MICROBIAL BIODIVERSITY AND MULTIFUNCTIONALITY IN TERRESTRIAL ECOSYSTEMS: ROLE IN ECOLOGICAL PROCESSES AND RESPONSE TO DISTURBANCE

Soil performs essential functions in maintaining terrestrial ecosystems. The ability of soil to simultaneously perform these functions is defined as multifunctionality, which is strongly influenced by variations in the structure and activity of microbial communities, in turn modulated by land use and management practices. This PhD thesis aimed to clarify how different land uses and related management practices influence soil chemical, physical, and biological properties, the edaphic microbial community, contributing to understanding the ecological mechanisms that regulate multifunctionality in forest, grassland, and cropland systems in the Mediterranean area. To this end, an experiment was conducted at both field and mesocosm scales to evaluate the short-term effects of polyethylene (PE) and biodegradable (BIO) plastic mulching films, compared with an untreated control (CNT). In parallel, in the Monte Matese area (Southern Italy), adjacent sites characterized by different land uses—forest (FO), pasture (PA), and meadow (ME)—were selected. Soils were sampled four times throughout the year in relation to the main management practices. A wide range of parameters was analyzed, including: (i) soil physicochemical properties, such as water content, pH, organic matter, and nutrient content; (ii) biological indicators, including enzymatic activities involved in the main biogeochemical cycles (C, N, P, and S); and (iii) molecular parameters related to microbial community structure and interactions among taxa, assessed through co-occurrence network analysis. Finally, soil multifunctionality was evaluated using an integrated approach combining chemical and biological indicators and quantified using both the averaging approach (through the calculation of a synthetic index, SMF index) and the threshold-based approach. Regarding plastic mulching, the observed effects differed depending on the material used and the scale of analysis. In the field experiment, BIO led to a 2-fold increase in β-glucosidase activity (enzyme involved in the C cycle) relative to PE. In the mesocosm experiment, PE increased total soil carbon by approximately 1.2-fold compared to BIO and CNT treatments. Despite these specific effects, no significant short-term changes in overall soil multifunctionality were observed with either plastic film; in addition, BIO showed potential to enhance soil multifunctionality. Concerning land use, the results showed that it was a key determinant of soil microbial biomass, community structure and functions. Co-occurrence network analyses showed that FO was characterized by more complex and highly interconnected microbial networks, suggesting a more stable and resilient community structure. In contrast, PA and ME showed a progressive simplification of microbial interactions, although ME maintained high levels of diversity. Functional differences also emerged. Nutrient acquisition strategies, assessed through enzymatic stoichiometric, indicated a greater phosphorus demand in FO, whereas PA and ME showed a more balanced relationship between microbial nutrient demand and soil nutrient availability. These structural and functional dynamics were reflected in soil multifunctionality. FO and PA exhibited overall higher levels of soil functions and multifunctionality compared to ME. In particular, in PA, after six months of grazing, C and S cycles, decomposition function, and soil multifunctionality increased compared to other times. In ME, mowing practice positively affected multifunctionality, which remained stable throughout the year, leading to an increase in the nitrogen cycle, as highlighted by the threshold approach. Overall, this research demonstrates that soil multifunctionality can be maintained under low-intensity management, whether through controlled grazing, annual mowing, or sustainable mulching practices. The findings of this thesis highlights that resilience in soil systems is embedded in microbial functional diversity and the emergent properties of their communities. Together, these practices represent key factors for conserving soil functions and associated ecosystem services in Mediterranean mountain systems.