Changes in total and functional bacterial genera following biochar application to planted soil

Abstract

Biochar has the recognized potential to sequester carbon, facilitate contaminant amelioration and enhance agricul-tural crop yield. Different types of biochar have different impacts on ecosystems, and those that are produced locally, relative to where they will be used, are considered more sustainable. It is important, therefore, to determine how the locally produced biochars affect total and functional microbial communities, especially in agronomic contexts. In this study we tested the hypotheses that biochar augmentation would: (1) increase plant yield; and (2) differentially affect total and functional microbial community composition and structure in bulk vs. rhizosphere (Trifolium pratense) soils. Triplicate randomised seedling cells of a 5% (w/w) mixture of sandy clay loam soil (26% clay, 21% silt and 53% sand), with/without locally-produced mixed broadleaf forestry biochar, and with/without 0.1 g clover seeds, were sampled destructively at 2-week intervals for 8 weeks post clover germination. Microbial DNA of bulk and T. pratense rhizos-phere soils were analysed with next-generation sequencing of the 16S rRNA gene. The results showed a statistically significant increase in plant biomass in response to biochar addition correlating to increased abundances of Armati-monadetes and Bacteroidetes specifically in the rhizosphere. Although no significant change in overall alpha diversity was observed, significant changes in abundance at the genus level were recorded particularly in the presence of biochar for a number of recognised nitrogen-fixing and plant growth-promoting bacteria, including those capable of indole acetic acid (IAA) production, plant disease suppression and degradation of toxic compounds. We conclude that although overall soil diversity may not be affected by biochar addition, key genera associated with soil health and nitrogen fixation, such as Pseudoxanthomonas, Variovorax, Pseudonocardia, Devosia, Lysobacter and Hydrogeno-phaga, increased and facilitated plant growth.