Environmental Engineering Reference
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2.7. Determination of Na + , K + , Cl - Content
The extraction of Na + , K + , Cl - were performed according to Yu et al. [16]. 15ml of
deionized H 2 O was added to 100mg of dried plant powder and boiled for 2h. After
centrifugation at 10000g for 20min, the supernatant was used for the measurement of Cl -
content and diluted 100 times with deionized H 2 O for Na + and K + content. The atomic
absorption spectrophotometer (PAS-990, PERSEE, China) was used for the measurement of
Na + and K + while Cl - was analyzed with a Cl - electrode (Leici, China). The amount of these
three ions was calculated from a standard curve prepared with pure NaCl (for Na + and
Cl - ) and KCl (for K + ) solutions.
2.8. Statistical Analysis
One-way ANOVA was performed using SPSS computer package (SPSS Inc., USA) for
all sets of data. Significant differences between means were determined through LSD test.
Differences were considered statistically significant when P < 0.05. All data were presented
as mean ±SD.
3. R ESULTS
3.1. Effects of Salt Stress on Growth Parameters
With increasing salinity, changes of all the growth parameters showed similar trends in
ZH13 and BB52. The plant height, fresh weight and leaf area were all significantly reduced.
What is more, the reductions of these indices in ZH13 were greater than those for BB52 at the
same stress. Especially at 300 mM NaCl stress, the three indices for ZH13 decreased
markedly to 54.5% 30.4% and 16.7% respectively. On the contrary, the root length, petiole
number and stem diameter were less affected in both soybeans with increasing salinity
(Figure 1).
3.2. Effects of Salt Stress on Gas Exchange and Chlorophyll Content
Under salt stress, the trends of photosynthetic rate, stomatal conductance, carboxylation
efficiency and transpiration rate (Figure2A, B, D, E) were similar in both ZH13 and BB52.
With increasing salinity, their values decreased gradually.
Compared with ZH13, the four indices were significantly higher in BB52 under the same
salt stress. The intercellular CO 2 concentration (Figure2C) was slightly decreased at the
concentration of NaCl lower than 200mM NaCl while a sharply increase appeared at 300mM
NaCl, especially for ZH13. Besides, chlorophyll content (Figure2F) displayed a significantly
decline in both ZH13 and BB52.
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