The Effect of Environmental Stresses on Germination and Vegetative Characteristics of The Seeds of Three Range Species Zygophyllum Eurypterum, Sanguisorba Minor and Salsola Orientalis in Semi-Arid Regions of Kohgilouye Va Boyer Ahmad

The growth of plants is affected by environmental stresses, particularly drought and salinity, which are the main problems of arid and semi-arid lands. Germination is a crucial stage in the life of most plants. Plant establishment in arid and semi-arid regions requires special tolerance to stresses like salinity and drought during the germination stage. In most plants, increasing salinity and drought stress during the germination stage prevents the plant from germinate. Therefore, knowing the resistance to salinity and drought in different plants can be used in the management of natural environments. Considering the increase in global temperature and the decrease in rainfall in Iran, as well as the soil salinization, it is very important to choose plants with high tolerance to salinity and drought in rangeland. In the southern rangeland of Kohgiluyeh Va Boyer Ahmad province, which are located in arid and semi-arid climates, non-native species such as Atriplex spp. and Prosopis spp. have been used for improvement and restoration in the past decades. The soil and native vegetation of the region are negatively impacted by non-native plants, which have problems like lack of natural regeneration. Identifying suitable native plants that can grow in specific ecological conditions of arid and semi-arid areas, such as drought and salinity, is necessary. The current research aims to identify native resistant species to the mentioned stresses for vegetation restoration in biological and bio-mechanical projects.

In order to identify the species tolerant to environmental stress in the rangeland of Kohgiluyeh Va Boyer Ahmad province, three native species including Zygophyllum eurypterum Boiss. & Buhse, Sanguisorba minor L. and Salsola orientalis S. G. Gmelin (Salsola rigida) were selected. The habitats of the species were identified through field surveys and the cooperation of experts from the General Department of Natural Resources and Watershed Management of Kohgiluyeh Va Boyer Ahmad province. Sampling of plant seeds for experiments was done in range habitats. Seed germination reaction of three species Z. eurypterum, S. minor. and S. orientalis were studied in the laboratory with respect to different levels of salinity and drought stress. The drought stress test included six levels (0, -0.3, -0.6, -0.9, -1.2, and -1.5 MP) which were prepared using polyethylene glycol 6000. The second experiment included 6 salinity levels (0, 50, 100, 150, 200, 250 mM). Sodium chloride was used to create salinity stress. Before conducting the salinity and drought tests, treatments were applied to break the seed dormancy of different species, and after identifying the best treatment for each species, dormancy tests were performed. Germination was done as a factorial experiment in a completely randomized design with 4 replications (20 seeds per replication) in a germinator at a temperature of 25°C. During a period of 20 days, every day the germinated seeds whose root length was more than 2 mm were counted and their germination percentage, germination rate, length of root, stem and seedling and their seed germination index were measured. Using SPSSVer.23 software, analysis of variance and comparison of average data was done.

Variance analysis shows that there is a significant difference between drought and salinity levels in the traits measured in plants (p<0.01). There is a significant difference between plant species and drought-salinity interaction and species(p<0.01). With the increase of dryness, a significant difference was observed in terms of germination percentage in all three species. In this condition, the highest amount of measured traits including, germination percentage and seed germination index was observed in Z. eurypterum. with increasing salinity, the germination rate of all three species decreases significantly. In the condition without salt stress (control treatment), the highest percentage of germination (77%) was obtained in S. minor. But with increasing salinity levels, the highest germination percentage is observed in S. orientalis, and also with increasing salinity levels, the lowest germination percentage is related to S. minor species. Plants responded differently to environmental stresses, as shown by the results in general. The restoration and improvement of rangelands requires knowledge of plants that are resistant to existing stresses in order to manage natural areas. According to the current research, the rate of germination and growth of seedlings decreases as salinity and drought levels increase. Among the studied species, Z. eurypterum is the most resistant to drought and S. minor is the most sensitive. It can be concluded that the highest germination is observed in S. orientalis, when salinity levels increase, and the lowest germination is observed in S. minor species. Therefore, S. orientalis can be considered as a salt resistant. As the species studied are indigenous and native in the south of Kohgiluyeh Va Boyer Ahmad provinces, the results of this research are suggested for use in biological projects.