Xylem exudate concentrations of cofactor nutrients in grapevine are correlated with exudation rate

Xylem exudates collected from the cut canes of Vitis vin‐ifera L. var. Waltham Cross for 10 weeks around the time of budburst were analyzed for nutrient concentrations. The seasonal variations of the inorganic constituents examined phosphorus (P), calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), zinc (Zn), iron (Fe), copper (Cu), sodium (Na), and chlorine (Cl)] are presented and discussed with respect to the metabolic needs of the plant as it breaks dormancy. Of particular interest was the observation that some of the nutrients (Ca, K, Mg, Mn, Zn, and Fe) showed similar seasonal variations in their concentrations. These variations were significantly correlated with the rate of xylem exudate flow. Other essential nutrients which are not enzyme cofactors did not show this variation. We propose that these variations, similar to the previously noted variation of organic acids in grapevine xylem exudate, reflect a flow‐dependent uptake and/or remobilization of nutrients to facilitate budburst through the provision of cofactors in large quantities at the critical time.