Type II Aerobic Methane Oxidizing Bacteria (AMOB) Drive Methane Oxidation in Pulsed Wetlands as Indicated by 13C-Phospholipid Fatty Acid Composition

Abstract

AbstractMethane (CH4) is a potent greenhouse gas and management strategies have been proposed to limit CH4 emissions from freshwater wetlands. The methanotrophic bacteria can intercept much of the CH4 produced by methanogenic archaea and thus management protocols for wetlands could conceivably include manipulations not only to limit the production of CH4 by methanogens, but also to enhance the consumption of CH4 by benthic or planktonic methanotrophs. The hydrological characteristic of a wetland is a major determinant of the CH4 emission rates. A major consideration for CH4 production is whether a wetland is static or flowing (wetlands connected to rivers and streams). Very little is known about the effects of hydrologic pulsing on wetland carbon dynamics and especially CH4 oxidation. Furthermore, although it has been established that methanotrophs are very active at the oxic sediment water interface of wetlands, little is known about the ecology of methanotrophs in the “pulsing fringe”. Stable isotope probing (SIP) of biomarker Phospholipid Fatty Acids provide a means to connect CH4 oxidation to specific methanotrophs and track the shifts in community structure. Three landscape treatments were: 1) upland aerobic soil, 2) the intermediately flooded zone, and 3) the permanently flooded site with two landscape level replicates in a freshwater pulsing experimental wetlands at the Olentangy River Wetland (ORW) Research Park, The Ohio State University, Columbus. Two soil depths (organic horizon, 0-8 cm that includes the oxidized layer in flooded sites and 8-16 cm depth of surface mineral layer) were sampled at each site four times/year over a two-year period (early spring, mid summer, early fall and mid winter). Immediately after sampling the samples are stored at -20° C and transported under dry ice to the Soil Microbial Ecology Lab, SENR, the Ohio State University, Columbus for analysis. Samples were taken back to the lab to determine potential CH4 oxidation and 13C-PLFA analyses after extraction and analysis on GC-C-IRMS.The PF sites had significantly higher (p<0.05) Potential Methane Oxidation (PMO) than the IF sites. PMO rates at 0-8 cm depth of soil were significantly higher than those at depth of 8-16 cm (p<0.05). PMO in Winter was also significantly higher than in Summer (p< 0.01). PLFA profiling of methanotrophs showed that the Type type II methanotrophs and I methanotrophs were more pronounced in winter that was highly correlated by the seasonal dynamics of PMO. Concentrations of the Type II methanotroph PLFA biomarker (18:ω8c, 18:ω9c and 18:ω7c) were significantly higher (p<0.05) than the Type I PLFA biomarkers (16:ω5c).The highest potential to oxidize the substrate-available methane in the Permanently Flooded site is entirely attributed to the methanotrophic population (as reflected by the relative abundance of the signature PLFAs). Even if with very low 13C incorporation, the PLFA profile in the Intermittently Flooded site is dominated by the Type II methanotrophs.