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Summer Research Project 2020

• Title: Nifty Microbes, Potent Enzymes, or Reactive Metals - What is Really Driving Organic Matter Decomposition in Forest Soils?
• Group Project Leader: Marco Keiluweit
• Mentors: Nathan Chin; Luiz Domeignoz Horta; Marco Keiluweit
• Collaborators: Kristen DeAngelis
• Project Description:

  Soil organic matter (OM) is the largest and most dynamic terrestrial carbon (C) reservoir and an important component of the global C cycle. Increasing rates of OM decomposition results in additional CO2 released into the atmosphere causing a positive feedback effect on climate change (Schmidt et al. 2011). Understanding the biogeochemical mechanisms responsible for the decomposition of OM is thus critical to creating accurate models for predicting how soil C drives and responds to climate change. It is increasingly clear that climatic factors alone do not sufficiently predict decomposition rates, but that soil biogeochemical factors play a key role. Multiple lines of evidence suggest that decomposition is controlled by the availability of widely overlooked, yet highly potent oxidants - reactive manganese (Mn) species (Berg et al. 2015; Keiluweit et al. 2015). Yet the mechanisms underlying the formation of reactive Mn species in forest soils and its subsequent impact on OM decomposition are poorly understood.
  
  We propose a project for an undergraduate researcher to determine if seasonal variations in emissions of climate-active carbon dioxide from forest soils are linked to the production of reactive Mn species. Previous work along a soil moisture gradient at Harvard Forest (Phillips et al. 2010) indicated elevated concentrations of reactive Mn at the upland to wetland transition, which is characterized by steep gradients in oxygen availability (Jones et al. 2018; Keiluweit, Pardi, Wilcots et al. in prep).
  
  The undergraduate researcher will monitor carbon dioxide fluxes along this moisture gradient with our portable greenhouse gas analyzer. In addition, the students will collect weekly soil samples for analysis of soil microbial biomass, enzyme activity, and reactive Mn species. While the student will spent most of their time in the field at the Harvard Forest, the student will be also be exposed to state of the art field and lab biogeochemistry equipment at UMass Amherst. Work will entail field measurements, sample collection, sample processing, wet-chemical analyses, data processing and statistical analysis. The student will mentored by Marco Keiluweit (Assistant Professor) and Nathan Chin (PhD student) and co-mentored by Kristen DeAngelis (Associate Professor) and Luiz Horta (Postdoc), all located at UMass Amherst.
  
  General Qualifications:
  An interest in microbiology and chemistry would be helpful
  Experience in soil and/or environmental science and related laboratory work
  Valid drivers’ license to enable the students to drive a Harvard Forest vehicle
  

• Readings:

  Berg, B. et al. Manganese in the litter fall-forest floor continuum of boreal and temperate pine and spruce forest ecosystems – A review. Forest Ecology and Management 358, 248–260 (2015).
  
  Keiluweit, M. et al. Long-term litter decomposition controlled by manganese redox cycling. PNAS 112, E5253–E5260 (2015).
  
  Madison, A. S., Tebo, B. M., Mucci, A., Sundby, B. & Luther, G. W. Abundant Porewater Mn(III) Is a Major Component of the Sedimentary Redox System. Science 341, 875–878 (2013).
  
  Phillips, S. C. et al. Interannual, seasonal, and diel variation in soil respiration relative to ecosystem respiration at a wetland to upland slope at Harvard Forest. J. Geophys. Res. 115, G02019 (2010).
  
  Schmidt, M. W. I. et al. Persistence of soil organic matter as an ecosystem property. Nature 478, 49–56 (2011).

• Research Category: Soil Carbon and Nitrogen Dynamics