The Cobalt Requirement of Non-legume Root Nodule Plants

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Abstract
As already shown for Alnus glutinosa, cobalt is found to be essential for the proper growth of nodulated plants of Casuarina cunninghamiana and Myrica gale in a nitrogen-free rooting medium. If cobalt is not supplied, the plants develop symptoms of nitrogen deficiency; under the conditions of the experiments such symptoms became pronounced during the second season of growth of these perennial plants. No cobalt requirement could be detected in non-nodulated plants of Alnus and Myrica supplied with nitrate or ammonium-nitrogen, and this suggests that in nodulated plants the need for cobalt is confined to the nodules. Vitamin B12 analogues are shown to be present in the nodules in relatively large amounts when cobalt is supplied, their formation being attributed to the endophytes, which may therefore require cobalt for their growth. The great reduction in fixation of atmospheric nitrogen in cobalt-deficient nodules may be due to a retarded growth of the endophyte, though this is not the only possibility. The cobalt relation of these non-legumes appears to be basically similar to that of legumes.