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

重点研究了伤流率作为反映大豆根系活力的一个指标，并通过对植株生长及其日变化的研究，阐明了伤流率的动态变化规律。从伤流率的变化可以看出，土壤塑型处理提高了根系活力，使干物质生产量和产量在干旱和湿润年份均有所提高。促进了不定根的发育，这些不定根比（即，不那么老）主根，有助于这增强根系活力。在淹水试验中，土壤水分过多严重抑制主根的生长。而不定根则由下胚轴和茎基部形成，在土壤表面分布和爬行。因此，研究了土壤塑型对大豆耐渍性的影响，它促进了不定根的形成，并为不定根的分布和发挥作用提供了土壤空间。在20 d的淹水处理中，塑膜并没有缓解对新梢生长（叶面积、叶色、干重）的抑制，但显著促进了处理后的恢复。塑型处理显著提高了涝渍大豆的最终地上部干生物量和产量。大豆霉变和淹水的根系非常浅，但通过土壤霉变部分不定根的发育维持了较大的总根长。结果表明，土壤造型可以很好地避免过度水分胁迫，经常发生在日本水稻田起源的大豆领域。

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.