2019 ASHS Annual Conference

Vineyard ecophysical variations limit vineyard efficiency in production and berry chemistry. A mechanically managed Cabernet Sauvignon (Vitis vinifera L.) vineyard was modeled to investigate the ecophysiological variability in Napa County, California, including soil electric conductivity (EC), plant water status, carbon isotopic discrimination analysis (δ¹³C), and berry primary and secondary metabolites. Plant water status can be used to delineate vineyard to homogenize grapevine physiological traits at harvest and δ¹³C is used as an alternative approach to assess plant water status without being time-sensitive as the traditional measurement in precision viticulture. An equidistant grid sampling was performed and stem water potential (Ѱ_stem), leaf gas exchange were measured weekly during the growing season, and their integrals were calculated. δ¹³C was measured at harvest, it was directly related to Ѱ_stem (R² = 0.69), stomatal conductance (R² = 0.27), carbon net assimilation (R² = 0.25), water use efficiency (R² = 0.67). Soil electric conductivity measurement only showed a relationship with plant water status at the depth of 1.5m (deep EC, R² = 0.23).The vineyard was then deliniated by k-means clustering of Ѱ_stem into two zones: Zone 1 with higher water stress, and Zone 2 with lower water stress. There was no difference between the two zones in total soluble solids, titratable acidity, and pH. Berry skin and weight were greater in Zone 2, but yield and cluster number per vine were the same between two zones. Zone 2 had higher peonidin-, malvidin-3-glucoside contents per berry, but lower tri- to di-hydroxylated anthocyanin ratio. There were no differences in berry skin flavonol content. Our results provided evidence that delineating vineyard by plant water status with δ¹³C can be a reliable assessor of vineyard water stress, as well as in assessing ecophysical variability in mechanically managed vineyards without traditional labor input in a precision viticulture approach.