C4 plants and their relations with desertification in Hunshandake desert grassland
浑善达克沙化草地C4植物资源及其与植被演替的关系

World wide, more than 1700 C_4 plant species have been identified since the work of Downton and Tregunna (1968) and Black (1971). Most of these studies focused on the classification of plant species as to their photosynthetic pathway types (C_3, C_4 and CAM), geographic distribution of C_4 plants and their relationships with climatic patterns. But very few have looked at the relations between C_4 species and vegetation dynamics, especially in deserts and dry regions. C_4 plants and their relations with desertification in Hunshandake desertification grassland were studied based on field survey and references. Of the total 169 species, in 98 genera and 30 families, identified in the region, only 27 species, in 7 families and 22 genera, were found with C_4 photosynthetic pathway. This indicated that the C_4 species mainly occurred in a few families in the region, but most of these species were common species and related with vegetation dynamics. More Gramineae (16 species) and Chenopodiaceae species (6 species) were identified as C_4 species (16 species) in the desertification grassland, this suggests that Gramineae is the leading family with C_4 photosynthesis, followed by Chenopodiaceae. Of the 27 C_4 species, 63 % were in therophyte and most of these therophyte C_4 species occur in early succession stages because they could use the limited water resource in the growing season and survive the dry season in the form of dormant seeds. The number of C_4 species and proportion of C_4/C_3 increase with desertification indicated that C4 species might have higher tolerance to environmental stresses (e.g. dry and poor soil) and could make greater contribution to sand land restoration in Hunshandake desert.