THE EFFECTS OF SUPPLEMENTARY HPS LIGHTING AND CARBON-DIOXIDE ENRICHMENT ON THE VEGETATIVE GROWTH, NUTRITIONAL-STATUS AND FLOWERING CHARACTERISTICS OF CHRYSANTHEMUM-MORIFOLIUM RAMAT

Supplementary high pressure sodium (HPS) lighting (140 .mu.mol m-2 s-1) and CO2 enrichment (1375 .mu.l l-1) improved the vegetative growth of C. morifolium cv. Dramatic by increases in stem length, stem diameter, root wt ratio, dry wt, relative growth and net assimilation rats. Three-week old chrysanthemums grown under CO2 enrichment and HPS lighting had lower left wt and stem wt ratios and lower foliar nutrient content than those grown under ambient CO2 and natural light. Plants grown on to maturity under CO2 enrichment and supplementary HPS lighting had the longest stem lengths, the most flowers and greatest increase in dry wt. The combination of both additional light and CO2 was superior to either factor used alone. With 24 h HPS supplementary lighting CO2 enrichment was most effective in improving vegetative growth and flower quality when applied during the daytime. Night CO2 enrichment was not commercially beneficial at the light levels employed in this study.