Submitted to: Soil Science Society of America Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 9/28/2003
Publication Date: 11/2/2003
Citation: Mclain, J.E., Martens, D.A. 2003. Environmental mechanisms controlling methane consumption in semi-arid soils. Proc. Soil Sci. Soc. Am. Annual Meeting, Poster Session, Nov. 2-6, Denver, CO.
Technical Abstract: Semi-arid ecosystems represent 25% of the Earth's land area and are increasing due to desertification. Moisture limitations have led to the belief that these soils are not significant consumers or producers of trace gases and thus, they are often largely overlooked in greenhouse gas inventories. We are studying environmental influences on CH4 oxidation in soils throughout southeastern Arizona. Since monitoring began, CH4 consumption across all sites has averaged -0.52 mg m-2 d-1, well within the range reported for temperate soils. Precipitation pulses have had little effect on the net CH4 sink, as consumption averaged -0.53 mg m-2 d-1 during the monsoon period and -0.52 mg m-2 d-1 post-monsoon, and only decreased to -0.31 mg m-2 d-1 after extreme drying in late spring. The finding of substantial year-round methanotroph activity is unexpected, as in vitro studies have shown that methanotrophs are not xerotolerant. Yet, we measured near-maximum oxidation when surface soils were moist (-20kPa) or extremely dry (-1500 kPa). Methanotrophs are confined to near-surface depths by limitations on gas diffusion in finer-textured soils but the coarse texture (80% sand) of our soils may allow them to exist throughout the profile, where their activity is controlled by available soil moisture. This work suggests that semi-arid soils represent a significant, previously underestimated, terrestrial CH4 sink.