High-resolution imaging of rhizosphere oxygen (O2) dynamics in Potamogeton crispus: effects of light, temperature and O2 content in overlying water

Abstract

Radial oxygen loss (ROL) for macrophytes is intimately involved in their survival and growth, thus detailed characterizations of ROL and its implication for geochemical processes are of particular interest. We experimentally investigated ROL patterns from the submerged macrophyte species Potamogeton crispus and determined how light, temperature and O2 content in overlying water regulate O2 micro-distributions in the rhizosphere. Planar optodes were firstly used for non-destructive imaging of the O2 micro-distributions around single roots of P. crispus planted in rhizotrons containing sediment. The dynamic changes in below-ground O2 concentrations and oxygenation expansion at different light intensities (0–216 μmol photons m−2), temperatures (14 and 25 °C) and O2 content in overlying waters (0–256 μmoL−1) were quantified. P. crispus-mediated ROL is predominantly localized to the root apices with an average rate of 168.1 ± 21.4 nmol m−2 s−1 under nearly natural conditions (light, saturated overlying water at 14 °C), maintaining a visible oxygenated rhizosphere zone with a radius of 1.33 ± 0.21 mm. ROL is closely correlated with light intensity, suggesting photosynthetic O2 evolution. In darkness, the rhizosphere O2 availability is significantly reduced and strongly affected by the O2 content in overlying water, which passively diffuses into the plant leaves. Elevated temperatures lead to diminished ROL as a result of increased O2 demand of the surrounding sediment. A high O2 microheterogeneity around P. crispus root apices is firstly demonstrated, and we provide direct empirical evidences that ROL are regulated dynamically by the shifting light, temperature and O2 content in overlying water.