LUCSES

Ongoing abandonment of mountain meadows leads to their shrub-encroachment and thus to functional changes. These changes affect the species composition, the water balance, but also the nutrient balance and thus the services of the mountain meadows for us humans: the ecosystem services (ES). Within previous common international projects, researcher involved in LUCSES were already able to identify important ES of mountain grasslands and to model these from the past to the future. Characteristic plant traits such as leaf area, nitrogen- and carbon content of the leafs as well as soil traits such as total nitrogen content and soil organic matter (SOM) are successfully used as indicators of ES (e.g., carbon storage, soil fertility, soil stability,...). As part of the LUCSES project, the characteristics of shrubs will now be incorporated into this trait-based approach. The core hypothesis of LUCSES is that shrub colonization results in a tipping point in relationships between traits and processes of nitrogen- and water cycling, and that this change can be related to characteristic plant traits and to mycorrhizal functions. For the first time, functional implication of mycorrhization, which especially in cold and nutrient-poor mountain regions contributes significantly to the nutrient- and the water supply, is also included in this type of trait-based approach. Within LUCSES, a large number of experimental plots with gradual shrub-encroachment are investigated in two study areas in the Alps (Lautaret, FRA and Stubaital, AUT), covering a broad range of grassland types and shrub species. A distinct experiment with small lysimeters analyses the effects of climate change (i.e. earlier snowmelt and drought in summer), linking involved biogeochemical cycles (i.e. nitrogen and water). LUCSES thereby also targets towards differences between summer and evergreen shrubs and to determine changes in the degree and type of mycorrhization. On the one hand, LUCSES provides an unprecedented database of plant characteristics for dwarf shrubs and, on the other hand, the prerequisites for the calculation of ecosystem functions and ecosystem services of shrub ecosystems over a wide range of succession stages. The combination of nitrogen and water balance with the quality and quantity of mycorrhization is a research frontier and leads to a better functional understanding and thus providing fundamental knowledge in alpine plant ecology. Results of LUCSES are published on the one hand scientifically, but on the other hand passed on the concept of ecosystem services to decision makers and practitioners within existing communication networks of the involved research institutions LECA Grenoble (Laboratoire d`Ecologie Alpine) and UIBK (University of Innsbruck).

Main point: As shrubs spread into mountain grasslands, plant communities and soils change in a clear, measurable, and gradual way. Such changes affect the amount of carbon and nutrient flow in these ecosystems, which is knowledge we can now use to better manage and forecast ecosystem services in the Alps. What we did and found We examined a high number of grassland plots across the French and Austrian Alps along a continuous gradient from open grass to shrub-dominated vegetation. We measured plant traits and soils together to see how change aboveground affects life belowground. As shrubs increased, plant communities shifted towards tougher, more carbonrich and nutrientpoorer tissues. In soils, this translated into an accumulation of soil organic matter, a higher carbontonitrogen ratio, lower pH (more acidic), and less available phosphorus. These changes were linear, meaning that shifts in plant communities and soils happen in a gradual way. A single, easytomeasure plant trait, dry matter content (a proxy for tissue toughness), was enough to explain these soil changes. This offers a practical earlywarning indicator for managers. The type of shrub matters: in plant communities where e.g., common juniper dominated, plant traits and some soil responses (especially soil pH and plant phosphorus) were distinct, showing that shrub identity can affect the link between plants and soil. Belowground, the root and fungal partnerships also reorganized. Roots of herbaceous species became tougher and less fine, and their collaboration with arbuscular mycorrhizal fungi (AMF), the tiny partners that help plants take up nutrients, declined. At the wholecommunity level (i.e., considering herbaceous and shrub species), AMF declined while ericoid mycorrhizal fungi (typical mycorrhizal partners of dwarf shrubs) gained a little, suggesting a partial swap of fungal partners rather than a full replacement. Overall, this points to reduced root soilexploring capacity and changing their relation to soil fungi. Why it matters Mountain grasslands provide fodder, clean water, fertile soils, and climate regulation. Encroachment with warming and landuse change (e.g., grazing reduction) changes these ecosystem services through the planttosoil cascade we documented. We show that traitbased models developed for grasslands can be extended to shrubencroached landscapes, enabling better projections of future ecosystem services under climate and landuse change. Practical takeaways Monitor simple plant traits (like dry matter content) as costeffective way to track links between vegetation and soil changes during shrub encroachment. Expect more soil carbon and acidity, and less available phosphorus, as shrubs increase: knowledge which will help plan grazing, restoration, or fertilization strategies accordingly. Anticipate shifts in belowground partnerships (less AMF, more ericoid fungi) that may alter how plants access nutrients, with potential consequences for productivity and biodiversity.