Leaf wax n-alkane carbon isotope values vary among major terrestrial plant groups: Different responses to precipitation amount and temperature, and implications for paleoenvironmental reconstruction

Studies focused on field measurements have been conducted to investigate how leaf wax n-alkane δ¹³C values vary among photosynthetic pathways (C₃ vs. C₄) or plant types (dicots, monocots, gymnosperms, magnoliids), and how n-alkane δ¹³C values respond to climate factors (precipitation, temperature). However, a systematic global analysis of plant n-alkane δ¹³C values with respect to major plant groups is still lacking, and the corresponding mechanism remains unknown. In this study, we compiled globally published n-alkanes δ¹³C data in modern plants. We find significantly negative correlations between δ¹³C_wt values and mean annual precipitation (MAP) for C₃ plants (R² = 0.30; p < .05), dicots (R² = 0.28; p < .05) and magnoliids (R² = 0.55; p < .05), but non-significant correlation between δ¹³C_wt values and MAP for C₄ plants (R² = 0.08; p = .12) or monocots (R² = 0.01; p = .89). However, there are significantly positive correlations between δ¹³C_wt values and mean annual temperature (MAT) in C₄ plants (R² = 0.33; p < .05) and monocots (R² = 0.35; p < .05), instead of weak correlations in C₃ plants (R² = 0.09; p < .05), dicots (R² = 0.03; p < .05) and gymnosperms (R² = 0.06; p = .06). These results indicate that n-alkane δ¹³C values in C₃ dicots have more potential for paleoprecipitation reconstruction, while those in C₄ monocots are more likely to indicate paleotemperature changes.