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Abstract:
While trees store substantial amounts of nonstructural carbon (NSC) for later use, storage regulation and mobilization of stored NSC in long-lived organisms like trees are still not well
understood.
At two different sites with sugar maple (Acer saccharum), we investigated ascending sap
(sugar concentration, d13C, D14C) as the mobilized component of stored stem NSC during early
springtime. Using the bomb-spike radiocarbon approach we were able to estimate the average
time elapsed since the mobilized carbon (C) was originally fixed from the atmosphere and to infer
the turnover time of stem storage.
Sites differed in concentration dynamics and overall d13C, indicating different growing
conditions. The absence of temporal trends for d13C and D14C indicated sugar mobilization from
a well-mixed pool with average D14C consistent with a mean turnover time (TT) of three to five
years for this pool, with only minor differences between the sites.
Sugar maple trees hence appear well buffered against single or even several years of negative
plant C balance from environmental stress such as drought or repeated defoliation by insects.
Manipulative investigations (e.g. starvation via girdling) combined with D14Cmeasurements of this
mobilized storage pool will provide further newinsights into tree storage regulation and functioning.
