Effects of soil temperature on Sphagnum moss litter quality and decomposition in a subarctic environment

Abstract

High latitude peatlands play a significant role in global soil carbon budgets, attributed to the slow decomposition rate of Sphagnum mosses that facilitates carbon sequestration through the build-up of peat. As climate change is predicted to increase soil temperatures and decomposition rates of organic matter, studying environmental and intraspecific mechanisms that controls decay resistance of Sphagnum mosses is central to understand potential shifts in peatland carbon storage. In this study, I show how soil temperature affects litter quality and decomposition rates of two Sphagnum species: S. papillosum and S. subnitens. I established a reciprocal litter bag experiment over a thermal gradient in Iceland to measure mass loss (%) of the Sphagnum moss litters over a 4-month period and used Diffused Reflectance Infrared Transform Spectroscopy (DRIFTS) to analyse the organic chemical structure of the fresh and decomposed litters. My results showed that Sphagnum papillosum and S. subnitens have different rates of decomposition under different soil temperatures which relates to intra- and inter-specific variations in organic chemical structures. Sphagnum papillosum decomposed significantly faster in warmer soil conditions compared to colder soil conditions. In contrast, Sphagnum subnitens did not decompose significantly faster in the warmer soil conditions. There was a significant difference in the organic chemical structure between the hot-originating and cold-originating litter of Sphagnum subnitens, which was not seen for Sphagnum papillosum. These results suggest that Sphagnum papillosum will decompose faster under warmer soil temperatures whereas Sphagnum subnitens can resist decay due to metabolome plasticity. These findings demonstrate that there are species-specific adaptations to changing environmental conditions that should be considered in climate models.