Abstract:

The two-year-old seedlings of Populus euphratica and Populus pruinosa were grown in pots to study the effects of soil water stress on the response of photosynthetic parameters to light intensities(PAR 0～3 000 μmol photons·m^-2s^-1).There were three soil water stress treatments:70%～80%(normal water supply),50%～60%(mild stress)and 30%～40%(severe stress)of field water-holding capacity.The results showed that light response curves of net photosynthetic rate(P_n)in P.euphratica and P.pruinosa were nonrectangular hyperbola function.Under Normal water supply condition,P.euphratica and P.pruinosa maximum net photosynthetic rates(P_{n max})were 24.59,16.68 μmol CO₂·m^-2s^-1,apparent quantum yields(AQY)were 0.059,0.036 μmol CO₂· μmol^-1 photons,light saturation points(LSP)were 603,517 μmol photons·m^-2s^-1,light compensation points(LCP)were 42,41 μmol photons·m^-2s^-1 and dark respiration rates(R_d)were 2.99、1.45 μmol CO₂·m^-2s^-1,respectively.Under the soil drought stress the values of P _{n max},AQY,LSP and R_d were declined and LCP values were not changed.Compared with P.pruinosa,there were higher values of P_n,P_{n max},LSP,AQY and R_d in P.euphratica,except for LCP.These results revealed that P.euphratica had higher capacity to acclimate to different soil water supply and light intensity than P.pruinosa grown under the same habitat type.

Key words: Populus euphratica, Populus pruinosa, soil water stress, photosynthesis