The “biochar effect” depicts a phenomenon in which biochar (a
byproduct of biomass pyrolysis) soil amendment promotes plant growth and suppresses
foliar disease. Although the “biochar effect” has been observed in numerous
studies, the mode of action that explains this phenomenon is still a mystery. In
this study, we applied a holistic approach in order to decipher the “biochar
effect” in a comprehensive greenhouse experiment. We monitored tomato plant
development by analyzing physiological parameters, minerals and metabolic profiles
as well as their resistance to the foliar fungal pathogen Botrytis cinerea,
with and without biochar (1% wt/wt). In tandem, rhizosphere bacterial community
succession was analyzed by high-throughput sequencing and by carbon-source
utilization profiling. The integrative data analysis revealed that plant
physiological age has a primary effect on plant nutrition parameters.
Nevertheless, significant effects of biochar on plant productivity and pathogen
resistance were observed, despite only minor effects on plant minerals and
metabolic composition. Although we were unable to detect significant taxonomic
differences among root-associated bacterial communities, the biochar amendment resulted
in a significant increase in bacterial diversity, mainly at lower taxonomic
levels. This diversity increase was clearly demonstrated by un-weighted uniFrac
analysis and was correlated to an overall shift in carbon-source utilization
profiles. These results suggest that “biochar effect” may be at least partially
explained by increasing bacterial and functional diversity in the rhizosphere, thus
underlying the key role of soil bacterial diversity in ecosystem functionality.
