Water use efficiency of two forage species with different photosynthetic pathways

Exchange rates of CO2 and H2O under drought conditions were investigated in two grass species (Dasypyrum villosum, Dichanthium ischaemum) with different photosynthetic pathways (C3, C4) in order to evaluate their water use efficiency (WUE). Our results indicated differences in photosynthetic (Pn) and transpiration rate (Tr) between the two species. At the same values of leaf water potential (LWP) D. villosum (C3) exhibited higher Pn and Tr in relation to D. ischaemum (C4). However, their WUE showed no obvious differentiation. It seems that under drought conditions at late successional stages D. villosum (C3) develops higher photosynthetic rates than D. ischaemum (C4), and about the same values of WUE. Thus, the productivity of C3 and C4 species is probably related not only to the photosynthetic process but also to the ambient conditions in which the plants have been developed.