关键词: 石斛兰, 光合特性, C3植物

Abstract: We examined the photosynthetic physiology of Dendrobium williamsonii and D. longicornu. Cross-sections of the leaves of the 2 Dendrobium species showed that they were bifacial. The abaxial epidermis showed a large amount of stomata, covered by the waxy stomata; vascular bundles showed no chloroplast or Kranz structures. Photosynthesis of the 2 species responded to light intensity, CO₂ concentration and temperature. Light compensation points were 5–10 μmol·m⁻²·s⁻¹, light saturation points were 800–900 μmol·m⁻²·s⁻¹; apparent quantum yields were ~0.02; CO₂ compensation points and saturation points were 80–90 μmol·mol⁻¹ and 800 μmol·mol⁻¹, respectively; and carboxylation efficiencies were 0.015–0.021. The optimal temperature for photosynthesis was 26–30°C. The diurnal variation in net photosynthetic rates (P_n) were all bimodal curves, with the first peaks at ~5 μmol CO₂·m⁻²·s⁻¹ and emerging at between 11:00–12:00, and the second peaks emerging at about 15:00; no CO₂ absorption occurred at night. Additionally, the chlorophyll a/b (Chl a/b) ratios of leaves were 2.51–2.66. Measurement of key enzymes in the photosynthetic pathway indicated relatively high RuBPCase and GO activities but low PEPCase activities. D. williamsonii and D. longicornu are typical semi-shade C3 plants.

Key words: Dendrobium, photosynthetic characteristics, C3 plants