Dynamic evaluation and improvement of environmental and physiological factors inducing midday depression of crop photosynthesis in greenhouses

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K05905
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 41040:Agricultural environmental engineering and agricultural information engineering-related
• Research Institution: Kyushu University
• Principal Investigator: Yasutake Daisuke 九州大学, 農学研究院, 准教授 (90516113)
• Co-Investigator(Kenkyū-buntansha): 北野 雅治 高知大学, 農林海洋科学部, 特任教授 (30153109) ; 森 牧人 高知大学, 教育研究部自然科学系農学部門, 教授 (60325496)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 昼寝現象 / 光合成速度 / 蒸散速度 / 気孔コンダクタンス / 水ストレス / CO2拡散 / 水噴霧

Outline of Final Research Achievements

In order to optimize crop production, it is important to bring out the potential of photosynthesis. However, photosynthetic rate temporarily decreases around noon even on a sunny day, which is called as “midday depression of photosynthesis”, and this phenomenon can be regarded as a loss of crop production. Therefore, it is required to elucidate limiting factors of the midday depression and improve them.
The present study showed that approximately 80% of limiting factors was attributed to an insufficient CO2 diffusion derived from mesophyll and stomatal behaviors and its ratio was not constant and changed dynamically during daytime. Furthermore, leaf wetting with an adequate mist spray improved the midday depression of photosynthesis through maintaining the CO2 diffusion by avoiding leaf water stress.

Free Research Field

農業気象学，生物環境調節学

Academic Significance and Societal Importance of the Research Achievements

昼寝現象に関わる既往の研究（文献）は多数あるものの，それらの文献の殆どのケースでは，昼寝現象を引き起こした要因をどれか単独のものに限定したり，詳細な調査が無いまま主要因の定説化も見られた．本研究成果では，昼寝現象の要因群を定量的に評価し，さらにそれらが動的に変化することを示したことが学術的意義を有する点である．
また，昼寝現象の主要因として特定したCO2拡散律速が葉面水噴霧によって改善され，その結果，昼寝現象の回避と水利用効率の向上を実現した．これは，作物生産上のロス（昼寝現象）に対して，水噴霧という比較的容易な手段が有効であることを示した点で意義がある．