The microbiomes and metagenomes of forest biochars

Abstract

Biochar particles have been hypothesized to provide unique microhabitats for a portion of the soil microbial community, but few studies have systematically compared biochar communities to bulk soil communities. Here, we used a combination of sequencing techniques to assess the taxonomic and functional characteristics of microbial communities in four-year-old biochar particles and in adjacent soils across three forest environments. Though effects varied between sites, the microbial community living in and around the biochar particles had significantly lower prokaryotic diversity and higher eukaryotic diversity than the surrounding soil. In particular, the biochar bacterial community had proportionally lower abundance of Acidobacteria, Planctomycetes, and β-Proteobacteria taxa, compared to the soil, while the eukaryotic biochar community had an 11% higher contribution of protists belonging to the Aveolata superphylum. Additionally, we were unable to detect a consistent biochar effect on the genetic functional potential of these microbial communities for the subset of the genetic data for which we were able to assign functions through MG-RAST. Overall, these results show that while biochar particles did select for a unique subset of the biota found in adjacent soils, effects on the microbial genetic functional potential appeared to be specific to contrasting forest soil environments.

Figure 1. Relative contributions of archaea and bacterial phyla to total prokaryotic community DNA extracted from soil and biochar samples from three forest sites.

*indicate phyla with significant (p < 0.05) differences in abundance between biochar particles and soil samples for the three replicates at each site.

Figure 2. Principal coordinates analysis of (a) Bray-Curtis and (b) UniFrac distances of 16S amplicon data and (c) Bray-Curtis and (d) UniFrac distances of 18S amplicon data.

White points are soil samples, grey black points are biochar samples, and shapes indicate forest site. Treatment effects (assessed through PERMANOVA) are shown in Table 2. Vectors represent soil chemistry variables that were significantly (p < 0.05) correlated with the PCoA results.

Figure 3. Relative contributions of eukaryotic groups to total eukaryotic community DNA extracted from soil and biochar samples from three forest sites.

*indicate groups with significant (p < 0.05) differences in abundance between biochar particles and soil samples for the three replicates at each site.

Figure 4. Level 2 Subsystems with the largest differences in relative abundance between soil and biochar samples at a single site.

Values are differences in z-scores (relative abundance compared to the mean) between soil and biochar samples for each site. Negative values (orange boxes) indicate higher abundance in biochar metagenomes and positive values (blue boxes) indicate higher abundance in soil metagenomes.