EFFECTS OF O2 ON AMMONIUM UPTAKE AND ROOT RESPIRATION BY SPARTINA ALTERNIFLORA

Previously the growth of Spartina alterniflora has been found to be limited by nitrogen and correlated with sediment redox potential. In this study we have investigated a possible connection between these two factors. We have found that internal O₂ transport is insufficient to saturate NH₄⁺ uptake in short S. alterniflora in hydroponic culture. Rates of NH₄⁺ uptake and root respiration were very sensitive to O₂ concentration in the rhizosphere, saturating at about 5% O₂. Ammonium uptake continued at a reduced rate for at least 4 hr under anaerobic conditions. Plant to plant variations in anaerobic rates of NH₄⁺ uptake and root respiration were significantly correlated to the diffusion rate of CH₄ tracer gas from the leaves to the roots of individual plants.