Spatial Variation in Leaf Stable Carbon Isotope Composition of Three Caragana Species in Northern China

Leaf stable carbon isotope (C-13) composition provides comprehensive insight into plant carbon cycles and water use efficiency and has also been widely used to evaluate the response of plants to environmental change. In the present study, leaf C-13 was analyzed in samples of Caragana microphylla Lam., C. liouana Zhao, and C. korshinskii Kom. from 38 populations. These species provide great environmental benefits and economic value and are distributed east to west continuously across northern China. We studied the relationship of C-13 to altitude, mean annual precipitation (MAP), mean annual temperature (MAT), mean annual relative humidity (RH), leaf nitrogen (N), and phosphorus (P) concentrations to examine the patterns and controls of leaf C-13 variation in each species. Results indicated that, across the three species, leaf C-13 significantly decreased with MAP, RH, and leaf N and P concentrations, while it increased with altitude and MAT. However, patterns and environmental controls of leaf C-13 varied proportionally with species. C. korshinskii was mainly controlled by MAP and leaf N concentration, C. liouana was controlled by both MAT and MAP, and C. microphylla was mainly controlled by MAT. Further analysis indicated significant differences in leaf C-13 between species, which tended to increase from C. microphylla to C. korshinskii. Overall, these results suggest that the three Caragana species may respond differently to future climate change due to different controlling factors on leaf C-13 variation, as well as differentiation in water use efficiency, which likely contributes to the geographical distribution of these species.