Leaf wax n-alkane patterns of six tropical montane tree species show species-specific environmental response

It remains poorly understood how the composition of leaf wax n-alkanes reflects the local environment. This knowledge gap inhibits the interpretation of plant responses to the environment at the community level and, by extension, inhibits the applicability of n-alkane patterns as a proxy for past environments. Here, we studied the n-alkane patterns of five Miconia species and one Guarea species, in the Ecuadorian Andes (653-3,507 m a.s.l.). We tested for species-specific responses in the average chain length (ACL), the C₃₁/(C₃₁ + C₂₉) ratio (ratio), and individual odd n-alkane chain lengths across an altitudinally driven environmental gradient (mean annual temperature, mean annual relative air humidity, and mean annual precipitation). We found significant correlations between the environmental gradients and species-specific ACL and ratio, but with varying magnitude and direction. We found that the n-alkane patterns are species-specific at the individual chain length level, which could explain the high variance in metrics like ACL and ratio. Although we find species-specific sensitivity and responses in leaf n-alkanes, we also find a general decrease in "shorter" (29) and an increase in "longer" (>C₃₁) chain lengths with the environmental gradients, most strongly with temperature, suggesting n-alkanes are useful for reconstructing past environments.