Allelopathy as Expressed by Sugar Maple on Yellow Birch

Abstract

This study involves investigation of alleged inhibitory effects of leachate from sugar maple (Acer saccharum Marsh., donor plant) on yellow birch (Betula alleganiensis Britton., receiver plant). The term allelopathy, introduced by Molisch in 1937 refers to this phenomenon in which one plant produces a chemical which inhibits the growth of another plant. The present investigation follows from that of Tubbs (1970) into competition between maple and birch for light and moisture. His results showed that there is a striking difference in birch growth between those grown in pure culture and those grown with maple, the latter being much lower. This reduced growth could not be accounted for by mere physical competition, and through further investigations, he was able to attribute some of this reduction in growth to allelopathic effects of maple leachate. Tubbs postulated that the active principle causing the inhibition was exuded from maple roots, that it was thermostable, water soluble and ephemeral. The following questions which form the basis for the present investigations arise from Tubbs' results: 1. Is there a phenologic pattern to the inhibition of birch by maple? 2. Do maple organs, other than the roots, also exude inhibitor(s)?

3. How may the inhibition be expressed in birch? 4. What further can one learn about the chemical nature of the inhibitor(s)? These questions are being investigated with a view to providing answers that may help better understanding of the phenomenon of allelopathy between sugar maple and yellow birch. Literature Review No less than sixteen reviews of biochemical inhibitioi starting with one by Molisch (1937) to the recent review by Whittaker and Feeny (1971), have been published, not to mention also the many research papers which invariably contain partial reviews of the subject. It is intended here to reiterate various points in some of these review's and papers, particularly with regard to their relevance to the present investigation. The field of chemical inhibition traces back to 1828 when de Candolle drew the attention of scientists in his theory of crop rotation as a way of circumventing unfavorable effects of one species on another in soils (Schreiner and Reed 1907; Bonner 1950).