Concentration and Age of Nonstructural Carbon Reserves in Two Trees at Harvard Forest 2012

We know surprisingly little about whole-tree nonstructural carbon (NSC;
primarily sugars and starch) budgets. Even less well understood is the mixing
between recent photosynthetic assimilates (new NSC) and previously stored
reserves. And, NSC turnover times are poorly constrained. We characterized the distribution of NSC in the stemwood, branches, and roots
of two temperate trees, and we used the continuous label offered by the
radiocarbon (14C) bomb spike to estimate the mean age of NSC in different
tissues. NSC in branches and outermost stemwood growth rings had the 14C signature of
the current growing season. However, NSC in older above- and below-ground
tissues was enriched in 14C, indicating that it was produced from older
assimilates. Radial patterns of 14C in stemwood NSC showed strong mixing of NSC
across the youngest growth rings, with limited.