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 delta C-13 values vary among photosynthetic pathways (C-3 vs. C-4) or plant types (dicots, monocots, gymnosperms, magnoliids), and how n-alkane delta C-13 values respond to climate factors (precipitation, temperature). However, a systematic global analysis of plant n-alkane delta C-13 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 delta C-13 data in modern plants. We find significantly negative correlations between delta C-13(wt) values and mean annual precipitation (MAP) for C-3 plants (R-2 = 0.30; p < .05), dicots (R-2 = 0.28; p < .05) and magnoliids (R-2 = 0.55; p < .05), but non-significant correlation between delta C-13(wt) values and MAP for C-4 plants (R-2 = 0.08; p = .12) or monocots (R-2 = 0.01; p = .89). However, there are significantly positive correlations between delta C-13(wt) values and mean annual temperature (MAT) in C-4 plants (R-2 = 0.33; p < .05) and monocots (R-2 = 0.35; p < .05), instead of weak correlations in C-3 plants (R-2 = 0.09; p <.05), dicots (R-2 = 0.03; p < .05) and gymnosperms (R-2= 0.06; p =.06). These results indicate that n-alkane delta C-13 values in C-3 dicots have more potential for paleoprecipitation reconstruction, while those in C-4 monocots are more likely to indicate paleotemperature changes. Our study supports use of leaf wax n-alkane delta C-13 values to gain information about paleoprecipitation and paleotemperature, but only in an appropriate paleoecological context