Abstract:

Salt stress to plants results from both osmotic stress, due to low water potentials, and direct salt-ion injury. Salt-tolerant mechanisms of plants are mainly ion compartmentalization, osmoregulation and metabolic changes. In the past, Sigle-salt experiments were usually conducted to study salt-tolerance in plants; however, experimental results were often contradicted to field observations. To better simulate actual field conditions, we conducted a laboratory experiment to study the physiological characteristics of salt-tolerance in Helianthus tuberosus using natural seawater. Potted plants of H. tuberosus were irrigated with seawater taken from the Laizhou coast, Shandong Province, China in 2000, and diluted with freshwater at the following ratios: 0∶1 (Pure freshwater), 1∶9, 1∶4 and 1∶3. The results showed that at the end of the growing period, the yield of fresh tuber in all treatments was the same following one irrigation treatment period. However, following two irrigation treatment periods, the tuber yield in the 1∶3 treatment was much higher than in the other treatments whereas the other treatments were similar. When H. tuberosus was treated with two irrigation treatment periods, the tuber yield was greater in all saltwater treatments than in the single irrigation treatment. The photosynthetic rate of H. tuberosus was consistent with changes in the salt concentration of the surface soil. On the first or second day after irrigation, the photosynthetic rate of H. tuberosus in the controls was much higher than other treatments while there was nearly no difference in rates among treatments except for the 1∶3 treatment that had lower photosynthetic rate. After sixty days of irrigation, the greatest leaf area index (LAI) was achieved in plants irrigated with pure freshwater, LAI was the lowest in plants in the most saline treatment (1∶3 seawater:freshwater), and similar in the other two treatments.

Key words: Physiological characteristics, Seawater irrigation, Helianthus tuberosus, Salt-tolerance