根圏ガス環境の制御に関する研究

(2) キュウリの生育に対する根圏空気中のCO₂の影響

抄録

The relationship between CO₂ concentration in the rhizosphere and the growth of cucumber plant was studied. Growth rates of cucumber plant growing in the sand culture were compared for CO₂ concentration varying from 0 to 5% in the rhizosphere. The effects of CO₂ and O₂ in the rhizosphere on photosynthetic rate were then investigated.
The results obtained were as follows.
(1) The growth suppression of cucumber plant occurred at 0.5-2% CO₂ in the rhizosphere. Total dry weight and leaf area decreased up to 80-90% by the increase of CO₂ concentration (2-5%) in the rhizosphere.
(2) The growth suppression by CO₂ was found five days after the beginning of treatments.
(3) Water content of the top decreased with increase in CO₂ concentration in the rhizosphere.
(4) Photosynthetic rate decreased two hours after the beginning of treatments even at 3-5% CO₂. After four hours, photosynthetic rate at 10% CO₂ declined up to 85% of that before the treatment, while it retained 95% when treated with 10% O₂.
As described above, it is proved that the growth of cucumber plant is suppressed with increase in CO₂ concentration in the rhizosphere before the suppression by decreasing O₂ concentration occurs.