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

摘要

Root-mediated CO2 uptake, O-2 release and their effects on O-2 and CO2 dynamics in the rhizosphere of Lobelia dortmanna were investigated. Novel planar optode technology, imaging CO2 and O-2 distribution around single roots, provided insights into the spatiotemporal patterns of gas exchange between roots, sediment and microbial community. In light, O-2 release and CO2 uptake were pronounced, resulting in a distinct oxygenated zone (radius: c. 3mm) and a CO2-depleted zone (radius: c. 2mm) around roots. Simultaneously, however, microbial CO2 production was stimulated within a larger zone around the roots (radius: c. 10mm). This gave rise to a distinct pattern with a CO2 minimum at the root surface and a CO2 maximum c. 2mm away from the root. In darkness, CO2 uptake ceased, and the CO2-depleted zone disappeared within 2h. By contrast, the oxygenated root zone remained even after 8h, but diminished markedly over time. A tight coupling between photosynthetic processes and the spatiotemporal dynamics of O-2 and CO2 in the rhizosphere of Lobelia was demonstrated, and we suggest that O-2-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.