Abstract
Humus forms are the morphological results of organic matter decay and distribution in the topsoil, and thus important indicators for decomposer activities in forest ecosystems. The first aim was to examine if humus forms are suitable indicators of microbiological properties of the topsoil in a high mountain forest (Val di Rabbi, Trentino, Italian Alps). The second aim was to predict microbiological parameters based on the topsoil pH value on two slopes of the study area (ca. 1200-2200 m a.s.l.). We investigated humus forms and determined pH values and microbiological parameters (enzymatic activities, carbon/nitrogen (C/N) ratio and the ratio of bacterial/archaeal abundance) of the uppermost mineral horizon. The results reveal significant correlations between pH value and microbiological parameters (except for bacterial/archaeal abundance), which enable upscaling to the landscape scale using linear models. Based on a random forest with kriging of model residuals, predictive maps of humus form, pH value and microbiological parameters show that decomposition processes in our study area correspond with the topography. As compared to locations on south-facing slopes or close to the valley bottom, locations on north-facing slopes or close to the upper treeline exhibit Moder (scarcely Mull or Amphimull), more acidic topsoil (around pH 4), a lower activity of leucine-aminopeptidase, a lower ratio of alkaline/acid phosphomonoesterase activity and a higher soil C/N ratio (above 20). Our results suggest a high potential of humus forms to indicate soil microbiological properties in a high mountain forest. Together with the pH values of the topsoil, humus forms proved to be a useful tool as a basis for predictive maps of leucine-aminopeptidase activity, ratio of alkaline/acid phosphomonoesterase activity and C/N ratio of the mineral topsoil.
Highlights
The humus form is an important indicator for decomposition in terrestrial ecosystems [1,2].Humus forms are the morphological results of different biological activities in the topsoil
A high soil biological activity as derived from a well-structured mineral topsoil was connected with mull-indicating enchytraeid species at southern slope exposure, whereas a low soil biological activity indicated by a poorly structured mineral topsoil was connected with moder-indicating enchytraeid species at northern slope exposure [9]
The significant correlations that we found between pH values, C/N ratio and enzyme activities correspond to the study of Leifeld and von LĂźtzow [59], who found that microbial soil organic matter decomposition depended on pH and substrate C/N ratio rather than on inherent chemical substrate properties
Summary
The humus form is an important indicator for decomposition in terrestrial ecosystems [1,2]. Humus forms are the morphological results of different biological activities in the topsoil. They thereby reflect the composition of the decomposer community [3]. Previous studies illustrated a strong correlation between the spatial distribution of enchytraeid species, humus forms and pH values of the topsoil (e.g., [5,6,7]), which has been shown for high mountain environments [8]. Extensive information on forest humus forms in a high mountain area can be used to upscale the spatial distribution of enchytraeid species to the landscape scale [9]. A high soil biological activity as derived from a well-structured mineral topsoil was connected with mull-indicating enchytraeid species at southern slope exposure (in case of sufficient soil moisture), whereas a low soil biological activity indicated by a poorly structured mineral topsoil was connected with moder-indicating enchytraeid species at northern slope exposure [9]
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