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Contributed Talk

Session: : Eco-Evolutionary Processes 2

COS 35-2 - Weakened global climate-carbon feedback due to the acclimation of leaf dark respiration coupled to photosynthesis

Monday, August 7, 2023
3:45 PM – 4:00 PM PDT
Location: D139
Abstract: Leaf dark respiration (Rd) acclimates to environmental changes, including warming. However, the magnitude, controls and time scales of acclimation remain unclear, and are inconsistently treated in land surface models.

Here, we hypothesized that Rd and carboxylation capacity (Vcmax) at 25˚C (Rd,25, Vcmax,25) are coordinated, so that Rd,25 variations support Vcmax,25 at a level allowing full light use; with Vcmax,25 reflecting daytime conditions (for photosynthesis), and the ratio of Rd,25 to Vcmax,25 reflecting night-time conditions (for starch degradation and sucrose export). We tested this hypothesis temporally using a five-year warming experiment, and spatially using an extensive field-measurement data set. We compared our results to three published alternatives: Rd,25 declines linearly with daily average prior temperature; Rd at average prior night temperatures tends towards constancy; and Rd,25 maintains a constant ratio to Vcmax25.

Our hypothesis accounted for more variation in observed Rd,25 over time (R2 = 0.74) and space (R2 = 0.68) than the alternatives. Night-time temperature dominated the seasonal time-course of Rd, with an apparent response time-scale of about two weeks. Vcmax dominated the spatial patterns. Compared with the instantaneous response, the new acclimation hypothesis halves the response of global Rd to warming and helps to mitigate the positive climate-carbon cycle feedback. This work promotes a better understanding of Rd acclimation and could straightforwardly be implemented in land surface models.