Abstract:

The growth and photosynthetic system of the clones under different salt stress conditions and the differences among the clones were investigated using one-year-old seedlings of single poplar hybridization clones (Populus tomentosa×P.alba var. pyramidalis), double cross poplar hybridization clones [(P. tomentosa×P.alba var. pyramidalis)×(P. alba×P. tremula)] and their parent species (P. tomentosa and P.alba var. pyramidalis). The results indicated that there was genotypic difference in leaf growth, height and dry biomass in response to salt stress. With increasing salinity, the growth factors decreased rapidly, but differently in extent. The dry biomass was affected most under salt stress. The parts above ground of the plant were more susceptible to salt stress than that below the ground, leading to a higher root/stem ratio with increasing salt. The diurnal change of photosynthetic rates (P_n) in the four clones generally presented a single peak curve, but the P_n value decreased quickly with increasing salt stress. Under the salt stress, the P_n showed a single peak curve from the young leaves to the aged leaves. The P_n of young leaves was hardly influenced by salt stress but the P_n of older leaves decreased significantly. The influence of salt stress on P_n of leaves was even stronger with time. It was also found that the chlorophyll content of different clones declined and the curve of chlorophyll fluorescence induction kinetics changed obviously under the salt stress, and the parameter q_N(coefficient of fluorescence non-photochemical quenching) increased, but q_P (coefficient of fluorescence photochemical quenching) and F_v/F_o (PSⅡ photochemical activity) decreased with increasing salt stress. According to the above analysis, the double cross hybrid clones of B430 was resistant, P.alba var. pyramidalis and P. tomentosa×P.alba var. pyramidalis were moderate resistant, P. tomentosa was the most susceptible to salt stress.

Key words: poplar hybridization clones, salt stress, growth, photosynthetic rate, chlorophyll fluorescence induction kinetics