Clarifying factors affecting above-ground floristic composition and soil seed banks for the conservation and restoration of plant species in rice paddy fields

人工田和撂荒稻田在植物区系上具有高度的多样性，但影响这种多样性的机制尚不清楚。进行了以下研究。首先，对栽培水田的实地调查表明，不同土地形态类型的土地改良强度对植物区系组成的影响存在差异。本研究还暗示了水稻收获期是控制植物区系组成的重要因素。因此，利用栽培稻田的表层土壤进行了发芽试验。结果表明，秋季作物收获后的植物区系组成受水稻收获时间的影响较大，而随后的春季植物区系组成受前一年水稻收获时间的影响较小。研究的第三个课题是对稻田土壤种子库的植物区系组成进行时序调查，研究了稻田土壤种子库中稀有湿地植物区系的组成。研究表明，遗弃时间明显减少了湿地物种的数量，而在可发芽条件下，遗弃开始时所观察到的不少于一半的物种在种子库中持续存在。

Cultivated and abandoned paddy field are floristically highly diverse, but the mechanisms affecting this diversity are not clear. The following studies were carried out. First, field surveys in cultivated rice paddy fields showed that influence of land improvement intensity on floristic composition was different among different land form types. This study also implied the importance of the period of rice harvest as a factor controlling floristic composition. A germination test was, hence, carried out using surface soils of a cultivated rice paddy. The results suggest that floristic composition just after the crop harvest in autumn was strongly different according to the timing of rice harvest, while in the subsequent spring floristic composition was less affected by the timing of rice harvest in the previous year. As the third study topic, floristic composition in the soil seed banks was investigated along a chronosequence in abandoned paddy fields, where soil seed banks of rare wetland floristic species are often maintained in the surface soils. This study illustrates that duration of abandonment clearly decreased the number of wetland species, whereas no less than half species observed in the start of abandonment persisted in the seed banks under germinable condition.