O₂ dynamics in the rhizosphere of young rice plants (Oryza sativa L.) as studied by planar optodes

Radial O₂ loss (ROL) strongly affect the O₂ availability in the rhizosphere of rice. The ROL create an oxic zone around the roots, protecting the plant from toxic reduced chemical species and regulates the redox chemistry in the soil. This study investigates the spatio-temporal variability in O₂ dynamics in the rice rhizosphere.

Applying high-resolution planar optode imaging, we investigated the O₂ dynamics of plants grown in water saturated soil, as a function of ambient O₂ level, irradiance and plant development, for submerged and emerged plants.

O₂ leakage was heterogeneously distributed with zones of intense leakage around roots tips and young developing roots. While the majority of roots exhibited high ROL others remained surrounded by anoxic soil. ROL was affected by ambient O₂ levels around the plant, as well as irradiance, indicating a direct influence of photosynthetic activity on ROL. At onset of darkness, oxia in the rhizosphere was drastically reduced, but subsequently oxia gradually increased, presumably as root and/or soil respiration declined.

The study demonstrates a high spatio-temporal heterogeneity in rhizosphere O₂ dynamics and difference in ROL between different parts of the rhizosphere. The work documents that spatio-temporal measurements are important to fully understand and account for the highly variable O₂ dynamics and associated biogeochemical processes and pathways in the rice rhizosphere.