Oxygen stress in wetland plants: Comparison of de-oxygenated and reducing root environments

1. Growth, photosynthesis and root adenine nucleotides were compared in two wetland plants, Phalaris arundinacea and Glyceria maxima, grown in aerated, deoxygenated or reduced (redox potential = -250 mV) nutrient solutions, to test the hypothesis that the stress of de-oxygenated conditions is mild compared with that of naturally reducing sediments. 2. Relative growth rate (RGR) was not significantly different between plants in the aerated and de-oxygenated treatments. However, plants in the reducing treatment stopped growing and some lost mass (RGR negative). Differences in root porosity were not significant between treatments. 3. Rates of net photosynthesis in both species were stable in the de-oxygenated and aerated treatments, at 3-8 mu mol CO(2)m(-2)s(-1). However, net photosynthesis in the reducing treatment declined over 5 days, becoming negative in P. arundinacea and falling below 1 mu mol CO2 m(-2)s(-1) in G. maxima. 4. Concentrations of adenine nucleotides in the roots of both species were significantly but only slightly lower in the de-oxygenated treatment than in the aerated treatment (0.65 times as much ATP and 0.70-0.87 times as much total adenine nucleotides). However, nucleotide concentrations were much lower in the reducing treatment (0.10-0.19 times as much ATP and total adenine nucleotides as the aerated treatment). Both species tolerated the de-oxygenated treatment but were sensitive to the reducing treatment.