A similar trend occurred for maize, although both the germination percentage and survival rate were lower than those of sunflower. In contrast, the sodic soil and FGD gypsum mixture effectively alleviated the salt- and nutrient-related issues, and the plants displayed robust germination and growth. The growth of plants in the FGD gypsum was inhibited mainly because of the reduced available nutrient contents, which resulted in significantly lower plant height, root length, and biomass compared with those of plants grown in the other two media. Unexpectedly, all sunflower seeds emerged and grew in all three media. Drainage was prevented, and no fertilizer was applied. Sunflower (Helianthus annuus L.) and maize (Zea mays L.) seeds were sown directly into highly sodic soil (whose pH was 9.1 and exchangeable sodium percentage was 31.5%), FGD gypsum, or a mixture of the two (mass ratio of 1:1). Thus, a pot experiment was carried out in which sandy loam soil collected from a typical sodic soil distribution area in Northeast China was used. However, excess of this material poses a hazard to crop emergence and growth.
The main component of flue gas desulfurization (FGD) gypsum is CaSO4♲H2O, a type of salt. Based on emergence, early seedling growth and physiological characteristics, the long ovate seeds had a higher salt tolerance than those of the other two shapes, followed by those with long seeds. The broadly ovoid seeds exhibited the greatest enzyme activities and the highest net photosynthetic rate (Pn) at both NaCl levels. The malondialdehyde (MDA) contents increased with the NaCl levels in all cultivars. The activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were lower in the NaCl-stressed plants than the controls. RL decreased with increasing NaCl levels, and plants with broadly ovoid seeds had longer roots than those with other shapes. A level of 1000 mg L–1 NaCl improved the GP and GI compared with the no NaCl-stressed control with the exception of the long ovate seeds. A level of 2000 mg L–1 NaCl delayed the seed mean germination time (MGT), reduced the germination percentage (GP) and germination index (GI) and caused shorter root length (RL). Increases in the WLR increased the 100-seed weight and kernel/hull rate (KHR) but decreased the water absorption rate (WAR). To determine whether sunflower (Helianthus annuus L.) grain shape should be considered as a predictor of salt tolerance, seeds of three grain shapes, namely long seeds (DC6009 and RH3146 with a width-length ratio of 0.39), long ovate seeds (SH909 and 135 with a WLR of 0.49) and broadly ovoid seeds (RH118 with a WLR of 0.61) were exposed to 0, 1000, and 2000 mg L–1 NaCl for 30 d.
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