Tree trunks and roots have a variable and often important proportion of live cells. Respiration provides energy and carbon skeletons required by these living cells for their maintenance and proliferation. In the process of respiration, soluble sugars previously synthesized by leaves and young stems are oxidized and carbon dioxide (CO₂) is produced as a byproduct. For this reason, it has been amply considered that rates of radial CO₂ efflux from trunks and stems are equivalent to rates of respiration. However, it has been observed that the CO₂ produced in respiration does not immediately or fully diffuse out to the atmosphere. Thus, even if in some circumstances radial CO₂ efflux is a good surrogate of wood respiration, we must not consider both variables as equivalent. In 2008, Teskey et al. reviewed the main factors affecting the concentration, mobility and emission of CO₂ in tree stems, namely: corticular photosynthesis, resistance of anatomical elements to radial CO₂ diffusion, and solubility and transport of CO₂ in xylem sap. Here we update this topic with recent findings reported in literature and in Spanish language. With this work we intend to engage a broader audience in the investigation of wood CO₂ efflux and respiration, an understudied topic of central importance for modeling the carbon balance of forest ecosystems and the atmospheric CO₂ concentration in the future.