Advances in research on the seed bank of a saline-alkali meadow in the Songnen plain

Abstract

Grassland degradation is common in arid and semi-arid areas of the world. The soil seed bank plays a critical role in vegetation restoration and biodiversity maintenance and has become a hot research topic. Due to human activities and global climate change, the Songnen meadow is being degraded by salinization, and about 90% of the Leymus chinensis vegetation has been degraded. This perennial grass was a high quality and useful species in this area before the 1960s. With the increase in degradation, i. e. increase in soil saline-alkalinity, secondary succession in this grassland began. In light saline-alkali areas, the dominant species is still L. chinensis. However, bare-soil patches occur in the most severe saline- alkali areas with high soil pH, in some of these patches Suaeda glauca grows only in the rainy season. In some moderate saline alkali areas, Chloris virgata, Puccinellia tenuiflora, Kochia sieversiana communities have appeared. The soil seed bank in the Songnen saline-alkali meadow has been investigated since the 1990s, with a focus on the floristics, seed density and seasonal dynamics in the succession stages of the Chloris virgata, Puccinellia tenuiflora, Kochia sieversiana, and Aeluropus sinensis communites and on the bare-soil saline-alkali patches. Seed rain and seed dispersal also have been investigated in several species. This paper summarizes these reports and points out problems that still exist. Researches on the following aspects of the ecology of this grassland should be increased in the future. Firstly, the mechanisms in the pattern of soil seed bank formation and the relationship between the seed bank pattern and the critical ecological environment factors such as soil salinity, soil pH, soil moisture, wind and so on should be investigated. Secondly, long- term monitoring of the persistent soil seed bank should be undertaken. Thirdly, some new technologies and methods should be introduced to help obtain more accurate and detailed research results on the soil seed bank.