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.