Diurnal fluctuations of O₂, N₂, and CH₄ in the rhizosphere of Thalassia testudinum1

Gas bubbles in the sediments and gases in the internal spaces of the rhizomes of T. testudinum contained O 2 , N 2 , and CH 4 . CH 4 was a minor component. The percentage composition of the major components, O 2 and N 2 , varied from 2.3% O 2 + 94% N 2 (sediment bubbles, early morning) to 30% O 2 + 69% N 2 (rhizome gases, midafternoon). The variations probably reflected changes in O 2 content of the gases caused by diurnal variations in photosynthetic and oxidative activities of the seagrasses and sediments. Apparently there is a net transfer of O 2 from T. testudinum , via its rhizome system, to the sediments.