Nonstructural Carbohydrates in Red Maple at Harvard Forest and Bartlett Forest 2011-2012

Nonstructural carbohydrates (NSC) are the primary products of photosynthesis, composed mostly of sugars and starch. Recent studies show that NSC pools in mature trees can be quite large and on average a decade old. Thus, NSC pools integrate years of carbon assimilation and represent significant ecological memory at the whole plant and ecosystem level. However, we know very little about how older stored NSC versus newly assimilated NSC are used to support growth and metabolism, or how available older NSC are to trees during stress or following disturbance. To better understand these potential lags in NSC allocation, we studied mature red maple (Acer rubrum) trees in two New England temperate forests. We determined stemwood concentrations of stored sugars and starch of five trees at each site. Applying the radiocarbon (14C) “bomb spike” approach, we estimated the age of carbon in stemwood NSC, ring cellulose, and bole respiration. We also collected stump sprouts regrowing from a separate set of recently harvested red maple trees at each site, and determined the radiocarbon age of this tissue. Our data show that younger NSC is preferentially used for growth and day-to-day metabolic demands. More recently stored NSC contributes to annual ring growth and metabolism in the dormant season. Older reserves are available to the tree after disturbance (e.g. harvesting).