Seasonal alterations of water status and gas exchanges in Cattleya granulosa juvenile plants submitted to different light regimes
Crassulacean acid metabolism, epiphytic orchid, light stress, seasonal variation. tropical sandbank
Cattleya granulosa is an endangered epiphytic orchid native to the Brazilian Atlantic Forest. Since its responses to light intensity and its CAM expression remain elusive, C. granulosa juvenile plants were grown under full sunlight, 60% shading, and 95% shading in a nursery and plant growth, water status, titratable acidity, and gas exchanges were assessed during the rainy and dry seasons. The plants exposed to full sunlight showed visual symptoms of light stress but survived throughout the experiment. These plants exhibited reduced shoots and extensive roots regarding the plants submitted to shading. The time-course of CO2 uptake and stomatal conductance in C. granulosa leaves over 24 h, independent of treatment, is compatible with constitutive CAM. However, changes in timelapse and magnitude of CO2 uptake and in accumulated acidity promoted by light regime and seasonality reveal that CAM expression in C. granulosa leaves may be modulated according to growing conditions.