Dynamics of oxygen and carbon dioxide in rhizospheres of <italic>Lobelia dortmanna</italic> – a planar optode study of belowground gas exchange between plants and sediment.

Summary: Root‐mediated CO₂ uptake, O₂ release and their effects on O₂ and CO₂ dynamics in the rhizosphere of <italic>Lobelia dortmanna</italic> were investigated. Novel planar optode technology, imaging CO₂ and O₂ distribution around single roots, provided insights into the spatiotemporal patterns of gas exchange between roots, sediment and microbial community. In light, O₂ release and CO₂ uptake were pronounced, resulting in a distinct oxygenated zone (radius: <italic>c</italic>. 3 mm) and a CO₂‐depleted zone (radius: <italic>c</italic>. 2 mm) around roots. Simultaneously, however, microbial CO₂ production was stimulated within a larger zone around the roots (radius: <italic>c</italic>. 10 mm). This gave rise to a distinct pattern with a CO₂ minimum at the root surface and a CO₂ maximum <italic>c</italic>. 2 mm away from the root. In darkness, CO₂ uptake ceased, and the CO₂‐depleted zone disappeared within 2 h. By contrast, the oxygenated root zone remained even after 8 h, but diminished markedly over time. A tight coupling between photosynthetic processes and the spatiotemporal dynamics of O₂ and CO₂ in the rhizosphere of <italic>Lobelia</italic> was demonstrated, and we suggest that O₂‐induced stimulation of the microbial community in the sediment increases the supply of inorganic carbon for photosynthesis by building up a CO₂ reservoir in the rhizosphere. [ABSTRACT FROM AUTHOR]