PHOTOSYNTHESIS OF DIFFERENT ECOTYPES OF MISCANTHUS SPP AS AFFECTED BY WATER-STRESS

Four clones of Miscanthus spp., collected from regions with different rainfall distribution, were transplanted in pots and subjected to five drying cycles (each of 6-7 d). Gas exchanges were measured on attached leaves. The light-saturated photosynthetic CO2 uptake (P-N) began to decline when the leaf water potential (psi(L)) was reduced to -1.3 - -1.5 MPa, and the psi(L) values corresponding to 50 % P-N decrease [psi(L)(1/2 P-N)] were -1.6 - -2.6 MPa. The psi(L)(1/2 P-N) values were lower in a clone collected from Kenting (northern Taiwan, highly frequent rainfall) than in clones collected from Kenting (southern Taiwan, distinct wet and dry season). Besides, the psi L(1/2 P-N) value became lower in all the tested clones when the drying cycle advanced (in the 3(rd) drying cycle of northern Taiwan clone and in the 5th drying cycle of southern Taiwan clones, respectively). Both the stomatal and nonstomatal factors of photosynthesis were affected by water deficit, and the osmotic adjustment mitigated the negative impact of water deficit on both factors. The clonal differences in the tolerance and acclimation of photosynthesis to water deficit are closely related to the osmotic adjustment, and the clonal differences in osmotic adjustment reflect the rainfall pattern of sampled region.