Studies on the Development of the Ventilating System in Relation to the Tolerance against Excess-Moisture Injury in Various Crop Plants : X. Effect of removal fo the top part of plant on nitrate reduction by the roots

Abstract

The attached roots as well as the detached roots of both rice and soybean plants were used for the comparison between respiration intensity, as measured by carbon dioxide output, under aerobic and anaerobic conditions. The results obtained are ds follows: (1) The attached roots of rice are able to respire almost aerobically even if they were kept in a medium. containing no oxygen, in spite of the detached roots being appreciably depressed in their respiration intensity under the same condition, eventually producing carbon dioxide for the most part due to anaerobic respiration. However; there occurs no marked difference in respiration intensity between the two kinds of roots, as far as they are growing in an oxygenated medium. (2) The roots of soybean are no sooner placed under the condition of poor aeration than they are depressed in their capacity to respire aerobically. It is no doubt that carbon dioxide evolved in this case should be as a result of anaerobic respiration. When the roots are kept in an oxygenated medium, on the cotrary, the rate of carbon dioxide output is definitely higher than when they are kept in a medium under poor aeration, regardless of whether they are connected with the top or removed from it. (3) These results indicate that in the plants which are equipped with the well-developed ventilating system, the roots are able to respire aerobically even if they were met by a condition of poor aeration, because of their possibility of receiving molecular oxygen from the top and, on the other hand, in the plants which are equipped with the feebly-developed ventilating system, the roots are incapable of carrying on aerobic respiration in case of being met by the same condition, eventually producing carbon dioxide quite anaerobically.