Source of Oxygen Fed to Adventitious Roots of Syzygium kunstleri (King) Bahadur and R.C. Gaur Grown in Hypoxic Conditions

Syzygium kunstleri, a woody plant species, adapts to hypoxic conditions by developing new adventitious roots. Here, we investigate its morphological adaptation to long-term water level changes and the sources and pathways of O(2) supplied to its adventitious roots. Cuttings were cultivated in hydroponic and agar media, and then, the water level was increased by 6 cm following adventitious root emergence; afterward, O(2) partial pressure changes were measured using a Clark-type O(2) microelectrode. O(2) concentrations in the adventitious roots decreased when N(2) was injected, regardless of the presence of light, indicating that the O(2) source was not photosynthetic when bark was removed. New adventitious roots developed near the surface when the water level increased, and O(2) conditions above the raised water level influenced O(2) concentrations in adventitious roots. O(2) concentrations in adventitious roots that developed before the water level increased were lower than in the newly developed adventitious roots but increased when the O(2) concentrations above the original water level increased. Our study highlights morphological changes, such as the development of adventitious roots, as environmental adaptation mechanisms. By revealing O(2) sources in S. kunstleri under hypoxic environments, we offer insights into the challenges of long-term adaptation to changing environments in woody plants.