Long-term manuring enhances glomalin-soil-carbon sequestration by increasing its recalcitrance and macro-aggregation

It’s well known that agroecosystems have a great carbon sequestration potential. Within this process plays Arbuscular mycorrhizal fungi (AMF) an important role. Glomalin is a recalcitrant carbon fraction processed from AMF, its accumulation in response to fertilization is unclear. Here, we used a 30-year various fertilization experiment, including CK, NPK, NPKM, NPKS, M, NPKMR, and Fallow treatments, to observe the temporal trend of GRSP in bulk soil as well as across different aggregates. Meanwhile, we combined soil abiotic (pH, nutrients, MWD, GRSP chemical composition) and biotic (AMF biomass and diversity) properties to distinguish the mechanisms of long-term different fertilization on GRSP accumulation. Our results showed that GRSP content increased with time under both the fertilization and fallow treatment, but remained unchanged under the CK treatment. Manuring (M, NPKM, NPKMR) significantly increased GRSP content by increasing recalcitrance (aromatic) C in GRSP and mass percentage of macroaggregates (>0.25mm) compared with no (CK) and mineral fertilization (NPK) treatments. Manuring increased mean weight diameter (MWD) and GRSP content in macroaggregates (>0.25mm), relative to CK and NPK. There was a significant positive correlation between MWD and GRSP content in macroaggregates (>0.25 mm). Organic fertilizer also increased the proportion of aromatic C in GRSP, AMF biomass and diversity in cropland. Random forest and variance partitioning analysis showed that chemical composition of GRSP and aggregate stability together controlled the accumulation of GRSP. The structural equation model indicated that AMF properties regulate soil aggregate stability and composition of GRSP, which mediates the effects of fertilization on GRSP accumulation. In summary, long-term manuring promotes the GRSP accumulation, mainly be ascribed to the increased of AMF biomass, diversity, corresponding GRSP recalcitrance and aggregate stability. This study contributes to the understanding of the fertilization impacts on GRSP accumulation, and provides a feasible way forward for long-term soil carbon sequestration in sustainable agriculture.