Comparative characterization of growth and phylogenetic relationship of some Poaceae C3 and C4 members in aquatic and terrestrial habitats

This study investigates the suitability of aquatic habitats to the growth of some Poaceae C3 and C4 members. Also, the phylogenetic relationship among these species was evaluated. Seven species were collected from aquatic and terrestrial habitats. Growth rate was higher in the C4 than in the C3 species in both habitats. Growth rate of the C4
species and Leersia hexandra (C3) was higher in the aquatic than in the terrestrial habitat. Water use efficiency (WUE) was not limiting to the growth of the C4 species in both habitats. However, high WUE could positively affect growth of the C4 compared to the C3 species in both habitats. The C4 species had not only higher photosynthetic efficiency (photosynthetic rate/Rubisco ratio, nitrogen use efficiency) than the C3 species but also this efficiency increased in the aquatic habitat. Aquatic conditions did not limit stomatal conductance (gs) in the C4 species and L. hexandra. In the aquatic C4 species, the increase in gs could lead to an increase in photosynthetic efficiency and growth rate. In the aquatic L. hexandra (C3), the increase in gs and Rubisco could enhance photosynthetic rate, but resulting in a decrease in photosynthetic efficiency compared to the C4 species. The accumulation of internal CO2 and sugars along with the increase in Rubisco may suggest that the C3 species had a limited growth rate compared to the C4 species even in the aquatic habitat. Aquatic habitats could be optimum to the growth of these C4 species.