Cyperus japonicus Mak., which has a widespread distribution in subtropical Asia and extends northwards into Europe, was found to be a C4 species based upon its Kranz leaf anatomy, low CO2 compensation concentration and isotopic composition of leaf carbon. A curious variant of the anatomical arrangement of photosynthetic celis is developed in this wetland species. Connected by veins, two groups of Kranz units, one undemeath the abaxial epidermis and the other in the middle of the blade, form elliptical mesophyll channels. This arrangement of Kranz units has been defined as Kranzkette (literally "the chain of garland"). Like Cyperus longus, another C4 species in the genus, the structure and arrangement of chloroplasts in the bundle sheath celis show it to be a NADP-ME type. Starch grains, however, are formed in both mesophyll and bundle sheath celis. This modified C4 Kranz anatomy with large intercellular air spaces within the chlorenchyma suggests that the arrangement of assimilatory celis may be related to gas transport through the large air-spaces.
A comparison of photosynthetic nitrogen (N) use efficiency between C3 and C4 species within the genus Cyperus was made at a range of available nitráte levels. Net photosynthetic rates (P^) of both types increased with N content but CO2 assimilation on a leaf area basis was consistently higher in C4 species in comparison to the C3 species. C4 plants had a higher photosynthetic N use efficiency than C3 plants, and achieved higher Pn at lower N and protein levels. The higher leaf photosynthetic N use efficiency (PNUE) in C4 plants is due to their high raťher than low N and protein contents. Because C^ leaves contain less N than C3 leaves for a given Py^, PNUE is significantly higher in C4 than C3 plants. Nitrogen supply had highly significant effect on the leaf N concentration, but had no significant influence on the CO2 compensation concentration. Carboxylation efficiency was significantly higher in C4 leaves than C3 leaves of Cyperus species, due to the CO2 concentrating mechanism of C4 photosynthesis.