Different sensitivity of photosynthesis and transpiration to some herbicides and transpiration inhibitors

Rates of transpiration and net photosynthesis in intact sugar beet and bean plants were measured during 14 hours’ exposure to some herbicides, to transpiration inhibitors, and to high osmotic pressure. Transpiration and photosynthesis were inhibited to the same extent or transpiration slightly stronger, by treatment of the roots with ioxynil, by application of PMA and DSA either to the rooting medium or to the foliage, and by high osmotic stress. Photosynthesis, however, was inhibited to a greater degree than transpiration by simeton and isocil applied both to the roots and the leaves, and by a foliar spray of ioxynil. Similar, but somewhat smaller differences were found when DNOC was applied to the nutrient solution or to the leaves.