GLOMALIN-RELATED SOIL PROTEINS AS MICROBIAL INDICATOR OF SOIL CARBON STABILIZATION UNDER COVER CROP MANAGEMENT

Glomalin-related soil proteins (GRSP), produced by arbuscular mycorrhizal fungi, have been increasingly recognized as key microbial compounds involved in soil organic carbon (SOC) dynamics, yet their relevance as indicators of soil carbon stabilization remains poorly constrained. Here, we assessed difficultly extractable GRSP (DE-GRSP) as a microbial indicator of soil carbon stabilization under contrasting cover crop management in tropical agroecosystems. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) from five treatments following a soybean rotation: fallow; ruzigrass (Urochloa ruziziensis); crotalaria (Crotalaria spectabilis); ruzigrass + crotalaria; and a cover crop mix (ruzigrass, crotalaria, millet – Pennisetum glaucum L., and forage radish – Raphanus sativus L.). DE-GRSP contents (mg g⁻¹), particulate (POC) and mineral-associated organic carbon (MAOC) were determined. In the topsoil layer (0–10 cm), DE-GRSP contents differed significantly among cover crop treatments, ranging from 4.4 mg g⁻¹ (fallow) to 6.5–7.0 mg g⁻¹ in ruzigrass, ruzigrass + crotalaria, and the cover crop mix, corresponding to increases of up to ~50% (Tukey, p<0.05). No significant differences among treatments were detected at deeper soil layers. Pearson correlations showed significant positive relationships between DE-GRSP and MAOC across soil depths (R² = 0.56, 0.49 and 0.48 for 0–10, 10–20 and 20–30 cm, respectively). In contrast, associations between DE-GRSP and POC weakened with depth and became non-significant in the 20–30 cm layer. These findings suggest that DE-GRSP provides a useful microbial proxy for assessing soil carbon stabilization and soil health responses to cover crop management.