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

Abstract

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.

Role of Bacterial Inoculant and Organic Matter in Improving some Soil Physical Properties and Water use Efficiency of Maize under Drought Conditions in Iraq

“…The stability values of soil aggregate significantly outperformed when adding the bacterial inoculated was 0.409% under bacterial inoculant, compared by 0.341% of that without addition (table 6). This relatively high increase in aggregate stability may explains the bacterial inoculant ability to the excretion of organic acids and polymeric materials which serve as a binder for soil particles [26]. The addition of organic fertilization had significant role in the soil aggregate stability values, as a gradual moral increase was observed for the treatments for which 1.5% was added, followed by the fertilized treatment at the level of 3% at a rate of 0.377 and 0.441%, respectively.…”

Final Response to Referee #1

“…We restructured our statistic analysis in matters of your suggestions: "The statistic analysis of microbial populations and SOC release comprised calculation of mean values, standard deviations and analysis of variance. After application of the Shapiro-Wilk test (Shapiro and Wilk, 1965) samples were assumed to be normally distributed. T-test for unequal variances (Welch test) was used to test for significant differences of class, domain and total DNA concentrations between both incubated variants (SPsoil and SPair) (Ruxton, 2006).…”

Final Response to Referee 2

“…16) L263 please note a reference on the statistics. Shapiro-Wilk test: (Shapiro and Wilk, 1965) Welch test: (Welch, 1947) Bonferroni correction: (Bonferroni, 1936) one way ANOVA: (Christensen, 1996) 17) L275-335 PLEASE explain all abbreviations like DNAEUB (is it equal to EUB338/EUB518 primer pair?) and their meaning with respect to microbial diversity within the materials and methods section.…”