Relation of aggregate stability and microbial diversity in an incubated sandy soil

Abstract. Beside physico-chemical interactions between particulate organic matter (POM), mineral particles and dissolved molecules, microbial biofilms are an important factor of aggregate stability as a proxy of soil quality. Soil primary particles are linked by the highly viscous extracellular biofilm matrix known as extracellular polymeric substance (EPS). Matrix composition depends on the community of biofilm producing species and environmental conditions affecting gene expression.

This work investigates the influence of microbial biodiversity on soil aggregate stability under controlled environmental conditions. We hypothesized that the formation of different microbial populations would cause different aggregate stabilities. Therefor a sterile sandy agricultural soil with pyrochar amendment from pine wood was incubated for 76 days in pF-bioreactors. One variant was inoculated with a soil extract, whereas the other one was infected by airborne microbes. A control soil remained unincubated. During the incubation, soil samples were taken for taxon-specific qPCR to determine the abundance of eubacteria, fungi, archaea, acidobacteria, actinobacteria, α-proteobacteria and β-proteobacteria. After incubation soil aggregates were separated for aggregate stability measurement by ultrasonication, density fractionation and SOC analysis.

As the eubacterial populations of both incubated variants reach a similar level after 49 days, the variant inoculated with the living soil extract shows a much higher fungal population compared to the air-born variant. Within the eubacterial population acidobacteria and β-proteobacteria differ significantly in their abundance between the variants. Although the variants show a strongly significant difference in eubacterial/fungal population structure, there are only marginal differences in aggregate stability.