Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2
1999
Gouk, S.S. | He, J. | Hew, C.S.
The effects on growth in super-elevated (1%) CO(2) in terms of photosynthetic capability and carbohydrate production were studied in an epiphytic CAM (Crassulacean acid metabolism) orchid plantlet, Mokara Yellow (Arachinis hookeriana x Ascocenda Madame Kenny). The growth of the plantlets was greatly enhanced after growing for 3 months at 1% CO(2) compared with the control plantlets (0.035% CO(2). CO(2) enrichment produced more than a 2-fold increase in dry matter production. The enhanced root growth at 1% CO(2) led to a higher root:shoot ratio. Plantlets grown at super-elevated CO(2) had higher F(v)/F(m) values, a higher photochemical quenching (q(p)) and a relatively lower non-photochemical quenching (q(N)). CO(2) at 1% appeared to enhance the utilization of captured light energy in the orchid plantlets. CO(2) enrichment also increased contents of soluble sugars (glucose and sucrose) and starch in the orchid plantlets. The extra starch formed under 1% CO(2) did not cause a disruption of the chloroplasts. Chlorophyll content was higher and a clear granal stacking was evident in young leaves and roots of plantlets grown at 1% CO(2). An extensive thylakoid system was observed in the young leaf chloroplasts of the CO(2)-enriched plantlets indicating an improved development of the photosynthetic apparatus when compared to that of the control plantlets. The increased photosynthetic capacity and enhanced growth of the epiphytic roots under CO(2) enrichment would facilitate the generation of more photoassimilates and acquisition of essential resources, thereby increasing the survival rate of orchid plantlets under stressful field conditions.
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