A desertificação da caatinga: impactos na estrutura da comunidade de fungos e na atividade enzimática do solo

Abstract

The loss of productive capacity in soils used for agricultural and livestock purposes has increased worldwide, mainly due to overexploitation and the adoption of inadequate management practices. Soil compaction, salinization, erosion, and reduced plant biomass growth are common consequences of soils undergoing desertification. However, the impacts of this process on soil fungal communities are still poorly understood. Several restoration techniques have been developed to mitigate or reverse soil degradation. Therefore, the hypothesis tested was that desertification alters soil fungal diversity, the composition of fungal groups, and soil enzymatic activity, and that environmental restoration techniques—such as grazing exclusion, cover crop planting, and reforestation—can restore and increase soil fungal diversity in degraded areas of the Brazilian semiarid region. Soil samples (0–10 cm) were collected from four desertification nuclei in northeastern Brazil and classified into three scenarios: (i) areas with native Caatinga vegetation, (ii) areas affected by desertification, and (iii) areas under environmental restoration. Soil samples were subjected to physical (aggregate stability), chemical (C and N content, pH, and salinity), and biological analyses (total organic carbon, microbial carbon, enzymatic activity and stoichiometry, glomalin content, and fungal diversity through DNA sequencing of the ITS region). Amplicon sequencing analyses were performed using QIIME 2, and uni- and multivariate analyses were conducted in RStudio to integrate the datasets. Extracellular enzymes were sensitive to degradation and restoration processes across all nuclei. Overall, the degradation process did not promote significant changes in alpha diversity but caused shifts in beta diversity in all nuclei. The fungal genera Aspergillus and Penicillium showed higher relative abundance in native vegetation and restoration areas, whereas Curvularia was more abundant in degraded areas. Both soil degradation and restoration appear to favor the emergence of specialist groups under different environmental scenarios. Enzymatic activity, microbial carbon, glomalin content, and soil C and N levels showed strong positive correlations with the fungal community structure. Co-occurrence network analysis demonstrated that both soil degradation and environmental restoration promote shifts in dominant fungal groups, which establish new and complex interaction networks. Overall, soil degradation alters the functional structure of fungal communities, characterized by an increase in phytopathogenic groups and a reduction in saprotrophic groups.