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Interactions among species are a fundamental aspect of biodiversity and drive ecosystem functioning and services. Species interactions include direct (pairwise) interactions among two species and indirect interactions that occur when a third species interacts and changes the pairwise direct interaction. In a three‐species interaction network, these interactions can be transitive (where one species outperforms all others) or intransitive (where each species outperforms another). Here, we investigate how direct and indirect interactions influence ecosystem functions in crop systems and how diversification and evolutionary adaptation can influence those interactions and therefore ecosystem functions.A common garden experiment was conducted with crop communities in monocultures, 2‐ and 3‐species mixtures that had either a common or no coexistence history (i.e. co‐adaptation) for the three previous years. Net, direct and indirect interaction intensities were estimated and compared between the diversity levels and coexistence histories. Furthermore, species interaction networks were inspected for transitive/intransitive interactions.We found evidence for less intense competition in mixtures and for reduced negative direct interaction intensity and enhanced facilitative effects upon co‐adaptation. We could further show that indirect interactions were generally less important for co‐adaptation than direct interactions. Additionally, we showed that co‐adaptation has the potential to shift interactions in the species interaction networks from competitive intransitive into pairwise competitive interactions where interactions occurred mainly between two species.Synthesis. Co‐adapted crop species with reduced negative interactions might have the potential to enhance productivity, especially in more diverse cropping systems. This supports the notion that intercropping is a vital part towards a more sustainable agriculture and one with further yield potential when developing cultivars optimised for growth in mixtures. [ABSTRACT FROM AUTHOR]

Plant interactions in extreme environments are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat‐sharing effects. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. We quantified spatial associations with the two methods at three sites that encompass different micro‐environmental heterogeneity and stress levels: Mediterranean environments in Canary Islands, Spain, and Sardinia, Italy, and a cold alpine environment in Hokkaido, Japan. Then, we simulated plant communities with different levels of species micro‐habitat preferences, environmental heterogeneity, and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in a homogeneous space. When simulating codispersion over a decreasing abundance gradient, both sampling methods correctly identified facilitation and distinguished it from codispersion. Yet, the pairwise method provided higher facilitation estimates than the random one. At each site, there were strong differences between beneficiary species in their spatial association with nurse species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro‐environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat‐sharing effects. Thus, the paired sampling method can provide significant insights into net and long‐term effects of plant interactions in spatially conspicuous environments. [ABSTRACT FROM AUTHOR]

Inspired by grassland biodiversity experiments studying the impact of plant diversity on primary productivity, the Crop Diversity Experiment setup in 2018 aimed at testing whether these biodiversity benefits also hold for annual crop systems and whether crop mixtures also achieved transgressive overyielding, i.e. yield in mixture that was higher than the most productive monoculture. The first 3 years of the experiment demonstrated that crop mixtures do not only increase yield compared with an average monoculture but often also compared with the highest yielding monoculture. The crop diversity effects were stronger under more stressful environmental conditions and were often achieved in mixtures with legume crops. However, we observed transgressive overyielding also under favorable conditions and in mixtures without legumes. With our investigation of the underlying mechanisms of the yield benefits we found both direct complementarities between crop species and indirect effects via other organisms. The former included chemical, spatial and temporal complementarity in N uptake, complementary root distribution leading to complementary water uptake, as well as spatial and temporal complementarity in light use. Among the indirect mechanisms we identified complementary suppression of weeds and more abundant plant growth-promoting microbes in crop mixtures, apart from complementarity in pest and disease suppression not yet studied in the Crop Diversity Experiment but demonstrated elsewhere. In consequence, the Crop Diversity Experiment supports not only the assumption that the ecological processes identified in biodiversity experiments also hold in crop systems, but that diversification of arable crop systems provides a valuable tool to sustainably produce food. [ABSTRACT FROM AUTHOR]

Intercropping, by capitalizing on positive biodiversity–productivity relationships, represents a promising option to increase agricultural sustainability. However, the complexity and context-dependency of plant–plant interactions can make it challenging for farmers to find suitable crop combinations. Furthermore, intercropping is usually implemented with standard inter-row spacing and plant densities based on monoculture practices, which might not be the ideal configuration to maximize yield. Here we present a spatially-explicit yield analysis method based on plant ecological interaction models that allowed to optimize crop species combinations and spatial configurations for maximal yield in intercropped systems. We tested this method with three crop species, namely oat, lupine, and camelina. In a first step, field experiments in which crop density and adjacent crop type were varied provided us with indications on which species would compete more with each other. The results showed us that oat and camelina strongly competed with each other. In addition, the distance experiments allowed us to understand how the changes in yield associated with the presence of neighbors vary with distance. This allowed us to find the sets of parameters (identity of neighbors, sowing density, distances between individuals) that optimise intercrop yield (measured as Land Equivalent Ratio [LER]) for the three considered species. Specifically, we show that alternating rows of species led to higher LERs than a homogeneous species mixing, and that 3-species combinations are not necessarily more performant than the best 2-species combinations. In addition, we show that increasing the density of oat is generally beneficial for LER, while increasing the density of lupine is not. By modelling crop yield from simple and reproducible density and distance experiments, our results allow to optimize crop mixtures in terms of species combinations and spatial configurations, for maximal crop yield. [ABSTRACT FROM AUTHOR]

Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant–insect interaction analysis and variance partitioning of biodiversity effects. We present a case‐study experiment in which facilitation by a cushion‐plant species and a dwarf‐shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects. [ABSTRACT FROM AUTHOR]

Where interspecific facilitation favors the establishment of high densities of a beneficiary species, strong intraspecific competition may subsequently impede beneficiary performance. Consequently, the negative influence of intraspecific competition between beneficiary individuals could potentially outweigh the positive influence of interspecific facilitation when, for example, higher densities of a beneficiary are negated by the negative effect of crowding on beneficiary reproduction. The aim of this study was, therefore, to examine the impact of an interspecific interaction on the outcome of intraspecific interactions within the context of plant–plant facilitation. We used the cushion‐forming Azorella selago and a commonly co‐occurring dominant perennial grass species, Agrostis magellanica, on sub‐Antarctic Marion Island as a model system. We assessed the impact of an interspecific interaction (between A. selago and A. magellanica) on the outcome of intraspecific interactions (between A. magellanica individuals), by testing if the impact of A. magellanica density on A. magellanica performance is mediated by its interaction with A. selago. We observed evidence for competition among A. magellanica conspecifics, with a decreasing proportion of A. magellanica individuals being reproductive under higher conspecific density. This negative intraspecific effect was greater on A. selago than on the adjacent substrate, suggesting that the facilitative effect of A. selago changes the intensity of intraspecific interactions between A. magellanica individuals. However, experimentally reducing A. magellanica density did not affect the species' performance. We also observed that the effect of A. selago on A. magellanica was positive, and despite the negative effect of intraspecific density on the proportion of reproductive A. magellanica individuals, the net reproductive effort of A. magellanica (i.e., the density of reproductive individuals) was significantly greater on A. selago than on the adjacent substrate. These results highlight that, in abiotically severe environments, the positive effects of interspecific facilitation by a benefactor species may outweigh the negative effects of intraspecific competition among beneficiaries. More broadly, these results suggest that both positive inter‐ and intraspecific biotic interactions may be key to consider when examining spatial and temporal variation in species' performance. [ABSTRACT FROM AUTHOR]

Interactions among neighbours can alter demography and traits of commingled species via adaptation or plasticity in phenotypic expression, and understanding these two mechanisms in diverse communities is important for determining the ecological and evolutionary consequences of plant–plant interactions.We reciprocally transplanted perennial species (Arenaria armerina and Festuca indigesta) among patches of two foundation shrub species and open ground to assess whether origin microsite (defined as the spatially distinct abiotic and biotic conditions associated with the two shrubs and open ground) determines germination, recruitment and growth that, in turn, promotes fine‐scale distribution of species among microsites. In addition, we tested the effect of origin microsite on traits, competitive ability, drought tolerance and outlier loci to assess whether origin microsite conditions drove differences in traits, strategies and adaptive loci.Germination was consistently greater for seeds planted back into their origin microsite relative to seeds sourced from foreign microsites, although this effect was weakened for recruitment. Plant growth was best in open sites regardless of origin microsite. In the greenhouse, A. armerina had conserved traits within origin microsite but distinct trait values among origins, specifically plants from the most productive microsite (e.g. sufficient light, high nutrients and improved water availability) had distinct trait values. Festuca indigesta had conserved trait responses among microsites while within microsite, individuals had significant trait plasticity to different environmental conditions. The combined field and greenhouse results suggest that fine‐scale distributions are supported by local adaptation among microsites of A. armerina and phenotypic plasticity of F. indigesta.Synthesis. Adaptation or plasticity in phenotypic expression has different implications for demographic rate and persistence of species in changing environments. Local adaptation to neighbours suggests that reductions in foundation species diversity could concomitantly lead to reduced genetic diversity of commingled species while a plastic response indicates a more robust and broad response to changing climatic and biotic conditions. [ABSTRACT FROM AUTHOR]

Biotic interactions can shape species’ distributions through their impact on species’ realized niches, potentially constraining or expanding the range of conditions under which species occur. We examine whether fine-scale plant–plant interactions scale up to shape broad-scale species’ distributions, using Azorella selago, a widespread cushion plant that facilitates other species, and the rest of the vascular flora of sub-Antarctic Marion Island as a model system. We compared the upper elevational distributional limit of each species when growing on vs. away from A. selago to test how the interaction with this cushion plant species affects species’ ranges. Three out of 19 vascular plant species occurred at higher altitudes in the presence of A. selago than in the absence of A. selago: Acaena magellanica (+26 m higher), Colobanthus kerguelensis (+37 m higher), and Lycopodium saururus (+19 m higher). Therefore, A. selago’s fine-scale impacts scaled up to shape the distribution of a subset of the vascular flora of Marion Island. Plant–plant interactions thus have the potential to expand species upper distributional limits by increasing the niche space that a species can occupy, although the influence of these interactions may be strongly species-specific. [ABSTRACT FROM AUTHOR]

Questions: Positive and negative associations among species influence the structure of plant communities. Yet how these plant associations are assembled at the community level is poorly understood. We propose a new approach that combines spatial ecology, network theory and trait‐based ecology to examine the assembly of plant–plant associations at the community level. Location: Gemmipass, Swiss Alps. Methods: We fully mapped an alpine plant community at the individual plant level, recording both plant coordinates and functional traits for each individual. We identified non‐random species associations using spatial point‐pattern analysis and partialled out the effect of abiotic heterogeneity. We then analysed the plant network structure and used plant traits to predict species associations. Results: We identified 36 significant spatial associations between plant species, 34 positive and two negatives. Dominant, stress‐tolerant species such as Dryas octopetala, Linaria alpina and Leontodon montanus were highly connected in the network, whereas rare, water‐ and nutrient‐demanding species such as Saxifraga aizoides, Galium anisophyllon and Thymus praecox were less connected compared to random expectation. The plant network was clustered, meaning that species were overall more connected among each other than expected by chance. Conclusions: Positive associations among species characterized the studied plant community. Besides the primary effect of associations of the "foundation" species D. octopetala with other species, these "subordinate" plants were also associated with each other. Our study reveals the assembly of plant communities as driven by positive associations among stress‐tolerant pioneer species, highlighting their role in supporting the cohesiveness of alpine plant communities. We unveiled the spatial organization of an alpine plant community by combining spatial pattern analysis and network analysis. Plant species were highly connected through many positive interactions. Dominant, stress‐tolerant species were the most important plants for supporting the network structure of plant community. [ABSTRACT FROM AUTHOR]

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Understanding how ecological networks are organised over the course of an organism’s lifetime is crucial for predicting the dynamics of interacting populations and communities across temporal scales. However, most studies so far considered only one life history stage at a time, such as adult, when studying networks of interacting species. Therefore, knowledge about how multiple life history stages affect the development and stability of plant–plant association networks is lacking. We measured the understory adult plant community and the soil seed bank across a plant age gradient of the nurse shrub Retama sphaerocarpa in an arid ecosystem in Spain. Using a multilayer network approach, we built adult understory–nurse and seed bank–nurse networks and analysed how network nestedness, species’ role, and species specificity varied between them and with nurse plant age. We found that seed bank and adult understory networks changed depending on nurse plant age in two different ways. With increasing nurse plant age, adult understory networks became significantly more nested than seed bank networks. The nested architecture of seed bank networks was therefore a poor predictor of adult understory network nestedness. The contribution and specificity of species to network nestedness increased with increasing nurse plant age more in the adult understory than in seed bank networks, despite high species turnover. Our data show that life history and ontogeny affect the development of plant–plant association networks. Niche construction and environmental filtering along nurse ontogeny seem pivotal mechanisms structuring adult understory networks while the assembly of seed bank networks seems rather stochastic. We highlight the importance of mature plant communities for maintaining rare species populations and supporting the stability of ecological communities through time. [ABSTRACT FROM AUTHOR]

Abstract: Questions: The exceptional occurrence of tall rain forest patches on foggy coastal mountaintops, surrounded by extensive xerophytic shrublands, suggests an important role of plant–plant interactions in the origin and persistence of these patches in semi‐arid Chile. We asked whether facilitation by shrubs can explain the growth and survival of rain forest tree species, and whether shrub effects depend on the identity of the shrub species itself, the drought tolerance of the tree species and the position of shrubs in regard to wind direction. Location: Open area–shrubland–forest matrix, Fray Jorge Forest National Park, Chile. Methods: We recorded survival after 12 years of a ~3600 tree saplings plantation (originally ~30‐cm tall individuals) of Aextoxicon punctatum, Myrceugenia correifolia and Drimys winteri placed outside forests, beneath the shrub Baccharis vernalis, and in open (shrub‐free) areas. We assessed the effects of neighbouring shrubs and soil humidity on survival and growth along a gradient related to the direction of fog movement. Results: B. vernalis had a clear facilitative effect on tree establishment and survival since, after ~12 years, saplings only survived beneath the shrub canopy. Long‐term survival strongly depended on tree species identity, drought tolerance and position along the soil moisture gradient, with higher survival of A. punctatum (>35%) and M. correifolia (>14%) at sites on wind‐ and fog‐exposed shrubland areas. Sites occupied by the shrub Aristeguietia salvia were unsuitable for trees, presumably due to drier conditions than under B. vernalis. Conclusions: Interactions between shrubs and fog‐dependent tree species in dry areas revealed a strong, long‐lasting facilitation effect on planted tree's survival and growth. Shrubs acted as benefactors, providing sites suitable for tree growth. Sapling mortality in the shrubland interior was caused by lower soil moisture, the consequence of lower fog loads in the air and thus insufficient facilitation. While B. vernalis was a key ecosystem engineer (nurse) and intercepted fog water that dripped to trees planted underneath, drier sites with A. salvia were unsuitable for trees. Consequently, nurse effects related to water input are strongly site and species specific, with facilitation by shrubs providing a plausible explanation for the initiation of forest patches in this semi‐arid landscape. [ABSTRACT FROM AUTHOR]

Background: Intensive farming affects farmland biodiversity, and some arable plants in particular. Increasing crop genetic diversity can increase crop productivity or resilience and could also benefit rare arable plants. Aims: We examined whether barley presence, sowing density and genetic diversity impacted the rare plant Valerianella rimosa and explored possible underlying mechanisms. Methods: In a field study near Dundee, Scotland, we sowed plots of five single barley genotypes, and all five genotypes combined, at three densities; we also had barley-free plots. Valerianella seeds were sown into half of all plots. Measured responses included early-season cover and harvest biomass of barley and common weeds, abiotic parameters (soil moisture, light) and establishment, biomass and seed production by V. rimosa. Results: Barley presence promoted V. rimosa establishment early in the growing season, but without barley density or genetic diversity effects. By harvest, the impact of barley presence on V. rimosa abundance was lost; there were no effects on Valerianella seed production. Barley negatively impacted common weeds, but V. rimosa did not benefit from any indirect facilitation by barley, being bigger without barley. Conclusions: Early beneficial effects of barley on V. rimosa abundance appear offset by late-season competition. However, limited impacts of barley on V. rimosa reproductive success, and negative impacts on common weeds, indicate crops might play a role in conservation management of rare arable plants by creating space in the weed community. [ABSTRACT FROM AUTHOR]

Question: In plant communities, the presence of a species has consequences for other species, with some being competitively excluded while others benefit from the close vicinity of neighbours. Even though such specificity in plant interactions is common and known, there is no empirical assessment of the mechanisms that would help us understand its importance for plant diversity. Here we asked whether analysing spatial associations between plant traits known to affect the environment (i.e. effect traits) and those known to respond to the environment (i.e. response traits) might explain plant-plant interactions and their role in community assembly. Location: Sierra Nevada Mountains, Spain. Methods: In a field study, we addressed the specificity of plant-plant interactions by quantifying effect traits of three co-occurring cushion-forming species and response traits of their associated plant assemblages. Traits were measured at the individual level and then aggregated to trait metrics (mean, range, dispersion) at the plot level. Finally, plot-level metrics of effect traits were related to response traits and the species composition of plant communities. Results: Each cushion-forming species had a distinctive combination of effect traits and harboured a unique plant community with an exclusive composition of response traits. With multivariate statistics we showed that differences in effect traits (branch density and canopy height) among and within cushion species significantly explained response traits (specific leaf area, leaf dry matter content) of associated species and the local-scale species composition. Conclusions: Using effect and response traits measured at the individual level, we provide a mechanistic understanding of the species specificity of plant interactions and demonstrate how important such specificity is for species diversity in an ecosystem. [ABSTRACT FROM AUTHOR]

Understanding species coexistence and regulation of biodiversity are major research challenges, yet there is no consensus on the effects of diversity on diversity, including their mediation through plant-plant interactions., We examined how the diversity of recipient communities impacted on the establishment of colonising species. We ran a greenhouse-based community experiment, creating artificial arable crop communities with varying levels of barley genotype and weed species diversity, analysed with structural equation modelling of responses across trophic levels., Colonising arable weed species establishment was significantly reduced when the recipient communities' weed species richness, but not barley genotype richness, increased. Recipient plant communities with higher species richness occupied more total niche space and showed stronger competition with colonising species. In contrast, recipient plant communities with higher genotype richness, even though they had slightly greater niche space occupancy, had no significant effects on the colonisation of additional species., Responses were species specific: colonising common weed species establishment was less affected by the recipient plant communities than that of colonising rare weed species. Strong responses of colonising rare species were related to the abiotic rather than the biotic environment created by the recipient communities. The stronger response of colonising rare species suggests greater niche overlap with and competitive inferiority to the recipient plant community, whereas the relative independence of colonising common species indicates less niche overlap and/or competitive equality or superiority., We observed a negative species diversity effect on colonising species, with the effect size increasing with increasing rarity of the colonising species. This differential responsiveness of colonising rare and common arable weed species to the presence of and diversity in the recipient arable plant communities may be crucial in understanding rarity and may result from differential evolutionary pathways in response to interactions. [ABSTRACT FROM AUTHOR]

Plant interactions are fundamental processes for structuring plant communities and are an important mechanism governing the response of plant species and communities to environmental changes. Thus, understanding the role played by the interaction network in modulating the impact of environmental changes on plant community composition and diversity is crucial. Here, we aimed to develop a new analytical and conceptual framework to evaluate the responses of plant communities to environmental changes., This framework uses functional traits as sensitivity measures for simulated environmental changes and assesses the consequences of microhabitat loss. We show here its application to an alpine plant community where we recorded functional traits [specific leaf area ( SLA) and leaf dry matter content ( LDMC)] of all plants associated with three foundation species or the surrounding open areas. We then simulated primary species loss based on different scenarios of environmental change and explored community persistence to the loss of foundation species., Generally, plant community responses differed among environmental change scenarios. In a scenario of increasing drought alone (i.e. species with lower LDMC were lost first) or increasing drought with increasing temperature (i.e. species with lower LDMC and higher SLA were lost first), the plant community resisted because drought-tolerant foundation species tolerated those deteriorating conditions. However, in scenarios with increasing nitrogen input (i.e. species having lower SLA were lost earlier), foundation species accelerated species loss due to their early primary extinctions and the corresponding secondary extinctions of species associated to their microhabitat., The resistance of a plant community depends on the driver of environmental change, meaning that the prediction of the fate of this system is depending on the knowledge of the main driver of environmental change. Our framework provides a mechanistic understanding of an ecosystem response to such environmental changes thanks to the integration of biology-informed criteria of species sensitivities to environmental factors into a network of interacting species., A is available for this article. [ABSTRACT FROM AUTHOR]

Arenaria polytrichoides (Caryophyllaceae) is a common cushion plant occurring at high elevations in the Himalaya-Hengduan Mountains, SW China. It frequently has other non-cushion species growing within its canopy, forming a contrast with the surrounding areas because it creates patches of higher diversity and greater biomass. In this study, we examined the relationship between the cushions and associated noncushion species along a gradient of cushion size. A total of 200 A. polytrichoides individuals were selected to fit four size classes. Field measurements were carried out to assess canopy structure, functional traits relevant to growth and reproduction, and soil quality below cushions along the size gradient. Furthermore, the size effect of cushions on the richness and abundance of species and biomass production was also examined. All the morphological variables examined exhibited a positive correlation with cushion size, as did the nutrients under cushions. Large and compact cushions were associated with higher soil nutrient contents compared with small and loose cushions. As a result of these biogenic environmental changes, there was a stronger facilitation effect performed by large cushions. Data pertaining to functional traits revealed that large cushions benefit from the enhanced resources within their compact structure and exhibit greater fitness and a higher reproductive output than small cushions. Our data indicated that interactions occur between cushion species and other plants depending on the size of the cushions, probably because of the greater heterogeneity of conditions beneath larger cushions. These findings provide a clear demonstration of the generally overlooked importance of the traits of nurse plants, such as size and age, in terms of their facilitative effects. [ABSTRACT FROM AUTHOR]

In facilitative interactions, the beneficiary feedback effect ( BFE) has been defined as the effect of beneficiary species (facilitated species) on their benefactor. BFEs have been shown to be dependent on environmental conditions and the composition of the beneficiary community. In alpine cushion systems, BFEs are more negative with more abundant, diverse and phylogenetically aggregated communities of beneficiary species., We tested the hypothesis that the functional composition of the beneficiary communities correlates with the direction and strength of BFE received by alpine cushion benefactors and specifically that a more negative BFE would occur with increasing density of graminoids and a more positive BFE would occur with increasing density of forbs and legumes. Additionally, we predicted that the negative BFE of graminoids would increase with increasing summer aridity., We used a data base of alpine cushion communities from 30 sites throughout the world to assess the overall relationship between the composition of beneficiary communities and the total flower density of cushion benefactors, and its variation with increasing drought. Additionally, in order to assess more precisely the role of the functional composition of the beneficiary communities on BFE in a very dry site with cushion benefactors exhibiting contrasting functional compositions of beneficiary communities, we also designed a field study in the Qilian Shan mountain range (China). At this site with a highly continental climate, we compared the number of flowers and fruits of different phenotypes of the alpine cushion species Thylacospermum caespitosum hosting numerous graminoids, numerous forbs or very few beneficiary species., In the intercontinental study, we found a negative relationship between graminoids and cushion benefactor flower density but no effect of other functional groups. The negative BFE of graminoids increased with increasing summer drought. In the dry Qilian Shan range, we found both a negative effect of graminoids on total flower density and a positive effect of forbs on flower density and fruit set., Our study indicates that the context dependence of BFE may be partially explained by the composition of beneficiary communities and in particular the negative effect of graminoids. [ABSTRACT FROM AUTHOR]

Food security is currently considered a major global problem. However, increasing intensity of food production in agricultural systems has driven reductions in farmland biodiversity. A major challenge is to enable biodiversity conservation whilst addressing the problem of food security., Here we describe how facilitative plant-plant interactions in crop systems could be used to help strike this balance. An obvious example is that of intercropping systems, where combinations of crop species can - under some circumstances - deliver reduced inputs of agrochemicals (fertilizers, pesticides) per unit yield, with potential knock-on benefits for biodiversity conservation., Other facilitative processes can also play a role in biodiversity conservation. Increased intraspecific crop genetic diversity can help protect crops from pests and diseases. Although overlooked in facilitation research, we argue that the mechanisms operate in a manner which is directly analogous to associational defence against herbivores, a process well recognized in the facilitation literature. As with intercropping, the benefits to nature conservation arise from reduced pesticide use per unit harvested crop., Crops may have facilitative effects on some arable weed species, particularly those that are currently considered rare in intensive farming systems. Work is in its early stages to understand the underlying mechanisms, but it appears that crops might create niche space to which some weed species are adapted. Increasing plant species diversity through niche space creation may then have cascading benefits for other components of farmland biodiversity., Our new understanding of facilitative processes arising from work on crop systems has lessons for the study of facilitative interactions in natural and semi-natural communities. We argue that, although easier to identify and quantify in crop systems, some of these facilitative processes have to date been overlooked in studies of non-crop systems and certainly deserve further consideration., Finally, we discuss what steps may be needed to move from our understanding of the role of facilitation to the development of new agricultural practice. In some cases the challenge may be one of the encouraging uptake of existing practices, and in others more research is needed to understand how new ecological understanding might deliver more sustainable agricultural practice. [ABSTRACT FROM AUTHOR]

Facilitative effects of some species on others are a major driver of biodiversity. These positive effects of a benefactor on its beneficiary can result in negative feedback effects of the beneficiary on the benefactor and reduced fitness of the benefactor. However, in contrast to the wealth of studies on facilitative effects in different environments, we know little about whether the feedback effects show predictable patterns of context dependence., We reanalyzed a global data set on alpine cushion plants, previously used to assess their positive effects on biodiversity and the nature of the beneficiary feedback effects, to specifically assess the context dependence of how small- and large-scale drivers alter the feedback effects of cushion-associated (beneficiary) species on their cushion benefactors using structural equation modelling., The effect of beneficiaries on cushions became negative when beneficiary diversity increased and facilitation was more intense. Local-scale biotic and climatic conditions mediated these community-scale processes, having indirect effects on the feedback effect. High-productivity sites demonstrated weaker negative feedback effects of beneficiaries on the benefactor., Our results indicate a limited impact of the beneficiary feedback effects on benefactor cushions, but strong context dependence. This context dependence may help to explain the ecological and evolutionary persistence of this widespread facilitative system. [ABSTRACT FROM AUTHOR]

Altitudinal gradients provide a useful space-for-time substitution to examine the capacity for plant competition and facilitation to mediate responses to climate change. Decomposing net interactions into their facilitative and competitive components, and quantifying the performance of plants with and without neighbours along altitudinal gradients, may prove particularly informative in understanding the mechanisms behind plant responses to environmental change., To decouple the inherent responses of species to climate from the responses of plant-plant interactions to climate, we conducted a meta-analysis. Using data from 16 alpine experiments, we tested if changes in net interactions along altitudinal gradients were due to a change in the performance of target species without neighbours (i.e. environmental severity effects only) or with neighbours (neighbour trait mediated effects)., There was a global shift from competition to facilitation with increasing altitude driven by both environmental severity and neighbour trait effects. However, this global pattern was strongly influenced by the high number of studies in mesic climates and driven by competition at low altitude in temperate climates (neighbour trait effect), and facilitation at high altitude in arctic and temperate climates (environmental severity effect)., In Mediterranean systems, there was no significant effect of competition, and facilitation increased with decreasing altitude. Changes in facilitation with altitude could not unambiguously be attributed to either neighbour trait effects or environmental severity effects, probably because of the opposing stress gradients of cold and aridity in dry environments., Partitioning net interactions along altitudinal gradients led to the prediction that climate change should decrease the importance of facilitation in mesic alpine communities, which might in turn exacerbate the negative effects of climate change in these regions. In xeric climates, the importance of facilitation by drought-tolerant species should increase at low altitudes which should mitigate the negative effect of climate change. However, the importance of facilitation by cold-tolerant species at high altitudes may decrease and exacerbate the effects of climate change. [ABSTRACT FROM AUTHOR]

Environmental gradients may influence a plant's physiological status and morphology, which in turn may affect plant-plant interactions. However, little is known about the relationship between environmental variation, physiological and morphological variability of plants and variation in the balance between competition and facilitation., Mountain ranges in dry environments have opposing altitudinal environmental gradients of temperature and aridity, which limit plant growth at high and low elevations. This makes them particularly suitable for exploring the relationships between environmental conditions, plant phenotype and plant-plant interactions. We hypothesized that different environmental stressors will differently affect the physiological status of a nurse plant. This, then, manifests itself as variation in nurse plant morphological traits, which in turn mediates plant-plant interactions by altering microhabitat conditions for the nurse and associated species., In an observational study, we measured a series of functional traits of Arenaria tetraquetra cushions as indicators of its physiological status (e.g. specific leaf area, relative water content) and morphology (e.g. cushion compactness, size). Measurements were taken along the entire elevation range where A. tetraquetra occurs. Furthermore, we analysed how these functional traits related to soil properties beneath cushions and the number of associated species and individuals compared with open areas., Cushions at high elevation showed good physiological status; they were compact and large, had higher soil water and organic matter content compared with open areas and showed the strongest facilitation effect of the whole elevation gradient - that is, the highest increase in species richness and abundance of beneficiaries compared with open areas. Physiological data at low elevation indicated stressful abiotic conditions for A. tetraquetra, which formed loose and small cushions. These cushions showed less improved soil conditions and had reduced facilitative effects compared with those at high elevation., Synthesis. Functional traits of the nurse species varied distinctively along the two opposing stress gradients, in parallel to the magnitude of differences in microenvironmental conditions between cushions and the surrounding open area, and also to the facilitation effect of cushions. Our data, therefore, provides a strong demonstration of the generally overlooked importance of a nurse plant's vigour and morphology for its facilitative effects. [ABSTRACT FROM AUTHOR]

Here, we incorporate facilitation into trait-based community assembly theory by testing two mutually compatible facilitative mechanisms: changes in the environmental filter, causing either an increase in the range of trait values (i.e. a range expansion effect) and/or a shift in trait distributions (i.e. a range shift effect); and changes in trait spacing, suggesting an effect on niche differentiation., We analyzed the distribution of three functional traits - leaf dry matter content, specific leaf area and lateral spread - of plant communities dominated by a cushion-forming foundation species at four sites differing in elevation and aspect., We found support for environmental filtering and niche differentiation mechanisms by cushions, with filtering effects (in particular range shifts) increasing with environmental severity at higher elevation. The effect size of cushions on trait distribution was similar to that of environmental gradients caused by elevation and aspect. The consideration of intraspecific trait variability improved the detection of cushion effects on trait distributions., Our results highlight the importance of facilitation in the modification of taxonomic and functional diversity of ecological communities, and indicate that facilitation can occur through combined effects on environmental filtering and niche differentiation, with strong environmental context dependence of each mechanism. [ABSTRACT FROM AUTHOR]

Background: Neighbour-removal experiments (NRE) and spatial pattern analyses (SPA) are commonly used methods to investigate plant–plant interactions. Although they address the same issue, they measure different aspects of plant interactions: experiments indicate contemporary processes, whilst observations of spatial patterns integrate the results of interactions that have prevailed in the past. Aim: The aim of this study was to propose a new conceptual approach that takes into account the chronological order between processes and the arising patterns i.e., the time lag between neighbour effects quantified with NRE and SPA, to detect shifts in the balance of plant interactions due to current environmental change. Methods: This conceptual approach was applied to alpine snowbeds. Data from NRE were used to calculate the importance index of current neighbour interactions. Spatial patterns were quantified using variance ratio statistics and were assumed to reflect historic interactions. Results: The results of the two approaches showed a consistent difference in the prevailing type of plant interactions and suggested a shift towards competition in recent times. Conclusions: The simultaneous application of NRE and SPA allows the detection of a recent shift in the balance of plant interactions and provides a deeper and more accurate insight into the temporal dynamics of plant communities that could not be gained using one method alone. [ABSTRACT FROM PUBLISHER]

Positive biodiversity–ecosystem‐functioning (BEF) relationships are commonly found in experimental and observational studies, but how they vary in different environmental contexts and under the influence of coexisting life forms is still controversial. Investigating these variations is important for making predictions regarding the dynamics of plant communities and carbon pools under global change. We conducted this study across 433 shrubland sites in northern China. We fitted structural equation models (SEMs) to analyze the variation in the species‐richness–biomass relationships of shrubs and herbs along a wetness gradient and general liner models (GLMs) to analyze how shrub or herb biomass affected the species‐richness–biomass relationship of the other life form. We found that the positive species‐richness–biomass relationships for both shrubs and herbs became weaker or even negative with higher water availability, likely indicating stronger interspecific competition within life forms under more benign conditions. After accounting for variation in environmental contexts using residual regression, we found that the benign effect of greater facilitation by a larger shrub biomass reduced the positive species‐richness–biomass relationships of herbs, causing them to become nonsignificant. Different levels of herb biomass, however, did not change the species‐richness–biomass relationship of shrubs, possibly because greater herb biomass did not alter the stress level for shrubs. We conclude that biodiversity in the studied plant communities is particularly important for plant biomass production under arid conditions and that it might be possible to use shrubs as nurse plants to facilitate understory herb establishment in ecological restoration. [ABSTRACT FROM AUTHOR]

Plants grow in communities where they interact with other plants and with other living organisms such as pollinators. On the one hand, studies of plant–plant interactions rarely consider how plants interact with other trophic levels such as pollinators. On the other, studies of plant–animal interactions rarely deal with interactions within trophic levels such as plant–plant competition and facilitation. Thus, to what degree plant interactions affect biodiversity and ecological networks across trophic levels is poorly understood. We manipulated plant communities driven by foundation species facilitation and sampled plant–pollinator networks at fine spatial scale in a field experiment in Sierra Nevada, Spain. We found that plant–plant facilitation shaped pollinator diversity and structured pollination networks. Nonadditive effects of plant interactions on pollinator diversity and interaction diversity were synergistic in one foundation species networks while they were additive in another foundation species. Nonadditive effects of plant interactions were due to rewiring of pollination interactions. In addition, plant facilitation had negative effects on the structure of pollination networks likely due to increase in plant competition for pollination. Our results empirically demonstrate how different network types are coupled, revealing pervasive consequences of interaction chains in diverse communities. [ABSTRACT FROM AUTHOR]

Recent meta-analyses demonstrate that intercropping can increase the land use efficiency of crop production by 20–30 % on average, indicating a strong potential contribution to sustainable intensification. However, there is substantial variability around this average: individual studies range from half to double the land productivity of monocrops. Legume-cereal intercrops and intercrops with high temporal niche separation tend to be more productive than the average, but these two combination types are not always suitable. There is a need to explore other possibilities to achieve productive intercrops. We explored whether two simple functional traits involved in radiation use, plant vegetative height and specific leaf area (SLA), could be used to predict intercrop productivity. Height and SLA together are associated with key plant life-history and resource economy strategies determining competitiveness and tolerance of competition, especially with regard to light, and could therefore be expected to underpin overyielding in intercrops. In the first year of our study, we grew crops as monocrops at one site in Kenya and measured their height and SLA. In the second year, we grew crops in monocrop, intercrop, and single plant treatments at two sites in Kenya and one site in Nigeria. Together, these treatments allowed us to identify whether each intercrop combination overyielded or underyielded, and whether any overyielding was driven by facilitation and/or differences in inter- vs intraspecific competition. We then related the strength of these interactions to the two traits. We found that intercrop grain yields varied in relation to the height and SLA of each species in the intercrop, but together these traits explained less than a third of variation in intercrop land equivalence ratios (LER). More variation could be explained by allowing for the effect of site, suggesting that the two traits interact with site conditions to determine yield. Biomass LERs responded differently to grain LERs, suggesting that plasticity in resource allocation in response to intercropping conditions may further influence yields. Our study found some evidence that combining species with traits indicating contrasting responses to competition (an avoidant species with a tolerant species) could increase resource use complementarity and thus intercrop overyielding. However, it was clear that other factors (such as additional traits, or the trait by site interaction) are needed to refine our understanding of intercrop productivity. A trait-based framework has potential to predict intercrop productivity, but simple measures of height and SLA alone are insufficient. • Intercrop yields vary from much lower than sole crops to much higher across different studies. • Plant traits may mediate competition and facilitation between intercrops, and predict yields. • Two simple traits, vegetative height and specific leaf area (SLA), explained some variance in yields. • Yields were higher when tall species with a low SLA were paired with short species with a high SLA. • Height and SLA alone cannot reliably predict intercrop yields: other traits should be explored. [ABSTRACT FROM AUTHOR]

• Nurse plants in alpine systems may enhance species survival under climate change. • We simulated climate change effects on an alpine cushion species. • We also assessed consequences of new climate on its facilitation effect. • Warming enhanced cushion performance but did not alter its facilitation effect. • Global change may alter carbon fixation and respiration, threatening plant survival. Climate change is more pronounced in high-elevation habitats than elsewhere, potentially causing disruptions in plant community structure and dynamics through changes in plant interactions. We tested the effect of warming and rainfall manipulations on growth and gas exchange of a cushion plant species, Arenaria tetraquetra , in the Sierra Nevada Mountains in SE Spain and assessed its consequences for plant interactions. Arenaria tetraquetra is a facilitator that often hosts a variety of beneficiary species within its canopy. Warming and drought could alter cushion growth patterns and canopy compaction, which in turn affect facilitation. We increased temperature using acrylic open-top chambers (OTC) and increased or decreased water availability with rainfall collectors. Our rainfall treatments did not have significant effects on cushion growth or facilitation. Three years of warming enhanced cushion photosynthesis and respiration, leading to larger cushions with thinner leaves, but did not change other cushion traits nor alter its facilitation effects. Some traits, however, readily responded to inter-annual climate variability. Global warming will change cushion plant physiology, as higher temperatures at times increase plant respiration above the level of carbon fixation. However, we did not find changes in interaction between benefactor and beneficiary species, perhaps due to the short-term nature of our experiment. Recorded physiological and morphological changes might be, however, signs of more pronounced, long-term consequences of warming on plant survival and community composition. [ABSTRACT FROM AUTHOR]