An experimental comparison of chemical traits and litter decomposition rates in a diverse range of subarctic bryophyte, lichen and vascular plant species

Abstract

Summary 1. Climate change in the subarctic is expected to influence vegetation composition, specifically bryophyte and lichen communities, thereby modifying litter decomposition rates and carbon (C) dynamics of these systems with possible feedbacks to climate. 2. In a 2‐year experiment, we investigated decomposition rates and chemical traits of 27 bryophytes, 17 lichens and 5 vascular plants in litter beds in subarctic Sweden. The majority of the sampled cryptogam species are widespread at higher northern latitudes. 3. Average 2‐year litter decomposition rates (exponential mass loss constant k) of lichen (0.44 ± 0.01) and vascular plant (0.56 ± 0.03) species were higher than that of bryophytes (0.11 ± 0.01), while within main cryptogam taxa, species identity was an important determinant of mass loss rates. At cryptogam group level, 2‐year litter mass loss of Sphagnum was significantly lower than for non‐Sphagnum mosses and liverworts. Within lichens, N2‐fixing versus non‐N2‐fixing lichens showed no variation in decomposability. 4. In a subset of the large species set, mass loss differed both among incubation environments (reflecting nutrient‐rich and poor birch forest and Sphagnum peatlands, respectively) and species. The pattern of mass loss across incubation environments was not consistent among cryptogam species. N2‐fixing, in contrast to non‐N2‐fixing lichens with lower nitrogen (N) levels displayed similar decomposition rates across incubation environments. Mass loss of non‐Sphagnum mosses was correlated with initial N irrespective of incubation environment. 5. Litter mass loss of cryptogam taxa could be predicted very well from infrared spectra of the initial chemical composition of the species, by application of Fourier transform infrared using an attenuated total reflectance probe. The initial macronutrient concentrations (N, phosphorus, C and cations) and initial litter pH correlated less well. 6. Synthesis. We showed comprehensively that decomposition rates of bryophytes are generally lower than those of lichens and vascular plants. Among bryophyte or lichen species there is also great variation in litter decomposability which depends strongly on species‐specific chemistry. Our data will help predict changing land surface feedback to C cycles and climate in cold biomes by understanding long‐term climate effects on litter decomposability through shifting vegetation composition.