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

Leaf dark respiration (R ) 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 and Rubisco carboxylation capacity (V ) at 25°C (R , V ) are coordinated so that R variations support V at a level allowing full light use, with V reflecting daytime conditions (for photosynthesis), and R /V 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 declines linearly with daily average prior temperature; R at average prior night temperatures tends towards a constant value; and R /V is constant. Our hypothesis accounted for more variation in observed R over time (R  = 0.74) and space (R  = 0.68) than the alternatives. Night-time temperature dominated the seasonal time-course of R , with an apparent response time scale of c. 2 wk. V dominated the spatial patterns. Our acclimation hypothesis results in a smaller increase in global R in response to rising CO and warming than is projected by the two of three alternative hypotheses, and by current models.