Mudanças no uso do solo impactam a decomposição foliar e a diversidade e ionoma de invertebrados de solo na Caatinga, NE, Brasil

Abstract

Land-use changes affect ecosystem health, soil productivity, and water, energy, and food resilience, particularly for smallholder agriculture in dryland landscapes. Understanding specific alterations in biological mechanisms and their responses to land-use change, across paired farms and forests and at different landscape scales, can help guide better management practices and inform strategies to restore degraded drylands. In this study, we tested the hypothesis that forest conversion in agricultural landscapes affects soil invertebrate diversity, litter decomposition, and the diplopod ionome. The research was conducted in 14 study sites, each comprising agricultural areas and adjacent remaining forests, located in the Caatinga, Northeast Brazil, during 2022 and 2023. Soil and soil fauna were sampled using soil cores, and litterbags, with and without macroinvertebrate exclusion, were used to assess litter decomposition. Active searches and transects were employed to collect diplopods and estimate their biomass, density, diversity, and ionome. Local predictors were obtained from chemical and physical analyses of the soil in the study units (forest remnants and agricultural areas), while landscape predictors were estimated from high-resolution orthomosaics generated from drone imagery, classifying seven land-cover types and calculating variables such as the proportion of natural cover, density of conserved fragments, matrix-use heterogeneity, and distance between study units at 100, 300, and 500 m scales. To address our research questions, we applied paired t-tests, GLMs, NMDS, PERMANOVA, PCA, and RDA. Our results show that conversion of forest areas to agriculture consistently impoverishes the soil invertebrate community, including diplopods, and reduces litter decomposition, with more pronounced effects at the local scale. At the landscape scale, more anthropized matrices exhibited less diverse macroinvertebrate communities in agricultural areas, while litter decomposition increased with a higher proportion of natural forest cover. Regarding the diplopod ionome, the elements Mg, Co, P, K, Mo, Cr, and Ni were found at higher concentrations in individuals from agricultural areas, with Ni, Co, and Cr positively correlated with their respective soil concentrations, and the overall ionic composition of these organisms was partially explained by Ni content. Finally, the distance between study units did not influence the ionome, diplopod diversity, soil macroinvertebrate diversity, or litter decomposition. This study reinforces that agricultural intensification in tropical dry forest landscapes affects soil biodiversity and key processes such as litter decomposition and diplopod ionic composition. Management strategies that promote the conservation of soil fauna and the maintenance of remaining forest fragments are essential to sustain the functionality and productivity of regional agroecosystems.