Dynamics of oxygen and carbon dioxide in rhizospheres of Lobelia dortmanna - a planar optode study of belowground gas exchange between plants and sediment.

Root-mediated CO uptake, O release and their effects on O and CO dynamics in the rhizosphere of Lobelia dortmanna were investigated. Novel planar optode technology, imaging CO and O distribution around single roots, provided insights into the spatiotemporal patterns of gas exchange between roots, sediment and microbial community. In light, O release and CO uptake were pronounced, resulting in a distinct oxygenated zone (radius: c. 3 mm) and a CO -depleted zone (radius: c. 2 mm) around roots. Simultaneously, however, microbial CO production was stimulated within a larger zone around the roots (radius: c. 10 mm). This gave rise to a distinct pattern with a CO minimum at the root surface and a CO maximum c. 2 mm away from the root. In darkness, CO uptake ceased, and the CO -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 O and CO in the rhizosphere of Lobelia was demonstrated, and we suggest that O -induced stimulation of the microbial community in the sediment increases the supply of inorganic carbon for photosynthesis by building up a CO reservoir in the rhizosphere.