Redução da precipitação e suas implicações na biologia do solo em áreas do semiárido paraibano

Abstract

Precipitation is one of the main abiotic factors regulating biogeochemical cycles, soil biodiversity, and ecosystem functionality. Climate projections indicate that the Brazilian semiarid region will experience a decline in rainfall over the next 100 years, leading to longer drought periods and reduced soil water availability. These changes are expected to alter soil community structure and ecosystem dynamics. In this context, the objective of this study was to quantify the physicochemical and biological attributes of soils subjected to reduced precipitation, evaluate its effects on soil microbial activity, and assess how decomposition processes may be affected under prolonged drought conditions. Additionally, the enzymatic profile of soils under water stress was investigated. For this purpose, rainfall exclusion shelters intercepting 30% and 50% of precipitation were installed in two Caatinga areas (a wetter site and a drier site) in the semiarid region of Paraíba State, both located in the Paraíba River Basin. Soil sampling was conducted every 90 days over one year (2022–2023). Microbial abundance was determined by microbial biomass carbon (C-MBC), while microbial activity was assessed through basal respiration (BR), metabolic quotient (qCO2), and β-glucosidase enzyme activity. Decomposition was evaluated by measuring plant material consumption under the combined effects of rainfall reduction and soil fauna suppression. Results showed that only soil organic matter and pH differed significantly between areas and treatments. In the wetter area, rainfall reduction increased C-MBC and BR, whereas no significant interaction was observed in the drier area. The qCO2 was higher under 50% rainfall exclusion in both areas. β-glucosidase activity was greater in the drier site; however, rainfall reduction decreased its activity in both locations, negatively affecting decomposition. Moreover, a significant interaction was found between rainfall interception levels and plant biomass consumption, with the lowest consumption recorded under 50% rainfall exclusion combined with soil fauna suppression at both sites. We conclude that reduced precipitation negatively affects soil microbial activity and nutrient cycling, although the magnitude of this impact depends on local soil characteristics. These findings provide scientific evidence to better understand how dryland ecosystems may respond to future climate projections of reduced rainfall, thereby supporting the planning of conservation strategies for these vulnerable environments.