The Composition of Bleeding Sap from Thompson Seedless Grapevines as Affected by Nitrogen Fertilization

Abstract

Bleeding sap from field-grown Thompson Seedless grapevines fertilized with ammonium nitrate at 0 (control), 112, 448, and 672 kg N/ha was collected at the initiation of budbreak in 1976 and 1977 and analyzed for different nitrogenous compounds, sugars, total dry matter, pH, and cations. Glutamine was the predominant nitrogen compound in the sap, accounting for slightly over half the total soluble nitrogen. Amino acids, nitrate, and ammonia respectively comprised 10 to 20%, 16 to 37%, and 2 to 7% of the total soluble nitrogen in bleeding sap. Of the 18 amino acids found in the sap, the most abundant were glutamic acid, aspartic acid, phenylalanine, valine, threonine, and serine. The concentration of amide, amino, ammonia, and total nitrogen, as well as total dry matter in sap was generally greater for nitrogen-fertilized vines than for unfertilized vines. Nine sugars were detected in the bleeding sap. Alpha- and beta-glucose were the main sugars, followed by fructose, sucrose, ribose, sorbitol, and inositol. Two sugars remain unidentified. Potassium was the main cation in the sap, followed by Ca, Mg, Na, and Zn. There were no qualitative or quantitative differences between fertilized and unfertilized vines in the sugars and cations in bleeding sap. The pH of the sap ranged from 5.7 to 6.9, with no consistent difference between nitrogen treatments.