Fig. 1

A schematic overview of radial and axial CO₂ fluxes in a dormant tree stem with a stem cuvette to measure stem CO₂ efflux under different light conditions. a Under light exclusion, only outward radial diffusion of respired CO₂ occurs from the inner bark (1a), cambium (1b) and xylem ray cells (1c). b Under light exposure of a stem section remote from the stem cuvette, woody tissue photosynthesis occurs (2), while light is excluded from the remainder of the stem and the cuvette. Stem CO₂ concentration ([CO₂]) decreases within the illuminated stem section relative to that in the stem section enclosed in the opaque stem cuvette, resulting in upward axial CO₂ diffusion (3) to the detriment of radial CO₂ diffusion (1a, 1b and 1c). Adapted from Teskey et al. (2008)