Influence of experimental extreme water pulses on greenhouse gas emissions from soils.

Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0-10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO, CH, and NO fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO ), and polymerase chain reaction-denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO (Wetland), >23,000% for CH (Creek), and >110,000% for NO (Forest Soils) following pulse events. The Creek soil produced the highest soil CO emissions, the Wetland soil produced the highest CH emissions, and the Forest soils produced the highest NO emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large NO emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes. [ABSTRACT FROM AUTHOR]

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