Soil quality and invertebrate dynamics in sandy soils under different land-use systems and seasonality

Abstract

Fragile tropical sandy soils are highly susceptible to degradation, yet how land-use systems (LUS) and seasonality interact to maintain their ecosystem services remains poorly understood. This study addressed this question by evaluating the soil functional integrity of four LUS in Southeastern Brazil: Forest Fragment (FF), Coffee Monoculture (CM), Vegetable Cultivation (VC), and an 8-year-old Agroforestry System (AFS). We integrated total organic carbon (TOC) fractions, acidity, cation exchange capacity (CEC), aggregate stability, and macroinvertebrate community structure across rainy and dry seasons. Soil was sampled (0 – 0.05 m) using both disturbed and undisturbed (monoliths) methods. Results indicated that organic matter dynamics, interacting with mineral texture and moisture, dictate nutrient storage potential. FF and CM exhibited high structural stability and resilient CEC, effectively buffering seasonal oscillations. Conversely, VC and AFS showed lower physical stability and degraded CEC. However, managed systems supported higher invertebrate richness, creating niches for opportunistic groups such as Acari and Isopoda, consistent with the Intermediate Disturbance Hypothesis. Multivariate analysis identified TOC, Particulate Organic Carbon (POC), pH, and clay content as the most sensitive sustainability indicators. Neither our initial hypothesis, that agricultural systems maintain forest-like integrity, nor that seasonality is negligible were corroborated. AFS management must prioritize Mineral-Associated Organic Carbon (MAOC) accumulation to enhance long-term sustainability and diminish dissimilarity from FF. We conclude that our multidimensional assessment provides a robust diagnosis for restoration strategies in fragile tropical landscapes, promoting functional maturity through reduced plant spacing and N-fixing species enrichment.