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Climate change and associated environmental alterations affect plant communities, potentially decoupling links between plants and their associated soil microbial communities. This may in turn affect processes like litter decomposition, an important function that controls nutrient and carbon cycling as well as many other ecosystem processes. Microbial decomposers have been proposed to specialize, being able to easier decompose litter from its 'home' community than litter from other communities, in what is termed the home field advantage (HFA) hypothesis. We report a litter decomposition experiment including four alpine meadow communities spread along a geographical gradient that ranged from the Atlas in Morocco to the Iberian Peninsula to the Swiss Alps. We tested whether litter decomposition rate would differ depending on litter and soil origin, expecting interactions between litter and soil microbial communities to be at the core of responses. We expected to find HFA in all four alpine communities. HFA ranged from very negative to neutral to positive along our geographical gradient, in a variation that could be attributed to the interaction of microbial communities with soil and plant traits, and linked to the relative abundance of microbial groups performing specific functions. Litter decomposition depended on litter quality and on the fungal community, which seemed adapted to deal with poor-quality, recalcitrant litter, leading to HFA. Climate plays a role as well, indirectly through plant community composition. Phyllosphere communities competed with soil communities when in interaction, a fact that may have blurred results of some previous HFA experiments. In summary, there is a clear HFA in systems with low-quality litter that requires a specialised fungal community to maximize decomposition. By contrast, high-quality, easy to decompose litter would be dealt with by any decomposer community, not showing evidence of HFA. • Litter decomposition depends on links between plants and soil microbial communities. • Microbes might decompose easier litter from its own community than from elsewhere. • Patterns of this so-called 'home-field advantage' (HFA) are unclear. • Systems with low–quality litter require specialised fungal communities, showing HFA. • Systems with high-quality litter have no specialised communities and show no HFA. [ABSTRACT FROM AUTHOR]

Plant interactions with soil microbiota are important drivers of biodiversity and ecosystem function, but climate change can modify these interactions by directly altering the soil community, which can affect the direction and magnitude of such interactions. We manipulated water quantity and soil microbiota of two populations of three plant species that differ in their interactions with soil microbiota and assessed germination and biomass production under conditions that mimicked a rainfall gradient in southeastern Spain. We assessed the importance of soil microbiota from home and away (drier) sites for alleviating or exacerbating the effects of drier conditions. Our results suggest that home soil microbiota enhanced germination of the legume Trifolium stellatum. Conversely, we found that the grass, Lagurus ovatus, and the forb, Sisymbrium erysimoides, produced more biomass under moderate drying with soil microbiota from a drier site than with home soil microbiota, suggesting that dry‐adapted soil microbiota alleviated the negative effects of drier conditions for these species. This maintenance of productivity with dry‐adapted soil microbiota under drier conditions was found despite simultaneous reductions in leaf dry matter content and root‐to‐shoot ratio that would typically be less optimal traits changes under reduced water availability. Severe water limitation resulted in decreased plant biomass regardless of the plant species and soil inoculum, indicating a threshold effect whereby severe water limitation on growth supersedes the beneficial effects of soil microbiota. Overall, our results show that species identity, the severity of water limitation, and soil microbiota interact to determine the response of plants to drier conditions. [ABSTRACT FROM AUTHOR]

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]

The stress-gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta-analysis to compare temporal differences of species diversity and productivity under a nurse plant ( Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plants in situ during a year with below-average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss. [ABSTRACT FROM AUTHOR]

Questions The relative importance of facilitation under different environmental conditions has raised some recent controversy centred on predictions of the stress gradient hypothesis ( SGH) for its apparent lack of predictive power under very stressful conditions. This criticism, however, is not widely shared nor fully supported by empirical data. We addressed whether changes in interaction intensity in plots under severe environmental stress determine an increase in facilitation and whether facilitation would expand the realized niche of some plant species. Location Four sites differing in elevation and environmental conditions along a N-S transect in the Central Tibetan Plateau, Qinghai Province, China. Methods We assessed plant interaction intensity between the cushion plant, Androsace tapete, and species growing inside its canopy. We recorded species and number of individuals in cushions and in gaps, and mass of the two most frequent species in each site. Results Interactions ranged from competition to facilitation, depending on environmental severity. Net interaction balance followed predictions of the SGH, from competition on the relatively more mesic sites to facilitation in the relatively more stressful sites. There were no hints of facilitation collapse even though our harsher sites posed extreme conditions for plant survival. The main limiting factor seems to be temperature, as interaction intensity responded most to this factor, rather than to elevation or rainfall. Conclusions Facilitation expanded the realized niche of some species, countering adverse environmental conditions. We found no collapse of facilitation under the most stressful conditions, even though some sites were at the edge of the distribution range for the cushion species. [ABSTRACT FROM AUTHOR]

Most research on the mycorrhizal positive-negative responsiveness continuum (or 'mutualism-parasitism continuum') has focused on individual plant species growing at different levels of P availability. Here, we explore this continuum in an experimental plant community inoculated with three arbuscular mycorrhizal (AM) fungal strains (both single and mixed) growing under four resource availability scenarios. These scenarios are a factorial combination of two levels of water and N availability. Each AM fungal strain had a different origin: an arid ecosystem, a farmland, and a mine. We hypothesized that the response of the plant community to mycorrhizal inoculum would depend on the associated AM fungal strain and would be negatively related with increased nitrogen and water availability. Our results showed that mixed-strain AM fungal inoculation had more positive effects along a wider range of water and N availability scenarios than single-strain inoculation. In contrast, mycorrhizal growth response of plants inoculated with a single AM fungal strain shifted from positive to neutral and negative depending on resource availability. Adaptation of each strain to its local conditions might confer different properties to the mycorrhizal symbiosis. Therefore, we conclude that AM fungal origin and environmental limiting resources are crucial factors to predict plant community mycorrhizal growth response in changing ecosystems. [ABSTRACT FROM AUTHOR]

Mediterranean oak savannas cover about 4 million ha in California (northwest America) and 3 million ha in Spain and Portugal (southwest Europe), and are ecologically and socio-economically important systems. Here we review literature on the interactions between the two dominant elements of savannas--the oak overstorey, the herbaceous understorey, and the surrounding grassland matrix. We focus on the main ecological factors affecting the oak understorey environment: shade, soil moisture, soil nutrients, and animal-mediated effects. We then review the main features of the herbaceous community in the oak understorey, as compared to the adjacent open grassland, in terms of species composition, biomass, diversity, and soil seed bank. We examine processes associated with oak regeneration and growth, and their relationships with the herbaceous layer and other woody plants cover. Finally, we discuss the complex facilitative and interference interactions that occur in oak--grassland systems and review models proposed to explain the dynamics and coexistence of oak trees and herbaceous plants in savannas. [ABSTRACT FROM AUTHOR]

In arid systems, most plant mortality occurs during long drought periods when water is not available for plant uptake. In these systems, plants often benefit from scarce rain events occurring during drought but some of the mechanisms underlying this water use remain unknown. In this context, plant water use and redistribution after a large rain event could be a mechanism that allows deep-rooted shrubs to conservatively use water during drought. We tested this hypothesis by comparing soil and plant water dynamics in Artemisia tridentata ssp. vaseyana (Rydb.) Beetle shrubs that either received a rain event (20 mm) or received no water. Soil water content (SWC) increased in shallow layers after the event and increased in deep soil layers through hydraulic redistribution (HR). Our results show that Artemisia shrubs effectively redistributed the water pulse downward recharging deep soil water pools that allowed greater plant water use throughout the subsequent drought period, which ameliorated plant water potentials. Shrubs used shallow water pools when available and then gradually shifted to deep-water pools when shallow water was being used up. Both HR recharge and the shift to shallow soil water use helped conserve deep soil water pools. Summer water uptake in Artemisia not only improved plant water relations but also increased deep soil water availability during drought. [ABSTRACT FROM AUTHOR]

Several charts are presented related to water uptake and redistribution during drought in a semiarid shrub, including the relationship between treatment and time to plants and frequency of mean annual and mean summer rainfall in Vernon, Utah.

Abstract: Arid environments are characterized by a patchy distribution of resources (soil nutrients and water availability) which often accrue under or around shrubs. These so-called ‘fertile islands’ have high levels of organic matter, nutrients, and mycorrhiza inocula. Interactions between arbuscular mycorrhizal fungi (AMF) communities and plants, as well as their distribution, are poorly known in these ecosystems, although elsewhere their relevance in ecosystem function is well known. Here, we characterized the AMF community colonizing roots of two plant species, Ballota hirsuta and Lobularia maritima, growing in both patches and open areas. We found differences between AMF genetic composition of communities associated with the two plant species, suggesting specificity. The similarity of AMF colonizing roots of the same plant species was higher in open areas than in patches, while there were differences in AMF genetic richness and diversity between target species in open areas. These data provide new information on the specificity of AMF–plant interactions in patchy environments, and suggest a control of AMF on plant population and community dynamics in arid ecosystems. [Copyright &y& Elsevier]

Abstract: Belowground plant competition is strong and mediated by resource depletion as well as by high variety of exudates. Both factors contribute to active root segregation, affecting neighbours’ growth. In field and greenhouse experiments we investigated the belowground zone of influence of Stipa tenacissima, a tussock-forming grass which is the dominant species in many semiarid communities of the western Mediterranean Basin. Sometimes tussocks show a fringe nearly devoid of annual plants, most likely caused by competition or interference. Fringe size was a function of water availability, so that the more water available the smaller the fringe and vice-versa. Aboveground mass of annual plants was higher in gaps than in the fringe, but root mass was higher in the fringe. More species emerged in soils from gaps than in soils from the fringe, and productivity was ten times higher in soils from gaps than in soils from the fringe. Growth of barley plants was inhibited in the vicinity of S. tenacissima tussocks. S. tenacissima produced a belowground zone of influence around the tussock through resource depletion, particularly water, but also likely through root exudates. Both mechanisms might inhibit the establishment of other annual and grass species within the fringe. Fringe area has important effects for plant establishment, influencing population and community dynamics in these semiarid environments. [Copyright &y& Elsevier]

Seedling establishment in harsh environments is often enhanced by the proximity of adult shrubs. This information has been used in restoration work by placing seedlings of species being restored under the canopy of some shrubs. However, monitoring this process is often restricted to a single species, and comparisons with practices that protect planted seedlings against harsh conditions are scant. Similarly, few studies have supplied seedlings with water in the summer to observe the effects of water availability on the interaction. We compared sapling survival of three woody species ( Olea europaea, Pistacia lentiscus, and Ziziphus lotus) under the leguminous shrub Retama sphaerocarpa and in gaps covered with piled branches that mimicked a shrub canopy. After 3 years, survival of saplings planted under Retama differed depending on species identity and water supply. Survival of Olea saplings placed under Retama shrubs was twice that under piled branches if not watered (35 ± 8 vs. 17 ± 2 %, respectively), whereas survival of saplings under Retama, if watered, was less (48 ± 11 vs. 68 ± 8%, respectively). Retama shrubs had a negative effect on Ziziphus; most saplings died under its canopy, whereas survival in piled branches ranged 10–54%. Pistacia was neither facilitated nor outcompeted by Retama. Facilitation of Olea by Retama shrubs was more apparent under dry conditions where watering increased competition and decreased facilitation. Overall, we conclude that Retama shrubs can help dry land restoration to a greater extent than artificial shade for Olea when not watered. The critical role played by water supply in determining nursing success rates warrants further study. [ABSTRACT FROM AUTHOR]

Question: How does the interaction between two dominant shrub species in a coastal sand dune community change during their life history? Does this interaction influence their population dynamics? Location: A semiarid coastal sand dune system in southeast Spain. Methods: For 3 years we monitored physiological status, growth and reproductive effort of Juniperus phoenicea and Pistacia lentiscus, the dominant shrub species, growing either alone or in close spatial association. We also recorded adult mortality patterns and characterized seedling survival, soil properties and microclimate conditions beneath canopies and in bare ground. Results and conclusions: There was a strong bi-directional interaction between the two studied species, with a net balance that changed in sign with increasing plant development. While mature individuals facilitated the establishment of seedlings of both species, adult mortality patterns suggested asymmetric competition at later life stages. The interaction with Pistacia negatively affected growth of juniper and contributed to its high mortality rates, while juniper had almost no effect on mature Pistacia individuals. Physiological data suggested that Pistacia had a competitive advantage over juniper, most likely because of differences in rooting patterns and tolerance to salinity, which may determine the source of water available for each species. Community dynamics are governed by facilitation at the seedling stage and shaped by differences in physiological traits in adult plants. Plant-plant interactions, which are strongly affected by environmental gradients, are important drivers of community dynamics in this system. [ABSTRACT FROM AUTHOR]

Mediterranean oak savannas cover about 4 million ha in California (northwest America) and 3 million ha in Spain and Portugal (southwest Europe), and are ecologically and socio-economically important systems. Here we review literature on the interactions between the two dominant elements of savannas - the oak overstorey, the herbaceous understorey, and the surrounding grassland matrix. We focus on the main ecological factors affecting the oak understorey environment: shade, soil moisture, soil nutrients, and animal-mediated effects. We then review the main features of the herbaceous community in the oak understorey, as compared to the adjacent open grassland, in terms of species composition, biomass, diversity, and soil seed bank. We examine processes associated with oak regeneration and growth, and their relationships with the herbaceous layer and other woody plants cover. Finally, we discuss the complex facilitative and interference interactions that occur in oak-grassland systems and review models proposed to explain the dynamics and coexistence of oak trees and herbaceous plants in savannas. [ABSTRACT FROM AUTHOR]

Ceanothus is a widely speciated genus with two sections that differ markedly in size, patterns of biomass allocation and reproductive strategies. On greenhouse-grown seedlings we tested whether divergence occurred in single traits or in suites of traits, and whether taxonomic affinity or the ability to fix nitrogen (N) influenced the relationships among functional traits. Species of the subgenus Cerastes differed from species in the subgenus Ceanothus in the following characteristics: reproduction by seed rather than primarily resprouting, high rates of photosynthesis and high stomatal conductance, thick leaves, low root allocation, and high leaf allocation. Correlations of traits across the entire genus showed positive correlations among traits that maximize photosynthesis and tradeoffs between root allocation and carbon gain patterns frequently observed in other broad taxonomic comparisons. Trait correlations differed between the two subgenera (divergence in allocation-photosynthesis tradeoffs in Ceanothus and divergence of growth-related traits in Cerastes). Similarly, N-fixers, which were distributed broadly between the two subgenera, differed in trait correlations (primarily among traits related to photosynthesis) from non-fixers (primarily among traits related to growth and allocation). These results indicate that 1) divergence in genus Ceanothus was associated with changes in entire suite of traits, rather than independent changes in individual traits and 2) evolution occurring under different environmental or nutritional circumstances alters the suites of traits exhibited by plants. [ABSTRACT FROM AUTHOR]

1 The structure and composition of plant communities are influenced by positive and negative interactions between plants, the balance of which may change in intensity and sign through time and space, depending on availability of resources and on plant life history. 2 Over a 2-year period we analysed the balance of interactions between different life stages of a perennial grass, Stipa tenacissima, and a shrub, Cistus clusii, the dominant species in a semi-arid community in south-east Spain. 3 Cistus shrubs acted as nurses for juvenile Stipa plants, improving their water status, nutrient content, carbon assimilation rates and growth. The mechanisms underlying this facilitation effect were mainly the improvement of microclimatic conditions and soil physical and chemical properties under shrub canopies. By contrast, juvenile Stipa plants had an overall neutral effect on Cistus shrubs, although Cistus suffered some competitive effects during periods of water shortage. At this life stage, the short-term outcome of the interaction for both species was dependent on resource availability. 4 Close spatial association between adult plants had no negative effects for the interacting species, although positive effects most likely counterbalanced negative effects. 5 The long-term outcome of the interaction is reflected in the spatial distribution of both species, and determines population dynamics in this semi-arid plant community. 6 Our data show that the short-term balance of plant interactions may easily shift in response to environmental variability, which in turn may have important consequences for plant community structure. [ABSTRACT FROM AUTHOR]

Predictable relationships among patterns, processes, and properties of plant communities are crucial for developing meaningful conceptual models in community ecology. We studied such relationships in 18 plant communities spread throughout nine Northern Hemisphere high-mountain subalpine and alpine meadow systems and found linear and curvilinear correlative links among temperature, precipitation, productivity, plant interactions, spatial pattern, and richness. We found that sites with comparatively mild climates have greater plant biomass, and at these sites strong competition corresponds with over-dispersed distribution of plants, reducing intraspecific patchiness and in turn increasing local richness. Sites with cold climates have little biomass, and at these sites a high proportion of species benefit from strong facilitative effects of neighbors, leading to an aggregated distribution of plants. Sites with intermediate, or relatively moderate climates are intermediate in biomass, and at these sites interactions are weak (or competition may be counterbalanced by facilitation), corresponding with a nearly random distribution of plants. At these sites species richness is lower than average. We propose that the relationship between interspecific spatial pattern and community richness reflects niche differentiation and/or construction, which allows for the coexistence of more species than would be possible with random, unstructured spatial distributions. Discovering the mechanisms that drive the relationships described here would further link functional and structural components of plant communities and enhance the predictive capability of community ecology. [ABSTRACT FROM AUTHOR]

Several mechanisms have been proposed to explain the success of invasive species in new environments. A species may become invasive when a new site provides the potential for positive rates of population growth. This may be the case of severalAgavespecies introduced to Spain in the 1940s. In this paper we document factors that promote large increases of populations of these species, and their effects on native plant communities in two sites of SE Spain. Results showed higher rhizome and bulbil production, and higher establishment rates by agaves in sandy soils than in clay soils. In their native habitats, agaves have low establishment rates and sandy soils are rare. This suggests that sandy soils are an opportunity which releases the clonal reproduction ofAgave. The effects of agaves on the physiological performance and reproduction of native species were negative, positive or neutral, depending on the size and rooting depth of neighbours. Assemblages of native species growing withinAgavestands had lower diversity than non-invaded sites. Our data show thatAgavestands have positive growth rates in SE Spain, and suggest that sandy soils are a niche dimension enhancing the invasion in these new habitats. [ABSTRACT FROM AUTHOR]

Competition and facilitation may occur simultaneously in plant communities, and the prevalence of either process depends on abiotic conditions. Here we attempt a community-wide approach in the analysis of plant interactions, exploring whether in a semi-arid environment positive or negative interactions predominate and whether there are differences among co-occurring shrub species. Most shrubs in our plot exerted significant effects on their understorey communities, ranging from negative to positive. We found a clear case of interference and another case where the effect was neutral, but facilitation predominated and the biomass of annuals under most shrubs in our community was larger than in gaps. Effects on soil water and fertility were revealed as the primary source of facilitation; the build-up of soil organic matter changed soil physical properties and improved soil water relations. Facilitation by shrubs involved decoupling of soil temperature and moisture. Sheltering from direct radiation had an effect on productivity, but significant differences in understorey biomass did not parallel understorey light environment. A positive balance of the interaction among plants, essentially mediated by changes in soil properties, is the predominant outcome of plant interactions in this semi-arid community. [ABSTRACT FROM AUTHOR]

To link spatial patterns and ecological processes, we analysed the distribution of two shrub species (one large and dominant, the other smaller) and estimated the reproductive consequences of their distribution for the smaller species. We tested the significance of the spatial distribution pattern of the two shrubs by second-order bivariate point pattern analysis (Ripley's K function). Performance of Asparagus albus, the smaller shrub, was measured as (1) survival of transplanted seedlings in two contrasting habitats: patches of the dominant shrub (Ziziphus lotus), and open interspaces; and (2) reproductive output of plants naturally occurring in both habitats. The two species were significantly aggregated. Transplanted Asparagus albus seedlings had higher survival rates in patches than in the open. Plants produced more flowers, fruits, and showed a higher mass of seeds when living in aggregates than when isolated. The mechanisms responsible for this facilitative effect seem to be related to soil enrichment in patches. These results suggest that the spatial aggregation of species can be indicative of a positive interaction among them, directly affecting fitness of at least one of the species. Facilitation, by inducing variations in the reproductive performance may play a major role in the demography and dynamics of plant populations. [ABSTRACT FROM AUTHOR]

A combination of competition and facilitation effects operating simultaneously among plant species appears to be the rule in nature, where these effects change along productivity gradients often in a non-proportional manner. We investigated changes in competition and facilitation between a leguminous shrub, Retama sphaerocarpa , and its associate understorey species along an environmental gradient in semi-arid southeast Spain. Our results show a change in the net balance of the interaction between the shrub and several of its associated species, from clearly positive in the water-stressed, infertile environment to neutral or even negative in the more fertile habitat. There was a weakening of facilitation along the fertility gradient as a consequence of improved abiotic conditions. Competition was the most intense for below-ground resources in the less fertile environment while total competition tended to increase towards the more productive end of the gradient. Changes in the balance of the interaction between and among different plant species along the gradient of stress were caused by a decline in facilitation rather than by a change in competition. As both competition intensity and facilitation change along gradients of resource availability, plant interactions are best viewed as dynamic relationships, the outcome of which depends on abiotic conditions. [ABSTRACT FROM AUTHOR]

Investigates the association between `Retama sphaerocarpa' and the understory herb `Marrubium vulgare' in a semiarid region of southeastern Spain. Measurement of the gas exchange between the two species; Measurements of biomass; Mutualistic relationship; Positive plant-plant interactions.

Presents a study that examines the relative importance of phenotypic and genotypic factors in controlling nutrient resorption by sampling several mediterranean trees and shrubs growing in serpentine and nonserpentine soils in northern California. Tissue analysis; Decline in concentrations of nitrogen in mature leaves in spring; No significant differences among species adapted to poor versus rich soils.

• 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]

Aim: One of the main goals of functional biogeography is to examine distribution patterns of trait diversity, and islands provide excellent study cases for this emerging field. We tested the hypothesis that multiple dispersals from a common mainland pool would promote functional similarity among island systems when environmental conditions are similar, but also novel phenotypic traits related to colonization history and exploitation of new habitats. Location: Mediterranean Basin and Macaronesian islands. Taxon: Wolfbane (Periploca laevigata) Methods: We used the well‐known biogeographical history of a woody plant complex (P. laevigata s.l.) to examine trait variation and how it relates to climatic conditions of mainland and subtropical island settings. In a common garden experiment, we measured a suite of leaf physiological and anatomical traits tightly related to plant performance in 320 seedlings representing 21 populations of five sublineages—the oldest (2.6 my) island colonization (western Canary Islands) as a reference, three sublineages stemming from independent events of island colonization in the last 0.5 my from NW Africa (Cape Verde, Fuerteventura, Lanzarote) and their widespread Mediterranean mainland counterpart. Results: We observed strong phenotypic divergence between island and mainland sublineages linked to contrasting climatic conditions. Mediterranean mainland populations displayed a very specialized leaf phenotype characteristic of arid plants (i.e. small leaves, amphistomaty, isobilateral mesophyll, high photosynthetic rates). In turn, low seasonality on islands was linked to the recurrent expression of a phenotype characterized by larger leaves and lower photosynthetic rates. Our analyses showed that the high investment in secondary compounds (i.e. tannins) on islands decouples photosynthesis from growth rates. Despite this pattern of parallel differentiation, each island sublineage displayed a distinctive phenotype, with some traits related to colonization time, which resulted in a mosaic of functional variation across island systems. Main conclusions: Our data suggest that the studied subtropical islands promote expression of traits specific to certain sublineages and other common traits that are no longer adaptive in the original mainland pool due to Pleistocene climatic shifts. These findings ultimately extend the role of islands as biodiversity refugia and hotspots of plant functional diversity. [ABSTRACT FROM AUTHOR]

Background and Aims Understanding patterns and mechanisms of nurse plant facilitation is important to predict the resilience of arid/semi-arid ecosystems to climate change. We investigate whether water availability and nurse species turnover interact to shape the facilitation pattern of widespread legume shrubs along a large elevation gradient. We also investigate whether leaf δ13C of nurse plants can track the facilitation pattern. Methods We measured the relative interaction index (RII) of the number of species within and outside the canopy of two widespread legume shrub species (Caragana gerardiana and Caragana versicolor) alternatively distributed along a large elevation gradient in the Trans-Himalayas. We also assessed the proportional increase of species richness (ISR) at the community level using the paired plot data. To determine site-specific water availability, we measured the leaf δ13C of nurse shrubs and calculated the Thornthwaite moisture index (MI) for each elevation site. Key Results Elevational variations in RII, ISR and δ13C were mainly explained by the MI when the effects of soil nitrogen and plant traits (leaf nitrogen and shrub size) were controlled. Variations in RII and ISR across the two nurse species were explained better by δ13C than by smoothly changing climatic factors along elevation. At the transition zone between the upper limit of C. gerardiana (4100 m) and the lower limit of C. versicolor (4200 m), RII and ISR were much higher in C. versicolor than in C. gerardiana under a similar MI. Such an abrupt increase in facilitation induced by nurse species replacement was well tracked by the variation of δ13C. Conclusions Water availability and nurse species replacement are crucial to shaping facilitation patterns by legume shrubs along a large elevation gradient in dry mountainous regions, such as the Trans-Himalayas. Turnover in nurse species under global change might significantly alter the pattern of nurse plant facilitation associated with water availability, which can be well tracked by leaf δ13C. [ABSTRACT FROM AUTHOR]

Comments on the variability of inorganic nutrient concentrations in leaves. Value of nutrient supply and acquisition; Details on heterogeneous distribution of nutrients in the soil; Approach to the differences in metabolism and constitution.

Abstract: Aim: We aimed to assess the effects of temperature rise and neighbour removal on growth and performance of juvenile individuals of Baccharis uncinella shrubs in a montane grassland. We hypothesized that removal of neighbouring grasses and increased air temperature would enhance B. uncinella growth. Location: High‐elevation forest–grassland patches, southern Brazil. Methods: An experiment with factorial design was carried out from Aug 2014 to Sept 2015 using air temperature and neighbour removal as factors with two levels each. Air temperature was increased using acrylic open‐top chambers (OTC). For the neighbour removal treatment we removed neighbouring grasses from 30 cm around randomly selected B. uncinella juveniles. Survival, growth and plant physiological status were assessed at the end of the experiment. Results: Plants with OTCs grew more than plants without them. Neighbour removal did not have a significant effect on plant growth. These data suggest that an increase in temperature may enhance encroachment of B. uncinella in the studied grasslands, and that neighbour grasses may act as facilitators for B. uncinella shrubs by improving water balance. Conclusions: Considering the capacity of B. uncinella to expand from forest edges towards grasslands, it is likely that montane grasslands in southern Brazil will be subject to B. uncinella encroachment within the next decades. The potential synergistic – negative – effects of global warming and habitat loss might jeopardize the high biodiversity of this ecosystem. Specific management actions and conservation public policies are needed to protect this already threatened montane system. [ABSTRACT FROM AUTHOR]

Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal ( AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses. [ABSTRACT FROM AUTHOR]

The authors encourage ecologists to submit their papers to the online journal.

Climate change has been modifying precipitation and temperature in many regions of the world, prompting changes in plant communities. It also affects soil microbial communities, indirectly influencing plant species distribution through plant-soil feedbacks. Here we report an experiment designed to test seed germination responses to global change, addressed through the interaction between increased temperature and soil microbial communities in a tree species in the Atlantic rainforest, a global biodiversity hotspot. Our objective was to test plant-soil feedbacks in an early colonizer tree species, Schizolobium parahyba , and their interaction with warming. We assessed the role of increased air temperature and soil microbiota in controlling seed germination as a function of distance to mother tree. Higher germination percentages were recorded with extracts of soil microbial communities from the edge of the canopy than with microbial extracts obtained closer to the trunk. These manipulations evidenced that soil microbiota influenced seed germination, being responsible for Janzen–Connell effects. Warming produced major changes in microbial composition but the effect on germination was unclear. Our results may help understand species distribution and coexistence in secondary patches of Atlantic rainforest under warmer conditions, and may contribute to the design of successful restoration programs. • Soil communities changed with distance to trunk, affecting seed germination and being responsible for Janzen–Connell effects. • Warming heavily disrupted prokaryotic and fungal soil communities. • Microbial effects on seed germination in the field would be confounded by other environmental variables, like the canopy. [ABSTRACT FROM AUTHOR]

Summary: The least‐cost economic theory of photosynthesis shows that water and nitrogen are mutually substitutable resources to achieve a given carbon gain. However, vegetation in the Sahel has to cope with the dual challenge imposed by drought and nutrient‐poor soils.We addressed how variation in leaf nitrogen per area (Narea) modulates leaf oxygen and carbon isotopic composition (δ18O, δ13C), as proxies of stomatal conductance and water‐use efficiency, across 34 Sahelian woody species.Dryland species exhibited diverging leaf δ18O and δ13C values, indicating large interspecific variation in time‐integrated stomatal conductance and water‐use efficiency. Structural equation modeling revealed that leaf Narea is a pivotal trait linked to multiple water‐use traits. Leaf Narea was positively linked to both δ18O and δ13C, suggesting higher carboxylation capacity and tighter stomatal regulation of transpiration in N‐rich species, which allows them to achieve higher water‐use efficiency and more conservative water use.These adaptations represent a key physiological advantage of N‐rich species, such as legumes, that could contribute to their dominance across many dryland regions. This is the first report of a robust mechanistic link between leaf Narea and δ18O in dryland vegetation that is consistent with core principles of plant physiology. [ABSTRACT FROM AUTHOR]

Facilitation by nurse plants plays an important role in determining community composition in severe environments. Although the unidirectional effect of nurses on beneficiary species has received considerable research interest, nurse-mediated interactions among beneficiary species (so-called indirect interactions) are less known. Consequently, community composition in nurse plant systems is generally considered as a simple consequence of the facilitative effect of the nurse even though beneficiary species may significantly contribute to community assembly and modulate the direct nurse effects on the community. In an observational study we assessed nurse effects and nurse-mediated beneficiary interactions in two contrasting nurse plant systems in dry environments using a newly developed framework. We quantified plant-plant interaction intensity using the relative interaction index (RII) at the community and species level for three Retama sphaerocarpa shrub size-classes in a semiarid shrubland and four Arenaria tetraquetra cushion plant communities differing in aspect and elevation in dry alpine gravel habitats. The observed RII was split into nurse and beneficiary effects, and related to individual mass, species frequency and abundance using generalized linear mixed models. Results showed predominantly positive nurse effects and negative beneficiary interactions. The effect size of nurse plants, however, was significantly higher than the effect size of beneficiary species in both systems. Individual plant mass and abundance of species was dependent on the combined effects of nurse and beneficiary species whereas species occurrence was related to nurse effects only. Despite evident differences, the semiarid and alpine nurse plant systems showed strong functional parallelisms. We found interdependence between the effects of nurse and beneficiary species on beneficiary plant assemblages emphasizing their combined role on community assembly in both systems. Our results highlight the need to consider indirect interactions to understand fully plant community dynamics. [ABSTRACT FROM AUTHOR]

Cushion plants are specialized keystone species of alpine environments that can have a positive effect on ecosystem structure and function. However, we know relatively little about how cushion plants regulate the diversity and composition of soil microbial communities, major drivers of soil processes and ecosystem functioning. Identifying what factors drive the diversity and composition of soil microbial communities in high-elevation ecosystems is also fundamental to predict how global changes will affect their conservation and the services and functions they provide. Thus, we sampled four sites along the southern Andes following the vegetation belt of Azorella cushion species. The field sites spread along a latitudinal gradient and had contrasting levels of aridity, UV-B radiation, mean temperature and soil properties. Overall, Azorella, as well as aridity and UV-B radiation, were the major drivers of the distribution, composition and diversity of soil microbial communities in the studied ecosystems of the Chilean Andes. UV-B radiation affected particularly soil fungi, while soil properties such as pH, total C and N content, essential predictors of microbial diversity globally, had a much lower effect on the composition of soil microbial communities. Understanding the factors driving the structure and composition of microbial communities, particularly the role of cushion plants and the feedbacks between plant, climate and soil is of uttermost importance for the preservation of the functionality of high-elevation ecosystems threatened by climate change. [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]

Abstract: Climate models predict for semi-arid Mediterranean regions a decline in mean annual rainfall as well as a seasonal re-distribution, leading to larger events separated by longer drought spells and increased winter rainfalls. These changes may affect arbuscular mycorrhizal fungi (AMF) and therefore have implications for terrestrial ecosystems. To assess these consequences we focused on AMF in semi-arid plant communities from SE Spain. We monitored root length colonization in Artemisia barrelieri, a shrub species endemic from the most arid systems in SE Spain, growing in plots subjected to different precipitation regimes according to scenarios predicted by the IPCC for this region. Our results showed that mycorrhizal associations responded to changing precipitation regimes. Specifically, vesicles decreased with decreasing annual precipitation and arbuscules increased with stronger seasonal drought but decreased with lower annual precipitation and other seasonal changes. It may then be expected that dryer conditions in arid ecosystems caused by climate change will alter arbuscular mycorrhizal interactions in different ways depending on the intensity of the drought, thereby influencing the dynamics of extant plant communities. [Copyright &y& Elsevier]

Summary: Hydraulic redistribution (HR) is the passive movement of water between different soil parts via plant root systems, driven by water potential gradients in the soil–plant interface. New data suggest that HR is a heterogeneous and patchy process. In this review we examine the main biophysical and environmental factors controlling HR and its main implications at the plant, community and ecosystem levels. Experimental evidence and the use of novel modelling approaches suggest that HR may have important implications at the community scale, affecting net primary productivity as well as water and vegetation dynamics. Globally, HR may influence hydrological and biogeochemical cycles and, ultimately, climate. ContentsSummary830I.Introduction830II.Mechanisms controlling HR832III.Below‐ground processes affected by HR833IV.Ecological implications of HR835V.Concluding remarks838Acknowledgements839References839 [ABSTRACT FROM AUTHOR]

Contents [ABSTRACT FROM AUTHOR]

Aims: The stress-gradient hypothesis (SGH) predicts how plant interactions change along environmental stress gradients. We tested the SGH in an aridity gradient, where support for the hypothesis and the specific shape of its response curve is controversial. Location: Almería, Cáceres and Coimbra, three sites in the Iberian Peninsula that encompass the most arid and wet habitats in the distribution range of a nurse shrub species - Retama sphaerocarpa L. (Boiss) - in Europe. Methods: We analysed the effect of Retama on its understorey plant community and measured the biomass and species richness beneath Retama and in gaps. We estimated the frequency (changes in species richness), importance and intensity of the Retama effects, and derived the severity-interaction relationship pattern, analysing how these interaction indices changed along this aridity gradient. Results and conclusions: The intensity and frequency of facilitation by Retama increased monotonically with increasing environmental severity, and the importance tended to have a similar pattern, overall supporting the SGH. Our data did not support predictions from recent revisions of the SGH, which may not apply to whole plant communities like those studied here or when interactions are highly asymmetrical. Facilitation by Retama influenced community composition and species richness to the point that a significant fraction of species found at the most arid end of the gradient were only able to survive beneath the nurse shrub, whereas some of these species were able to thrive in gaps at more mesic sites, highlighting the ecological relevance of facilitation by nurse species in mediterranean environments, especially in the driest sites. [ABSTRACT FROM AUTHOR]

Hydraulic lift (HL) is the process by which plants can passively transfer water from deep, moist soil layers to shallow, dry soil layers. Although it has attracted recent research interest, a mechanistic understanding and its implications for ecosystem functioning are still lacking. Here we describe HL seasonal patterns in a semi-arid shrub species and its influence on plant water dynamics. We measured soil water availability and plant water status over the course of 1 year. Soil water potential in the rhizosphere of Retama sphaerocarpa (L.) Boiss (Fabaceae) individuals and in adjacent land was recorded using soil psychrometers. Sap flow was recorded simultaneously using the stem heat balance method (SHBM). Our results show a seasonal HL trend linked to mean seasonal soil water potential with greatest HL amplitudes at moderately low water potentials (ca −4 MPa). HL amplitude was negatively affected by nocturnal transpiration, and HL patterns were recorded in all seasons and at water potentials ranging from −0.1 MPa to −8.5 MPa which is consistent with R. sphaerocarpa deep rooting habit and its steady access to ground water. [ABSTRACT FROM AUTHOR]

The different abilities of plant species to use ephemeral or permanent water sources strongly affect physiological performance and species coexistence in water-limited ecosystems. In addition to withstanding drought, plants in coastal habitats often have to withstand highly saline soils, an additional ecological stress. Here we tested whether observed competitive abilities and C–water relations of two interacting shrub species from an arid coastal system were more related to differences in root architecture or salinity tolerance. We explored water sources of interacting Juniperus phoenicea Guss. and Pistacia lentiscus L. plants by conducting physiology measurements, including water relations, CO2 exchange, photochemical efficiency, sap osmolality, and water and C isotopes. We also conducted parallel soil analyses that included electrical conductivity, humidity, and water isotopes. During drought, Pistacia shrubs relied primarily on permanent salty groundwater, while isolated Juniperus plants took up the scarce and relatively fresh water stored in upper soil layers. As drought progressed further, the physiological activity of Juniperus plants nearly stopped while Pistacia plants were only slightly affected. Juniperus plants growing with Pistacia had stem-water isotopes that matched Pistacia, unlike values for isolated Juniperus plants. This result suggests that Pistacia shrubs supplied water to nearby Juniperus plants through hydraulic lift. This lifted water, however, did not appear to benefit Juniperus plants, as their physiological performance with co-occurring Pistacia plants was poor, including lower water potentials and rates of photosynthesis than isolated plants. Juniperus was more salt sensitive than Pistacia, which withstood salinity levels similar to that of groundwater. Overall, the different abilities of the two species to use salty water appear to drive the outcome of their interaction, resulting in asymmetric competition where Juniperus is negatively affected by Pistacia. Salt also seems to mediate the interaction between the two species, negating the potential positive effects of an additional water source via hydraulic lift. [ABSTRACT FROM AUTHOR]

Abstract: Climate change may cause profound effects on terrestrial ecosystems. Changes in rainfall patterns may have large effects on a wide range of biological processes such as seed germination, seedling establishment, plant growth, community composition, and population and community dynamics. Climate change models for the Mediterranean region forecast reduced annual precipitation and more extreme rain events (i.e., fewer rainy days and longer drought periods between rainfall events), along with seasonal changes. We experimentally addressed the response of a semiarid Mediterranean community to higher aridity and changes in seasonal rainfall patterns in two glasshouse experiments in which we manipulated water supply. We simulated a delay in the onset of autumn rainfalls (i.e., a longer summer drought period), decreased watering amount and frequency as predicted by climate models, and manipulated the seasonality of water supply. We found that delayed watering led to decreases in plant community productivity and to delays in flowering time, in terms of both date and number of days of water supply. Decreased watering amount and frequency, and accentuated seasonality, also diminished biomass and individuals recruited, but did not change flower phenology. Species diversity was not affected by watering delays; however, it was reduced by changes in frequency, amount and seasonality. Overall, these data underline the need to consider rainfall patterns as an important element that might alter community dynamics and ecosystem structure and functioning. Therefore, the analysis of climate change consequences must not depend on climatic means-based scenarios but must take into account expected seasonal changes in rainfall quantity and frequency. [Copyright &y& Elsevier]

Since very young seedlings are sensitive to dehydration, soil desiccation is often responsible for seedling death in water-stressed environments. Roots play a major role in overcoming water stress and plant establishment, thus early root development in response to limited water availability becomes a strategy that may ensure seedling recruitment. We explored whether different water availabilities altered growth patterns of very young seedlings, focussing on root elongation, and hypothesized that seedling responses would depend on species-specific drought tolerance and seed size. We carried out a greenhouse experiment exposing 2-week-old seedlings of three Mediterranean shrubland species, the drought-tolerant and small-seeded Genista umbellata (L’Hér.) Dum. Cours. and Lycium intricatum Boiss., and the drought-sensitive, large-seeded Retama sphaerocarpa (L.) Boiss., to two watering quantities and monitored plant and root growth weekly in glass cases for 5 weeks. We found that at such early stages, reduced water quantity enhanced root growth in all three species, regardless of drought tolerance and seed size, although root plasticity was the highest in the small-seeded and drought-tolerant Genista. In contrast, shoot elongation and mass allocation, root-to-shoot mass (R:S) ratio, was unaffected by watering. Seedlings responded to lower water availability with faster root elongation rate and greater absorptive root surface, which can account for the enhanced relative growth rate (RGR) of the small-seeded Genista and Lycium under reduced watering. By contrast, a larger root absorptive surface did not lead to higher RGR in the large-seeded Retama probably because of its greater independence from external mineral resources. Our data evidence the importance of water availability on the initial developmental stages of these three species regardless of seed size and drought tolerance. Root growth can be interpreted as an adaptive strategy to deal with drying soils and decreasing soil moisture since larger roots enable to exploit unexplored soil areas of soil, which may ensure recruitment success. [ABSTRACT FROM AUTHOR]

Failure to distinguish between‘importance’ and‘intensity’ of competition has hindered our ability to resolve key questions about the role interactions may play in plant communities. Here we examine how appropriate application of metrics of importance and intensity is integral to investigating key theories in plant community ecology and how ignoring this distinction has lead to confusion and possibly spurious conclusions. We re-explore the relationship between competition intensity and importance for individuals across gradients, and apply our review of concepts to published data to help clarify the debate. We demonstrate that competition importance and intensity need not be correlated and show how explicit application of the intensity and importance of competition may reconcile apparently incompatible paradigms. [ABSTRACT FROM AUTHOR]

We propose an index to measure the relative interaction intensity in plants (Ru) with strong mathematical and statistical properties which overcome problems shown by other frequently used indices. Ru has defined limits [-1, + 1]; is symmetrical around zero, with identical absolute values for competition and facilitation; is linear; and does not have discontinuities in its range. It is therefore safe to use in statistical and mathematical operations. Rh distribution is approximately normal, with means equal to the true population index and a sampling variance that can be derived. Its strong statistical properties make Rh proper for use in parametric meta-analyses. It can be applied to any kind of interaction (from competitive exclusion to symbiosis) and in commonly published ranges of interaction intensity it offers the most consistent results. Because RIl uses basic arithmetical operators, it can be scaled up and used to measure multispecific interactions at the community level. [ABSTRACT FROM AUTHOR]

Background and Aims Plants in dry Mediterranean mountains experience a double climatic stress: at low elevations, high temperatures coincide with water shortage during summer, while at high elevations temperature decreases and water availability increases. Cushion plants often act as nurses by improving the microclimate underneath their canopies, hosting beneficiary species that may reciprocally modify their benefactors' microenvironment. We assess how the nurse cushion plant Arenaria tetraquetra subsp. amabilis adjusts its hydraulic system to face these complex abiotic and biotic constraints. Methods We evaluated intra-specific variation and co-ordination of stem xylem anatomy, leaf functional traits and plant architecture in response to elevation, aspect and the presence of beneficiary species in four A. tetraquetra subsp. amabilis populations in the Sierra Nevada mountains, southern Spain. Key Results Xylem anatomical and plant architectural traits were the most responsive to environmental conditions, showing the highest mutual co-ordination. Cushions were more compact and had smaller, more isolated conductive vessels in the southern than in the northern aspect, which allow minimization of the negative impacts of more intense drought. Only vessel size, leaf mass per area and terminal branch length varied with elevation. Nurse cushions co-ordinated plant architecture and xylem traits, having higher canopy compactness, fewer leaves per branch and fewer, more isolated vessels than non-nurse cushions, which reflects the negative effects of beneficiary plants on nurse water status. In non-nurse cushions, plant architecture co-ordinated with leaf traits instead. The interacting effects of aspect and elevation on xylem traits showed that stress due to frost at high elevation constrained xylem anatomy in the north, whereas stress due to drought had a parallel effect in the south. Conclusions Trait co-ordination was weaker under more demanding environmental conditions, which agrees with the hypothesis that trait independence allows plants to better optimize different functions, probably entailing higher adjustment potential against future environmental changes. [ABSTRACT FROM AUTHOR]

How the relationship between species richness and productivity changes along environmental gradients remains poorly understood.We examined the context dependency of complementarity processes underpinning this relationship (biotic feedbacks, resource partitioning and facilitation) using the framework of Grime's (1973) humped‐back model. We considered several scenarios of variation in competition and facilitation along environmental gradients, either monotonic with the most common or intense facilitation at the most abiotically severe end of gradients or nonlinear with the strongest facilitation at intermediate positions along gradients.How competition shifts to facilitation along environmental gradients is a key for determining where the effect of species richness on productivity occurs. Based on the literature, the original Stress Gradient Hypothesis would likely predict that complementarity effects should be the greatest, or the most important, in the most abiotically stressful environments. Alternatively, both the 'collapse of facilitation' and the 'shift back to competition' scenarios predict that the highest overall complementary effects on productivity, not biomass, would most likely occur at intermediate positions along environmental stress gradients, but this might vary depending on the source of stress. This latter prediction is consistent with a great deal of literature on natural gradients of productivity and species richness.Synthesis. Our predictions illustrate the importance of better understanding the context dependency of complementarity processes and the key role of facilitation along environmental gradients to better focus conservation efforts where ecosystem functioning is more likely to be negatively affected by species loss, in particular in species‐rich communities. [ABSTRACT FROM AUTHOR]

Biological diversity depends on multiple, cooccurring ecological interactions. However, most studies focus on one interaction type at a time, leaving community ecologists unsure of how positive and negative associations among species combine to influence biodiversity patterns. Using surveys of plant populations in alpine communities worldwide, we explore patterns of positive and negative associations among triads of species (modules) and their relationship to local biodiversity. Three modules, each incorporating both positive and negative associations, were overrepresented, thus acting as "network motifs." Furthermore, the overrepresentation of these network motifs is positively linked to species diversity globally. A theoretical model illustrates that these network motifs, based on competition between facilitated species or facilitation between inferior competitors, increase local persistence. Our findings suggest that the interplay of competition and facilitation is crucial for maintaining biodiversity. [ABSTRACT FROM AUTHOR]

Aims: Nurse plants facilitate the establishment of other species under their canopies through improvement of microclimate and soil conditions beneath their canopies. We aimed to test whether the effect of nurse soil on understorey communities was independent of the canopy effect, and to what extent soil properties (i.e., nutrients, pH, moisture, temperature, aggregates) can predict understorey biomass and diversity. Methods: In a field experiment, we extracted three soil blocks (20 × 20 × 15 cm) under the canopy of eighteen Retama sphaerocarpa shrubs --grouped into small, medium, and large canopy sizes (n = 6). Soil blocks were distributed in a stratified-random design, so that each shrub received back three soil blocks (one from under each Retama canopy size). At the end of the growing season plant biomass, abundance, diversity and soil properties were recorded. Results: Canopy and soil independently affected understorey community structure. Biomass and diversity increased under large Retama canopies irrespective of soil origin, whereas biomass was higher -and plant diversity lower- in soils from large Retama shrubs irrespective of canopy size. Biomass and species abundance were influenced more by soil than by canopy. There was, however, complementarity between these factors, as biomass increased in soils with high moisture and low temperature, while diversity was highly influenced by canopy size. Conclusions: Soil, rather than microclimate amelioration by the nurse, was the main driver of understorey community structure, soil moisture playing a pivotal role. This is highly relevant as drought is expected to increase in drylands worldwide. [ABSTRACT FROM AUTHOR]