Synergistic interaction of NaCl and Cd on growth and photosynthetic parameters in soybean genotypes differing in salinity tolerance.

The effects of salinity (50 mmol/L NaCl) and Cd (1 micromol/L CdCl(2)) as sole and combined on growth and photosynthetic parameters were studied using two soybean genotypes, Huachun 18 and NGB. The concentrations of Cd(2+), Zn(2+), Ca(2+), Mg(2+), K(+) and Na(+) were also determined in seeds and pods. Huachun 18 suffered a more serious decrease than NGB in net photosynthetic rate (P(n)) in the treatments of salinity stress alone and combined stress (NaCl+Cd), showing that it is relatively sensitive to salinity. The decrease in P(n) caused by salt stress in Huachun 18 was mainly due to the reduced total chlorophyll content and photosynthetic efficiency (the ratio of variable fluorescence to maximal fluorescence, F(v)/F(m)), whereas the decease in NGB was mainly related to reduced stomatal conductance (G(s)). The combined stress of both Na and Cd did not induce further decrease in photosynthesis and fluorescence in the two genotypes relative to salt or Cd stress alone. Greater change in the pod concentrations of Zn(2+), Ca(2+), Mg(2+), K(+) and Na(+) was detected under salt stress for Huachun 18 than for NGB. The results suggested that the interactive effect of NaCl-Cd on growth and nutrient uptake differs between the two soybean genotypes.