Changes in Carbon Dioxide and ethylene concentrations in the closed ecological chamber in which lettuce and shiitake mushroom are cultivated

Abstract

The closed ecological experiment facility is used as a simulator for a CELSS and for the earth, in order to clarify the interaction between the ecological components, such as plant and human beings, and the gas balance. In this report, a closed ecological experiment was conducted with a closed small chamber (1.37m³in volume) in which lettuce plants and shiitake mushroom were cultivated. We monitored CO₂ and ethylene concentrations inside the chamber for 4 days and investigated the interactions between these gases and the biological components.
The CO₂ concentration inside the chamber depended on the combination of lettuce and shiitake mushroom, and varied from 190 to 5, 000 ppm. In each experiment CO₂ concentration changed with time, because the net photosynthetic rate of the lettuce and the respiration rate of the mushroom mycelium changed. The former changed with the increase in its leaf area and with the change in CO₂ concentration and the latter gradually decreased with time.
The concentration of ethylene, which was released from the lettuce and the mushroom, increased to 0.15 ppm at the end of the experiment. The visible injury was observed in the lettuce leaves, which might be due to the increased ethylene concentration. It is essential to identify and quantify trace contaminants including ethylene and to investigate the effects of trace contaminants on the growth of the lettuce and the mushroom.
From these results, the interactions between gas balance and the biological components in the closed chamber were clarified. Some of problems for the establishment of the closed ecological cultivation system were also pointed out.