Not that long ago, the CO₂ efflux from a plant organ was attributed to metabolic reactions and activity only in that same organ. For tree stems, however, we know that CO₂ transported in the xylem and originating from other plant compartments compromises stem respiration measurements. Now, Stutz et al. (2017) have shown that leaf CO₂ efflux, in addition, does not solely represent leaf metabolic processes but is affected by xylem-borne CO₂.