UC Irvine

Nonstructural carbon (NSC) reserves act as buffers to sustain tree activity during periods when carbon (C) assimilation does not meet C demand, but little is known about their age and accessibility; we designed a controlled girdling experiment in the Amazon to study tree survival on NSC reserves. We used bomb-radiocarbon (¹⁴ C) to monitor the time elapsed between C fixation and release ('age' of substrates). We simultaneously monitored how the mobilization of reserve C affected δ¹³ CO₂ . Six ungirdled control trees relied almost exclusively on recent assimilates throughout the 17 months of measurement. The Δ¹⁴ C of CO₂ emitted from the six girdled stems increased significantly over time after girdling, indicating substantial remobilization of storage NSC fixed up to 13-14 yr previously. This remobilization was not accompanied by a consistent change in observed δ¹³ CO₂ . These trees have access to storage pools integrating C accumulated over more than a decade. Remobilization follows a very clear reverse chronological mobilization with younger reserve pools being mobilized first. The lack of a shift in the δ¹³ CO₂ might indicate a constant contribution of starch hydrolysis to the soluble sugar pool even outside pronounced stress periods (regular mixing).