Isotopic carbon composition and related characters of dominant species along an environmental gradient in Inner Mongolia, China

Carbon isotope composition (δ13C value) provides a useful measure of integrated water-use efficiency (WUE) of plants and can be used to rank the drought tolerance of different species. We determined the δ13C values, leaf water content (LWC) and free proline content of 52 plant species selected from eight plant communities along a moisture gradient in the Xilin River Basin, Inner Mongolia. The δ13C values and WUE of C3 plant species tended to increase as the occurrence frequency and relative biomass of the species increased in the entire basin. The mean foliage proline concentration of all species in a community was higher when the habitat was drier and the mean LWC of plants decreased with increasing soil aridity. Significantly positive relationships existed between the foliar proline concentration and occurrence frequency and relative biomass of the species, respectively. Our results indicated that inter- and intra-species variations in WUE might significantly influence the outcome of competitive interactions and played a large role in determining species composition of plant communities. In addition, proline accumulation in leaves might strengthen competitive ability of plants growing in drought prone habitats.