Seasonal variability and differences in n-alkane deltaD values between dicotyledonous tree and monocotyledonous grass

Understanding seasonal variability in n-alkane δD values (δD_wax) among plant forms/lineages and the underlying physiological and biochemical factors that causes it is crucial for δD_wax-based quantitative paleoclimate reconstruction. Herein, we present parallel controlled study of Stipa bungeana (monocotyledonous grass) and Quercus aquifolioides (dicotyledonous tree) by conducting semimonthly paired δD analysis of precipitation, soil and leaf water, and n-alkanes over two years. We show that δD_wax in both plants inherit precipitation hydrogen isotopic compositions throughout the growing season. However, it is synchronous in S. bungeana and belated in Q. aquifolioides. We reveal previously unrecognized phenomenon that, for trees alkanes with higher concentration percentages utilize lighter deuterium preferentially, whereas grasses do not. We conclude that dicotyledonous trees have a selection mechanism whereby leaf water hydrogen is utilized for n-alkane biosynthesis, whereas monocotyledonous grasses do not. This fundamentally explains δD_wax discrepancy between dicotyledonous trees and monocotyledonous grasses, having significant implications for δD_wax paleoapplication.