Aim High alpine regions are threatened but understudied ecosystems that harbor diverse endemic species, making them an important biome for testing the role of environmental factors in driving functional trait-mediated community assembly processes. We tested the hypothesis that plant-soil feedbacks along a climatic and elevation gradient influence plant community assembly through shifts in habitat suitability, which drive plant functional, phylogenetic, and spectral diversity. Location In a high mountain system (2400-3500 m) of Región Metropolitana in the Chilean Andes (33°S, 70°W). Methods 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. Results At high elevation, colder temperatures reduced 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 increased with elevation at the community level and within individual species, consistent with global patterns of increasing leaf nitrogen with colder temperatures. Main conclusions 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.

Plant roots and their fungal associates have a dominant role in terrestrial carbon and nutrient cycling. Yet, how different root orders that vary in their production, quality, and function impact ecosystem processes remains uncertain. Across five orders of fine roots taken from forty woody plant species, we found consistently decreasing carbon and nitrogen release during four years of decomposition in the field the finer and more short-lived the roots (i.e., with decreasing root order from 5th to 1st order roots). Differences among root orders were remarkably well predicted by root carbon chemistry and diameter, with mycorrhizal type effects only in the coarsest roots (4th and 5th order roots). Our data shed an entirely new light on how different root orders and associated mycorrhizae contribute to biogeochemical cycling, refining the understanding and predictions of drivers and pathways of soil carbon and nitrogen dynamics.