Drivers of plant diversity, community composition, functional traits and soil processes along an alpine gradient in the central Chilean Andes

Abstract

High alpine regions are threatened but understudied ecosystems that harbor diverse endemic species, making them an important biome in which to test the role of environmental factors in driving functional trait-mediated community assembly processes. In a high mountain system in the central Chilean Andes, we tested hypotheses about the drivers of plant community diversity, functional composition and soil processes along an elevation gradient. We surveyed vegetation and spectroscopic reflectance (400-2400 nm) to quantify taxonomic, phylogenetic, functional, and spectral diversity at five sites from 2400 m to 3500 m elevation. We characterized soil attributes and processes by measuring water content, carbon and nitrogen, and net nitrogen mineralization rates. At high elevation, colder temperatures led to a reduction in available soil nitrogen, while at warmer, lower elevations, soil moisture was lower. Metrics of taxonomic, functional, and spectral alpha diversity peaked at mid-elevations, while phylogenetic species richness was highest at low elevation. Leaf nitrogen followed global patterns of increasing leaf nitrogen with colder temperatures, a pattern consistent at the community level as well as within individual species. The increase in leaf nitrogen, coupled with shifts in taxonomic and functional diversity associated with turnover in lineages, indicate that the ability to acquire and retain nitrogen in colder temperatures may be important in plant community assembly in this range. Such environmental filters have important implications for forecasting shifts in alpine plant communities under a warming climate.