Elevational differentiation in metabolic cold stress responses of an endemic mountain tree

Abstract

The decline of mountain forests under global change is alarming and conservation is challenged by the need to assemble populations able to deal with the predicted environmental shifts. Assessing intraspecific differentiation in stress susceptibility of tree species along elevational gradients is crucial to identify adequate genetic sources for forest restoration. Here, we assessed injury and metabolic responses across cold stress intensity gradients in low and high elevation populations of the endangered mountain tree Polylepis australis. We hypothesized that populations from high elevational origins will show weaker increases of injury and morepronounced metabolic responses with rising frost stress intensity than low elevation populations. The expected differentiation among elevational origins was not observed for frost stress injury,but for metabolic stress responses. Plants responded to cold with enhanced concentrations of sugars, organic acids, amines and specialized metabolites with freezing point depressing, cryoprotective and anti-oxidative properties. As predicted, these responses were more pronounced and partially increased more strongly with stress intensity in high than low elevation populations,indicating local adaptation to a higher frequency and intensity of cold events at high elevations. We discuss the power of metabolomics approaches in unravelling intraspecific differentiation in tree stress resistance across small geographic scales as well as implications for future research onthe evolution of cross-resistance to multiple stressors and for forest restoration.