The complete apoplastic enzymatic antioxidant system, composed by class I ascorbate peroxidases (class I APXs), class III ascorbate peroxidases (class III APXs), ascorbate oxidases (AAOs), and other class III peroxidases (PRX), of wood-forming tissues has been studied in Populus alba, Citrus aurantium, and Eucalyptus camaldulensis. The aim was to ascertain whether these enzymatic systems may regulate directly (in the case of APXs), or indirectly (in the case of AAOs), apoplastic H2O2 levels in lignifying tissues, whose capacity to produce and to accumulate H2O2 is demonstrated here. Although class I APXs are particularly found in the apoplastic fraction of P. alba (poplar), and class III APXs are particularly found in the apoplastic fraction of C. aurantium (bitter orange tree), the results showed that the universal presence of AAO in the extracellular cell wall matrix of these woody species provokes the partial or total dysfunction of apoplastic class I and class III APXs, and of the whole plethora of non-enzymatic redox shuttles in which ascorbic acid (ASC) is involved, by the competitive and effective removal of ASC. In fact, the redox state (ASC/ASC+DHA) in intercellular wash fluids (IWFs) of these woody species was zero, and thus strongly shifted towards DHA (dehydroascorbate), the oxidized product of ASC. This imbalance of the apoplastic antioxidant enzymatic system apparently results in the accumulation of H2O2 in the apoplast of secondary wood-forming tissues, as can be experimentally observed. Furthermore, it is hypothesized that since AAO uses O2 to remove ASC, it could regulate O2 availability in the lignifying xylem and, thorough this mechanism, AAO could also control the activity of NADPH oxidase (the enzyme responsible for H2O2 production in lignifying tissues) at substrate level, by controlling the tension of O2. That is, the presence of AAO in the extracellular cell wall matrix appears to be essential for finely tuning the oxidative performance of secondary wood-forming tissues.