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 non-invasive imaging technology was utilized to map O-2 micro-distribution around Valli.sneria spiralis. Long-term imaging results gathered during a 36 day-period revealed an abundance of O-2 spatiotemporal patterns ranging from 0 to 250 mu mol 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 rimol 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 02 release may be an important contribution to the high-capacity of V spiralis for quickly colonizing anaerobic sediment. (C) 2016 Elsevier B.V. All rights reserved.