Characteristics of chemical components in the trunk xylem sap of pine trees by means of a centrifugation collection method.

Abstract

Knowledge of the characteristics of chemical components transported in the xylem sap of trunks remains deficient and limited because no appropriate method exists to extract the xylem sap from this part of the tree. We thus explored the differences in xylem sap components extracted by means of centrifugation and water displacement methods and depicted the level and behavior of chemical components in the xylem sap of trunks and branches of different aged trees from a pine forest in northern China. There were no significant differences between the two methods with respect to nitrogen (N) compounds and inorganic ions in the xylem sap. Potassium concentrations obtained by the methods were similar and consistent with the values obtained from earlier publications on woody species. This suggests that contamination of the xylem sap by the centrifugation method is negligible, and this method would be a reliable and robust tool for collection of the trunk xylem sap. Dissolved organic N was the dominant component of total N followed by nitrate (NO3-) and ammonium (NH4+). Potassium and chloride were the predominant cation and anion, respectively, of the xylem sap. The NO3- concentration basically did not change, whereas the NH4+ concentration was larger transported from the trunk to branches for the large tree class during foliage senescence. More inorganic N components (mainly NO3-) were found in young trees than in old trees. Our study contributes to improve the diagnostic assessments of tree physiological processes and growth in mature forest trees under environmental changes.