Abstract:

The carbon isotope composition (δ13C value) of plants is a useful index for assessing intrinsic water use efficiency (WUE) and can also provide information on long term WUE, because the δ13C value integrates photosynthetic activity throughout the entire life span of the leaf tissue. Water is the limiting environmental factor for growth and reproduction of steppe plants in the Xilin River Basin, Inner Mongolia. Carex korshinskyi, a perennial forb, is widely distributed throughout the Xilin River Basin and shows strong adaptive characteristics enabling it to survive in habitats with widely varying nutrient and water conditions. In this study, six plant communities were selected which differed in floristic composition and soil water status but had similar climatic conditions, such as temperature and precipitation. Foliar δ13C values, leaf water content (LWC) and population characteristics (including height, density and aboveground biomass) of C. korshinskyi were measured in each of the six communities. Our objectives were to study the variations in foliar δ13C values, LWC and population characteristics of C. korshinskyi along a soil water gradient to better understand the adaptive strategies of C. korshinskyi to water stress. Results showed that: 1) There were significant variations in foliar δ13C values of C. korshinskyi in different habitats (changing range 1.8‰). The foliar δ13C values of different C. korshinskyi populations tended to increase with decreasing soil water content (SWC). A significant negative correlation was found between foliar δ13C values and SWC in different soil layers, indicating that C. korshinskyi populations could change WUE in response to water availability. 2) A significantly negative correlation was found between foliar δ13C values and LWC of C. korshinskyi. Only small variations in LWC were found among the six different C. korshinskyi populations indicating that the WUE of C. korshinskyi was sensitive to changes in leaf water status. 3) There were significant differences in height, density, aboveground biomass and frequency of occurrence among C. korshinskyi communities along the soil water gradient. The C. korshinskyi populations with higher δ13C values had higher occurrences in the plant community and contributed more to total aboveground biomass and community productivity. Our results suggest that C. korshinskyi can adjust its water use pattern (such as enhancing WUE) to adapt to habitats with different soil water availability increasing its competitive ability across a wide range of habitats.