Photosynthetic pathway types in rangeland plant species from inner Mongolia, North China

Abstract

Photosynthetic pathway types, based on δ 13C measurements, were determined for 125 species in 95 genera and 32 families growing in rangelands from Inner Mongolia. Of the total species, 4 species from 3 genera and 2 families had C 4 photosynthesis (2 species in Gramineae and 2 in Chenopodiaceae) and 118 species from 90 genera and 31 families had C 3 photosynthesis. The number of C 4 species differed significantly among four rangeland sites, 4 species in desert, 3 species in steppe, but no C 4 species were identified in meadow and dune. Six species [e.g. Agriophyllum arenarium Bieb., Bassia dasyphylla O. Kuntze, Saussurea japonica (Thunb.) DC.] earlier identified as C 4 species using the enzyme ratio method were found as C 3 species using the carbon isotope ratios (δ 13C). Hence the enzyme ratio method for C 3 and C 4 identification may not always be reliable. The δ 13C values of 3 species of Crassulaceae, which had been considered as CAM species, differed remarkably [-25.79 ‰ for Sedum aizoon L., -24.42 ‰ for Osostachys fimbriatus (Turcz.) Berger, and -16.97 ‰ for O. malacophyllus (Pall.) Fisch], suggesting that the use of δ 13C method as a diagnosis for CAM photosynthetic pathway type may not always be reliable and supplementary measurements are needed.