High-resolution characterization of rhizosphere oxygen (O2) dynamics in different wetland plant species after light/dark transitions

Abstract

Radial oxygen loss (ROL) is crucial for wetland plant survival and interactions with rhizosphere microenvironments. The ubiquitous presence of light/dark transitions can significantly influence ROL function by regulating photosynthetic activity; however, overall magnitude and direction of these effects are unclear. Herein, high-resolution planar O₂ optodes were employed to quantify the O₂ dynamics around the roots of three typical wetland plant species during light/dark transitions. The 2D and 1D O₂ distributions confirmed that ROL activity was heterogeneously distributed, with millimeter-wide zones of intense leakage around the roots of all three plants. Significant species-specific variations in root-derived O₂ leakage capacity during light/dark transitions were also observed. Specifically, the average O₂ concentrations declined by ca. 10.2%, 23.9%, and 17.0%, respectively, for Oryza sativa, Vallisneria spiralis, and Acorus calamus upon switching from light to darkness. In comparison, the oxic microzone area around their roots decreased by 23.03%, 7.21%, and 13.67%. Correspondingly, the ROL rates showed a pronounced decrease from light to darkness, dropping in O. sativa by 14%, in V. spiralis by 23%, and in A. calamus by 25%. Acorus calamus has the highest ROL capacity, which was likely facilitated by its well-developed lacunar system and efficient O₂ transport. Additionally, our results directly support the existence of oxic microzones and continuous O₂ release throughout light/dark transitions; this could guarantee that a continuous oxic environment surrounds the roots and shields plants from anaerobic phytotoxins in the rhizosphere. The passive diffusion of O₂ from the air or water column in total darkness may be the primary source of the modest aerobic sphere that surrounded each root. This study advances our understanding of the complex interplay between photosynthesis and ROL, contributing new insights into plant–sediment interactions and adaptive strategies of wetland plants to environmental fluctuations.