolism at this site. Instead, seasonal biogeochemical patterns at the brackish marsh were affected by factors including flooding duration and iron-sulfur interactions. At the tidal freshwater site, our results suggest that changes in rates of Fe(III) reduction and methanogenesis were directly affected by plant-mediated processes in the rhizosphere. In mid summer, Fe(III) reduction accounted for a greater fraction of total anaerobic metabolism in rhizosphere-influenced soils at the expense of methanogenesis. Due to microbial competition for electron donors, plant-mediated changes in rates of iron cycling ultimately affect the balance between Fe(III) reduction and methanogenesis within tidal freshwater marsh soils and therefore play a key role in wetland carbon cycling and greenhouse gas production.
Key words: methanogenesis, iron reduction, microbial respiration, wetland carbon cycling