DISSERTATION RESEARCH: Will Ecosystem Recovery From Acid Precipitation Jeopardize Soil Carbon Storage?

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While acid rain has significantly decreased across the United States over the past thirty years, many forested ecosystems are only beginning to recover, with full recovery expected to take decades to centuries. Recent evidence suggests that, while forests will grow better as they recover from acid rain, the soil in forests may also lose a substantial amount of the carbon and nutrients. In this Doctoral Dissertation Improvement Grant (DDIG) project, the student is working to understand the mechanisms by which forest recovery from acid rain may increase the vulnerability of soil organic matter that contains soil carbon and nutrients. The investigators are particularly interested in understanding how rising soil acidity and calcium content may alter the solubility and lability (decomposability) of soil carbon. The project will test this by studying the physical, chemical and microbiological properties of soils in response to changing acidity. This research is necessary to predict future trends of forest growth and carbon storage throughout the Northeastern United States. To facilitate and inform evidence-based management decisions, this research will be incorporated into a web-based application that is geared toward letting the general public explore and understand long-term ecological data. To examine the mechanisms by which ecosystem recovery from acid rain may alter soil organic matter (SOM) dynamics, the researchers will perform a long-term greenhouse mesocosm experiment. Soils will be collected from Hubbard Brook Experimental Forest, a Northeastern hardwood forest that is impacted by acid rain. The team will reconstruct soil mesocosms by horizon, both with and without sugar maple seedlings, a co-dominant species in the forest where the soils were obtained. Soils will be experimentally amended to increase soil pH and Ca in a fully factorial design. The student will measure SOM solubility and microbial respiration of SOM to determine the responses of SOM pools to these treatments. In addition, researchers will measure proximate mechanisms of SOM dynamics (Aluminum-SOM complexation, soil exoenzyme activity, bacterial:fungal microbial biomass ratios, etc.) that may drive changes to SOM solubility and microbial respiration. These measurements will be compared between planted and unplanted mesocosm to identify possible plant-mediated effects on SOM dynamics.