Aggregate-related changes in living microbial biomass and microbial necromass associated with different fertilization patterns of greenhouse vegetable soils

Knowledge on soil aggregation and microbial-driven soil C dynamics at the aggregate scale is beneficial for longterm sequestration of C in greenhouse vegetable production (GVP) systems. Here, we used an eight-year fertilization experiment to compare the effects of organic vs. chemical fertilization on soil aggregate stability, as well as living microbial biomass, microbial necromass, and soil C dynamics at the aggregate scale. Relative to chemical fertilization treatment, organic amendments (e.g., manure and/or straw) could improve soil physical quality (as indicated by the value of mean weight diameter), increase microbial biomass and residues, as well as enhance the contributions of microbes to soil organic C (SOC) accumulation within large macroaggregates, small macroaggregates, microaggregates, and silt/clay fractions. Microbial biomass and residues were unevenly distributed among aggregates under different fertilization patterns, i.e., organic amendments made microbial biomass and fungal residues enriched from in silt/clay fractions to in macroaggregates. The low proportions of microbial residue C in SOC in microaggregates demonstrated that the microhabitat of microaggregates limits microbial necromass contributions to SOC accumulation. The changes of microbial biomass were closely related to extractable organic C (EOC), while the variations of fungal and bacterial residues were intimately associated with its corresponding microbes (i.e., fungal and bacterial PLFAs) and enzymes. Moreover, microbial associated ratios (e.g., fungal/bacterial PLFAs) were largely influenced by aggregates and strongly associated with soil chemical associated ratios (e.g., EOC/EON). Our findings provide useful insights on soil microbial-driven C dynamics at the aggregate scale in GVP systems under different fertilization patterns in China.

Automated summary

The use of organic fertilizers can improve soil physical properties, increase microbial biomass and residues, and enhance the contributions of microbes to soil organic carbon accumulation. Microbial biomass and residues are unevenly distributed among aggregates under different fertilization patterns, which affects their contribution to soil organic carbon.