pH is the primary determinant of the bacterial community structure in agricultural soils impacted by polycyclic aromatic hydrocarbon pollution

Abstract

Acidification and pollution are two major threats to agricultural ecosystems; however, microbial community responses to co-existed soil acidification and pollution remain less explored. In this study, arable soils of broad pH (4.26-8.43) and polycyclic aromatic hydrocarbon (PAH) gradients (0.18-20.68 mg kg^-1) were collected from vegetable farmlands. Bacterial community characteristics including abundance, diversity and composition were revealed by quantitative PCR and high-throughput sequencing. The bacterial 16S rRNA gene copies significantly correlated with soil carbon and nitrogen contents, suggesting the control of nutrients accessibility on bacterial abundance. The bacterial diversity was strongly related to soil pH, with higher diversity in neutral samples and lower in acidic samples. Soil pH was also identified by an ordination analysis as important factor shaping bacterial community composition. The relative abundances of some dominant phyla varied along the pH gradient, and the enrichment of a few phylotypes suggested their adaptation to low pH condition. In contrast, at the current pollution level, PAH showed marginal effects on soil bacterial community. Overall, these findings suggest pH was the primary determinant of bacterial community in these arable soils, indicative of a more substantial influence of acidification than PAH pollution on bacteria driven ecological processes.

Figure 1

Relationship between (A) soil pH, (B) PAH and bacterial diversity as measured by the Chao 1 estimator.

Figure 2. Canonical correspondence analysis (CCA) biplot of bacterial 16S rRNA genes in the arable soils showing regulating factors and samples.

C/N, ratio of total carbon to nitrogen.

Figure 3. Correlations between soil pH and relative abundances of dominant bacterial phyla.

Linear regressions were used to describe the relationship between the taxa’s relative abundances and pH.

Figure 4. Class-level composition of Acidobacteria.

The samples are arranged by their pH values.

Figure 5. Heatmap of dominant phylotypes which were selected if their relative abundance accounted for >2% of any library.

Rows representative of phylotype were centered and clustered based on Euclidean distance. The numbers at the bottom of the heatmap indicate the pH value of each sample.