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Harvard Forest Research Project 2024

• Title: Assessing the Generation of Anoxic Microsites and Anaerobic Microbial Processes in Hurricane-Impacted Forests
• Principal investigator: Hannah Naughton (hnaughton@umass.edu)
• Institution: University of Massachusetts - Amherst
• Primary contact: Hannah Naughton (hnaughton@umass.edu)
• Team members: Marissa Hanley
  Julia Marquis
  Hannah Naughton
  Naturi Scott
• Abstract:

  Anoxic microsites are minority volumes within aerobic upland soils known to carry out outsized anaerobic microbial and geochemical functions relative to bulk soil measurements and expectations assuming full aeration. These anaerobic functions contribute to global warming through nitrous oxide (N2O) and methane (CH4) release, lose soil nutrients through denitrification and reductive dissolution of nutrient-sorbing minerals, contribute to metal-facilitated decomposition of litter, but also potentially store more soil organic carbon (SOC) than aerobic soils. Any soil feature that promotes microbial respiration and slows oxygen diffusion – e.g., aggregate size, carbon content, and moisture – should increase the abundance of anoxic microsites. However, no study directly assesses how soil structure and carbon jointly determine the presence and function of anoxic microsites. Moreover, anoxic microsites have not been studied in the context of environmental change, such as in forests with higher litter as a result of storms or infestations. We propose to use natural variation in carbon inputs to typical New England hardwood forest soils beneath downed trees 30 years after a simulated hurricane event to test for the contribution of carbon versus aggregation to anoxic microsite formation. Moreover, we will link these micro- to core-scale observations to the plot scale (50 m x 200 m) by performing plot-wide gas flux and nutrient measurements over the following year. Methods for the anoxic microsite experiment will include measurement of nutrient, redox and microbial soil features in five aggregate size fractions taken from composite soil cores coupled with synchrotron-based imaging of soil pore structure and anoxic microsite distribution. Methods for the plot-level experiment will include routine gas flux measurements coupled with litter bag nitrogen (N) transformation tests and in situ soil temperature, moisture, and redox measurements. Combined, these two experiments will 1) follow up on a study showing minimal changes to soil biogeochemical function two years post-hurricane, and 2) link observed changes in soil gas and nutrient dynamics to carbon- and structure-mediated changes to soil chemistry and microbial functioning.