Long-term Dynamics of Nitrogen and Carbohydrate Reserves in Woody Parts of Minimally and Severely Pruned Riesling Vines in a Cool Climate

Abstract

Seasonal dynamics of reserve nitrogen (N) over five years and nonstructural carbohydrates over three years were monitored at six vine phenological stages in one-, two-, or older than two-year-old wood fractions of minimally (MP) and severely pruned (VSP) Riesling (Vitis vinifera L.) under cool-climate conditions. Levels of reserve nitrogen were highest in all woody fractions and both pruning systems at leaf fall, dormancy, and budbreak and lowest at bloom, bunch closure, and veraison. In general, N-concentrations were lower in older wood fractions. The magnitude of N-mobilization between budbreak and bunch closure and N-replenishment after veraison was higher for MP vines than for VSP vines and correlated with leaf area formation and leaf area loss, respectively. During the observation period, MP attained higher concentrations of N at most sampling dates in all wood fractions as compared with the VSP system, with the greatest differences in 2002 and 2003. Over a five-year period, N-concentration at veraison declined in both systems, which may have been related to the long-term trend in seasonal plant water status. Changes in dry matter and total nonstructural carbohydrates (TNC) in different wood fractions followed a similar general pattern as changes in N, but mobilization and replenishment occurred at earlier phenological stages. Concentrations in glucose, fructose, and sucrose decreased to almost the lowest values during the season at budbreak and increased again before leaf fall, whereas starch degradation occurred after budbreak and its re-formation between bunch closure and veraison. Minimum TNC concentration, usually observed between full bloom and bunch closure, increased with age of the woody fraction but decreased over the three seasons for all fractions and both systems. With the exception of 2001, MP had slightly lower concentrations in TNC and its component sugars for most sampling dates.