CARBON-DIOXIDE AND LIGHT EFFECTS ON PHOTOSYNTHESIS, TRANSPIRATION ANDEX-VITRO GROWTH OF HOMALOMENA EMERALD GEM PLANTLETS

Micropropagated plantlets of Homalomena cultivar 'Emerald Gem' were gr own ex vitro at two CO2 concentrations (350 and 1200 mumol mol-1) and two light levels (50 and 150 mumol m-2 s-1 photosynthetic photon flux density (PPFD)). Plants grown at 1200 mumol mol-1 CO2 and at 150 mumol m-2 s-1 PPFD accumulated dry weight of shoots and roots three and two times higher, respectively, and had a leaf area 2.4 times higher than that of plants grown at 350 mumol mol-1 CO2 and 50 mumol m-2 s-1 PPFD . These plants also had the highest rate of photosynthesis. Carbon dio xide enrichment was more effective than supplementary light to increas e plant growth. The CO2 assimilation rate, photorespiration, transpira tion and stomatal conductance to water vapour were strongly promoted b y light al 150 mumol m-2 s-1, irrespective Of CO2 concentration. CO2 e nrichment enhanced the CO2 assimilation rate and quantum efficiency bu t decreased the rate of transpiration at 50 mumol m-2 s-1 PPFD and sto matal conductance to water vapour at 50 and 150 mumol m-2 s-1 PPFD.