Soil is a hyper-heterogeneous environment, and how plants respond to changes in belowground variations in soil properties and microclimate is poorly understood. Environmental gradients are useful for examining how root traits mediate plant responses to soil heterogeneity. We measured soil/air temperature, soil water potential and physical/chemical properties in 30 plots along elevational gradients located in France and Mexico, both above- and below the treeline. High elevations were colder than lower elevations at both sites. but in Mexico. precipitation decreased at high elevations. Where as in France, higher elevations Were wetter than lower altitudes. Soil properties Were more idiosyncratic along both gradients. We selected 11 (France) and 14 (Mexico) woody and herbaceous species based on their abundance along the gradients. A range of root and leaf functional traits were measured. Data showed that trends in root traits along gradients were often masked by the hyper-heterogeneous belowground environment. whereas patterns in leaf traits were more evident. Results will be discussed with regard to the effect of elevation as an environmental filter on plant traits.