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Enhanced Ultraviolet-B Radiation and Carbon Cycling in Northern Peatlands: Substrate Controls on Decomposition

EPA Grant Number: F6F10360
Title: Enhanced Ultraviolet-B Radiation and Carbon Cycling in Northern Peatlands: Substrate Controls on Decomposition
Investigators: Conlin, Molly R.
Institution: Michigan State University
EPA Project Officer: Manty, Dale
Project Period: September 1, 2006 through September 1, 2008
Project Amount: $111,344
RFA: STAR Graduate Fellowships (2006)
Research Category: Academic Fellowships , Fellowship - Ecosystem Ecology , Ecological Indicators/Assessment/Restoration

Description:

Objective:

Since the mid 1980s, stratospheric ozone concentrations have declined, enhancing UVB at the Earth’s surface. Adapted to a naturally low UVB regime, northern peatlands, which store 30% of the world’s terrestrial soil carbon (C), may be particularly sensitive to expected UVB increase. Little is known about the impact of UVB on processes that affect C storage and emissions in peatlands.

My research will address how UVB controls peatland decomposition and emissions of CO2 and CH4 to the atmosphere. I propose to test the effects of UVB on decomposition rates and greenhouse gas fluxes with a combination of field and laboratory experiments. I will establish replicate plots in 3 bogs and 3 fens located within the Bonanza Creek Long Term Ecological Research (LTER) site in Alaska. I will manipulate UVB levels passively by blocking UVB. I will quantify the effects of elevated UVB on C gaseous and dissolved fluxes from bog and fen monoliths in a growth chamber experiment. I will core peat monoliths from the bog and fen sites and I will expose the monoliths to UVB using fluorescent lamps.

Approach:

Field Experiment: Within each plot, net ecosystem CO2 exchange and ecosystem respiration (Rh) of CO2 and CH4 will be quantified. Decomposition rates will be measured during a litterbag experiment.

Lab Experiment: CO2 and CH4 fluxes from each monolith will be measured across the UVB treatments. I will measure soil water from each monolith for DOC and DIC.

These data will allow me to evaluate the vulnerability of both bog and fen peat to altered decomposition rates under enhanced UVB and how UVB influences C gas fluxes and DOC production in peatlands. I will collect water samples from the field plots and analyze for total dissolved C, DOC concentrations, and compound specific organic matter quality. To determine whether increased photodegradation has the potential to stimulate Rh, I will conduct a laboratory incubation experiment where autoclaved water incubated in the various UVB treatments will be added to incubation jars to quantify the effects of UVB-induced DOC signatures on gaseous C production rates in bog and fen peat. Soil incubations will be conducted under aerobic and anaerobic headspaces to examine both CO2 and CH4 production. I will measure stem growth rates across the field plots. To determine whether litter produced under the high UVB treatments decomposes more rapidly due to changes in C allocation and organic matter quality, I will design a reciprocal litter bag experiment utilizing litter produced in the ambient and excluded field UVB treatments.

Expected Results:

Hypothesis 1: Enhanced UVB increases decomposition rates in peatlands, thereby increasing the fluxes of CO2 and CH4 across peatland-atmosphere interfaces. I predict ambient UVB will increase decomposition across sites relative to excluded UVB, due to changes in substrate quality and Rh.

Hypothesis 2: Enhanced UVB increases decomposition rates in peatlands by stimulating photodegradation of DOC, which contributes to labile C compounds available to decomposers. I hypothesize that enhanced UVB stimulates decomposition at least partly through increased photodegradation of DOC. I predict that UVB will stimulate DOC photodegradation and increase labile DOC compounds. I predict greater C production rates in the incubations receiving UVB-exposed waters due to more labile C substrates and consequent increases in Rh. These results would suggest that changes in DOC chemistry via UVB-induced photodegradation can indirectly control decomposition rates by influencing substrate quality for decomposers.

Hypothesis 3: Enhanced UVB indirectly increases decomposition in peatlands by altering moss allocation strategies to favor rapid metabolism, producing labile C pools readily accessible to soil decomposers. I predict that UVB will favor plant allocation into metabolic sugars to support fast growth rates. Subsequently, greater concentrations of metabolic, labile sugars in plant litter will stimulate decomposition rates in surface peat.

Supplemental Keywords:

ultraviolet-B radiation, carbon flux, northern peatlands, global change, , POLLUTANTS/TOXICS, INTERNATIONAL COOPERATION, Air, Scientific Discipline, RFA, Global Climate Change, climate change, Air Pollution Effects, Atmosphere, Chemicals, Environmental Monitoring, CO2 concentrations, UV radiation, carbon dioxide, atmospheric carbon dioxide, ozone, methane, carbon sequestration, greenhouse gases, emissions impact

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