Continuous investigation on the response of carbon isotopes of C3 plants to climate change in north China and application in paleoprecipitation reconstruction

Interpreting the climate information recorded by carbon isotope composition (δ¹³C) in geological archives aids climatology research and climate prediction. However, this interpretation depends on accurately calibrating modern plant δ¹³C responses to climate change. We here present a long-term calibration conducted at a fixed location adjacent to a meteorological station. By eliminating the effects of geographical variables on C₃ plant δ¹³C, as well as errors arising from inaccuracies in meteorological data, this study yields reliable relationships between δ¹³C and climatic factors. This study demonstrates that precipitation is the predominant factor influencing C₃ plant δ¹³C, accounting for approximately 65 % of the variance in year-averaged δ¹³C for all C₃ plants. The coefficients between year-averaged δ¹³C and annual precipitation, growing season precipitation, and summer precipitation are −0.0039 ‰/mm, −0.0048 ‰/mm, and −0.0040 ‰/mm, respectively. Furthermore, we examined the response pattern of δ¹³C to environmental factors at the species level and observed significant variation in these patterns across different C₃ plant species. This indicates that isotope variation of a single species or a limited number of species cannot adequately reflect regional climate information due to microenvironmental influences. Consequently, only δ¹³C-climate factor conversion equations based on community-level data are appropriate for paleoclimate reconstruction. Finally, we used our δ¹³C-precipitation conversion equation to reconstruct the precipitation in the western Loess Plateau during the last glacial period. This study provides a robust constraint of the response pattern of C₃ plant δ¹³C to environmental factors and develops a refined isotope-precipitation conversion equation for rainfall reconstruction, promoting the application of δ¹³C in paleoclimate research.