Quantitative imaging of radial oxygen loss from Valisneria spiralis roots with a fluorescent planar optode.

Oxygen (O 2 ) availability within the sediment–root interface is critical to the survival of macrophytes in O 2 -deficient sediment; however, our knowledge of the fine-scale impact of macrophyte roots upon the spatiotemporal dynamics of O 2 is relatively limited. In this study, a no n -invasive imaging technology was utilized to map O 2 micro-distribution around Vallisneria spiralis. Long-term imaging results gathered during a 36 day-period revealed an abundance of O 2 spatiotemporal patterns ranging from 0 to 250 μmol L − 1 . The root-induced O 2 leakage and consequent oxygenated area were stronger in the vicinity of the basal root compared to that found in the root tip. The O 2 images revealed V. spiralis exhibited radial O 2 loss (ROL) along the entire root, and the O 2 distribution along the root length showed a high degree of small-scale spatial heterogeneity decreasing from 80% at the basal root surface to 10% at the root tip. The oxygenated zone area around the roots increased as O 2 levels increased with root growth and irradiance intensities ranging from 0 to 216 μmol photons m − 2 s − 1 . A weak ROL measuring < 20% air saturation around the basal root surface was maintained in darkness, which was presumably attributed to the O 2 supply from overlying water via plant aerenchyma. The estimated total O 2 release to the rhizosphere of V. spiralis was determined to range from 8.80 ± 7.32 to 30.34 ± 17.71 nmol m − 2 s − 1 , which is much higher than many other macrophyte species. This O 2 release may be an important contribution to the high-capacity of V. spiralis for quickly colonizing anaerobic sediment. [ABSTRACT FROM AUTHOR]