Laboratory-scale investigations using individual T. latifolia and J. effusus plants in hydroponic systems were carried out to evaluate the potentials and differences in the species regarding the release of oxygen into their rhizospheres. Their oxygen release intensities were found to vary between the species and also to depend on the redox state of the rhizosphere. The highest release rates with mean values of 1.1 mg/h plant for T. latifolia and 0.5 mg/h plant for J. effusus were estimated at Eh ≈ — 200 mV for both species. The amounts of oxygen released were sufficient to be of biotechnological relevance for oxidative processes in constructed wetlands. The plants even released oxygen under oxidized rhizospheric conditions and for individual plants, an intensification of the oxygen release was estimated, forming further local release maxima at Eh = 250—400 mV with about 0.2 mg/h plant.

The total size of the root system does not significantly affect the intensity of oxygen release; instead, the oxygen release state was governed by the size of the above-ground biomass. The intensification of illumination causes an increase in the oxygen release rates, which is pronounced for T. latifolia but small for J. effusus.

Further investigations involving other wetland species and using laboratory-scale, pilot-scale and fullscale wetland systems to evaluate oxygen release are of biotechnological interest.