Mixed effects of CO2 concentration on photosynthesis of lettuce in a closed artificial ecosystem

The photosynthetic response of higher plants to CO₂ concentration in the controlled ecological life support system (CELSS) was investigated using a closed artificial ecosystem. As the representative cultivar, five batches of lettuce were cultivated in a staged mode to eliminate the influence of other biological and technical factors. Carbon dioxide was supplied by the routine respiration of researchers. A mixed effects model was established to describe the photosynthesis of lettuce crops. The fixed and random effects of parameters were estimated based on the selected data sets. The model adequacy was evaluated by the statistical analyses. The frequency histograms of the random effects were regressed using the probability density equations. The distribution of photosynthetic rate at each point of CO₂ concentration on the random effects was obtained. The predictions of the model compared favorably with the experimental measurements. The model was sufficient to describe the photosynthetic property of the lettuce crops. The method discussed in this paper could be extended to investigate the mixed effects of other environmental conditions on the photosynthesis of higher plants.