Microtopography affects the relationship between soil, plant distribution and decomposition rates in a subalpine grassland

Earth hummocks are small cryogenic mounds closely spaced in grassland or wetlands. The microtopography of hummocky terrain establish specific microclimatic conditions which may cause variations on soil chemico-physical properties and a selective distribution of plant species. The work has been carried out at the LTER site of Torgnon (Aosta Valley, Italy), characterized by a Nardus stricta subalpine hummocky grassland located at 2100 m. The concave-convex pattern shows a differentiated distribution of vegetation with the dominance of Nardus on hummocks and a prevalence of dicotyledons in interhummocks. Such distribution indicates variations in water and nutrient fluxes. In order to confirm this hypothesis, we collected topsoil samples and opened a soil pit. In addition, to investigate different litter decomposition rate, in relation to microtopography and plant species, litter bags were positioned in hummocks and interhummocks positions. The results verify a faster decomposition of dicotyledons in the nutrient-richer interhummocks topsoils compared to the podzolized hummocks positions, and an overall slower decomposition rate of Nardus litter.