Oxic microzones and radial oxygen loss from roots of Zostera marina

Inter Research
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Journal Article
Marine Ecology Progress Series, 2005, 293 pp. 49 - 58
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Oxygen microelectrodes and planar oxygen optodes were used to map the microdistribution of oxygen and the radial oxygen loss (ROL) from roots of Zostera marina kept in natural sediment. Substantial heterogeneity in the oxygen distribution was seen along the roots, with oxygen mainly leaking out from the root tips. Maximum oxygen levels at the root surface reached 19 to 80% of air saturation in the light and the oxygenated zone extended 1 to 2 mm away from the root tip. The oxygen concentration at the root surface decreased to 05% of air saturation at positions 3 to 6 mm behind the root apex. The high oxygen levels at the root tip surface were due to an effective barrier to ROL on the older part of the roots and the presence of an effective gas-transport system in the plant, with numerous intercellular spaces extending very close to the apical meristem of the root. Radial diffusion of oxygen from the root surface created a dynamic 0 to 1 mm-wide oxic microzone around the ~0.3 mm wide roots of Z. marina that varied with irradiance and distance from the root tip. Root-surface oxygen concentrations and ROL measured 2 mm behind the apex increased with increasing irradiance until ROL saturation was reached at irradiances >400 µmol photons m2 s1. The ROL increased from 16.2 nmol O2 cm2 h1 in darkness to 21.6, 28.8 and 36.0 nmol O2 cm2 h1 at incident irradiances of 25, 111 and 467 µmol photons m2 s1, respectively. Based on measured steady-state radial oxygen profiles, the total oxygen export from one 6 cm long root of the first actively growing root bundle with a total surface area of 0.56 cm2 was estimated to be 6.0 to 6.7 nmol O2 h1 in saturating light.
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