Research

Ongoing Research Projects

1. Understanding the mechanisms underlying heterotrophic CO2 and CH4 fluxes in a peatland with deep soil warming and atmospheric CO2 enrichment

Peatlands are a diverse group of wetlands that store approximately one-third of the terrestrial soil carbon and are responsible for a significant but poorly quantified fraction of the global flux of methane (CH4) to the atmosphere.  Despite their importance in the global carbon cycle, there is currently a limited mechanistic understanding of the controls of CO2 and CH4 fluxes in these ecosystems and less is known about how these fluxes will respond to global change in these ecosystems. This project will leverage cutting-edge infrastructure in the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) program run by the Department of Energy.  This ongoing project simulates multiple global change factors at a bog in Minnesota.
We will engage in this project by exploring CO2 and CH4 fluxes using a combination of laboratory experiments, field measurements, and computational modeling.  This project is funded by the Department of Energy’s Office of Biological and Environmental Research and is a collaboration with my long-term colleague Scott Bridgham at the University of Oregon and a new colleague with expertise in ecosystem modeling, Charlie Zhuang at Purdue.

2. Why does methane production vary dramatically among peatland ecosystems?

In collaboration with colleagues at the University of Oregon and the Smithsonian Environmental Research Center, I am working on a project funded through the Ecosystem Science Program at the National Science Foundation exploring the controls on CH4 production in northern peatland ecosystems.  Students at Chapman University have been leaders on two particular projects in the context of this larger experiment.
Jillian Wade (Biology, Class of 2011) designed and conducted a project exploring the influence of divalent cations on anaerobic carbon mineralization (as CO2 and CH4 production) in these soils.  Her results suggest that despite low concentrations, these cations are not generally limiting to soil microbes in peatlands.  The results of this work were presented in a poster entitled “Limited effects of trace metals on peatland soil decomposition,” which received the Chapman University Excellence in Presentation Award at the 2011 Undergraduate Research Fair.
Crissand Anderson (Chemistry, Class of 2011) completed a project exploring the importance of humic reduction in peatland decomposition.  The results from this work are extremely exciting and suggest that this novel microbial pathway plays an important role in regulating peatland decomposition and CH4 production.  Crissy’s results were presented at the 2011 meeting of the American Chemical Society in a poster entitled “Electron shuttling by humic substances in wetland soils: exploring a novel control on anaerobic decomposition.”  Crissy also gave an oral presentation on this research at the Orange County American Chemical Society student meeting.
During her time as a post-doc in the lab, Kim Takagi, continued work on the humic aspects of this project and generated some amazing results using an improved experimental protocol.  Her work with a bog soil shows, for the first time, that there is a quantitative relationship between the number of electrons shuttled to solid phase humic materials by microbes and the amount of CO2 produced by this process.  Kim also worked with Jes Mosolf (Environmental Science & Policy, Class of 2013) to explore how temperature influences the competition between humic reducers and methanogens in peatland soils.

3.  Tidal wetland carbon sequestration and greenhouse gas modeling

This work stems from past work at the National Center for Ecological Analysis and Synthesis on a working group  exploring the potential for carbon sequestration in tidal wetland soils.  This work has important implications for the conservation and resilience of these ecosystems in the face of rising sea level and is also of interest in the context of state, national and international carbon trading initiatives.  With collaborators at the University of California, Los Angeles we are collecting data on soil carbon storage and greenhouse gas dynamics in Southern California salt marsh ecosystems.
Madison Hoffacker (Environmental Science and Policy, Class of 2013) and Morgan Brown (Biology, Class of 2012) explored the carbon content of soils dominated by two different wetland plant communities.  They presented their preliminary findings at the 2011 Schmid College of Science Research Fair in a poster entitled, “Carbon sequestration in two different wetland communities in a Southern California salt marsh: preliminary results.”
Students in my Fall 2011 Ecosystems Ecology (BIOL319) course have expanded on this work by collecting data on soil carbon storage in two restored salt marshes in Huntington Beach, CA.  The first site, Talbert Marsh, was restored in 1989 and the second site, Brookhurst Marsh, was restored in 2009.  These data will allow us to test they hypothesis that organic carbon in salt marsh soils accumulates following wetland restoration.  Ten students from this course have agreed to continue working on this project, and we have recently submitted a manuscript for publication in a peer-reviewed journal!

4.  The importance of leaf nitrogen allocation in litter decomposition

It is well understood that nitrogen is an important control on both plant physiology and litter decomposition.  Plant physiologists have begun to appreciate that the allocation of that nitrogen between various pools (e.g., soluble proteins vs. structural compounds) is important for plant success in the environment; but, the importance of this allocation has not been explored in the context of decomposition.  Together with Dr. Jennifer Funk at Chapman University, we have recently completed an 18-month litter bag study to explore the relationship between litter nitrogen biochemistry and rates of litter decomposition.  Catrina Clausen (Environmental Science and Policy, Class of 2011) presented the initial results of this work at the 2011 Schmid College of Science Research Fair in a poster entitled, “Importance of leaf nitrogen allocation for decomposition.”

Past Research Projects

1. Novel experimental research on deep soil (NERDS)

The response of forest ecosystems to elevated atmospheric concentrations of CO2 are an important component of the land surface models used to predict atmospheric and climatic change.   Many of these responses will be mediated by carbon and nitrogen dynamics in deep soils which have not been well studied.  Along with Dr. Colleen Iversen and other collaborators at Oak Ridge National Laboratory, we are exploring carbon and nitrogen processes to depths of 90 cm in soils from the recently decommissioned Free-Air CO2 Enrichment (FACE) experiment.  Our results suggest that deep root inputs under elevated [CO2] may stimulated carbon and nitrogen storage in these soils. This manuscript has recently been accepted to Global Change Biology, and can be viewed here.  There is also an Oak Ridge press release on the project which can be found hereCitation: Iversen, C.M., J.K. Keller, C.T. Garten, and R.J. Norby.  2012.  Deep root inputs under elevated [CO2] may increase soil C and N storage.  Global Change Biology. doi: 10.1111/j.1365-2486.2012.02643.x.


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