THE TOLERANCE OF TREE ROOTS TO WATERLOGGING

Abstract

SUMMARY Seedling root systems, or individual roots of cuttings, were submerged in reduced indigo‐carmine solution so that only the seedling shoot, or basal part of the cutting root, was exposed to air or oxygen. Oxygen diffusing out of the roots produced a localized blue colouration of the previously clear reduced dye; this process was employed to study internal oxygen movement. Using plants grown in freely drained soil it was evident that seedlings of the flood‐tolerant species, Lodgepole pine, had a greater capacity for oxygen transport than the flood‐intolerant Sitka spruce. Oxygen diffusion was also observed in roots detached from Lodgepole pine cuttings and was greatly enhanced in plants which had grown in waterlogged conditions; in the latter plants oxygen diffusion was detected from the root tips after a short exposure of the basal region of the root to oxygen, whereas roots from plants grown in freely drained soil showed diffusion of oxygen only from the upper submerged portion during the same treatment period. Oxygen diffusion over distances of more than 30 cm was detected in certain experiments. Observations on the movement of gas supplied under pressure to Lodgepole pine root segments showed that the rate of gas flow was much greater in roots grown in waterlogged soil than in those grown in freely drained soil and that the gas movement occurred in the stelar tissues. The regions of oxygen entry included the needles, and lenticels on the roots.