## 4 Discussion
### Responses of Physiological Functions of Halophytes to Salt Stress  
Chlorophyll is an important carrier for light energy aggregation and transmission, and it is one of the important physiological indexes for measuring the stress resistance of plants; its content can also reflect the growth status of plants [27]. Many studies have found that the chlorophyll content of plants can reflect the salt tolerance of plants to a certain extent [28]. [PERSON] et al. found in Haryana, India, that the chlorophyll content of _Triticum aestivum_ has a clear correlation with the degree of salt stress [29]. [PERSON] et al. found in South Africa that with an increase in salt concentration, the chlorophyll content of _Tetragonia decumbens_ showed a \"single peak\" pattern change trend [30]. In this study, with the increase in salt concentration, the chlorophyll content of Ha, Tc, and Pa showed different changes. The contents of chlorophyll a, chlorophyll b, and total chlorophyll in Ha and Tc increased first and then decreased, and the turning point was a salt concentration of 150 mmol-L\({}^{-1}\). However, Pa shows a decreasing trend. This may be because Ha is composed of eulahophytes and Tc is composed of reteohalophytes. When the salt concentration is low, the special organ structure of Ha and Tc enables them to adapt to adversity and promote the increase in chlorophyll. However, when the salt concentration is too high, too many harmful ions enter the plant body, causing damage to the grana lamella and thylakoid structure in chloroplasts, which makes the salt-discharging ability of Ha and Tc reach the limit. Therefore, the chlorophyll leading to Ha and Tc reached the highest when the salt concentration was 150 mmol-L\({}^{-1}\) and then gradually decreased [31]. Pa is composed of pseudohalophytes. The absorption of salt can be limited by the suberization in the roots. However, on the one hand, the soil salinity in the study is high. On the other hand,on this basis, plants are irrigated with high-salt-concentration solutions, which enhances the negative impact on plant leaves and leads to salt gradually entering plants. When the salt in plants is too high, some toxic substances, such as cadaverine and putrescine, are often produced. However, the characteristics of Pa, such as impermeability to water and air, make it difficult to discharge toxic substances from plants, so the chlorophyll of Pa gradually decreases [32]. Different from Ha and Tc, which can actively excrete salt in the body, Pa's salt rejection mechanism is passive, so chlorophyll shows a downward trend.  
Salt stress can make plants produce reactive oxygen species, lower cell membrane integrity, and cause membrane lipid peroxidation. Malondialdehydedehyde is the main product of membrane lipid peroxidation, which can directly reflect the damage degree of the plant cell membrane. The higher the content, the more serious the cell membrane damage and the weaker the stress resistance [33]. In this study, with the increase in salt concentration, the malondialdehydedehyde content of three different types of haplotypes showed an obvious increasing trend. This is the same as the research findings of [PERSON] et al. in Korea that, with the increase in salt concentration, the synthetase activity of _Oryza sativa_ decreased continuously and the malondialdehydedehyde content increased continuously [34]. This is because with the gradual increase in salt concentration, whether it is Ha, Tc, or Pa, the dynamic equilibrium state in the body is broken and the physiological metabolism process is destroyed. Once the physiological metabolism process and cell membrane of plants are damaged, the cell membrane permeability of plants will continue to increase, and the membrane lipid peroxidation will gradually strengthen, so the malondialdehydedehyde content of Ha, Tc, and Pa will gradually increase [35].