Reduced global plant respiration due to the acclimation of leaf dark respiration coupled with photosynthesis.

Leaf dark respiration (R _d ) acclimates to environmental changes. However, the magnitude, controls and time scales of acclimation remain unclear and are inconsistently treated in ecosystem models. We hypothesized that R _d and Rubisco carboxylation capacity (V _cmax ) at 25°C (R _d,25 , V _cmax,25 ) are coordinated so that R _d,25 variations support V _cmax,25 at a level allowing full light use, with V _cmax,25 reflecting daytime conditions (for photosynthesis), and R _d,25 /V _cmax,25 reflecting night-time conditions (for starch degradation and sucrose export). We tested this hypothesis temporally using a 5-yr warming experiment, and spatially using an extensive field-measurement data set. We compared the results to three published alternatives: R _d,25 declines linearly with daily average prior temperature; R _d at average prior night temperatures tends towards a constant value; and R _d,25 /V _cmax,25 is constant. Our hypothesis accounted for more variation in observed R _d,25 over time (R ²  = 0.74) and space (R ²  = 0.68) than the alternatives. Night-time temperature dominated the seasonal time-course of R _d , with an apparent response time scale of c. 2 wk. V _cmax dominated the spatial patterns. Our acclimation hypothesis results in a smaller increase in global R _d in response to rising CO ₂ and warming than is projected by the two of three alternative hypotheses, and by current models.
(© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)