title: Diurnal dynamics of oxygen and carbon dioxide concentrations in shoots and rhizomes of a perennial in a constructed wetland indicate down-regulation of below ground oxygen consumption.
abstract: Wetland plants actively provide oxygen for aerobic processes in submerged tissues and the rhizosphere. The novel concomitant assessment of diurnal dynamics of oxygen and carbon dioxide concentrations under field conditions tests the whole-system interactions in plant-internal gas exchange and regulation. Oxygen concentrations ([O2]) were monitored in-situ in central culm and rhizome pith cavities of common reed (Phragmites australis) using optical oxygen sensors. The corresponding carbon dioxide concentrations ([CO2]) were assessed via gas samples from the culms. Highly dynamic diurnal courses of [O2] were recorded, which started at 6.5-13 % in the morning, increased rapidly up to 22 % during midday and declined exponentially during the night. Internal [CO2] were high in the morning (1.55-17.5 %) and decreased (0.04-0.94 %) during the rapid increase of [O2] in the culms. The observed negative correlations between [O2] and [CO2] particularly describe the below ground relationship between plant-mediated oxygen supply and oxygen use by respiration and biogeochemical processes in the rhizosphere. Furthermore, the nocturnal declining slopes of [O2] in culms and rhizomes indicated a down-regulation of the demand for oxygen in the complete below ground plant-associated system. These findings emphasize the need for measurements of plant-internal gas exchange processes under field conditions because it considers the complex interactions in the oxic-anoxic interface.
authors.affiliation: Ulm University, Institute of Systematic Botany and Ecology, Ulm, Germany Anna.fausser@alumni.uni-ulm.de.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Faußer
authors.affiliation: CzechGlobe - Global Change Research Centre AS CR, Department of Matters and Energy Fluxes, v.v.i. České Budějovice, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Dušek
authors.affiliation: CzechGlobe - Global Change Research Centre AS CR, Department of Matters and Energy Fluxes, v.v.i. České Budějovice, Czech Republic University of South Bohemia, Faculty of Agriculture, Department of Biology, České Budějovice, Czech Republic.
authors.forename: Hana
authors.initials: H
authors.lastname: Čížková
authors.affiliation: Ulm University, Institute of Systematic Botany and Ecology, Ulm, Germany.
authors.forename: Marian
authors.initials: M
authors.lastname: Kazda
keywords: Aeration; Phragmites australis; constructed wetland; in-situ field study; internal carbon dioxide; internal oxygen dynamics