LAUSR

Abstract The introduction of nitrogen-fixing trees in a mixed system with Eucalyptus can improve soil chemical and microbiological properties, especially C-N contents and microbial diversity. However, the effects of this forest management on soil mesofauna remain poorly understood. Thus, we hypothesized that higher mesofauna abundance and diversity, microbial activity and soil quality are greater in the mixed plantation of Eucalyptus grandis and Acacia mangium than in pure Eucalyptus plantations. We aimed at evaluating the density and diversity of soil mesofauna, and its interaction with microbiological and chemical soil attributes in pure Acacia mangium (AC), Eucalyptus grandis (EU) and mixed E. grandis and A. mangium plantations (M). We also intended to adapt a general indicator of soil quality for such forest plantations. It is common for soil macrofauna studies to employ the general indicator of soil quality (GISQ). Since our study did not comprise soil macrofauna, but included only soil mesofauna, we adapted the GISQ to contemplate mesofaunal attributes, introducing the great interaction between them and microorganisms. Soil samples (0–5 cm) were collected at 2015, when trees were six years old. The only faunal order to show a higher density is Diplura. Our results show that the metabolic quotient (qCO2) is lower in AC, while the cation exchange capacity (CEC), H + Al and soil moisture are higher in AC than in EU and M. We verified that intercropping of A. mangium in E. grandis improves soil quality and our indicator showed that soil mesofauna correlates with soil microbial attributes density. Thus, our results provide a novel evidence of ecological interactions between soil mesofauna and microorganisms under field conditions for pure and mixed plantations of Eucalyptus grandis and Acacia mangium.