Decomposition processes interacting with microtopography maintain ecosystem heterogeneity in a subalpine grassland

Grasslands are among the largest ecosystems in the world and store up to 30% of the global reserves of carbon. Decomposition processes have a crucial role in maintaining carbon balance, but few studies have investigated the heterogeneity of this process at small scale, especially in alpine ecosystems. We aimed at investigating the interactions between decomposition and environmental heterogeneity at microscale (i.e. elevation gradient <1 m) in a subalpine grassland on the western Italian Alps characterised by the presence of parallel hummock and hollow areas. In the study area we monitored microenvironmental drivers (soil temperature and soil water content), plant distribution and decomposition. The latter was studied through a litter bags approach followed by elemental analysis, 13C NMR and FT-IR spectroscopies. Microtopography exerted a direct and indirect control over litter decomposition by affecting plant species distribution and microclimatic conditions. The different elemental and biochemical properties of plants, interacting with microtopography, led to a higher decomposition rate of forb than grass litter, and in hollow than in hummock areas. The observed differences were both quanti- and qualitative. Decomposition processes bridge the gap between plant community structure and ecosystem functioning, determining a feedback mechanism that maintains ecosystem heterogeneity at the microscale.