Moss species effects on peatland carbon cycling after fire

Abstract

Summary1. Peatlands are a significant store of global carbon (C) and may be particularly sensitive to climate change. Understanding the drivers of C cycling in peatlands is therefore important for predicting feedbacks to climate change. One such driver may be the identity of component plant species.2. Moss species contribute significantly to peatland vegetation, yet we understand comparatively little of their role in short‐term C cycling and whether that role is consistent regardless of environmental context.3. We examined the impact of three dominant, co‐occurring moss species (Hypnum jutlandicum, Sphagnum capillifolium and Plagiothecium undulatum) on C cycling across a long‐term fire frequency experiment, where plots have been burnt every 10 years, every 20 years or have not been burnt since 1954. We measured species effects on in situ net ecosystem exchange (NEE) and decomposition environments, and moss species litter decomposition rates in a laboratory experiment. The fire experiment also provided an ideal opportunity to test whether moss species effects were consistent regardless of context.4. Moss‐dominated patches were on average net sources of CO2 over the main growing period, with Sphagnum‐dominated patches showing the lowest NEE. The presence of mosses reduced peat temperature, but this was insufficient to cause differences in the decomposition rate of a standard substrate. Sphagnum and Hypnum litter decomposed more slowly (17 and 16% mass loss, respectively) than Plagiothecium litter (64% mass loss) over a 42‐week incubation period.5. Fire frequency treatments had few effects on measures of C cycling. Moss effects were generally consistent regardless of fire frequency treatment, but Plagiothecium and Sphagnum litter collected from the no‐fire plots had higher rates of decomposition than litter collected from the plots burnt more frequently.6. In summary, postfire, both inter‐ and intraspecific differences in mosses had significant effects on short‐term C cycling. Consequently, changes in both moss species composition and variation within species may need to be taken into account to accurately predict C cycling in peatland ecosystems subject to fire.