Living on borrowed time – Amazonian trees use decade‐old storage carbon to survive for months after complete stem girdling
2018
Muhr, Jan | Trumbore, Susan | Higuchi, Niro | Kunert, Norbert
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 (¹⁴C) to monitor the time elapsed between C fixation and release (‘age’ of substrates). We simultaneously monitored how the mobilization of reserve C affected δ¹³CO₂. Six ungirdled control trees relied almost exclusively on recent assimilates throughout the 17 months of measurement. The Δ¹⁴C 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 δ¹³CO₂. 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 δ¹³CO₂ might indicate a constant contribution of starch hydrolysis to the soluble sugar pool even outside pronounced stress periods (regular mixing).
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