Effects of Topographic Gradients and Plant Physiological Factors on Leaf Wax n-Alkanes in Quercus buckleyi and Juniperus ashei

Understanding environmental factors influencing the composition and concentration of leaf wax n-alkanes angiosperm and gymnosperm trees is crucial to for reconstructing paleovegetation and paleoclimate variables. Here we demonstrated that seasonal variation within extent tree species landscape position or local climatic factors significantly affect leaf n-alkanes in a tree species to understand whether these issues to the use of in variables. Leaf samples of Quercus buckleyiand Juniperus ashei, common trees of central Texas, were collected monthly (April 2019 to January 2020) across topographic gradients in an undisturbed woodland at Cameron Park Waco Texas 31.5837° N 97.1563° W. Leaf relative water content (RWC) was measured to investigate correlation between water status and concentration of leaf lipids. Our results demonstrated that abundance of n-alkanes (odd chains, nC25 to nC31, except for nC27) in Q. buckleyi was significantly affected by topographic gradients (p<0.001) rather than seasonality (p>0.05), while the n-alkanes (odd chains, nC31 to nC35) concentration in J. ashei was influenced by both topographic gradients and seasonality (p<0.05). The concentration of n-alkanes for Q. buckleyi was highest in early growing season (April), that decreased with leaf maturation. The trajectory of n-alkanes concentration in J. ashei, was highest in early summer (June), decreased through fall, and increased in winter (January). However, those seasonal variations in both species differed across topographic gradients. For example, the concentration of nC31 in both species was significantly correlated with RWC, but with Q. buckleyi, the correlation was a topographic dependent only apparent in relatively flat terrain. Correlation of nC31 and RWC in J. ashei was seasonally dependent with significance only observed in late summer (September), which with maximum daily high temperature (37°C) and low precipitation (0.17 in). Therefore, we hypothesized that n-alkanes as climatic proxies may be unreliable to apply directly due to influences of topography particularly with deciduous broadleaf species.