ENRICHING BACTERIAL DIVERSITY AND BENEFICIAL MICROORGANISMS BY PRECONDITIONING OF BIOCHAR MEDIUM FOR THE SUPPRESSION OF PYTHIUM DAMPING-OFF DISEASE AND PLANT GROWTH PROMOTION
2Department of Soil Chemistry, Plant Nutrition and Microbiology, ARO, The Volcani Center, Bet Dagan, Israel
3Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
Amending biochar, the solid carbon-rich co-product of biomass pyrolysis, to soil has potential environmental and agricultural benefits due to its long-term carbon-sequestration capacity and its ability to improve crop productivity. Recent studies have demonstrated that soil-applied biochar reduces the severity of foliar and soilborne diseases in various crops. However, a confounding effect was that biochar dose-dependent disease reduction and plant growth response inverted U-shaped curves may be shifted relative to each other along the biochar dose abscissa, and may also be different in their breadth (termed "Shifted Rmax Effect"). Furthermore, in some cases biochar have either minor or no effect on plant growth and health. Understanding the mechanisms will surely assist in "extending the border of biochar’s positive effects" or "improving efficacy of biochar" for disease suppression and plant growth promotion. Nevertheless, the mechanisms associated with disease suppression are currently a black box. This study tested the effects of preconditioning of growing medium with two contrasting biochars on damping-off of cucumber caused by Pythium aphanidermatum, while emphasizing the link between the preconditioned biochar-induced microbial population and soilborne-disease suppression. To illustrate the effect of biochar on bacterial community structure, we used culture-dependent and independent (PCR-DGGE and Illumina sequencing analyses of 16S rRNA genes) methods. Non-conditioned biochar substrate (NCS) did not significantly suppress damping-off as compared with the biochar-free control. On the other hand, the preconditioned biochar substrate (PCS) exhibited significantly improved disease suppression and damping-off decreased by up to 58%. Similarly, preconditioning significantly enhanced plant growth and physiology as compared with the non-conditioned treatments. Preconditioned biochar substrate significantly increased the culturable counts of general bacteria, fluorescent Pseudomonas spp., Trichoderma spp. (a well-known biocontrol agents and PGPR), and other microbes. Both culture-independent techniques showed substantial differences in root-associated bacterial community composition between biochar-amended and control soil. Bray-Curtis distance matrix based nMDS ordination demonstrated significant shifts of bacterial communities in preconditioned biochar-amended, non-conditioned biochar-amended, and unamended soil. Nevertheless, preconditioned biochar amendment caused a significant increase in microbial Shannon’s diversity and phylotype richness concurrent with increased plant growth and disease suppression. Finally, this study revealed that preconditioning of biochar medium (a simple and novel approach) enriched bacterial diversity and beneficial microorganisms that may play a key role in disease suppression and growth promotion and thus helping to "extend the borders of biochar’s positive effects" and "improve efficacy of biochar".
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