Abstract: Amorphous calcium carbonate is of importance to plant growth. The characteristics of amorphous calcium carbonate content in the main constructive plant species in the steppe-desert ecotone are not clear. In this study, we measured the contents of calcium carbonate in leaves of constructive species in Ningxia Habahu National Nature Reserve and Hongsipu District of Wuzhong City of Ningxia. The results showed that the contents of calcium carbonate significantly varied across different herbaceous species, but not among shrub species. As for the herbaceous species, the content of calcium carbonate decreased gradually with succession stages, from the early successional species (Agriophyllum squarrosum and Salsola collina), to the middle successional species (Aneurolepidium dasystachys and Pennisetum centrasiaticum), and to the late successional species (Stipa bungeana and Cleistogenes squarrosa). The content of calcium carbonate in the constructive species at the late succession stage of typical steppe was significantly higher than that in the late succession stage of desert steppe. The content of calcium carbonate in the leaves of Artemisia ordosica at the young stage was significantly higher than that at the adult and old stages. There was no significant difference in calcium carbonate content in the leaves of different canopy positions for three leguminous shrub species, Ammopiptanthus mongolicus, Caragana microphylla, and Amorpha fruticose. We conclude that the significant change of calcium carbonate content in herbaceous species at different succession stages in steppe-desert ecotone is the result of long-term adaptation to the environment.

Key words: steppe-desert transition zone, amorphous calcium carbonate, gasometrical method, plant community.