O2 distribution and dynamics in the rhizosphere of Phragmites australis, and implications for nutrient removal in sediments

Root-triggered microscale variations in O-2 distribution in the rhizosphere of young Phragmites australis are important for nutrient removal in sediments. In this study, the micro-scale O-2 dynamics and the small-scale changes of soluble reactive phosphorus (SRP) and ammonium (NH4+) in the rhizosphere of P. australis were investigated using planar optodes and high-resolution dialysis (HR-Peeper), respectively. Results suggested that root O-2 leakage has a highly variable distribution depending on the stage of root growth, the site of O-2 leakage gradually shift from the entire emerging main roots to the main root tip and subsequently shifted the emerging lateral roots. The O-2 concentration increased in the rhizosphere with increasing light intensity and O-2 levels in the overlying water. Continuous O-2 release from the lateral roots causes the formation of iron plaque on the surface of lateral roots, which reduce the mobility of P by adsorption of iron plaque in the rhizosphere. The oscillation of oxic-anoxic root zones improves nitrogen removal through the processes of anammox, hetemtmphic denitrification and nitrification. This work from the micro-scale demonstrates that the O-2 concentration is the spatio-temporal variations in the rhizosphere, and it presents an important role for nutrient removal in sediments.