Fertilizations and aggregate sizes regulate the roles of dissolved organic matter and GH1 beta_glucosidase community in the mineralization of organic matter

Soil organic matter mineralization, closely related to climate change, are largely controlled by labile organic fractions and functional microbial community. Regulation of fertilizations and aggregate sizes on the roles of dissolved organic matter (DOM) and microbial community of typical beta_glucosidase encoding genes (glycoside hydrolase family 1, GH1) in organic matter mineralization remains unclear. The mineralization of organic matter in large macroaggregates (LMA), small macroaggregates (SMA), and microaggregates (MI) from an Ultisol treated with long_term no fertilizers (Ck), chemical fertilizers (NPK) and animal manure (AM) was observed in this study. The concentration and structure of DOM, the activity of beta_glucosidase, and the abundance, diversity, and composition of GH1 beta_glucosidase community were investigated. The cumulative CO2_C emissions followed the sequence Ck, NPK, AM in each aggregate, and the order LMA, SMA, MI in each fertilization treatment. The concentration of DOM increased in the fertilized and the small aggregates, while the structural complexity of DOM followed the opposite trend. The activity of beta_glucosidase in the fertilized and the smaller aggregates was higher than that in the unfertilized and the larger aggregates, and the abundance and diversity of GH1 beta_glucosidase community generally showed the same trend. The fertilizations significantly changed the GH1 beta_glucosidase community structure of bacteria and fungi, while the aggregate sizes only markedly shifted the fungal GH1 beta_glucosidase community structure. The dominant classes of the GH1 beta_glucosidase community in the soil aggregates were Actinobacteria, Alphaproteobacteria, Gammaproteobacteria, Flavobacteria, Eurotiomycetes, and Sordariomycetes. Redundancy analysis showed that the GH1 beta_glucosidase community of bacteria and fungi in the soil aggregates were primarily regulated by the DOM concentration and pH. Moreover, structural equation modelling revealed that the fertilizations and the aggregates mainly regulated the beta_glucosidase activity and DOM concentration and then the abundance and diversity of the GH1 beta_glucosidase community in controlling organic matter mineralization.