通気系の発達と耐湿性との関係 : 第6報 麦類及び数種牧草類の湛水処理に対する生態学的並に解剖学的反応

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A series of experiments was made to find the relationship between the tolerance agaist excess-moisture injury and the development of the ventilating system, through which molecular oxygen should be transported from the top to the roots for the purpose of respiration. Potted plants of barley, Kentucky-31-fecue, alsike clover, and Genge (Astragalus sinicus) were grown in a green-house, and the soils were flooded during periods of various lengths until the time of harvest. The results obtained are as follows: (1) The barley plant, when flooded continuously from the tillering stage of growth to the time of its death, was to some extent able to adapt itself to an overmoist habitat by generating secondary roots to supersede the injured primary ones, and by improving the ventilating system in the primary tissues so as to facilitate oxygen transport from the top to the roots (cf. Figs. 3-5). These modifications affected directly the ventilating pressure as shown in Fig. 2. A shallow root system formed during the treatment caused the plant to absorb less amount of nutrients from the soil, resulting in a poor growth of plants. When the plant had grown up to heading, however, the ventilating System was virtually blocked up, so that no roots remained alive, being severely afflicted with deficient oxygen supply (cf. Figs. 6-8). The leaves dried up more rapidly and accordingly smaller amonts of grains were produced. The plant, when flooded at the heading stage and kept treated thereafter, did not reveal any longer such effective modifications as above-described in response to adverse circumstance, because of its senescence, e.g. blocking up of the ventilating system and inactivity of root formation. Simultaneous drying up of all leaves within a week after flooding brought forth a remarkable reduction in grain yield. (2) The plant of Kentucky-31-fescue as well as of reed canary grass was equipped with well-developed ventilating system even in the senescent stage of growth under standard conditions, as inferred from the seasonal changes in the ventilating pressure (cf. Figs. 9-11). They were highly resistant to excess-moisture injury by flooding as an excellent ventilating system might They always be ready for furnishing their roots with sufficient supply of oxygen necessary for respiration. showed a slightly suspended growth for a while after treatment, but it was not nearly until the time of establishment of a new root system and of improved ventilating facilities, in adaptation to their new habitat, that they resumed vigorous growth. In consequence, the flooded plants could yield larger dry weights than those by the check plants. (3) Alsike clover, too, was capable of adapting itself to overmoist habitat almost in the same way as seen in Kentucky-31-fescue. Ecological responses to flooding were reflected upon a lower ventilating pressure throughout after flooding, suggesting that oxygen transportation from the top to the roots had been accelerated. Noteworthy was the anatomical feature of the ventilating system particular to this crop (cf. Figs. 12-14). (4) Genge was found susceptible to excess-moisture injury. Upon flooding, it could neither improve the ventilating system nor generate new roots, resulting in a simultaneous shedding of almost all the leaves and consequently in a stunted growth of plants. The epidermis of the stem undr water was reformed likely enough to absorb some water and nutrients, taking the place of poorly functioning roots (cf. Figs. 15-16). It was for this reason that the flooded plant could survive so far as to ploduce a few mature seeds. (5) From these results it may be concluded that the tolerance against excess-moisture injury is closely related to the development of the ventilating system, whose mode and degree are particular to the kind of crops. In this case the improvement of the ventilating system as well as the reformation of the root system is necessary for making the plant possible to transport more oxy