HR: 1340h
AN: B53A-0944    [Abstracts]
TI: Methane Production Pathways and Concentration Profiles in Rice Cultivation
AU: * Xiong, Z
EM: zhengqin@pdx.edu
AF: Portland State University, Department of Physics, Portland State University, POB 751, Portland, OR 97207, United States
AU: Shearer, M
EM: mshearer@pdx.edu
AF: Portland State University, Department of Physics, Portland State University, POB 751, Portland, OR 97207, United States
AU: Khalil, M
EM: aslamk@pdx.edu
AF: Portland State University, Department of Physics, Portland State University, POB 751, Portland, OR 97207, United States
AU: Butenhoff, C
EM: psu23819@pdx.edu
AF: Portland State University, Department of Physics, Portland State University, POB 751, Portland, OR 97207, United States
AU: Rice, A
EM: arice@pdx.edu
AF: Portland State University, Department of Physics, Portland State University, POB 751, Portland, OR 97207, United States
AB: Rice agriculture is a significant source of global atmospheric methane (CH4) and a model system to study the mechanisms of CH4 production and emissions. We find that CH4 production occurred throughout the soil profile (0-20cm) and production via hydrogenotrophic pathway was dominant near the surface. Results of CH4 concentration and redox potential measurements indicate that CH4 production occurred throughout the soil profile. Straw amendment led to overall higher CH4 concentrations throughout the soil profile, and particularly soon after rice transplanting. Under continuous flooding, CH4 concentrations in the straw-added treatment increased as the rice season progressed and approached steady state, while in the control concentrations slowly continued increasing at lower concentrations throughout the season. CH4 concentrations decreased during intermittent flooding and resumed at much lower levels after re-flooding. Based on our measurements of ¦Ä13CH4 profiles and the fact that hydrogenotrophic methanogenesis leads to the production of lighter CH4 than acetate-dependent methanogenesis, we infer that the fraction of CH4 production due to acetate-dependent methanogenesis was higher at depth (5cm-20cm) than at the surface (0- 5cm). The contribution of acetate-dependent methanogenesis increased when straw was added. Surface root zone, defined by confining the whole rice root system to a 25¦Ìm mesh nylon bag, had heavier CH4 in the pore water than the bulk soil zone, which may indicate a greater role of oxidation near the roots. Hence stable isotope is important for studying CH4 production and secondary isotope fractionation processes such as CH4 oxidation. To understand the underlying processes, we need to study both concentration and the isotopic composition of CH4 in the soil profiles. This research was supported by US Department of Energy (No. DE-FG02-04ER63913).
DE: 0402 Agricultural systems
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting