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.