Effects of phosphorus and sulphur on dark respiration of subterranean clover leaves

Abstract

Respiration rates in the dark (oxygen uptake) of leaves sampled from subterranean clover plants (Trifolium subterraneum L. cv. Mt Barker) increased with the phosphorus supply in the culture solutions in which the plants were grown. Over a period of 3 hr no differences were detected in respiration rates when leaves of these plants were placed in Warburg flasks containing complete solutions or solutions without phosphorus. However, when whole plants were transferred to complete and no-phosphorus solutions, the differences in respiration rates of leaves sampled from the two groups of plants depended on the phosphorus status of the plants at transfer. Leaves from plants raised at an adequate phosphorus level showed no differences over a period of 96 hr after transfer, but leaves from plants raised at suboptimal phosphorus levels before transfer to complete and no-phosphorus solutions showed significant differences in respiration rates as early as 18-19 hr after transfer. Similar results were obtained for leaves sampled from plants raised at different sulphur levels when transferred to complete solutions and to solutions without sulphur. However, these differences took longer to develop than in the phosphorus experiments. When phosphorus-deficient plants were transferred to complete solutions and to other solutions each without a different element, the respiration rates of the leaves sampled from the plants in the solutions without phosphorus were much lower than for the leaves of plants in the other solutions.