THE SALT RESPIRATION OF EXCISED BEECH MYCORRHIZAS

Abstract

Experimental work on respiration and phosphate absorption by beech mycorrhiza has demonstrated a general similarity between these complex salt-absorbing organs and normal root systems. Not only may the rates of salt absorption be dependent upon the concentration of salt applied, upon the temperature and upon the availability of oxygen in the medium; but also mycorrhizas may be brought, by storage in water, into a condition where large respiratory responses to the application of salts are observable. In a previous paper (Harley, McCready and Geddes, I954) a general account was given of the development of respiratory response to salts during storage in distilled water. The response was shown to be developed by both fungal and host tissues and to result from the application of numerous nutritive salts and sugars. Of these, salts of ammonium and phosphate elicited the greatest increases of oxygen consumption and carbon dioxide emission by stored roots. In this present paper a more detailed study of the connexion between 'the respiration and phosphate absorption of excised mycorrhizas, both fresh and stored, is presented. It is based upon the results of experiments in which various oxygen concentrations, phosphate concentrations and inhibitors have been used. Its aim has been both to provide the necessary background knowledge for the interpretation of the functioning of mycorrhizal roots and also to show how experiments with mycorrhizas may contribute to the general problems of salt absorption by plant material. The paper is divided into two parts. The first describes experiments upon freshly excised roots using different oxygen concentrations and inhibitors to study their effects on respiration and phosphate absorption. In the second part, the results of experiments with roots stored for several days in water are used in an attempt to solve the problems raised. METHODS