Effects of mixed saline-alkali stress on germination of rice

Soil salinization has an important effect on seed germination of plants. In recent years, the effects of soil salinization on plant growth and crop yield have become more severe, and the area covered by salinized soil has increased. In order to study the effects of combined salt and alkali stress on the germination of rice seeds, two neutral salts (NaCl and Na₂SO₄) and two alkaline salts (NaHCO₃, Na₂CO₃) were mixed in five proportions: A (1:1:0:0), B (1:2:1:0), C (1:9:1:0), D (1:1:1:1), and E (9:1:1:9); and each proportion had four concentrations (50 mmol·L^-1, 100 mmol·L^-1, 150 mmol·L^-1 and 200 mmol·L^-1) to simulate 20 kinds of saline-alkali stress environments. Deionized water was used as the control (CK). The germination rate, germination potential, final germination rate, germination index, and average germination time of rice seeds were determined during the experiment, and the influences of the various salt solutions on the germination of rice seeds were explored. The results showed that, compared with the control, the germination rate, germination potential, and germination index of rice seeds were reduced by 9.2%-74.4%, 10.0%-48.9%, 5.6%-55.6%, and average germination time was prolonged by 3.2%-96.4% after culture under two neutral salt mixed stress solutions. When the proportion of alkaline salts in the stress solution increased, respectively, compared to the control, the germination rate in the B-E groups decreased by 8.9%-96.5%, 15.0%-98.0%, 7.5%-98.7%, and 18.9%-95.7%; the germination potential decreased by 20.0%-94.4%, 13.2%-97.8%, 3.3%-100%, and 36.7%-94.4%; the germination index decreased by 16.7%-94.4%, 22.2%-100%, 16.7%-100%, and 27.8%-94.4%; and the average germination time was extended by 0.8-4.5 times. These results showed that a stress solution containing two neutral salts and two alkaline salts had a stronger inhibitory effect on the germination of rice seeds than that only containing two neutral salts. After the non-germinated rice seeds in saline-alkaline stress solution were transferred to distilled water and cultured for 7 d, the final germination rates of rice seeds were above 73.33%, indicating that the stress solution did not destroy the activity of rice seeds, but only temporarily inhibited the germination. The experimental results showed that, compared with the single application of neutral salt, the mixed stress of neutral salt and alkaline salt inhibited the germination of rice seeds to a greater extent, and when the concentration of the mixed neutral salt and alkaline salt solution reached 200 mmol·L^-1, the seed germination rate was close to zero.