Does Bienertia cycloptera with the single-cell system of C4 photosynthesis exhibit a seasonal pattern of δ13C values in nature similar to co-existing C4 Chenopodiaceae having the dual-cell (Kranz) system?

Family Chenopodiaceae is an intriguing lineage, having the largest number of C-4 species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C-4 functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (delta C-13 values) of leaves deviated from C-4 to C-3-C-4 intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species usually co-occurs with several Kranz type C-4 annuals. The development of B. cycloptera morphologically and delta C-13 values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a salt flat in north central Iran, along with eight Kranz type C-4 species and one C-3 species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf anatomy and C-4 biochemical subtype. Among the nine C-4 species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C-4 anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in the delta C-13 values found in plants grown in the natural habitat. The nine C-4 species had average seasonal delta C-13 values of -13.9% (with a range between species from -11.3 to -15.9%). The measurements of delta C-13 values over a complete growing season show that B. cycloptera performs C-4 photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average delta C-13 value of -15.2%.