RESPONSES OF 4 ARID ZONE GRASS SPECIES FROM VARYING HABITATS TO DROUGHT STRESS

The effects of 4 or 8 drought cycles on four grass species, Cenchrus pennisetiformis, Leptochloa fusca, Panicum turgidum, and Pennisetum divisum were assessed in a pot experiment. There were significant differences between the species in biomass production under water stress. C. pennisetiformis and P. turgidum produced significantly greater fresh and dry matter than P. divisum and especially than L. fusca. L. fusca had the lowest and P. divisum highest osmotic potentials compared with the other species after the completion of 4 or 8 drought cycles. Osmotic adjustment (difference between osmotic potential of droughted/rehydrated plants and control plants) was highest in L. fusca. The stomatal conductance was significantly decreased with increased drought stress in C. pennisetiformis. The elasticity of C. pennisetiformis, P. turgidum and P. divisum increased with increase in number of drought cycles, whereas that of L. fusca remained unchanged. L. fusca and P. turgidum had the lowest leaf hydration of all species after 8 drought cycles. The chlorophylls a and b in all species remained unaffected by drought treatments. The proline content of C. pennisetiformis and L. fusca increased significantly with increased drought stress, whereas that of P. turgidum remained unaffected after 4 or 8 drought cycles. L. fusca synthesized great amount of leaf soluble proteins during 8 drought cycles, whereas P. divisum had low protein content after 4 drought cycles. The protein contents of C. pennisetiformis and P. turgidum remained unaffected after 8 drought cycles. The leaf epicuticular wax of L. fusca increased consistently with increased drought stress, but leaf wax of P. divisum increased only at the highest drought stress and that of C. pennisetiformis and P. turgidum increased after 4 drought cycles. On the basis of these results it was established that C. pennisetiformis and P. turgidum were the most tolerant, P. divisum intermediate, and L. fusca the most sensitive to drought stress. The osmotic adjustment did not positively correlate with the degree of drought resistance.