Biological characterisation of humus profiles along a climatic gradient in subalpine forest soils.

A field study was conducted in subalpine spruce forests in Val di Fassa (Southern Alps, Trento, Italy) to assess the effect of climate (solar radiation and altitude) on the biological and morphological development of humus profiles. We investigated 4 sites that differed in exposure (south-facing, north-facing) and altitude (1600 m asl, 1900 m asl) allowing paired comparisons of sites (same altitude, different exposure vs. same exposure, different altitude). The morphological humus forms corresponded to Mull, Amphi, Moder and Mor following the sequence from warmer to cooler temperatures. We measured abundance, species composition and vertical distribution of microannelids as proxy for the mesofaunal activity in the humus profile as well as soil microbial parameters by denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty analysis (PLFA). Highest similarities in community structure were found to be between sites with same exposure. Along the elevation gradient to higher altitude (and therefore cooler climate) the humus forms at the south-facing sites shifted from Mull to Amphi. At the north-facing sites a shift from Moder to Mor took place. The biological characterisation of humus profiles offers insights into humus form dynamics under future warming scenarios.