Litter decomposition rate and soil organic matter quality in a patchwork heathland of southern Norway

Norwegian heathland soils, although scant and shallow, are major reservoirs of carbon (C).We aimed at assessing whether vegetation cover and, indirectly, its driving factor soil drainage are good proxies for soil organic matter (SOM) composition and dynamics in a typical heathland area of southern Norway consisting in a patchwork of three different types of vegetation, dominated by Calluna vulgaris (L.) Hull., Molinia caerulea (L.) Moench, or Sphagnum capillifolium (Ehrh.) Hedw. Such vegetation covers were clearly associated to microtopographic differences, which in turn dictated differences in soil moisture regime, Calluna growing in the driest sites, Sphagnum in the wettest, and Molinia in sites with intermediate moisture. Litter decomposition was followed over a period of 1 year by placing litterbags filled with biomass from each dominant species in each type of vegetation cover. The composition of the plant material and SOM was investigated using chemical methods and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Litter decomposition was faster for Molinia and Calluna, irrespective of the vegetation cover of the site where they were placed. Sphagnum litter decomposed very slowly, especially under Calluna, where the soil environment is by far more oxidising than under itself. In terms of SOM quality, Calluna covered areas showed the greatest differences from the others, in particular a much higher contribution from lipids and aliphatic biopolymers, apparently related to biomass composition. Our findings showed that, in the studied environment, litter decomposition rate and SOM composition are actually dependent on vegetation cover and/or soil drainage. On this basis, monitoring changes in the patchwork of vegetation types in boreal heathlands could be a reliable cost-effective way to account for climate-changeinduced modifications to SOM and its potential to last.