Whole-Tree Nonstructural Carbohydrate Budgets in Five Species at Harvard Forest 2014

Despite the importance of nonstructural carbohydrates (NSC) for growth and survival in woody plants, we know little about whole-tree NSC budgets. The conventional model suggests that NSC reserves will increase over the growing season and decrease over the dormant season. Here, we compare storage in five temperate tree species to determine the size and seasonal fluctuation of whole-tree total NSC budgets as well as the contribution of individual organs. NSC concentrations in the branches, stemwood, and roots of 24 trees were measured across twelve months. We then scaled up concentrations to the whole-tree level using allometric equations. While whole-tree total NSC budgets followed the conventional model, sugar budgets peaked in the dormant season and starch budgets in the growing season. Seasonal depletion of total NSCs was minimal at the whole-tree level, but substantial at the organ-level, particularly in branches. Surprisingly, roots were not the major storage organ as branches stored comparable amounts of starch throughout the year, and root reserves were not used to support springtime growth.