Response of leaf morphological traits of relict-endemic Symplocos species (S. coccinea and S. speciosa) to elevation and abiotic fluctuations

Abstract

Abiotic fluctuations in montane ecosystems trigger changes in the hydric functional traits of tree species. These variations are better recognized in tree species inhabiting montane humid ravine slopes with different elevation, as is the case of many areas across the Mexican Neotropical montane forests. Little is known about the response of tree towards elevation gradients and abiotic changes. In this study, we analyzed the leaf morphological variation of two rare and Mexican endemic Symplocos species (S. coccinea and S. speciosa) occurring eastern Mexico on sites with different microclimate and elevation but similar floristic composition. We quantified how the abiotic factors (i.e. canopy openness, soil temperature, soil moisture, and litter depth) and site elevation influence the leaf traits of these tree species. Symplocos coccinea (with toothed leaf margins) is adapted to high humid conditions and high canopy coverage, while S. speciosa (with almost entire leaf margins) is resilient to environments with moisture deficit and high temperatures. Process-based research with fine-spatial scales at montane ecosystems are needed to understand the resilience and morphological variations of montane tree species under climate change worldwide. In this study, we confirmed that the Symplocos leaf morphological traits (i.e. leaf length, leaf width, leaf shape index, leaf base angle and vein density) are strongly influenced by abiotic conditions (i.e. canopy openness, litterfall depth, soil moisture and soil temperature).