MANIPULATION OF FLOODING AND NUTRIENTS INFLUENCES PLANT-MICROBE INTERACTIONS AND WETLAND FUNCTION

Abstract

The largest global stocks of organic carbon are in soils, where plants fix atmospheric carbon dioxide into biomass at higher rates than soil organic carbon is lost through decomposition and microbial respiration. Specifically, wetlands store about 30% of global carbon stocks, but changes in soil hydrology and nutrient concentrations can stimulate microbial activities and result in soil organic matter decomposition. This leads to carbon loss as carbon dioxide and decreases wetland carbon storage potential. The aim of this work was to determine the degree that soil hydrology and nutrient status interact to affect plant-microbe relationships, microbial community structure, and functions related to carbon and nitrogen cycling within wetlands. A combination of field and laboratory mesocosm manipulations in constructed, restored, and natural wetland ecosystems were used to examine wetland plant-soil-microbial interactions. In a constructed (Chapter 1) and restored (Chapter 2) wetland, hydrology explained variation in microbial community composition and function, while plant presence also mediated soil carbon loss (methane and carbon dioxide). Further, in a nutrient-poor coastal plain wetland experiment (Chapters 3 and 4), long-term nutrient additions stimulated plant-microbial feedbacks in a way that increased microbial activity and carbon losses in these wetland soils. Together, these results highlight how plant-microbial interactions regulate carbon loss and nitrogen cycling in wetland soils and the need to include these interactions to improve predictions of wetland carbon storage potential. In addition, considering hydrologic and nutrient controls on plant-microbial regulation of microbial functions could enhance wetland construction and restoration efforts. Results from this dissertation provide insights in how plant-microbial interactions can be leveraged to enhance soil carbon storage and increase climate change mitigation potential from wetlands ecosystems.