PHYSIOLOGICAL RESPONSE OF MAPLE AND BIRCH ROOTS TO RHIZOSPHERE HYPOXIA

ROBERT ROCCO TRIPEPI, Purdue University

Abstract

The purpose of this study was to determine if internal aeration of roots by lower stems, changes in gross morphology of lower stems, or both, contribute to flood tolerance of certain tree species. Greenhouse-grown seedlings of red maple (Acer rubrum L.) and river birch (Betula nigra L.) tolerated at least 30 days of flooding, whereas sugar maple (Acer saccharum Marsh) and European birch (Betula pendula Roth) were intolerant. Flood treatment induced lenticel intumescences and adventitious root formation on red maple stems, but only adventitious roots formed on river birch stems. Stem morphology of sugar maple and European birch was unchanged by flooding. Flood stress decreased oxygen consumption capacity of excised roots from both tolerant and intolerant species. Exclusion of oxygen from the lower stems of red maple and river birch prevented lenticel intumescence and adventitious root formation, but flood tolerance and root respiration capacity were unchanged. Neither internal aeration nor changes in stem morphology appear to account for flood tolerance of red maple and river birch. In the second part of this study, several biochemical and physiological responses of river and European birch roots to hypoxia were compared in order to determine root metabolic activity under low oxygen tension. Although hypoxia decreased total adenosine phosphate and adenosine triphosphate contents in roots from both species, river birch roots contained greater quantities of these nucleotides after 18 days of treatment. Adenylate energy charge of river birch roots decreased between 6 and 12 days of hypoxia, whereas energy charge of European birch roots decreased significantly after only one day. In vitro activity of cytochrome c oxidase and oxygen consumption capacity of excised roots from both birch species decreased under hypoxia. In vitro activity of alcohol dehydrogenase from roots of both species increased after 1 day of hypoxia. However, alcohol dehydrogenase activity from river birch roots increased 25 fold by 6 days of hypoxia, whereas that in European birch roots decreased back to control levels. Metabolic adaptation within the root, rather than internal aeration, appears to be responsible for tolerance of river birch to hypoxia.

Degree

Ph.D.

Subject Area

Plant sciences

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