Shrub encroachment is a global process driven by land use and climate changes. Although the effects of shrub encroachment on ecosystem functions have been increasingly researched, effects on aboveground-belowground interactions are still not fully understood. In this study, we aim to elucidate the ecosystem-level effects of plant community traits and soil properties on key fungal functional groups, arbuscular mycorrhizal fungi (AMF), ericoid mycorrhiza (ErM) and ligninolytic fungi. Across two subalpine grassland sites in the Alps, community weighted means (CWM) of plant traits and soil properties measured along gradients of increasing shrub density varied along two leading axes representing plant woodiness and accumulation of soil organic matter (SOM). Woodiness was associated with CWM of plant traits representing tissue quality, while SOM accumulation was mainly associated with SOM, soil carbon, soil phosphorus and pH. Both of these functional gradients had significant, linear effects on the three fungal functional groups. Plot-level relative abundances of AMF decreased, ErM increased and ligninolytic fungi increased in response to increasing woodiness and SOM accumulation. These responses were consistent across plant communities with different dominant shrub species, although for mycorrhizal fungal groups shrub identity modulated the magnitude of effects. This study demonstrates that both the amount of woody tissue, and the accumulation of organic material impact soil fungal functional groups, reflecting the direct and indirect effects of shrub encroachment. These gradual effects are consistent across plant communities, showing general mechanisms that underpin aboveground-belowground interactions and thereby ecosystem functions central to nutrient cycling and carbon sequestration. As such, soil fungal functional groups deserve specific attention as key players of ecosystem transformation under global changes.

The development of a robust taxonomy for the genus Rubus remains a real challenge, due to apomictic reproduction and hybridization that led to a very large number of "taxa" with undefined frontiers. Using an untargeted metabolomic approach and a two-year leaf sampling along an elevational gradient in the French Alps we provide new tools to assess boundaries between nine Rubus taxa. Multivariate analyses on ionic intensity matrices (of 566 and 668 features for 2023 and 2024 sampling respectively) have shown that R. idaeus species, the two sections Corylifolii and Rubus, and Caesii section related taxa, formed three distinct super groups. Thirty-eight compounds have been annotated, including 8 detected in genus Rubus for the first time. Discriminant compounds have been annotated, allowing to propose ursane triterpenoids, flavonoids glycosides, lignans and gallotannins as taxonomic classifiers of the genus Rubus. Among those, quercetin - and kaempferol - 3-O-methylglutaryl hexoside were detected at higher levels in R. idaeus, whereas neolignans glycosides have been mostly detected in sections Corylifolii and Rubus. The intermediate position of Caesii between the two others did not allow to propose specific biomarkers of the section. The need for a precise and detailed description of the phytochemical profiles of the various Rubus subgroups is reinforced by the growing use of some of these compounds in pharmacology and cosmetics.

In the context of climate change, shrub encroachment is expected to advance in temperature-sensitive ecosystems such as arctic and alpine grasslands. In mountain regions, shrub encroachment is further triggered by grassland management changes (i.e., land abandonment or extensification). Shrub encroachment is expected to significantly impact ecosystem properties and functions like carbon stocks in both aboveground and belowground compartments, nutrient concentrations, and to slow down biogeochemical cycles. While studies of shrub encroachment processes and their effects on plant and soil functioning have increased our understanding of underpinning processes, there is still a lack of integrated studies and knowledge gaps on the interaction between plant-soil changes and their cascading effects. Our study focuses on understanding these effects on plant community traits and soil properties, and whether these changes are linear. We took herbaceous, shrub and soil samples along gradients of encroachment in sub-alpine grassland communities at two sites in the Alps: Lautaret (France) and the Stubai Valley (Austria). We used a trait-based approach to analyze hypothesized nonlinear functional changes in communities, using community-weighted means (CWM) to scale herbaceous and shrub functional traits and plant allometries. Structural equation models (SEM) support our hypothesis that changing CWM with increasing shrub biomass flows on to changes in soil properties. Dwarf shrub encroachment leads to more conservative and less nutrient-rich plant communities, resulting in an accumulation of recalcitrant organic matter and nutrient-poor soils. Nevertheless, contrary to our expectations, decreased nitrogen in plant communities along the encroachment gradient did not lead to decreased soil available nitrogen. Our results generally suggest it is possible to characterize shrub encroached ecosystems in the Alps using well-studied traits of the global plant economic spectrum, like nitrogen content or dry matter content. With these findings, we are confident that well-researched trait-based models are also applicable for dwarf shrubs, allowing to scale-up from plant traits to the delivery of ecosystem services. This research provides a novel understanding of shrub encroached ecosystems and is a first step in understanding the patterns and mechanisms underpinning their provision of ecosystem services.

Shrub encroachment alters ecosystem functions. Yet, changes in plant community traits and soil properties along succession from grassland to shrubland in European mountains are poorly understood. We used a trait-based approach to investigate the indirect effects of shrubs from community weighted means (CWM) of plant traits to soil properties along a gradient of encroachment in subalpine grasslands at two sites in the Alps. We hypothesized that increasing shrub density shifts plant communities towards more conservative traits, which nonlinearly increases carbon sequestration and impacts nutrient cycling. We tested our hypothesized model of indirect effects using structural equation models, which accounted for biomass allocation to leaves and stems in CWM calculations. As expected, CWM dry matter content (DMC) increased and CWM of nitrogen (N) and phosphorus (P) decreased with increasing shrub biomass. Increasing CWM DMC resulted in increasing soil C:N ratio and soil organic matter (SOM) concentration, and decreasing pH. Decreasing CWM P resulted in decreasing soil available P, but changes in CWM N had no effect on available N. There was no indication of nonlinear changes. This study demonstrates that with shrub encroachment plant communities gradually become more conservative with tougher and nutrient-poor tissues, which leads to soil acidification, SOM accumulation and lower P availability. We also demonstrate that DMC, an easy measurable trait, is a sufficient indicator for effects of plant tissue quality on soils of shrub encroached subalpine grasslands and could be used in future trait-based models, allowing projections under climate change scenarios.

Throughout European mountains, changes in livestock production systems since the 1950s have resulted in the gradual segregation between more accessible, flatter, and productive grasslands with intensified fodder production, and more remote, steeper, and less productive meadows used for extensive grazing, and some abandoned. After cessation of grazing in subalpine grasslands, secondary succession promotes the gradual colonization of species and functionally diverse herbaceous communities by shrubs. Although shrub encroachment is considered a ‘Plant Functional Type transformation’, our knowledge about the impact of climate change on shrub encroached ecosystems is still limited. Mechanistic analyses of alpine grassland responses to drought have focused on carbon fluxes, and a few studies have targeted components of the ecosystem water budget or nutrient cycling. However, these studies are focused on herbaceous functional groups, and shrubs are usually neglected. Moreover, despite the prevalence of this original climate change driver in mountains, snow manipulations are still rare.To improve understanding of nitrogen and water cycling processes of shrubs with expected increased drought and advanced snowmelt, small high-precision lysimeters (SFL®, Meter Group AG, Munich, Germany) were used to analyze the effects and mechanisms of climate change on shrub species. In a garden experiment in the LTSER-site Stubai Valley (970 m a.s.l.), Tyrol Austria, two congeneric shrubs contrasting a deciduous (Vaccinium myrtillus) and evergreen (Vaccinium vitis-idaea) were planted into 16 lysimeters. In a split-plot design of 3.5m x 3.5m each, two plots were subject to either (1) control, (2) earlier snowmelt, or (3) summer drought treatments.The manipulative experiments indicate that a shortening of the period with snow cover at the end of winter affects soil freezing and hence, soil nitrogen (N) and carbon (C) availability. Results further highlight the interacting effects of climate manipulations on key plant traits, and their consequences for N- and water availability. Furthermore, summer drought seems to additionally affect biogeochemical cycling and evapotranspiration for both investigated shrub types. This study's results reveal the importance of addressing the impact of shrub encroachment not only from a land management perspective but also to increasingly raise awareness about climate change effects on shrubs. Moreover, it provides valuable insights into challenges and chances of growing shrubs in lysimeters, being a promising approach for future climate impact studies. The study was conducted as part of the LUCSES project, ANR-FWF (ANR-20-CE91-0009 and FWF-I 4969-B).

Cushion plants, which dominate nival ecosystems, are known to host a large diversity of plant, microbe, and animal life. However, a comprehensive assessment of this diversity is still lacking, particularly with regard to invertebrate soil fauna. In this study, we sampled soil beneath cushion plants in various climatic and geological conditions throughout the French Alps. Our results demonstrate that cushion plants host a remarkably high abundance and diversity of invertebrates, with some individual cushions hosting nearly 400 specimens belonging to 15 different families. Across all samples, 8845 specimens were found. The taxonomic diversity is particularly notable, with groups such as Collembola, Acari, and Nematoda, as well as Gastropoda, Diptera, Coleoptera, Hymenoptera, and Hemiptera. In total, 44 different families were identified. In particular, our findings show that cushion plants not only function as habitats for adult invertebrates, but also as site for the egg laying and larval development of several insect groups, including Diptera, Hemiptera, and Lepidoptera. In addition, different species of cushion plant tend to host distinct invertebrate communities, which makes them a key driver spatial variation in invertebrate populations. However, the factors determining the alpha diversity of invertebrates assemblages in nival environments remain unclear. Overall, our results emphasize the key role of cushion plants in maintaining biodiversity in the nival vegetation belt.

Shrub encroachment influences fungal communities, but detailed knowledge of this influence missing. Using DNA metabarcoding, measure of plant functional traits, soil properties and laccase activities, we studied soil fungal communities along an ericaceous shrub encroachment gradient in two similar subalpine sites (Stubai, Austria and Lautaret, France) that differ in their shrub composition. Fungal taxonomic richness, driven by evergreen shrub cover and soil P, was 1.4 times lower in Stubai than Lautaret. Shrub density affected community taxonomic turnover only at Lautaret, with a qualitative change between 32 % and 63 % cover. Across sites, soil parameters were the primary determinants of fungal community turnover, along with shrub cover, herbaceous biomass and plant functional traits related to tissue quality. At Stubai, fungal community turnover responded to Calluna vulgaris cover, community weighted mean (CWM) lignin and soil properties (P, pH). In contrast, at Lautaret, the change in fungal community composition between low and high shrub cover was significantly explained by shrub cover, herbaceous biomass, plant traits (community-level C:P and herbaceous leaf dry matter content: LDMC) and soil pH. These differences in fungal community turnover translated to varying abundances of fungal functional groups between and within sites. In particular, high shrub cover was associated with a sharp decrease (12 times less) in ectomycorrhizal fungi and a sharp increase (1.3 times more) in saprophytes. Soil laccase activities were low and constant in Stubai, not exceeding 60 nmol. Min(-1). mu g protein(-1) but were higher and decreased with increasing shrub density, from 281 to 125 nmol. Min(-1). mu g protein(-1) at Lautaret. Our study demonstrates a significant impact of shrub functional composition on fungal communities, related to shrub density and functional traits associated with tissue quality. Such changes are expected to alter the biogeochemical functioning of subalpine grasslands.

In extreme environments such as the nival vegetation belt, isolated cushion plants create islands of soil fertility within a mostly mineral environment. It, however, remains unknown whether different co-occurring cushion plant species engineer soils with contrasted properties, and to what extent plant functional traits mediate this process. We sampled 117 individual cushions from seven species, together with 26 bare soil controls from 2600 to 3200m of elevation. Soil property (carbon and nitrogen content, soil C:N and available phosphorus) were compared between species, and the role of cushion plant traits was assessed using Structural Equation Modelling (SEM). The soils beneath cushion plants showed similar characteristics to those found 1000m below, where vegetation is continuously distributed. Isotopic signatures showed that the soil organic matter beneath cushions originated from the plant itself. Soil characteristics (C, N, C:N, P) differed among plant species. SEM revealed that soil characteristics were not driven by leaf C/N or phenolic content, but rather by cushion size and bedrock type. Providing a unique overview of soil formation in nival ecosystems, our study provides novel insights into the mechanisms of ecosystem engineering by foundation plants and shows how interspecific variability contributes to this process.

In the challenging environmental conditions of high elevation ecosystems, cushion plants create micro-climatic and fertile shelters which host a vast diversity of organisms. Yet, the taxonomic diversity of these hosts remains poorly described, and to what extent cushion plants structure these communities remains unclear. We sampled soils beneath six different species of cushion plants, along with bare-ground controls, across two different elevation gradients in the French Alps. We used environmental DNA metabarcoding to investigate the effect of different species of cushion plants on the alpha and /3 diversity of fungi, bacteria, eukaryotes, and for the first time in these ecosystems, unicellular eukaryotes and soil worms. Cushion plants hosted a surprisingly large diversity of organisms, from bacteria to mites and collembolans, forming rich and complex ecosystems. alpha-diversity between cushion plant and bare soil samples differed only for fungi, with communities partly structured by the cushion plant species' identity. The effect of cushion plant species on composition and /3-diversity of eukaryotic and fungal communities surpassed the environmental effect, while it equaled the site effect for bacterial communities. These results highlight the key role of biotic interactions in shaping the composition of high elevation communities, and clarify the role of cushion plants as engineer and foundation species in these harsh environments. By sheltering highly diverse communities at such high elevation, cushion plants may play a prominent role in the ecological assembly of these diverse, yet poorly known, ecosystems.

Herbivory can have contrasted impacts on soil microbes and nutrient cycling, which has stimulated the development of conceptual frameworks exploring the links between below- and aboveground processes. The “productivity model” predicts that herbivores stimulate microbial activities and accelerate nutrient mineralization in productive ecosystems, while they have an opposite effect in less productive ecosystems. In parallel, the “diet model” predicts that herbivores feeding on conservative plants accelerate nutrient cycling while those feeding on exploitative plants decelerate nutrient cycling, due to changes in litter inputs. Since these two frameworks can lead to conflicting predictions in some cases, experimental evidence combining herbivore diet and plant productivity is required. During two consecutive years, we conducted an experiment controlling the presence of three grasshopper species consuming either grasses, forbs or both in twelve natural and managed alpine grasslands with contrasted productivities. In order to assess the effects of herbivory on soil microbes, we measured their extracellular enzymatic activities, biomass and potential nitrogen mineralization (PNM). Soil and vegetation were also characterized to test how much they modulated the effects of herbivory on microbes. Contrary to the predictions of the diet model, the effects of herbivory on microbial characteristics did not depend on the herbivores diet, but were influenced by primary production, though in a way that differed from the productivity model. The most productive sites were constituted by exploitative plant species which depleted N resources in the soil, and by microbes producing relatively few extracellular enzymes, leading to a lower PNM. Herbivory increased microbial biomass and decreased the production of extracellular enzymes in those sites, possibly through the stimulation of root exudates produced by exploitative species. The least productive sites were characterized by conservative plants, high soil C content, and by microbes having a resource acquisition strategy (more extracellular enzymes, higher PNM). Herbivory decreased microbial biomass and increased the production of extracellular enzymes in those sites. This pattern can be explained by the loss of carbon associated with insect respiration, which increases the resource requirements of microbes and by a lower production of root exudates by conservative species. Therefore, the effects of two years of herbivory on soil microbes were at odds with the productivity model, which focuses instead on longer term effects corresponding to herbivory-induced changes in plant species composition. This highlights the multidimensional feature of the impacts of herbivory on ecosystem functioning, both in space and time.

In the absence of top-down and bottom-up controls, herbivores eventually drive themselves to extinction by exhausting their host plants. Poorly mobile herbivores may experiment only local disappearance, because they can recolonize intact plant patches elsewhere, leaving time to previously over-exploited patches to regrow. However most herbivores such as winged insects are highly mobile, which may prevent the formation of spatial heterogeneity. We test if long-distance dispersal can preclude coexistence using the invasion of box tree moth (Cydalima perspectalis) in Europe as a model system. We build a lattice model and estimate the parameters with a combination of field measurements, experimental data and literature sources. Space corresponds either to a realistic boxwood landscape in the Alps, or to theoretical landscapes of various sizes. We find that both species persist under a large range of realistic parameter values, despite a severe reduction in boxwood biomass, with an alternation of outbreaks and near-to-extinction moth densities. Large landscapes are necessary for coexistence, allowing the formation of spatial structure. Slow plant regrowth combined with long-distance dispersal could drive moths to extinction, because of resources depletion at the global scale even without a complete synchronization of the local dynamics. The spatial dynamics leads to formation of small plant patches evenly distributed in the landscape, because of a combination of local plant dispersal and global indirect competition between plants through their positive effect on moth population size. Coexistence is favoured by such heterogeneous landscapes, because empty patches increase moth mortality during dispersal: the system thus creates its own stability conditions.

Aims In cold biomes, snow cover mitigates the harsh winter soil conditions, thereby enhancing overwinter decomposition of organic matter which controls the availability of nutrients for plants and microbial uptake at the beginning of the growing season. Yet, how this buffering effect is modulated by litter traits, soil characteristics and herbivory remains poorly studied. Methods We conducted a litter-bag experiment in four types of subalpine grasslands, two of which being naturally free of snow during most of the winter. Litter bags were filled either by grasses or forbs sampled in plots submitted the preceding summer to grasshopper grazing treatments. Results Snow cover strongly increased the decomposition of forbs, but not of grasses. Litter quality (low C:N and polyphenols triggering a priming effect) and soil ammonium content were correlated with litter decomposition rate in the presence of snow only, whereas soil organic matter content was positively associated with decomposition rate under both snow regimes. Herbivory did not affect decomposition. Conclusions Our findings may be explained by the functional differences between copiotrophic and oligotrophic microbes, copiotrophs being more sensitive to harsh abiotic conditions than oligotrophs. As long as copiotrophs are favored by high litter quality and nutrient-rich soils (high ammonium content), litter decomposition is enhanced in the absence of snow only.

Oak regeneration in temperate forests often fails in the presence of understorey grass. Competition by resource exploitation between plants has been extensively studied. By contrast, competition by interference, especially chemical interference (allelopathy), has been much less thoroughly examined and its relative importance remains unclear. We investigated the influence of allelopathic interaction on plant performance (biomass production) in a pot experiment with sessile oak (Quercus petraea) and purple moor grass (Molinia caerulea), either sole- or mixed-grown. Plants were watered with either Quercus root exudates or Molinia root exudates. After 6 months of growth, oak biomass increment was significantly lowered by Molinia root exudates. The oak’s root system was more strongly affected than its aerial part. Quercus root exudates favoured oak growth but did not affect moor grass. Conversely, Molinia root exudates had a small depressive effect on its own growth, but its biomass was favoured by the presence of oak grown in the same pot. Resource exploitation had a more detrimental effect than allelopathy and both processes together decreasing oak biomass by 50%. Although untargeted metabolomic analysis by UHPLC failed to identify any potentially allelopathic substances involved, our study demonstrates a lower but critical contribution of chemical interference on oak seedling-moor grass competition compared to exploitation processes. To ensure oak regeneration, management of forest ecosystems should thus first focus on reducing moor grass close to oak seedlings to help decrease its allelopathic effect and ease resource competition.

Helianthemum nummularium is a European shrub growing at high altitude where it copes with a high level of stress. It was found to be overexpressed in ungulates diets compared to more abundant surrounding plants. These elements combined with the fact that H. nummularium from the Alps has never been investigated prompted us to study the phytochemical composition of its aerial parts. The analysis of the polar extract allowed for the isolation of eight compounds: p -hydroxybenzoic acid, tiliroside, kaempferol, astragalin, quercetin, plantainoside B, quercetin-3- O -glucoside, and quercetin-3- O -glucuronide. We investigated the effect of the polar extract and isolated compounds on nuclear factor erythroid 2-related factor 2 transcription factor, which regulates the expression of a wide variety of cytoprotective genes. We found that the ethanolic extract activates the expression of nuclear factor erythroid 2-related factor 2 in a dose-dependent manner, whereas the pure compounds were much less active. The activation of the nuclear factor erythroid 2-related factor 2 pathway by the plant extract could pave the way for studies to promote healthy aging through protection of cells against oxidative stress. Moreover, the isolated compounds could be investigated alone or in combination in the perspective of making the link between the ungulates preference for this plant and possible use of it for self-medication.

AimsIn subalpine grasslands, litter decomposition controls soil nutrient availability and is highly sensitive to increasing intensity and frequency of extreme climate events, potentially impacting grasslands diversity and functioning. Here, we assessed the effects of early snowmelt and summer drought on decomposition, and how these were modulated by agricultural management.MethodsIn a common garden, conservative and exploitative assembled communities were submitted for two years to combined snow removal and drought, and to cutting and fertilization. We measured decomposition rates of standard and native leaf material from each plant communities on their respective soils.ResultsWe observed relatively weak climatic stress effects on decomposition rates. Management increased decomposition rates and remaining litter N contents through leaf quality improvement rather than changed soil biotic activity. Climate events impacted the decomposer community and limited litter N immobilization in conservative communities. Less recalcitrant litter of exploitative species facilitated decomposition and counterbalanced the negative effects of climate stress.ConclusionOur results suggest that drought and earlier snowmelt could decrease N availability in subalpine grasslands due to reduced litter biomass and decomposition. In the long-term climate change may shift subalpine grasslands towards more conservative plant composition and lower soil fertility.

Recruitment is a key process for forest sustainability, especially in warm margin of distribution area. The influence of climate (temperate or warm), of soil water availability, and of allelopathic interactions from different forest species have been tested on the germination of Fagus sylvatica in controlled climatic conditions. Germination rates of nondormant Fagus seeds were improved by relatively warm temperatures (20 degrees C), but reversibly stopped under heat constraint (27 degrees C). The relative growth rate of Fagus seedlings was better under temperate climatic conditions. Foliar extracts of Hedera helix showed the highest allelopathic effect on Fagus recruitment, especially in temperate conditions. Our results suggest a limitation of Fagus recruitment in warm margin of its distribution area, and a modulation of recruitment success according to the identity of plant neighbourhood. (C) 2018 Published by Elsevier Masson SAS on behalf of Academie des sciences.

En tant que consommateurs primaires, les herbivores jouent un rôle essentiel dans la dynamique de la végétation. Leur influence peut se manifester de l’échelle de la plante, via la modification de son métabolisme, jusqu’à l’échelle de la communauté végétale, par un changement de sa composition floristique ou de l’abondance des espèces qui la composent. Quelle que soit l’échelle considérée, les effets sur la végétation peuvent se répercuter sur la qualité des litières et ainsi impacter le processus de décomposition. Il en résulte souvent une modification des cycles biogéochimiques et plus largement du fonctionnement de l’écosystème. Cet article se propose de faire l’état de la littérature concernant les interactions entre plantes et grands herbivores, en développant plus particulièrement les moyens par lesquels les herbivores affectent les plantes, les stratégies mises en place par ces dernières pour se défendre, ainsi que les processus par lesquels les herbivores peuvent nfluencer le fonctionnement de l’écosystème via la décomposition des litières.

As primary consumers, herbivores play an important role in vegetation dynamics. Their effects run from the plant level by influencing plant metabolism, to the community level by changing the floristic composition and the abundance of plant species. These effects on vegetation can impact litter quality and can thus alter the decomposition process. This can in turn impact soil biogeochemical cycles and modify ecosystem functioning. Here, we review the literature on plant and large herbivore interactions, focusing on the means by which herbivores affect plants, the plant strategies to cope with herbivory, and the mechanisms by which herbivores can affect ecosystem functioning via the alteration of litter decomposition.

Summary A broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms. We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning. Synthesis . Gaining a greater understanding of plant–soil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio‐temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning.