Oxygen transport by Apium nodiflorum

Apium nodiflorum is a partially submerged aquatic plant able to oxygenate its substrate. This work focuses on the elucidation of the process by which A. nodiflorum oxygenates the substrate, and whether this ability differs during ontogenesis. Young, mature and aged whole plants were examined for the pattern of their process. The contribution of the various plant organs to the increase of the dissolved oxygen concentration in the substrate under hypoxic conditions was also evaluated. Young, mature and aged plants required different amounts of oxygen. When facing hypoxia, young and mature plants elevated their substrate dissolved oxygen concentration. In contrast, aged plants oxygenated their substrate poorly. Changes in dissolved oxygen concentration, both under light and dark conditions, presented no statistical differences at any plant age. An internal oxygen transfer may take place within the plant, apparently without the release of oxygen into the substrate. Thus, it is the existence in petioles of an outer air transport pathway, similar to that of rice, that makes A. nodiflorum plants capable of facing hypoxic conditions in their substrate. This pathway is absent in stems. This fact explains the phenomenon of aged plants poorly oxygenating their substrate, since it is their stems that are inserted into the medium and not their petioles.