Glucoproteins in particulate and mineral-associated organic matter pools during grassland restoration

Glomalin related soil proteins (GRSP) produced by arbuscular mycorrhizal fungi are important stabilizing components of soil aggregates, and consequently helping to entrap organic matter and encapsulate it from microbial decomposition. Grasslands provide excellent opportunity to study GRSP effects because arbuscular mycorrhiza responsible for GRSP production is well development on roots of grasses. Fast GRSP production will accelerate soil organic carbon (SOC) accumulation, but the contribution of GRSP to particulate organic C (POC) and mineral-associated organic C (MAOC) pool remain unclear. We investigated GRSP content and thermal stability of POC and MAOC in topsoil (0–10 cm) as dependent on grassland restoration. SOC content had a nonlinear rise tendency with grassland restoration, and SOC changes were largely dependent on MAOC (>64 %). The POC content decreased by 58 %, while the MAOC content increased by 34 % after 40 years of restoration, microbial transformation of POC plays important role for MAOC formation. The GRSP content contributed 1.7 times more to MAOC (15 %) content than to POC (9 %), but the potential accumulation of GRSP in POC was higher than that in MAOC. The GRSP in the POC pool (less protected) is more sensitive to grassland restoration than in the MAOC pool (more protected). Thermally easily decomposable and refractory organic matter was quantified in POC and MAOC. Thermal stability of MAOC was higher than POC, and GRSP contribute to increase in SOC thermal stability. The GRSP content and thermal stability of POC pool gradually decreased with grassland restoration, reflecting production of more organic matter available for microorganisms and with fast turnover. In conclusion, we must account for the role of GRSP in maintaining SOC thermal stability, and the potential for GRSP sequestration during grassland restoration.