N, P, and K Supply to Pinot noir Grapevines: Impact on Berry Phenolics and Free Amino Acids

Abstract

Understanding the direct role that macronutrient supply (N, P, and K) has on berry chemistry was evaluated in Pinot noir grapevines grown in sand culture. Self-rooted Pinot noir vines were grown for three years with either full nutrition (Control) or three reduced levels of either N, P, or K supply while holding all other nutrients constant. Vines were managed to minimize differences in vine water status (altering irrigation to achieve similar daily soil moisture content) and fruit cluster solar exposure (altering leaf pulling to achieve similar cluster irradiance) due to varying nutrient supply so that indirect effects on berry chemistry could be largely eliminated. Berry chemistry was evaluated in the second and third years after different nutrient supply treatments were imposed. Results showed that low N, but not low P or K, altered berry free amino acid (FAA) and phenolic profiles. Low N supply reduced FAA and yeast assimilable nitrogen (YAN) in both years by up to 70% and altered certain FAAs more than others, thus changing berry FAA profile. The concentration of sugars, anthocyanins, and flavonol-glycosides increased in low N vines during the third season, but the increase in sugars and anthocyanins was attributed to the decline in berry size that year. Condensed tannins and total phenolic acids were increased in low N vines across both years, independent of changes in berry size. Results indicated that low N supply altered YAN to the greatest degree, while anthocyanin enhancement did not occur until yield and berry size were also reduced. Increased concentrations of tannins and phenolic acids in berries occurred in response to low N supply independent of reductions in yield and berry size.