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

Abstract

Knowledge on soil aggregation and microbial-driven soil C dynamics at the aggregate scale is beneficial for long-term 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.