Monday, November 13, 2006

Effects of Waterlogging on Nitrogen Fixation, Photosynthesis and Growth in Supernodulating Soybean Cultivar Kanto 100.

Gun-Ho Jung, Toshinori Matsunami, Yukihiko Oki, and Makie Kokubun. Grad. Schl. Agric. Sci., Tohoku Univ., Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, 981-8555, Japan

   The supernodulating soybean cultivar Kanto 100 (formerly named as Sakukei 4) was previously characterized by its superior capabilities of nitrogen (N) fixation and photosynthesis, and thereby is expected to have a potentiality of high-yielding. Since the N absorption and growth of Kanto 100 are largely dependent on N fixation, it is likely to be susceptible to waterlogging during the vegetative growth stage, which frequently occurs in major soybean producing areas. The objectives of the present study were, therefore, to investigate the effects of waterlogging on nodulation, N fixation, photosynthesis and growth of a supernodulating soybean cultivar, Kanto 100, and thereby to evaluate the adaptability of this cultivar to flooding condition. The supernodulating cultivar Kanto 100 and its normally-nodulating parental cultivar Enrei grown in pots were subjected to waterlogging treatment which was imposed at the successive three vegetative growth stages for two years and the physiological responses were compared. The waterlogging treatment reduced significantly the number and weight of nodules of both cultivars, and the magnitude of the reduction was more pronounced in Kanto 100, but the absolute values were always larger in Kanto 100 than in Enrei. The acetylene reduction activity (ARA) of nodules and apparent photosynthetic rate (AP) of leaves were generally depressed immediately after waterlogging treatment, but both functions exhibited a marked recovery at the pod-filling stage irrespective of cultivar. Although no marked cultivar difference was found in the magnitude of the reduction of ARA per plant and AP measured immediately after waterlogging and at the pod-filling stage irrespective of year, the growth reduction was more pronounced in Kanto 100 in one of two years. These results suggest that the supernodulating cultivar Kanto 100 is more susceptible to waterlogging under a certain growing condition than its normally-nodulating parent cultivar.