OXIDATION OF THE ROOT-ZONE BY AQUATIC PLANTS GROWING IN GRAVEL-NUTRIENT SOLUTION CULTURE

The root zone oxidation state was monitored over a period of 87 d for alpine rush (Juncus alpinus Vill.), canarygrass (Phalaris arundinaea L.), and cattail (Typha latifolia L.) growing in gravel-nutrient solution culture. The dissolved oxygen concentration in the root zone of cattail and canarygrass was less-than-or-equal-to 1 mg L-1, whereas in alpine rush it ranged from 0 to 2 mg L-1. All planted treatments consistently had a dissolved oxygen concentration 1 to 2 mg L-1 lower than gravel without plants. Redox potentials in the root zone of alpine rush were normally between 400 and 700 mV, indicating an aerobic root zone. The root zone of cattail also tended to be aerobic, although redox potentials of <400 mV were obtained 40% of the time. Canarygrass had the most reduced root zone with 85% of the redox potential measurements <400 mV. Dissolved oxygen concentrations and redox potentials in the root zone did not change significantly on a diurnal basis for any of the plant species. The results show that there was a plant species effect on the oxidation state of the root zone as measured by dissolved oxygen and redox potential.