Soil microbial activity along an altitudinal gradient: Vegetation as a main driver beyond topographic and edaphic factors

An altitudinal gradient in the mountains constitutes a unique 'open-lab' to examine environmental hypotheses and analyse the expected effects of global warming. The distribution of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzyme activity, microbial catabolic activity as represented by a community-level physiological profile (CLPP), and microbial functional diversity (HCLPP) within mountainous ecosystems consisting of mixed, fir and deciduous forests, as well as subalpine and alpine meadows (1260-2480 m a.s.l., Mt. Tkachiha, the Northwest Caucasus, Russia) has been studied. Concerning potential drivers, vegetation (plant projective cover, plant functional group composition, plant richness and diversity) and edaphic (soil nutrients: total and available C and N, total P, pH, texture, temperature, microbial biomass C) and topographic (elevation, slope, mean annual temperature calculated using biannual monitoring data) properties have been considered. The distribution patterns of the studied hydrolytic enzymes along an altitudinal gradient cannot be explained solely by elevation change and soil nutrient content. The activity of soil leucine aminopeptidase depends on vegetation type and graminoid abundance. beta-D-glucosidase activity was mainly driven by the quality of soil organic matter (SOM), demonstrating a significant relation with the soil C:N ratio. The chitinase and phosphatase turned out soil temperature-sensitive enzymes. The CLPP depends on the available N content in the soil. The HCLPP distribution with altitude was driven by available N and forbs abundance represented by the widest spectrum of plant families and species. An altitudinal gradient determines the spread of the vegetation zone. In turn, vegetation properties, such as plant functional group composition, species richness and diversity, play a significant role in the distribution of soil microbial activity along an altitudinal gradient that controls the decomposition of SOM and nutrient cycling. Thus, the significant role of vegetation in the distribution of soil microbial activity across a wide range of natural ecosystems and in consideration of topographic and edaphic factors has been demonstrated.