Cover crops increase direct contribution of glomalin-related soil proteins to soil carbon accumulation in tropical agroecosystems

Glomalin-related soil proteins (GRSP) contribute to soil carbon accumulation both directly through carbon within the protein structure and indirectly by promoting soil aggregation. This study aimed to evaluate the direct contribution of the GRSP to C accumulation under contrasting land-use in tropical agroecosystems. A field experiment   was conducted over 9 years in Lucas do Rio Verde, Mato Grosso, Brazil. Soil samples from 0-10 cm were collected once from six treatments following soybean: fallow under tillage; fallow under no-tillage; maize (Zea mays L.); crotalaria (Crotalaria spectabilis), brachiaria (Urochloa ruziziensis); and mixed cover crops (ruzigrass, crotalaria, millet - Pennisetum glaucum L; and forage radish - Raphanus sativus L.). A native forest was used as reference and sampled without replication. The total GRSP was extracted, purified, and lyophilized, then C content associated with GRSP (C-GRSP) and soil C content were determined by dry-combustion. C and C-GRSP stocks were calculated; the direct contribution of C-GRSP to carbon accumulation was determined by calculating the ratio between the two stocks and compared using Tukey HSD test (p<0.05). The results indicated that GRSP contributes 0.58-1.62 Mg C ha^-1, which represents 2.7-4.4% of the total soil C stock. Cover crops increased C-GRSP stocks, particularly under ruzigrass and mixed crops, with ruzigrass showing the greatest contribution. Native forest had a lower relative contribution of C-GRSP (3.0%) compared the average of cover crops (3.8%), despite having the greatest C stocks (46.9 Mg ha⁻¹). These results highlight the importance of GRSP for C sequestration in agricultural systems, especially in grass monocultures.