Jason Keller - US grants

The objective of this research is to understand the factors that control the production of the greenhouse gases carbon dioxide and methane in wetland soils under anaerobic (i.e., waterlogged with oxygen depletion) conditions in current and future climates. These two gases are the end products of a complicated, interlinked set of microbial processes during the anaerobic decomposition of soil organic matter, and the goal of this project is to understand the relative ratio at which these two gases are produced within the context of the larger anaerobic carbon cycle. Both field and laboratory experiments will be used to examine the chemical, environmental, and biological factors (including microbial community structure) that control the ratio at which these important greenhouse gases are produced in six wetlands in northern Michigan. These wetlands represent a broad range of conditions in terms of hydrology, chemistry, and plant community composition.

The proportion of soil carbon that ends up as carbon dioxide and methane during anaerobic decomposition varies by several orders of magnitude among different types of wetlands, and the factors that control this variation are not well understood. Because methane is a much more potent greenhouse gas than carbon dioxide, the ratio at which these two gases are produced can have a substantial impact on the Earth?s climate system. Also, methane emissions from wetlands have been sensitive to climate change in the past and may have strong feedbacks to future human-induced climate change.

Funds from this Major Research Instrumentation award will be used to purchase a carbon-hydrogen-nitrogen (CHN) elemental analyzer for research in plant and ecosystem ecology by faculty and students at Chapman University, an undergraduate serving institution in Orange, California. Carbon and nitrogen are key elements in a number of important ecological processes ranging from plant responses to the environment to rates of microbial decomposition and soil formation in ecosystems. Through student-faculty collaborations, the CHN elemental analyzer will initially be utilized to explore carbon and nitrogen dynamics in three ecological research programs. (1) Carbon and nitrogen sequestration through sediment deposition in coastal marshes in Southern California. This work will explore sedimentation dynamics and sequestration of carbon and nitrogen in salt marsh soils in order to better understand the fate of these important ecosystems in the face of ongoing sea level rise. (2) The importance of leaf nitrogen allocation in litter decomposition. This project aims to elucidate the links between leaf nitrogen pools (e.g., nucleic acids, amino acids, soluble proteins) and rates of litter decomposition. (3) Integrating biochemical, physiological and morphological responses of plants to changes in water availability. This work will determine how plant species differentially respond to changes in the intensity and timing of precipitation events and how these responses relate to plant fitness.

The acquisition of a CHN elemental analyzer will facilitate research, teaching and outreach at Chapman University by allowing students and local educators to gain hands-on experience with an instrument commonly used in ecological research. In particular, the instrument will increase faculty scholarship and create new opportunities for student-faculty mentorship with a diverse group of undergraduate collaborators. The CHN elemental analyzer will also increase access to modern research instrumentation for student and faculty as well as local high school and community college instructors. Through mentored student research and inclusion into new and existing curricula, this instrumentation will facilitate education in a research-intensive environment and prepare our students for future scientific careers.

An award is made to Chapman University to acquire a cavity ring down spectroscopy (CRDS) analyzer for research in wetland carbon cycling. The acquisition of a CRDS analyzer will increase opportunities for research training by leveraging a number of existing mentoring and teaching programs at Chapman University, an undergraduate-serving institution in Orange, California. These include mentored undergraduate research; integration into an existing Ecosystem Ecology laboratory course; use in an established research training program for local high school students; and training of community college students supported by an ongoing NSF REU-Site program. These training efforts will continue a successful track record of engaging females and underrepresented minorities in cutting edge scientific research using world-class instrumentation.

Wetlands are among the most important ecosystems in the global carbon cycle because of their large soil carbon pools and high methane emissions. Given their importance in the global carbon cycle, wetlands have been important drivers of climate change in the past. A pressing question in global change biogeochemistry remains whether a significant fraction of the large carbon pool in wetland soils will be released as methane in future climates. A more complete mechanistic understanding of the complex microbial processes that mediate wetland carbon cycling is necessary to accurately model the response of wetland decomposition and methane dynamics to ongoing global change. Stable isotopes are a powerful tool for exploring wetland carbon cycling and can provide important insights into the production and consumption of methane in wetlands. The acquisition of a cavity ring down spectroscopy (CRDS) analyzer will allow for the measurement of stable isotopic composition of carbon dioxide and methane. The acquired instrument will provide important insights into the processes of decomposition, methane production and methane consumption in wetland ecosystems to better understand their role in the global carbon cycle.

Globally important carbon (C) stores in northern (boreal) peatlands are vulnerable to changes in altered precipitation and runoff patterns, groundwater inputs, and changes in the extent of frozen ground in high latitudes (called ?permafrost?, or the ?cryosphere?). These changes can affect the extent of boreal wetlands as well as their ability to sequester and transform C and other nutrients. In 2005, the Alaska Peatland Experiment (APEX) was created to examine the role of changing soil climate and vegetation on peatland C cycling. Over the past fifteen years, core data has been collected on soil moisture and temperature, plant composition and amount, and the fluxes of important atmospheric gases emitted (as methane and carbon dioxide) from water table treatments that simulate floods and droughts. A key result from this group's prior investigations was that C emissions from this experimental site appeared to be high, regardless of water table position, revealing that interactions among changes in plant species composition in response to the treatments were strongly controlling the ability of this ecosystem to retain C. This is a five-year renewal of a Long-Term Research in Environmental Biology (LTREB) project, DEB-1354370. The study is examining the interactions among changes in hydrology, plant species composition and changes in climate (particularly flooding and drought) in controlling C storage in this peatland complex; this work is necessary for understanding the consequences of an altered climate for C cycle processes. Undergraduates, graduate students and post-doctoral researchers will all be trained and in field and laboratory techniques. Results from the research will also be incorporated into new high school curricula for use in the Fostering Science summer camp.

The current view of peatland carbon cycling is that the majority of soil carbon mineralization occurs in the relatively shallow aerated peat layer above the water table (acrotelm), and that deeper peat carbon occurring in anoxic layers (catotelm) undergoes minimal decomposition. As such, the position of the water table (and the associated thickness of the acrotelm) is used as a predictor of overall decomposition rates and long-term peat accumulation rates. However, findings from this team's fifteen-year manipulation of water table position in an Alaskan fen (Alaska Peatland Experiment, APEX) challenge this view, and in particular suggest that carbon mineralization in saturated peat is faster than previously expected, leading to high fluxes of anaerobic CO2 production. Prior analyses indicated no significant effect of water table position on ecosystem respiration, but it is possible that this result was due at least partially to changes in vegetation that have occurred both under lower (drier) and higher (wetter) water table positions. The initial experimental design could not disentangle the effects of changes in vegetation from hydrology on peat redox and C fluxes. As such, understanding the interactive effects of altered hydrology and vegetation on anaerobic decomposition processes, and how this governs the turnover of deep soil C pools in peatlands, was the prime objective of the first phase of LTREB funding. Results during that initial LTREB funding period showed that sedge and Equisetum (horsetail) rhizospheres indeed had oxidizing effects on peat and dissolved organic matter. However, persistent flooding over this period of research has presented key gaps in mechanistic understanding of controls on trace gas production in this system, and revealed that plant community structure and the dominance of algae likely have unique controls on soil redox processes and C fluxes. Flooding history also exerted strong control over the relative activity of algae vs. heterotrophic microorganisms, depending on changes in C substrates from different plants. Exactly how changes in plant community interact with altered water tables in governing the supply of electron donors and acceptors, and how this controls anaerobic metabolism in low- and high-water table years, are key questions this collaborative team will examine in the next five years.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.