Effects of timing of irrigation on community structure and biodiversity in rice fields

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K20009
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 64040:Social-ecological systems-related
• Research Institution: Center for Environmental Science in Saitama
• Principal Investigator: Yasuno Natsuru 埼玉県環境科学国際センター, 自然環境担当, 主任 (80850007)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 水田 / 群集 / 水生動物 / 底生動物 / サギ / カエル / 水生昆虫 / 田植え時期

Outline of Final Research Achievements

I compared aquatic communities in rice paddies cultivated under three management　regimes [early-planting culture (transplanting rice seedlings in early May),　normal season culture (transplanting in early June), and a wheat-rice double cropping system (transplanting in late June)]. Significant differences in the aquatic community structure among the three agricultural management regimes were observed. Loach (Misgurnus anguillicaudatus) and larvae of Tokyo daruma frog (Pelophylax porosus porosus) and dragonfly (Sympetrum spp.) characterized the aquatic community in early-planting culture, whereas chironomid larvae and carnivorous aquatic insects characterized the community in wheat and rice double cropping. Additionally, I monitored use of paddies by herons with time-lapse photography. Herons often visited paddies within 40 days after transplanting, but they did not visit the paddies after 50 days. Thus, irrigated paddies functioned as their foraging sites for short periods.

Free Research Field

生態学

Academic Significance and Societal Importance of the Research Achievements

近年、有機農法等の環境保全型農業が水田生態系に与える効果が注目されてきたが、田植え時期や輪作の有無といった耕作条件が生物多様性に及ぼす影響については不明な点が多かった。本研究では、田植え時期によって特定の水生動物が生息することを明らかにした。つまり、田植え時期をコントロールすることで、特定の分類群を保全できる可能性がある。また、サギ類が水田内で採餌可能なのは田植えから概ね40～50日程度であることが明らかとなり、田植え時期の異なる水田が混在すればより長期に亘って水田での採餌が可能になると考えられる。