The Effect of Micro-organisms on the Absorption of Inorganic Nutrients by Intact Plants: II. UPTAKE AND UTILIZATION OF PHOSPHATE BY BARLELY PLANTS GROWN UNDER STERILE AND NON-STERILE CONDITIONS

Abstract

The uptake of phosphate by barley plants grown under sterile and non-sterile conditions has been compared from solutions ranging in concentration between o-ooi to io o ppm P. If special precautions are not taken to exclude micro organisms their activity on or in plant roots greatly modifies the absorption and utilization of phosphate in plants, especially when the external concentration is low. More phosphate is incorporated into nucleic acids, phospholipids, and phosphoproteins in the roots; at o ooi ppm P these compounds account for over 60 per cent of the phosphate absorbed compared with about 15 per cent in plants grown under sterile conditions and even at i-o ppm P there is a twofold difference. The immobilization of phosphate in the roots reduces its transfer to the shoots ; at 0 001 ppm P, 2 as compared with 20 per cent of the phosphate absorbed is trans ferred to the shoots. This effect decreases with increasing concentration but small differences are still apparent up to about 0-5 ppm P. A further effect of micro-organisms is apparent when plants are transferred from dilute solutions to phosphate-free solutions. Under non-sterile conditions there is an almost tenfold increase in the loss to these solutions of previously absorbed phosphate. It is evident that conclusions on the mechanism of absorption of phosphate, based on experiments in which the actions of micro-organisms have been ignored, require reinvestigation.