Influence of soil physicochemistry and rhizosphere microbial communities on Pinot noir grape composition in two biodynamic vineyards

Abstract

Soil properties and rhizosphere microbial communities are increasingly recognised as critical determinants of grapevine performance and fruit composition, yet their combined influence remains underexplored in cool-climate viticulture.

This study investigated how soil physicochemical characteristics and rhizosphere microbial communities shape amino acid and phenolic compositions of Pinot noir grapes in two closely located biodynamic vineyards in Central Otago. Despite their geographic proximity, the vineyards exhibited distinct soil attributes that exerted a stronger influence on grape composition and rhizosphere community structure than rootstock. Among all soil parameters measured, pH and cation exchange capacity (CEC) showed the most consistent associations with grape metabolites. Higher soil pH and CEC were linked to increased concentrations of amino acids but lower levels of phenolic compounds in the fruit.

Analysis of interrelationships among variables indicated that soil properties influenced grape composition both directly and indirectly through their effects on rhizosphere microorganisms. Bacterial communities displayed stronger correlations with grape metabolites than fungal communities, suggesting taxon-specific pathways through which the soil environment contributes to fruit chemical expression.

These findings highlight the combined roles of soil chemistry and rhizosphere microbiota in generating vineyard-level variation in grape composition, reinforcing their importance in shaping terroir expression in cool-climate Pinot noir systems.