Soyasaponins are triterpenoid saponins widely found in legume plants. These compounds have drawn considerable attention because they have various activities beneficial for human health, and their biosynthesis has been actively studied. In our previous study, we found that legume plants including soybean secrete soyasaponins from the roots in hydroponic culture throughout the growth period, but the physiological roles of soyasaponins in the rhizosphere and their fate in soil after exudation have remained unknown. This study demonstrates that soyasaponins are secreted from the roots of field‐grown soybean, and soyasaponin Bb is the major soyasaponin detected in the rhizosphere. In vitro analysis of the distribution coefficient suggested that soyasaponin Bb can diffuse over longer distances in the soil in comparison with daidzein, which is a typical isoflavone secreted from soybean roots. The degradation rate of soyasaponin Bb in soil was slightly faster than that of daidzein, whereas no soyasaponin Bb degradation was observed in autoclaved soil, suggesting that microbes utilize soyasaponins in the rhizosphere. Bacterial community composition was clearly influenced by soyasaponin Bb, and potential plant growth–promoting rhizobacteria such as Novosphingobium were significantly enriched in both soyasaponin Bb–treated soil and the soybean rhizosphere. These results strongly suggest that soyasaponin Bb plays an important role in the enrichment of certain microbes in the soybean rhizosphere.

中文翻译：

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大豆根中大豆皂苷的分泌动态及其对细菌组成的改变作用


大豆皂苷是广泛存在于豆科植物中的三萜皂苷。这些化合物由于具有多种有益于人类健康的活性而引起了人们的广泛关注，并且它们的生物合成已得到积极研究。在我们之前的研究中，我们发现包括大豆在内的豆科植物在水培的整个生长期都会从根部分泌大豆皂苷，但大豆皂苷在根际的生理作用以及渗出后在土壤中的命运仍然未知。本研究表明，大豆皂苷是从田间种植的大豆根部分泌的，而大豆皂苷 Bb 是在根际检测到的主要大豆皂苷。体外分配系数分析表明，与大豆苷元（大豆根部分泌的典型异黄酮）相比，大豆皂苷 Bb 可以在土壤中扩散更远的距离。土壤中大豆皂苷Bb的降解速度略快于大豆皂苷元，而在高压灭菌的土壤中未观察到大豆皂苷Bb的降解，表明微生物在根际利用大豆皂苷。细菌群落组成明显受到大豆皂苷 Bb 的影响，并且在大豆皂苷 Bb 处理的土壤和大豆根际中，潜在促进植物生长的根际细菌（如新鞘氨醇菌）显着富集。这些结果强烈表明大豆皂苷 Bb 在大豆根际某些微生物的富集中发挥着重要作用。