Abstract
Adding biochar, the solid coproduct of biofuel production, to peat can enhance strawberry growth, and disease resistance against the airborne fungal pathogen Botrytis cinerea. Additionally, biochar can induce shifts in the strawberry rhizosphere microbiome. However, the moment that this biochar-mediated shift occurs in the rhizosphere is not known. Further, the effect of an above-ground infection on the strawberry rhizosphere microbiome is unknown. In the present study we established two experiments in which strawberry transplants (cv. Elsanta) were planted either in peat or in peat amended with 3% biochar. First, we established a time course experiment to measure the effect of biochar on the rhizosphere bacterial and fungal communities over time. In a second experiment, we inoculated the strawberry leaves with B. cinerea, and studied the impact of the infection on the rhizosphere bacterial community. The fungal rhizosphere community was stabilized after 1 week, except for the upcoming Auriculariales, whereas the bacterial community shifted till 6 weeks. An effect of the addition of biochar to the peat on the rhizosphere microbiome was solely measured for the bacterial community from week 6 of plant growth onwards. When scoring the plant development, biochar addition was associated with enhanced root formation, fruit production, and postharvest resistance of the fruits against B. cinerea. We hypothesize that the bacterial rhizosphere microbiome, but also biochar-mediated changes in chemical substrate composition could be involved in these events. Infection of the strawberry leaves with B. cinerea induced shifts in the bacterial rhizosphere community, with an increased bacterial richness. This disease-induced effect was not observed in the rhizospheres of the B. cinerea-infected plants grown in the biochar-amended peat. The results show that an above-ground infection has its effect on the strawberry rhizosphere microbiome, changing the bacterial interactions in the root-substrate interface. This infection effect on the bacterial rhizosphere microbiome seems to be comparable to, but less pronounced than the effect of biochar-addition to the peat. The biological meaning of these observations needs further research, but this study indicates that biochar and an above-ground pathogen attack help the plant to recruit rhizosphere microbes that may aid them in their plant growth and health.
Highlights
Biochar is the solid coproduct of a biomass pyrolysis process for the production of biofuel (Gravel et al, 2013)
It has been proposed that adding biochar to peat or soil enhances plant growth through a direct effect by nutrient addition, and by an indirect effect on the rootassociated bacteria, which shift in composition after biochar addition (De Tender et al, 2016; Egamberdieva et al, 2016)
The effects of biochar incorporation and B. cinerea leaf infection on peat chemical parameters were measured at the end of the experiment, after 13 weeks of plant growth (Table S2)
Summary
Biochar is the solid coproduct of a biomass pyrolysis process for the production of biofuel (Gravel et al, 2013). Studies show that adding biochar to growth substrate can enhance crop productivity and performance (De Tender et al, 2016), but can reduce crop susceptibility to diseases (Meller Harel et al, 2012; De Tender et al, 2016). Biochar addition has been proven to affect the soil microbial community structure (Kolb et al, 2009; Anderson et al, 2011; Lehmann et al, 2011; Abujabhah et al, 2016). The effect of biochar addition on the microbial community structure and diversity of the rhizosphere (the environment immediately surrounding the plant roots) is less well-understood, . It has been proposed that adding biochar to peat or soil enhances plant growth through a direct effect by nutrient addition, and by an indirect effect on the rootassociated bacteria, which shift in composition after biochar addition (De Tender et al, 2016; Egamberdieva et al, 2016)
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