Comparative recovery of soil microbial activity and invertebrate abundance and richness in abandoned and planted pastures in Southeastern Brazil

Abstract

The ecological restoration of pastures is a complex process, as these sites may suffer from degraded soil quality and reduced abundance and diversity of invertebrates. Nevertheless, their restoration can contribute to the return of essential ecosystem services, making them an important research area. To better understand the initial process of soil restoration in tropical pastures, we examined soil microbial activity, litter invertebrate abundance and species richness across a land-use gradient in southeastern Brazil. This gradient included a pasture in continuous use (PCU), three 5-year-old moderately assisted recovery (MAR) and unassisted natural recovery (UNR) pastures, and a reference forest (REF). We hypothesized that, owing to soil preparation and enhanced structural complexity, MAR (planted) sites would exhibit higher microbial activity and support a more diverse and abundant invertebrate population than UNR (naturally regenerating) sites. We also predicted that the MAR and REF sites would foster higher soil quality, tree species richness, and tree abundance, accounting for most of the variation in microbial activity and litter invertebrates. Contrary to our hypotheses, the UNR sites showed slightly better levels of microbial activity than the MAR sites, and PCU exhibited the highest levels of microbial biomass carbon, microbial respiration, and β-glucosidase. The MAR and UNR sites were similar in terms of invertebrate abundance and richness, both showing total abundance and taxonomic group numbers comparable to those of REF. We found no correlation between microbial activity and vegetation or soil quality. Only Thysanoptera and Hemiptera invertebrate groups showed a weak association with litter production and soil quality. Our findings suggest that site preparation for tree planting, which is indispensable for areas lacking natural regeneration potential, appears to temporarily disrupt the soil conditions. This implies a longer recovery period for the microbial activity. However, this is not a drawback of tree planting but rather an integral part of the process that contributes to long-term ecosystem restoration. Vegetation variables and general soil quality may have an indirect effect on microbial activity and litter invertebrates. It would be beneficial to consider additional variables to gain a more comprehensive understanding of these interactions.