'Concord' grapevine nutritional status and chlorosis rank associated with fungal and bacterial root zone microbiomes

Leaf chlorosis in vineyards is associated with reduced crop yields and quality. While iron (Fe) is understood to play a crucial role in chlorosis, total plant and soil Fe are not always indicative of chlorosis in grapevines. Physiology of chlorosis in vineyards has been well-studied, but the soil microbial consequences of and contributions to chlorosis have received little attention. We used next-generation sequencing (NGS) to examine the bacterial and fungal communities associated with grapevines demonstrating varying degrees of visual chlorosis symptoms. Additionally, chemical analyses of soils and grape leaves were used to explore the influence of plant nutritional status and soil chemistry on microbial community composition. Finally, factors influencing bacterial community composition were correlated with predicted bacterial community function. Leaf tissue magnesium (leaf Mg) concentrations and chlorosis rank were correlated with bacterial community composition as determined via dbRDA (distance-based Redundancy Analysis) using Bray-Curtis dissimilarities. Non-metric multidimensional scaling (NMDS) revealed a significant correlation between fungal community composition and soil Fe and pH, along with leaf N, Mg, and Ca (mg.kg^-1). Chlorosis rank was moderately correlated with KEGG Orthology (KO) terms associated with nitrogen (N) and carbon (C) metabolism in soils, while leaf Mg was associated with a spectrum of KO terms including glycosphingolipid biosynthesis, glycan degradation, transporters, and porphyrin and chlorophyll metabolism. Additionally, abundance of many bacterial operational taxonomic units was significantly correlated with leaf Mg, including those from the following orders: Rhodobacterales, Acidobacteriales, Opitutales, Sphingomonadales, Burkholderiales, Saprospirales, and Flavobacteriales. Our findings suggest grapevine chlorosis is interrelated with soil microbial community structure and function, plant nutrition, and soil chemistry.