Growth responses of Brassica chinensis var. chinensis under CO₂- enriched controlled environment production system in the tropical lowlands

A prototype capable of CO₂ enrichment was developed to investigate the possibility of establishing CO₂ enrichment technique for controlled environment (CE) production system in the hot and humid lowland tropics. A model crop Brassica chinensis var. chinensis was used to demonstrate the impact of the established CO₂ enrichment technique on growth and development. Four levels of CO₂ enrichment viz. ambient as control (= 350 ppm), 750 ppm (double CO₂), 950 ppm (triple CO₂) and 1150 ppm (quadruple CO₂) were imposed on to 7-day Brassica chinensis var. chinensis seedlings. The growth responses were investigated by measuring the plant height, leaf area and leaf number, and biomass accumulation. Both the fresh and dry biomass accumulation increased with increasing carbon dioxide concentration between 22.6% and 36.5%, and 16.5% and 23.5% respectively, in the prototypes. The increased biomass could have resulted from the enhanced root growth and leaf area by ascending CO₂ enrichment. When enriched with carbon dioxide, root fresh weight increased between 26% and 47%. Consecutively, the leaf area expanded by nearly 20% (1117 cm₂) at 1150 ppm CO₂ enrichment level> 13% (1063 cm₂) and 14% (1074 cm₂) at respective 950 and 750 ppm CO₂ enrichment levels compared to 942 cm₂ area at ambient CO₂ level. The leaf area was also positively correlated with carbon dioxide concentrations. Similarly, plant height was enhanced by high carbon dioxide concentration in a descending manner1150 ppm (31.4 cm) > 750 ppm (30.7 cm) > 950 ppm (29.9 cm) > ambient 350 ppm (28.9 cm). The number of leaves, however, decreased when the highest level of CO₂ enrichment (1150 ppm) was imposed, although slightly higher leaf numbers were produced when carbon dioxide doubled the ambient concentration. The positive growth responses of Brassica chinensis var. chinensis in many of the vegetative parameters with increasing carbon dioxide concentration implied that a CO₂ enrichment technique established for CE production system for the lowland tropics was feasible and the prototype, practical.