Physiological responses of potted Dendrobium orchid to salinity stress

Abstract

The effects of salt stress on the growth, flowering, osmotic potential, and cellular Na⁺, K⁺, and Cl⁻ accumulation were investigated in potted Dendrobium Sonia ‘Earsakul’. Six NaCl solute concentrations with an electrical conductivity of 0, 2, 4, 6, 8 and 15 dS m⁻¹ were applied to the orchids continuously for 30 days. The results showed that NaCl at 2 dS m⁻¹ or greater significantly reduced the number and dry weight of leaf and flower size. At a NaCl dose of 4 dS m⁻¹ or greater, a reduction in the diameter and number of pseudobulb, and inflorescence lengths were observed. With exposure to a high salinity level of 15 dS m⁻¹ NaCl for 30 days, plants had lost nearly 50% of their leaf dry weight and flower quality. In response to salt stress, osmotic adjustment by accumulation of organic solutes was clearly detected when the orchids were treated with 4 dS m⁻¹ NaCl or greater. This caused a decrease of leaf water and osmotic potential. In addition, it appears the Dendrobium orchid has adapted itself to high salinity conditions by limiting Na⁺ and Cl⁻ exportation to the shoot by accumulating these ions in the roots. Dendrobium also maintained a similar level of K⁺ afflux in their leaves, pseudobulb, and roots compared to the non NaCl treated control. This created extremely high Na⁺/K⁺ ratios in the roots at increasing NaCl concentrations. The overall results suggest that the Dendrobium orchid responds to salinity by performing osmotic adjustment and sequestering Na⁺ or Cl⁻ in the roots, preventing their movement to the upper plant parts.