PHOTOSYNTHESIS OF DIFFERENT ECOTYPES OF MISCANTHUS SPP AS AFFECTED BYWATER-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 attache d 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 [ps i(L)(1/2 P-N)] were -1.6 - -2.6 MPa. The psi(L)(1/2 P-N) values were l ower in a clone collected from Kenting (northern Taiwan, highly freque nt rainfall) than in clones collected from Kenting (southern Taiwan, d istinct 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 cycl e of southern Taiwan clones, respectively). Both the stomatal and nons tomatal 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 acclimati on of photosynthesis to water deficit are closely related to the osmot ic adjustment, and the clonal differences in osmotic adjustment reflec t the rainfall pattern of sampled region.