Seasonal drought surpasses the effects of irrigation regime in the microbial dynamics of grapevine rhizosphere and presents high impact in mycobiome

<underline>Background</underline> – Drought is expected to have a major impact for viticulture and other agriculture worldwide. The soil microbiome has been shown to be an important sustainable tool to mitigate the effects of climate change since its manipulation leads to increased plant resilience with little ecosystem disturbance and low cost. However, the identification of drought-induced shifts in bulk soil and rhizosphere microbiota associated with grapevine remains largely unexplored. We conducted a thorough analysis of this holobiont over two seasons in a Syrah vineyard submitted for six years to three irrigation strategies (absent, deficit and full irrigation). The study combined 16S rRNA and ITS1 based metabarcoding, physiological measurements, and edaphic and climate data. <underline>Results</underline> – Leaf water potential and stomatal conductance agreed with the irrigation regime applied but one of the studied growth seasons presented more pronounced differences in microbiome diversity and structure than the other, highlighting the effect of climate. Prokaryotic members of the community may present growth promoting properties, but a wider array of putative functionalities were identified in the mycobiome ranging from pathogenicity and biofertilization to biocontrol. Fungal members also showed higher sensitivity to drought than prokaryotes. The mycobiome enrichment in Basidiomycota, the abundance of the basidiomycetous yeast Solicoccozyma aeria and the abundance of the bacterial family Chitinophagaceae have not been previously reported for grapevine associated microbiome. <underline>Conclusions</underline> – This study highlighted the specificities of restructuring of grapevine rhizosphere microbiomes under drought stress where the irrigation strategy, climate, genotype, and soil parameters interact. The stability of the prokaryotic component may be eventually due to their functional redundancy while a lower ecological memory of fungi may be balanced by diverse functional attributes. Ultimately, our results suggest that members of the altered grapevine microbiota might contribute to grapevine survival under extreme environmental conditions, opening the door to more sustainable practices in viticulture.