Land use effects on soil carbon retention through glomalin-mediated aggregation

• Grassland increased the content of macroaggregates, SOC and GRSP. • TG and EEG both promoting the formation and stability of macroaggregates. • TG contributed more to SOC in macroaggregates, while EEG in microaggregates. The glomalin-related soil protein (GRSP), produced by arbuscular mycorrhizal fungi, plays a critical role in soil organic carbon (SOC) storage and stabilization across terrestrial ecosystems. We examined the effects of four contrasting land-use types (bare land, cropland, grassland, and woodland) originating from the same soil matrix on GRSP dynamics, soil aggregation, and SOC accumulation. We found that grassland and woodland ecosystems exhibited significantly higher contents of macroaggregates (>0.25 mm), SOC, total nitrogen (TN), total GRSP (TG), easily extractable GRSP (EEG) and aggregate stability compared with cropland and bare land. Across all land uses, the EEG/SOC and TG/SOC ratios in Mi and SC were higher than other aggregates sizes. Correlation analyses showed that TG was significantly and positively correlated with SOC in bulk soil and macroaggregates (>2 mm), while EEG exhibited significant positive correlations with SOC in smaller macroaggregates and microaggregates. Furthermore, GRSP was strongly and positively correlated with aggregate stability, and the content of TG and the TG/SOC ratio were mainly influenced by microbial biomass carbon (MBC) and SOC. Our findings highlight the contrasting correlations of TG and EEG to SOC storage across aggregate size classes, with TG playing a more prominent role in bulk soil and large macroaggregates, and EEG more significantly associated with SOC accumulation in small macroaggregates and microaggregates. This study advances our understanding of the mechanisms by which GRSP facilitates SOC sequestration and soil aggregate formation under different land-use regimes, informing sustainable land management strategies for climate change mitigation.