Leaf functional traits have more contributions than climate to the variations of leaf stable carbon isotope of different plant functional types on the eastern Qinghai–Tibetan Plateau

Elucidating the mechanisms that control the leaf stable carbon isotope values (δ13Cleaf) is the prerequisite for the widespread application of δ13Cleaf. However, the competing effects of physiological and environmental factors on δ13Cleaf variations of the different plant functional types (PFTs) have not been disentangled, and the corresponding mechanisms remain unclear. Based on large-scale δ13Cleaf measurements on the eastern Qinghai–Tibetan Plateau, the relative contributions and regulatory pathways of leaf functional traits (LFTs) and climatic factors to δ13Cleaf variations of the different PFTs were investigated. We found that δ13Cleaf of the different PFTs was correlated with annual mean precipitation negatively, but not a simple linear relationship with annual mean temperature and varied by PFTs. Leaf nitrogen content per unit area and leaf mass per area (correlated with δ13Cleaf positively) had more substantial effects on the δ13Cleaf variations of the different PFTs than other LFTs. The relative contributions of LFTs to the δ13Cleaf variations were greater than that of climatic factors, and the direct and indirect effects of climatic factors on δ13Cleaf variations varied by PFTs. Our findings provide new insights into understanding key drivers of δ13Cleaf variations at the PFT level on a regional scale.