Cover crop-based under-row dry mulching enhances phyllosphere and rhizosphere microbial biodiversity in a non-irrigated vineyard

Background: In viticulture, temporary cover crops and organic mulching are sustainable practices that enhance biodiversity, improve soil fertility, and strengthen grapevine health/resilience, particularly in Mediterranean regions. However, their impact on microbial communities associated with grapevines in non-irrigated vineyards remains largely unexplored. Inter-row soil management included a cereal-based cover crop (CC), a mixed cereals, legumes and brassicas cover crop (MC), and a control with alternating soil tillage and spontaneous grass (GT). In spring, cover crops were terminated to form a dry mulch under the vine rows. Results: At veraison, under-row dry mulching significantly maintained higher soil water availability and reduced soil temperature by approximately 2.5 °C compared to the GT treatment. CC, in particular, enhanced grapevine physiological performances. These different soil conditions positively shaped the rhizosphere microbiome by maintaining higher microbial richness and promoting nutrient-cycling microorganisms (e.g., Bradyrhizobium sp., Nitrospira japonica) in both CC and MC. In contrast, the GT treatment selectively favored drought-tolerant plant growth-promoting rhizobacteria (PGPR) taxa such as Bacillus zanthoxyli, Gaiella occulta, Roseiflexus sp., Pseudarthrobacter sp., and Paenibacillus sp. In the phyllosphere, the abundance of Erysiphe necator, the powdery mildew agent, was lower in CC and MC, which also showed a higher presence of Aureobasidium pullulans, a species reported in the literature as a potential biocontrol agent. Conclusions: Our results suggest that under-row dry mulching, by modifying soil conditions, can have a positive effect on grapevine microbial richness and biodiversity during the dry summer period, serving as an indicator of improved vineyard agroecosystem health and sustainability.