CAREER: Microbial controls on wetland carbon stabilization and storage

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While wetlands only occupy about 7% of Earth's land surface, they are estimated to hold about 40% of its carbon (C). Wetlands are effective at storing C due to their high rates of vegetation growth and generally low rates of soil C losses from decomposition by microbes. Like many ecosystems, wetlands are subjected to nutrient enrichment via fertilization from agricultural runoff. Often, fertilization effects can increase microbial activity, leading to higher rates of C loss through microbial decomposition. Thus, wetland C storage is vulnerable to changes in the environment, which, in turn, can result in a reduced capacity for wetlands to compensate for change. Wetland C storage potential could be overestimated when impacts of nutrient enrichment and microbial physiology are not incorporated into the earth-system context. This research will provide insights into microbial controls on soil C processes, which have implications for broad national interests in energy, natural resources management and conservation. This research will advance the fields of ecosystem science, ecology, and microbiology by examining the relationships among microbial diversity, microbial metabolisms, and C-cycling functions. It will also benefit society through classroom educational content focused on microbial diversity and processes at the K-12, undergraduate and graduate levels that will reach under-served populations, enhancing diversity of the STEM workforce.

This study will test the hypothesis that inorganic nutrient enrichment causes shifts in microbial communities from slow growing oligotroph- to fast growing copiotroph-dominated assemblages, resulting in changes in microbial processing of C and nutrients in soils. An altered ecosystem may lead to soil organic matter (SOM) destabilization, due to decreased mineral-protected SOM and increased respiration rates, thereby reducing soil C storage in wetlands. The specific objectives of this project include: (1) determine how variation in above- and below-ground plant biomass relates to SOM buildup in a historically nutrient-poor wetland now experiencing nutrient enrichment; (2) relate microbial resource-use strategies to atmospheric gas exchange (methane, carbon dioxide), and soil organic matter pools under ambient and nutrient-enriched conditions; and (3) examine how shifts in microbial biomass, community structure, and metabolic diversity affect SOM stabilization and C storage potential due to long-term fertilization. Since 2003, replicated fertilization and disturbance (by mowing) treatments have been applied to a nutrient-poor wetland ecosystem in the North Carolina coastal plain. This new project will leverage the field experiment to determine whether ongoing fertilization influences plant-microbe relationships and soil C storage potential. If nutrient enrichment disrupts wetland C storage, then predictions for wetland C pools may be overestimated since wetlands experience both human and temperature-induced nutrient enrichment. This study will also determine whether physiological assessments of microbial communities (used to characterize oligotrophic and copiotrophic taxa) provide a better predictor of ecosystem responses than taxonomy or biomass-based metrics.

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.