Temperature controls on the C4 plants expansion in the mid-latitudes and its ecological implications for dryland paleoclimatic reconstruction: A stable carbon isotope perspective

Knowledge of the dynamic evolution of vegetation and its forcing mechanisms in the mid-latitude zone is critical to understanding how climate change modulates ecosystems. However, the forcing mechanism of changes in the relative abundance of C3/C4 plants in terrestrial vegetation is unclear due to the lack of comprehensive data sets from the vast study area. Here, the organic carbon isotope (δ13Corg) data of mid-latitude modern plants (n = 2833) and topsoil (n = 2017) are compiled, and the linear relationship with the corresponding mean annual temperature (MAT) and precipitation (MAP) is established. Our results demonstrate a close relationship between MAT and the δ13Corg values of C3/C4 mixed plants in the soil, implying that temperature is the primary climatic factor determining the relative abundance of C3/C4 plants at mid-latitudes. The results of quantitative reconstruction of paleo-temperature in the Xiaolongwan Lake in Northeast Asia are consistent with the published reconstruction records based on pollen and phytolith, which confirms the reliability of our δ13Corg-MAT conversion function. Using the transformation function established in this study, we quantitatively reconstruct the paleo-temperature variation of the Harbin loess in Songnen Plain since the Holocene. The reconstructed MAT shows a continuous increase in the C4 plants abundance with increasing temperature since the mid-Holocene, which is consistent with changes in summer solar insolation at 65° N, oxygen isotopes of cave stalagmite, and phytolith records in the Songnen Plain. Compilation of 715 absolute ages, δ13Corg data, regional and global climate records, and human activity intensity records from five dune fields at high risk of desertification from the edge of the East Asian monsoon shows the importance of climate and human activity to the expansion of C4 plants and solidification of dunes.