Effect of biochar
Impact of biochar application on the root-associated bacterial community structure in fully developed greenhouse peppers
The objective of this study was to assess the effect of soil biochar amendment (3% w/w) on the root-associated bacterial community composition of mature pepper (Capsicum annuum L.) plants. Pyrosequencing of barcoded 16S rRNA amplicons from the rhizoplane of control and biochar-amended samples generated a total of 20,142 sequences, 85-91% of whom were affiliated with the Proteobacteria, Bacterioidetes, Actinobacteria, and Firmicutes phyla. The relative abundance of the Bacterioidetes phylum increased from 12% to 30% in the biochar-amended samples, while that of the Proteobacteria decreased from 69% to 44%. Flavobacterium was the most significant biochar-induced genus. The relative abundance of this group increased from 4.2% of total root-associated OTUs in control samples to 19.6% in the 3% biochar amended samples, explaining to a great extent the proliferation in the relative distribution of the Bacteroidetes phylum. Additional biochar-induced genera included chitin and cellulose degraders Chitinophaga (Bacteroidetes) and Cellvibrio (Betaproteobacteria) and the aromatic degraders Hydrogenophaga and Dechloromonas.
Adding biochar to soil has environmental and agricultural potential due to its long-term carbon sequestration capacity and its ability to improve crop productivity. Recent studies have demonstrated that soil-applied biochar promotes the systemic resistance of plants to several prominent foliar pathogens. One potential mechanism for this phenomenon is root-associated microbial elicitors whose presence is somehow augmented in the biochar-amended soils. The objective of this study was to assess the effect of biochar amendment on the root-associated bacterial community composition of mature sweet pepper (Capsicum annuum L.) plants. Molecular fingerprinting (denaturing gradient gel electrophoresis and terminal restriction fragment length polymorphism) of 16S rRNA gene fragments showed a clear differentiation between the root-associated bacterial community structures of biochar-amended and control plants. The pyrosequencing of 16S rRNA amplicons from the rhizoplane of both treatments generated a total of 20,142 sequences, 92 to 95% of which were affiliated with the Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes phyla. The relative abundance of members of the Bacteroidetes phylum increased from 12 to 30% as a result of biochar amendment, while that of the Proteobacteria decreased from 71 to 47%. The Bacteroidetes-affiliated Flavobacterium was the strongest biochar-induced genus. The relative abundance of this group increased from 4.2% of total root-associated operational taxonomic units (OTUs) in control samples to 19.6% in biochar-amended samples. Additional biochar-induced genera included chitin and cellulose degraders (Chitinophaga and Cellvibrio, respectively) and aromatic compound degraders (Hydrogenophaga and Dechloromonas). We hypothesize that these biochar-augmented genera may be at least partially responsible for the beneficial effect of biochar amendment on plant growth and viability.