Selection of soil biochemical indicators according to seasonal variation and vegetation cover for long-term soil monitoring in a mountain valley of the Alps

Abstract. The complexity of soil organic matter and the multifunctional role of its components on soil processes make the characterization of soil ecological status challenging. Due to its ready responsiveness to environmental changes, the soil microbial community has gained increasing attention for its relationship to the dynamics of C pools and soil chemical and physical processes. Its activity can be monitored by the enzymatic profile, which enables the detection of early changes in soil status, supported by direct or indirect measurement – e.g., by double-stranded DNA (dsDNA) – of microbial biomass and parameters, such as dissolved fractions of C and N, which are linked to soil activity as rapidly available energy sources. This study analyzed the seasonal response of these indicators in a subalpine ecosystem, using sampling date and vegetation cover as predictors capable of capturing long-term and short-term changes in the ecosystem, respectively. Most of the bioindicators showed higher values in the warmest and least rainy summer season. In the cold season, two distinct trends were evident: the values of dsDNA and enzyme activities decreased to their minimum in early winter and rose to their maximum in late winter, while those of soil organic matter (SOM), dissolved C, and N continued to decline until the end of winter. The study also found that the dynamics of SOM in the woodland and meadow ecosystems differed, with the former achieving the highest SOM content during the summer period of greatest plant and faunal activity. Overall, this study suggests that the use of bioindicators and high-throughput techniques can contribute to improving soil quality assessment and monitoring. Additionally, they can be used to characterize humus forms and motivate the preservation of Alpine meadows and surrounding wooded habitats for their non-wood products.