Soil plays a pivotal role in the distribution of plants, their traits and ecosystem functions in the French Alps

Experiments and observations have shown that plants and soil biotic and abiotic properties are linked by feedback loops at local scale, in particular because plant functional traits determine the decomposability of the organic matter, which in turn influences the availability of nutrients essential for plant growth. However, the influence of plant-soil linkages on plant distributions and ecosystem functions is understudied at large biogeographic scales.

Here, I present results of studies along 18 elevational gradients in the French Alps. In a first study, I show how the distributions of 44 plant species does not only depend on climate but also on soil physico-chemical properties and microbial decomposition activity and that plant functional traits play an important role in these distributions. Using hierarchical effects and multi-species distribution models, we found that, in addition to climate, the combination of soil C/N, as a measure of organic matter quality, and exoenzymatic activity, as a measure of microbial decomposition activity, strongly improved predictions of plant distributions. In accordance with the ‘fast-slow’ plant economics spectrum, species with conservative traits performed better under limiting nutrient conditions but were outcompeted by exploitative plants in more favorable environments, resulting in a spatial segregation of plants with different ecological strategies. In a second study, we moved from species to community level to estimate the impact of these plant-soil linkages on ecosystem functions. Using an undirect partial correlation network revealed that the influence of plant traits on the quality of organic matter links aboveground and belowground ecosystem functions. Finally, I show how specific soil trophic groups, notably saprophytic fungi, play key roles in these linkages. This result highlights that decomposition and the organisms involved in this process are the corner stone of ecosystem multifunctionality in nutrient depleted ecosystems such as mountains. Together these results highlight the importance of considering plants and soil biodiversity along with abiotic predictors for better understanding and modelling ecosystem processes and functions in a world where both climatic and soil systems are undergoing profound and rapid transformations.