Composition and variation of stable carbon and nitrogen isotope in south-western Tibetan Plateau

Abstract Ecosystem stable isotopic values of carbon and nitrogen (δ13C and δ15N) can offer valuable insight into terrestrial ecosystem. However, the factors influencing δ13C and δ15N in alpine grasslands are not clear enough. To address this gap, we measured δ13C and δ15N for soil and Astragalus plants along an altitudinal gradient (3500 — 5000 m) in the south-western Tibetan Plateau, which was unreported by previous studies. As an ecological indicator reflecting nitrogen (N) cycling, soil δ15N values are higher than the mean value of the plateau. Soil δ13C is significantly correlated with soil carbon (C) content, C and N ratio and soil pH. Additionally, we found significant positive correlation between plant δ13C and MAT or MAP. Soil δ15N is negatively correlated with MAP but no relationship was revealed with MAT. In summary, our study highlights the importance of altitude induced MAT changes in the variation of plant δ13C and the independent control of MAP in the variation of both plant δ13C and soil δ15N.