Patterns in wetland microbial community composition and functional gene repertoire associated with methane emissions.
Bottom Line: Methanogenic archaea were observed in all samples, as were nitrate-, sulfate-, and metal-reducing bacteria, indicating that no single terminal electron acceptor was preferred despite differences in energetic favorability and suggesting spatial microheterogeneity and microniches.We found that methanogenesis gene abundance is inversely correlated with genes from pathways exploiting other electron acceptors, yet the ubiquitous presence of genes from all these pathways suggests that diverse electron acceptors contribute to the energetic balance of the ecosystem.These investigations represent an important step toward effective management of wetlands to reduce methane flux to the atmosphere and enhance belowground carbon storage.
Affiliation: DOE Joint Genome Institute, Walnut Creek, California, USA.Show MeSH
Mentions: From the inlet to interior sites, pH, sulfate, nitrate, and dissolved oxygen (DO) at the standing water-peat interface decreased, and soluble iron (Fe) and manganese (Mn) increased in February (Fig. 1a and b). Increasing solubilization of Fe and Mn results from solid-phase Fe(III) and Mn(IV) reduction (12). These physicochemical patterns across sites were similar for August (Fig. 1d and e), although weaker than those in February. The pH of river water inputs was ~7.7 and decreased from the inlet to interior sites (from 7.0 to 6.5 in February and from 6.5 to 6.2 in August), likely due to anoxic decomposition of plant detritus, which releases carbonic, fulvic, humic, and other organic acids (15). River water had a DO concentration of ~8 mg/liter and was the primary source of nitrate, sulfate, and oxidized Fe (10). The observed decreases in electron acceptors in conjunction with increases in reduced Fe and Mn suggest that a variety of electron acceptors were being consumed along the water passage, although at these concentrations nitrate is predicted to be the most energetically favorable electron acceptor. Additionally, interior sites (“backwater” areas) experienced less hydraulic mixing and chemical exchange with river water than did the inlet site, which likely further decreased the influx of electron acceptors to the interior.
Affiliation: DOE Joint Genome Institute, Walnut Creek, California, USA.