Soil Microbial Co-Occurrence Networks Across Climate and Land Use Gradient in Southern Italy

Abstract

Despite extensive research on microbiota across land use gradients, it remains unclear if microbial co-occurrence relationships exhibit consistent patterns. Here, we assessed microbial co-occurrence networks of seven natural ecosystems—Quercus ilex forest, Fagus sylvatica forest, Abies alba forest, Mediterranean and mountain grasslands, and subalpine and Mediterranean shrublands—and five agroecosystems, including vineyards, horticulture, greenhouse, a polluted agricultural system, and an arid greenhouse. Soil chemistry, such as pH, organic carbon and total nitrogen, was characterised, and soil microbiota were profiled using high-throughput sequencing from 242 soil samples. Our results revealed that mountain grasslands had the highest organic carbon (86.4 g/kg), while the arid greenhouse had the lowest (6.1 g/kg). Mediterranean grasslands had the lowest pH of 5.79, and vineyards had the highest electrical conductivity of 0.901 dS/m. Notably, natural ecosystem networks exhibited greater modularity, with protected horticulture showing exceptionally the highest (0.937), while intensive agriculture within agroecosystems had a significantly lower modularity of 0.282. Modularity and the number of modules were positively correlated with soil P₂O₅, while network diameter, path length and clustering coefficient were correlated with soil pH. Additionally, edges and nodes number, average degree and microbial diversity were positively associated with organic carbon and total nitrogen. These findings highlight that natural ecosystems foster more complex and resilient microbial networks, underscoring sustainable land management's importance to preserve soil health and microbial diversity.