Habitat-specific differences in plasticity of foliar δ (13)C in temperate steppe grasses

A decrease in foliar δ (13)C with increasing precipitation is a common tendency in steppe plants. However, the rate of decrease has been reported to differ between different species or populations. We here hypothesized that plant populations in the same habitat of temperate steppes may not differ in foliar δ (13)C response patterns to precipitation, but could differ in the levels of plasticity of foliar δ (13)C across different habitats. In order to test this hypothesis, we conducted controlled watering experiments in northeast China at five sites along a west-east transect at latitude 44°N, which show substantial interannual fluctuations and intra-annual changes in precipitation among them. In 2001, watering treatment (six levels, three replicates) was assigned to 18 plots at each site. The responses of foliar δ (13)C to precipitation (i.e., the sum of watering and rainfall) were determined in populations of several grass species that were common across all sites. Although similar linear regression slopes were observed for populations of different species growing at the same site, significantly different slopes were obtained for populations of the same species growing at different sites. Further, the slope of the line progressively decreased from Site I to Site V for all species in this study. These results suggest habitat-specific differences in plasticity of foliar δ (13)C in temperate steppe grasses. This indicates that species' δ (13)C response to precipitation is conservative at the same site due to their long-term acclimation, but the mechanism responsible behind this needs further investigations.