Abstract: The natural abundance of stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) in leaves can provide comprehensive information on the physiological and ecological processes of plants and has been widely used in ecological research. However, recent studies on leaf δ¹³C and δ¹⁵N have focused mainly on woody species, few studies have been conducted on herbs in different vegetation types, and their differences and driving factors are still unclear. In this study, we focused on the herbs in subalpine coniferous forests, alpine shrublands, and alpine mea-dows on the eastern Qinghai-Tibet Plateau, and investigated the differences in leaf δ¹³C and δ¹⁵N of herbs and the driving factors. The results showed that there were significant differences in leaf δ¹³C and δ¹⁵N values of herbs among different vegetation types, with the highest δ¹³C and δ¹⁵N values in alpine meadows, followed by alpine shrublands, and the lowest in subalpine coniferous forests. Using variation partitioning analysis, we revealed that differences in leaf δ¹³C and δ¹⁵N of herbs among various vegetation types were driven by both leaf functional traits and climate factors, with the contribution of leaf functional traits being relatively higher than that of climate factors. Hierarchical partitioning results indicated that mean annual temperature (MAT), chlorophyll content index, leaf nitrogen content per unit area (N_area), and leaf mass per area were the main drivers of leaf δ¹³C variations of herbs across different vegetation types, while the relative importance of N_area and MAT for variation in leaf δ¹⁵N of herbs was much higher than those other variables. There was a strong coupling relationship between leaf δ¹³C and δ¹⁵N as indicated by the result of the ordinary least squares regression. Our findings could provide new insights into understanding the key drivers of leaf δ¹³C and δ¹⁵N variations in herbs across different vegetation types.

Key words: herbs, carbon stable isotope, nitrogen stable isotope, leaf functional trait, climatic factor