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Harvard Forest Research Project 2022

  • Title: Macrosystems litter decomposition
  • Principal investigator: Mark Bradford (mark.bradford@yale.edu)
  • Institution: Yale University
  • Primary contact: Fiona Jevon (fionajevon@gmail.com)
  • Team members: Fiona Jevon; Alexander Polussa
  • Abstract:

    Leaf litter decomposition is a fundamental process in ecosystem carbon and nutrient cycling. Soil animals and microorganisms feed on leaves from trees and herbaceous plants that senesce and fall to the ground. The soil organisms derive energy and nutrients to grow, and in turn as they carry out this process and are themselves consumed by other organisms, some of the nutrients are released into the soil in forms available to plants for the synthesis of new leaves. Further, the carbon in the leaves is primarily released to the atmosphere as carbon dioxide, with a smaller proportion being stored as soil organic carbon, which imparts characteristics to soil that sustain fertility. As such, by mediating litter decomposition, soil organisms play a fundamental role recycling plant nutrients and maintaining ecosystem health. Decades of research on litter decomposition suggests that this process is controlled by soil temperature and moisture, and the quality of the litter that the organisms get to consume. Recent work suggests that knowledge of the soil organisms themselves is also important for understanding how the decomposition process will respond to global change. Yet whether differences among belowground communities directly affect litter decomposition at regional scales is unknown. Ecosystem theory and biogeochemical models are based on the assumption that they do not, with different belowground communities then assumed to function similarly under the same environmental conditions. Emerging evidence challenges the validity of this assumption of scale invariance and suggests instead that the activities of decomposer communities are uniquely shaped by regional climate. This project tests these competing hypotheses of scale invariance versus scale dependence for litter decomposition. The project addresses this information gap through field experiments, extensively replicated within 15 NEON sites - including the Harvard Forest - arrayed across the eastern United States, which fall within six ecoclimatic domains. The field research will be combined with controlled laboratory studies to quantify site-specific relationships between temperature, moisture, litter quality and decomposition rates, and to evaluate whether the relationships arise through selection by the domain-level climate for particular microbial functional traits. The data generated through this empirical work will inform a biogeochemical model. The model will be used to forecast the sensitivity of regional decomposition patterns to the possibility that they emerge from scale-dependent relationships generated by trade-offs which dictate the activities of belowground communities.