Abstract:

The Song-nen grassland in China, where Leymus chinensis is the dominant plant, ordinarily belongs to meadow grassland, but now there exists a mass of degraded alkali-saline grassland, with secondary bare alkali-saline patches in a regressive succession, caused by irrational exploitation in past years. It is an imperative and difficult task for scientists and grassland managers to improve or ameliorate these secondary bare alkali-saline patches. There have been extensive studies of the eco-physiological properties of many salt-tolerant plants and the property of soil in the Song-nen grassland. Many scientists and managers consider that the too high content of soluble saline ion in soil is the dominant cause, which made the natural restoration process of secondary bare alkali-saline patches so slow, and have brought forward some effective measures to improve them. However, relatively little is known about the survival rate of some salt-tolerant plants in secondary bare alkali-saline patches under natural conditions. It is a very important factor to the improvement of these bare patches and will to some extent influence the improving effect in practice. So, determining the survival rate of these salt-tolerant plants in natural conditions will help to find an economic and operable way to restore these secondary alkali-saline bare patches. We have investigated the growing dynamics of two salt-tolerant plants (Suaeda corniculata and Chloris virgata) in secondary bare alkali-saline patches in natural conditions through seeding experiments. Moreover, we have also inspected whether some simple experimental treatments can enhance the survival rate of plants in natural conditions through inserting cornstalks in secondary bare alkali-saline patches and seeding. Finally, based on our results and previous work, we have discussed the potential causes, which made their natural restoration process so slow in natural conditions, and ways of optimizing ecological restoration patterns. The results show that Suaeda corniculata is able to grow in the secondary bare alkali-saline patches in natural condition without any auxiliary utilities, and its ultimate survival rate arrives at 61.2%±16.5% in fall; the survival rate of Chloris virgata is very low, and its ultimate survival rate is only 5.7%±6.1%. The mortality rate of the two plants is comparably high in their initial growth period. The treatment of inserting cornstalks significantly enhances the survival rate of Suaeda corniculata and Chloris virgata, and their ultimate survival rates are 74.8%±18.4% ant 43.1%±20.8% respectively. More importantly, they both can reproduce successfully and provide the necessary seeds for subsequent natural succession in these bare patches. The soil seed bank is the template of plant restoration and influences the restoration speed and direction on these secondary bare alkali-saline patches. Natural restoration should be accelerated if there exist substantive seeds of salt-tolerant plants, such as seeds of Suaeda corniculata. Therefore, lack of propagulum in soil (including seeds and other propagulum) should be another important restricting factor, besides the too high content of soluble saline ion in soil, which made their natural restoration process so slow in natural conditions. The experiment shows that it is possible to boost the survival rate of these salt-tolerant plants in secondary bare alkali-saline patches in natural condition, if we take some effective measures. Then, based on these properties of the secondary bare alkali-saline patches, we have put forward a new ecological restoration pattern to accelerate their natural restoration, i.e., rationally integrating the ecological theories into ecological engineering and making the best of local seed resources and local specific climate to improve secondary bare alkali-saline patches. Restoration of these secondary bare alkali-saline patches looks promising, especially where the area of these secondary bare patches is relatively small and their distribution is patchy in Song-nen grassland.