Association of functional trait variation of Quercus castanea with temperature and water availability gradients at the landscape level

Abstract

Background: Phenotypic variability of tree species is often associated to environmental factors. Quercus castanea is a Mexican red oak with a wide geographical and altitudinal distribution along contrasting environments. It is the most abundant oak species in the Cuitzeo basin, which is characterized by highly heterogeneous environmental conditions.  Hypothesis: We hypothesized that gradients in temperature, precipitation and soil characteristics across the distribution of Q. castanea within the Cuitzeo basin promote variability in functional traits related to the adjustment to differential water availability at a landscape level. Studied species: Quercus castanea Née (Fagaceae). Study site and years of study: Cuitzeo basin in Central Mexico. 2015-2016. Methods: We quantified leaf chlorophyll concentration (CC), leaf area (LA), leaf thickness (LT), leaf mass per area (LMA) and the Huber value (HV) in 10 individuals from 22 populations of Q. castanea throughout the basin. Results: Despite the relatively small geographical area (4,000 km2), our results revealed significant differentiation among populations in the studied functional traits. The strongest variation found was in LT, which was negatively correlated with precipitation seasonality. This pattern is opposite to previous reports on Mediterranean oaks but similar to tropical oaks and suggests that the combination with other traits such as leaf phenology is important in the response to water availability. Conclusions:  Significant functional differences exist among populations of Q. castanea separated by a few kilometers in the heterogenous landscape of the Cuitzeo basin. This species shows clearly sclerophyllous leaves, but leaf thickness varies to a considerable degree across populations.