PLANT PHYSIOLOGY , Vol 105, Issue 3 847-852, Copyright © 1994 by American Society of Plant Biologists
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PLANT-MICROBE INTERACTIONS |
Microsensor Analysis of Oxygen in the Rhizosphere of the Aquatic Macrophyte Littorella uniflora (L.) Ascherson
P. B. Christensen, N. P. Revsbech and K. Sand-Jensen
National Environmental Research Institute, Vejlsovej 25, DK-8600 Silkeborg, Denmark (P.B.C)
Oxygen released by the roots of submerged plants may oxidize organic
compounds from the roots and reduced substances continuously supplied by
diffusion from the surrounding anoxic hydrosoil. We provide here the first
visualization of this gradient environment obtained by microsensor analysis
of oxygen in the rhizosphere of the freshwater plant Littorella uniflora
(L.) Ascherson. The plants were rooted in an agar medium, in which
amorphous FeS provided the main oxygen sink. The oxygen concentration at
the root surface ranged from 20 to 450 [mu]M (atmospheric saturation = 280
[mu]M) between darkness and saturating light, and the oxic shell
surrounding the roots varied from about 0.5 to 5 mm in thickness. The
oxygen flux from the roots was a saturating function of the incident light
intensity on the leaves, and the oxygen released was consumed mainly at the
fluctuating oxic/anoxic interface. The oxic zones around individual roots
are under dynamic control by light, root morphology, root density, and
sediment reducing capacity, and, therefore, oxygen concentrations should be
subject to substantial diurnal fluctuations in dense Littorella populations
in nutrient-poor sediments.
