The microbiomes and metagenomes of forest biochars.

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 ß-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.

Biochar mitigates negative effects of salt additions on two herbaceous plant species.

Addition of pyrolyzed biomass ("biochar") to soils has commonly been shown to increase crop yields and alleviate plant stresses associated with drought and exposure to toxic materials. Here we investigate the ability of biochar (at two dosages: 5 and 50 t ha(-1)) to mitigate salt-induced stress, simulating road salt additions in a factorial glasshouse experiment involving the broadleaved herbaceous plants Abutilon theophrasti and Prunella vulgaris. Salt additions of 30 g m(-2) NaCl to unamended soils resulted in high mortality rates for both species. Biochar (Fagus grandifolia sawdust pyrolyzed at 378 °C), when applied at 50 t ha(-1) as a top dressing, completely alleviated salt-induced mortality in A. theophrasti and prolonged survival of P. vulgaris. Surviving A. theophrasti plants that received both 50 t ha(-1) biochar and salt addition treatments showed growth rates and physiological performance similar to plants without salt addition. Biochar treatments alone also substantially increased biomass of P. vulgaris, with a ∼50% increase relative to untreated controls at both biochar dosages. Biochar did not significantly affect photosynthetic carbon gain (Amax), water use efficiency, or chlorophyll fluorescence (Fv/Fm) in either species. Our results indicate that biochar can ameliorate salt stress effects on plants through salt sorption, suggesting novel applications of biochar to mitigate effects of salinization in agricultural, urban, and contaminated soils.