Morphological and metabolic adjustments for enhanced oxygen transport in <i>Phragmites australis</i> under anaerobic stress

Wetland plants with high aeration capacity can produce energy and maintain growth in waterlogged, anaerobic soils. In this study, we aimed to gain insight into the survival mechanisms of wetland plants in anaerobic soils by comparing the morphological characteristics and respiratory metabolism of Phragmites australis with high aeration capacity under aerobic and anaerobic hydroponic conditions. We examined growth, root aerenchyma formation, O₂ concentration in roots, and respiratory traits in shoots and roots. In low-O₂ treatments, P. australis exhibited morphological changes, including shorter shoots, more tillers, and increased adventitious root formation, which enhanced O₂ transport in waterlogged soils. The O₂ concentration in root aerenchyma significantly decreased toward the root tip in low-O₂ treatment. The O₂ uptake rates and maximal activities of alternative pathways were comparable between two O₂ treatments in both organs. The ratio of ATP production rate of the whole roots to that of the whole plant was low in plants grown in low-O₂ treatment. The maximal enzyme activities in the glycolysis and the TCA cycle were also comparable between O₂ treatments. However, under low-O₂ conditions, estimated ATP production rates and total ATP contents of whole shoots increased, but those of whole roots did not. The enhanced ATP production in shoots may support growth under low-O₂ conditions. In conclusion, P. australis, with high aeration capacity, can adapt to long-term rhizosphere hypoxia by modifying morphological and respiratory traits in both shoots and roots. These ecophysiological traits may have applications in ecological engineering for improving wastewater and soil quality in anaerobic rhizospheres.