Elucidating the types of carbon assimilation pathways in Dendrobium section Densiflora
Dendrobium section Densiflora species hold important ornamental and medicinal value. To improve the efficiency of breeding and cultivation,in this study,we aimed to elucidate the types of photosynthetic carbon assimilation pathways in D. brymerianum,D. chrysotoxum,D. densiflorum,D. harveyanum,D. sulcatum,D. thyrsiflorum,D. jenkinsii,D. lindleyi,all of which are known native Chinese species of Dendrobium section Densiflora,by analyzing stable carbon isotope ratios (δ13C),diurnal net CO2 assimilation,and titratable acidity. The results showed that the δ13C values of D. Jenkinsii and D. Lindleyi were greater than-20‰,identifying as crassulacean acid metabolism (CAM) plants,while the δ13C values of other 6 species were less than-20‰,identifying as C3 plants. Following drought stress,D. Jenkinsii had net CO2 uptake during the whole night,and D. Lindleyi had net CO2 exchange for over two-thirds of the night. The difference in titratable day and night acid level (△H+) between these two plants was markedly higher than that of C3 plants,providing further evidence that both are CAM plants. All C3 species exhibited marked net CO2 uptake during the daytime;however,acid accumulation in them was more markedly at night,exceeding 4 mmol·kg-1 . The only exception was D. Brymerianum,which did not show night acid accumulation,indicating that this effect is unique to the obligate C3 plants,while the remaining five species were facultative CAM plants.
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