عنوان مقاله [English]
Introduction: Despite grazing in pastures, animals are fed on such sources as manual forage, farm straw, and so on. Therefore, rangelands are influenced by overgrazing and forage shortage for various socioeconomic reasons, resulting in their degradation. On the other hand, excessive exploitation of rangelands and their land-use change are blamed for the expansion of invasive species as they change the species composition of the rangelands, influence their ecosystem functions and services, and destroy ecosystems at the global level. In this respect, when invaluable species are grazed, it is recommended to cultivate perennial, high-yielding, and palatable species in pastures to restore their production capacity, reduce the competitiveness of invasive species, and increase vegetation cover quantity and quality. The investigation and identification of the factors influencing the germination and growth of invaluable species in rangeland ecosystems is a necessary step for the rangeland management, modification, and restoration programs.
Materials and Methods: The present study explored the effect of irrigation interval, water salinity, and soil clay content on the seed germination and germinated seedling height of the endangered species Hedyasrum criniferum as an indigenous and palatable species in Iran’s rangelands under greenhouse conditions and in natural habitats. The study was, therefore, conducted as a factorial experiment based on a completely randomized design with three factors including irrigation interval at three levels of 7, 10, and 14 days, water salinity at three levels of <1, 1-2, and 2-4 dS m-1, and clay variations at three levels of 0, 10, and 20% in greenhouse conditions with three replications. The GLM method was employed to study the factors influencing the plant parameters of the studied species.
Results: The results showed that only the treatment of irrigation interval influenced germinated seedling height and germination percentage of H. criniferum significantly (α = 5%) so that, based on the comparison of means, the highest germination percentage and germinated seedling height were observed in plants irrigated every seven days. According to the species response curves, the species height had an ascending trend in response to the precipitation whereas its relationship with salinity was negative. Regarding clay, the species height was decreased as the clay content was increased up to 25% beyond which the height started to increase.
The species response curve in terms of germination percentage showed an increase in this parameter with the increase in precipitation while it declined at higher salinity levels. However, its response to clay was similar to that of the species height so that germination was decreased as the clay content was increased up to 25%.
Discussion and Conclusion: Based on the results, irrigation interval is more important than the other two treatments. The tolerance level of germination and seedling growth was found to be at the irrigation interval of 14 days, the salinity level of 4 dS m-1, and the clay content of 20%. Reducing irrigation interval can contribute to root growth and moisture retention at the 0-4 cm soil profile, which can facilitate root growth and thereby increase photosynthesis. Higher irrigation intervals disrupt photosynthesis due to the deficiency of soil moisture. This reduces photosynthate synthesis for mobilization to growth parts of the plants, resulting in the loss of plant height. On the other hand, it was revealed that in the natural habitat, the likelihood of the species presence was increased with the increase in precipitation up to 650 mm. The precipitation range of the habitats of this species shows that H. criniferum can be present in different climatic regions, including arid, semi-arid, and semi-humid regions. Therefore, with the increase in precipitation from arid to semi-arid and finally, semi-humid regions, the species is more likely to be present. The optimal precipitation rate for this species indicates that it prefers semi-humid climates.