Harvard Forest >

Summer Research Project 2017

• Title: Linking forest soil Mn cycling to organic matter decomposition along oxic-anoxic interfaces
• Group Project Leader: Marco Keiluweit
• Mentors: Morris Jones; Marco Keiluweit
• Collaborators: Marco Keiluweit
• Project Description:

  Soils play a critical role in the global carbon (C) cycle, having a C stock that is greater than the amount stored in biosphere and atmosphere combined. Of prime importance for future climate predictions is a detailed understanding the factors that control the rate at which soil C is metabolized by microbes and subsequently released to the atmosphere as climate-active greenhouse gases (e.g., CO2 and CH4) (Schmidt et al. 2011). What remains unclear is to what extent the availability and reactivity of manganese (Mn), one of the most abundant and reactive metal species in temperate forest floors (Keiluweit et al. 2015; Berg et al. 2015), impacts greenhouse gas release from forest soils.
  
  We propose a project for an undergraduate researcher to determine the abundance of reactive Mn(III) species in forest soils. Previous work along a wetland to upland slope at Harvard Forest (Phillips et al. 2010) indicated elevated Mn(III) concentrations at the soil-water interface, which characterized by steep redox gradients from oxic to anoxic (M. Wilcots, Harvard Forest REU, 2016).
  
  The undergraduate researcher will deploy novel electrochemical redox sensors to directly measure the microscale distribution and temporal variation of Mn(III) species along oxic-anoxic gradients. In addition, we will measure dissolved organic carbon, Mn(II) and Mn(III) concentrations in pore waters collected in lysimeters, and solid-phase concentrations from soil extracts obtained in the lab. Mn redox cycling will be related to soil moisture and CO2 and CH4 fluxes monitored using a mobile greenhouse gas analyzer unit equipped with moisture probes. The student will be exposed to state of the art field and lab equipment in soil biogeochemistry and co-advised by Marco Keiluweit (Assistant Professor, UMass-Amherst) and Morris E. Jones (Research Associate, 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