Greenhouse Temperature Control Research Articles

Effect of temperature on photosynthesis of lettuce adapted to different light and temperature conditions

Gas exchange of lettuce plants, pre-grown in growth chambers at different irradiances (18, 37, 70 W m −2) and temperatures (6, 14, 22°C) were measured in the range of 2–22°C. In weak light (18 W m −2) there was no increase in CO 2 uptake above 2°C, and even in 70 W m −2 the highest rates were obtained at about 10°C only. The response of net photosynthesis of lettuce to temperature is diminished as a result of morphological plant adaptations, i.e. specific leaf area or top-to-root weight ratio. The temperature optimum for dry-matter production is much higher than that for CO 2 uptake. Therefore, photosynthesis is an unsuitable criterion for temperature control in greenhouses.

A simple automatic window‐opening device for temperature control in greenhouses

The apparatus described opens greenhouse windows within 2 min. of the closing of a thermostatically controlled electric circuit, and shuts them with a time lag of 12 min. after the circuit is broken. Power is consumed, during the time that the circuit is closed only, at about 250 W.; the apparatus can readily be extended to operate more windows or other similar devices and is easily adaptable to existing greenhouses.