Data from: Humus forms and organic matter decomposition in the Swiss Alps

Organic matter decomposition is influenced by abiotic factors (i.e.,
climate) and biotic factors (i.e., plants and soil decomposers). To
qualitatively assess the rate at which organic matter is degraded and
integrated into the topsoil layers, a classification of humus forms has
been developed. Yet, whether different humus forms could be experimentally
linked to litter decomposition has still to be fully assessed. To
determine the relative influence of humus systems on organic matter
decomposition, we worked in two regions of the Swiss Alps (Valais and
Ticino) along elevational gradients by following a north/south exposure
design. First, we quantified humus forms macrorests proportion types by
the Ponge small-volume method (Ponge, 1984). Second, we measured
the decomposition of green tea and rooibos teabags within the Parasystems
and Terrosystems. We found that Parasystems and Terrosystems differed in
teabags decomposition rates, with a slower decomposition in Parasystems
and a faster decomposition in Terrosystems. We also observed that
elevation, and hence, vegetation type (i.e., forest versus grassland),
drives humus forms distribution with Parasystem at the alpine and
subalpine levels in Ticino. In contrast, in Valais, Parasystem were found
only at the alpine level and Terrosystems at the subalpine level. Our
results thus indicate that organic matter decomposition is influenced by
climate but also by different soil biota, for instance, highlighting more
fungal activity in the subalpine level with wooden debris and the presence
of earthworms in the less woody litters. Further analyses are however
needed to identify other variables that best correlate with variation in
decomposition processes within humus systems, such as soil decomposer’s
community composition.