Improvement of structure and function of root system and investigation of signal substrates in Soybean for the enhancement of waterlogging tolerance.

重点研究了大豆根系活力指标出血率，阐明了其在植株生长过程中的动态及其日变化规律。随着出血率的增加，土壤成型处理在植株生长的整个过程中都增强了根系活力，导致干物质产量和产量在干湿年份都有所增加。不定根比主根更新（即没有主根那么老），促进了不定根的发育，促进了根系活力的增强。在涝渍试验中，土壤水分过高严重抑制了主根的生长。而不定根则由茎的下胚轴和基部形成，沿土壤表面分布和爬行。因此，土壤成型促进了不定根的形成，为其提供了分布和发挥作用的土壤空间，对大豆耐涝能力具有重要影响。在涝渍处理20 d期间，塑枝处理并未减轻对芽部生长（叶面积、叶色、干重）的抑制，但显著促进了处理后的恢复。淹水大豆的终梢干生物量和产量显著提高。淹水后大豆的根系很浅，但由于土壤成型部分不定根的发育，根系保持了较大的总长度。结果表明，土壤模塑可以很好地避免日本稻田大豆田经常出现的过度水分胁迫。

We focused on the bleeding rate as an index of root-system vitality of soybean, and made its dynamics through the plant growth and its diurnal change clear. With the bleeding rate, it was shown that the treatment of soil molding enhanced the root-system vitality all through the plant growth, resulting in higher shoot dry matter production and yields in both dry and wet years. The promoted development of adventitious roots, which are newer than (i.e., not so aged as) taproot, contributed to this enhancement of the root-system vitality. In an experiment on waterlogging, the growth of taproot was severely inhibited by the excessive soil moisture. and, instead, adventitious root were formed from the hypocotyl and basal part of the stem, which distributed and crawled around the soil surface. Thus, the effects of soil molding, which promotes adventitious roots formation and offer them the soil space for distribution and functioning, on the tolerance against waterlogging in soybean. The molding did not alleviate the inhibition of shoot growth (leaf area, leaf color, dry weight) during the 20-day waterlogging treatment, but remarkably enhanced the recovery after the treatment. The final shoot dry biomass and yield of waterlogged soybean was significantly enlarged by the molding. The root system of the molded and waterlogged soybean was very shallow but maintained large total root length by the development of adventitious roots in the molded part of the soil. The results indicated that soil molding can be a good management to avoid the excessive water stress that often occurs in paddy-fielded-originated soybean fields in Japan.