Water use and photosynthesis of Dendrobium Sonia ‘Earsakul’ under water deficit stress

Abstract

Dendrobium Sonia ‘Earsakul’ orchids in three developmental stages (plantlet, mature, flowering) were exposed to water deficit stress for 7 d. The average daily evapotranspiration rate (ET) ± SD under the well-watered condition was lowest in the plantlet stage (10.51 ± 1.96 mL/d). The ET of the mature and flowering stages was 45.80 ± 6.90 mL/d and 50.97 ± 7.23 mL/d, respectively. However, the ET was not significantly different between the mature and flowering stages. Under the water-limited condition, the ET values of all stages for the orchid were continuously depleted from the well-watered control at the 2^nd day in the plantlet stage and the 3^rd day of the mature and flowering stages after withholding water. The CO₂ exchange rate (CER) of the water-stressed plant substantially decreased compared to the control due to strong decreases in the stomatal conductance (g_s) and the transpiration rate (TR) in all developmental stages. In addition, water deficit stress led to a substantial decline in the water use efficiency (WUE) in the plantlet stage while the WUE of the mature and flowering stages remained similar to the control. However, the water deficit stress induced increased C_i/C_a in the plantlet stage. Moreover, shrinking of the stressed pseudobulb was seen in the plantlet and flowering stages but leaf wilting occurred only in the stressed plant of the plantlet stage. These results demonstrated that water deficit stress led to decreased photosynthesis in Den. Sonia ‘Earsakul’ due to stomatal limitation.