From plant water status to wine flavonoid composition: a precision viticulture approach in a Sonoma county vineyard

Abstract

Context and Purpose of the Study- Plant water status of grapevine plays a critical role in affecting berry and final wine chemical composition. The environmental variabilities existing in vineyard system have significant impacts on plant water status, but it is challenging to individualize environmental factors from the temporal and spatial variabilities in vineyard. Therefore, there is need to monitor the ecophysical variation through utilizing precision viticulture tools in order to minimize the separation in berry composition. This study aims at delineating vineyard into different management zones based on plant water status explained by soil texture, and utilize differential harvest to equilibrate the final berry and wine composition.

Material and Method – Ecophysical variation affecting wine flavonoid composition in a Cabernet Sauvignon/110R vineyard was modeled for 2016 and 2017. Soil properties of the vineyard were proximally sensed to acquire soil texture. An equi-distant 30 m × 30 m grid was overlaid to characterize grapevine primary and secondary metabolism. The mid-day stem water potential (􀀁stem) integrals were calculated and delineated by k-means clustering into two water status zones in 2016: severely stressed (Zone 1) and moderately stressed (Zone 2). Primary metabolism, including total soluble solids, titratable acidity, pH, and berry weights; also, secondary metabolism, including anthocyanins and flavonols were measured throughout the whole season. The primary metabolism decoupled when Zone 2 reached 26 and 24 °Brix in 2016 and 2017, respectively with significantly higher °Brix values of 30 and 27 in Zone 1. Based on this decoupling in °Brix between two water stress zones, fruits were harvested differentially and vinified separately from two zones in both years.

Results – The research site received 39 mm of precipitation in 2016 and 162 mm in 2017. The surface soil texture could explain 84.20% of the variations in 􀀁stem while subsurface soil texture could explain 79.57%, depending on the loam to sandy loam contribution. In 2016, total anthocyanidins were higher in Zone 2. Di- and tri-hydroxylated anthocyanidins were more than 2× concentrated in Zone 2. Myricetin-, quercetin-, kaempferol-3-O-glucosides and total flavonols were higher in Zone 2. Proanthocyanidin subunits were also higher in Zone 2 in 2016. However, there was no difference in any flavonoid compound in 2017 except kaempferol-3-O-glucoside which was lower in Zone 2. The results indicated that in 2016, the water stress between the two zones was great enough to alter flavonoid concentration in base wine. However, in 2017, harvestcommenced earlier when two zones started separating in °Brix, and wine flavonoid concentration coalesced accordingly. This study provides fundamental knowledge to coalesce vineyard variability through linking soil texture to plant water status by using precision viticulture tools, further, their influences on flavonoid profiles in the final wine products.