Methane Cycling Contributes to Distinct Patterns in Carbon Stable Isotopes of Wetland Detritus

Abstract

Increasing global temperatures are changing the balance between carbon sequestration and its microbial processing in wetlands, making the tracking of these processes important. We used detrital carbon stable isotopes (δ13C) to trace aerobic decomposition and CH4 production in two experiments conducted in Alaskan wetlands. In laboratory bottle incubations, larger decreases in detritus δ13C corresponded to higher net CH4 and CO2 production rates. Because net CH4 production was the stronger predictor and its effect was negative, we hypothesize that decreases in δ13C trace concurrent CH4 production and oxidation. In a field experiment, decreases in detritus δ13C were not correlated with aerobic decomposition rates, but were positively correlated with CH4 production potentials as estimated from bottle incubations. We hypothesize that the positive relationship reflects only CH4 production, rather than concurrent production and oxidation. Although CH4 production rates were correlated with changes in detrital δ13C in both experiments, the direction of this relationship differed between laboratory and field with important consequences for the scale of ecological experiments. Our study demonstrates that CH4 cycling can create distinct patterns in δ13C of wetland detritus. Future studies should conduct explicit mass balance experiments to clarify mechanisms and determine the importance of scale in shaping isotopic patterns.