Integrated Multi-Trait Analysis of Photosynthetic Carbon Assimilation Strategies in Dendrobium Species

Dendrobium species are valuable medicinal and ornamental orchids whose epiphytic or lithophytic growth exposes them to fluctuating water availability. Comparative evidence on their carbon-assimilation strategies can help identify physiological traits relevant to conservation and cultivation. We compared nine Dendrobium species using diel net CO2 exchange, leaf carbon isotope composition (δ13C), dawn–dusk titratable acidity differences (ΔH+), leaf anatomy, and the mesophyll succulence index (Sm), and evaluated agreement between physiological and structural indicators. D. parishii, D. aphyllum, and D. anosmum showed concordant patterns consistent with substantial CAM-associated carbon assimilation. D. cariniferum, D. gibsonii, and D. hancockii showed predominantly C3-associated patterns under the conditions examined. D. linawianum, D. moschatum, and D. crystallinum combined C3-like isotope signatures with weak reported nocturnal CO2 exchange and variable acidity differences; these observations are described provisionally as CAM-like characteristics and do not establish facultative CAM or definitive C3/CAM intermediate status. Leaf thickness and Sm overlapped among physiological groups, limiting their diagnostic value. Exploratory correlations across nine species suggested associations among physiological indicators, but small sample size and unaccounted phylogenetic relatedness limit generalization. This comparative dataset supports complementary physiological measurements when evaluating Dendrobium carbon assimilation.