A sand-fixing pioneer C3 species in sandland displays characteristics of C4 metabolism

A better understanding of the ecophysiology of sandy plants will facilitate the prediction of the community succession in sandy environment. The photosynthetic characteristics of Hedysarum fruticosum var. mongolicum, a sand-fixing leguminous C3 species in Hunshandak Sandland (HS) of northern China, were monitored and compared with those of Salix gordejevii, a typical C3 species co-existing with H. fruticosum in semi-fixed or fixed sand dunes. The maximal photosynthetic rate (Amax) and instantaneous water use efficiency (WUEi) of H. fruticosum was approximately two times higher than those of S. gordejevii. Except Ribulose-1.5-bisphosphate carboxylase (RuBPcase), the activities of photosynthetic carbon assimilation enzymes such as phosphoenolpyruvate carboxylase (PEPcase), NAD-malic enzymes (NAD-ME), NADP-malic enzymes (NADP-ME), NAD-malate dehydrogenase (NAD-MDH), NADP-malate dehydrogenase (NADP-MDH) and pyruvate phosphate dikinase (PPDK), were at least five times greater in H. fruticosum than those in S. gordejevii, suggesting H. fruticosum might have a C4 photosynthetic syndrome. However, stable carbon isotope analysis revealed that H. fruticosum had the δ13C value of −23‰, which was close to that of C3 plants. Therefore, it is likely that H. fruticosum is either a C3–C4 intermediate species, or a C3 species displaying C4 metabolic characteristics in habitat of sand dune. The involvement of C4 metabolism in H. fruticosum might account for its greater efficiencies for photosynthesis and water use, allowing H. fruticosum to colonize the shifting sand dune with high temperature, light intensities and water stress.