Dynamic changes in the strawberry rhizobiome in response to biochar

The interaction of soil-borne microorganisms with the plant root is crucial for plant growth and health. This complex microbial community is called the rhizobiome and can constitute up to 109 microbial organisms per gram of soil. Within our research, we investigated the effects of biochar peat amendment on the rhizobiome of strawberry. Biochar is the solid coproduct formed during pyrolysis of biomass for biofuel production. Strawberry plants were grown for three months in peat amended with 0 or 3% dry weight biochar produced from holm oak in the frame of the FP7-Fertiplus project. After 12 weeks of growth, strawberry leaves were infected with Botrytis cinerea. The composition of the bacterial and fungal rhizobiome was studied during the growing season using 16S rRNA gene (V3-V4) and ITS2 amplicon sequencing. We showed that addition of biochar to peat induced changes in the strawberry root microbiome. Temporal profiling of the taxonomic shifts showed that the rhizosphere microbiome stabilised after six to nine weeks for bacteria, while the fungal community only changed in composition and diversity within the first week of plant growth. Biochar addition induced shifts in the bacterial composition of the strawberry rhizosphere from week six of plant growth onwards, whereas the fungal community wasn’t affected by the addition of biochar to the peat. These shifts in the bacterial composition due to biochar amendment were linked with increased plant growth and disease resistance, which might partly be explained by the higher microbial diversity observed in the rhizobiome of biochar-amended peat.. Notably, biochar amendment raised the relative abundance of agents described for their biocontrol activity such as Bdellovibrio, Haliangium and Rhodanobacter, which might partly explain the increased resistance against B. cinerea infection. Complementary, only small changes in the chemical composition of the peat were observed by the addition of biochar, confirming that the observed plant growth and health promotion was mostly driven by micro-organisms in the rhizosphere.