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The occurrence of multi‐year drought is predicted to increase globally with climate change. However, it is unclear whether drought effects on ecosystems are progressive through time.Here, we experimentally reduced growing season precipitation (GSP) by 45% at seven North American temperate grasslands for four consecutive years to determine the following: (a) whether the effects of reduced precipitation on plant community structure and biomass components (shoot, root, litter) are compounding over time; (b) whether prior year climatic and soil conditions influence subsequent drought impacts on plant community structure and biomass components; and (c) whether the effects of reduced precipitation on individual ecosystem components are related to one another.Across the seven field sites, we observed neither consistent nor progressive effects of reduced precipitation on any biomass component during the experiment, despite having extreme drought conditions imposed for four consecutive years. Relative to the ambient treatment, above‐ground net primary productivity (ANPP) declined in response to drought during the early years of the experiment but increased above the ambient treatment in the fourth year, while root and litter biomass were stable across the sites throughout the study. Similarly, graminoid cover decreased initially but recovered by the final year of the experiment, contributing to observed differences in species composition between treatments across sites. Compositional changes were not associated with any declines in species richness or evenness. Divergent responses among years were not driven by lag effects based on prior year climatic and soil conditions. Furthermore, precipitation effects on ecosystem components were largely independent as we found only two positive links: between ANPP and plant species richness, and between species evenness and composition.Synthesis. Overall, our results suggest that these northern grasslands are relatively resistant to short‐term multi‐year drought in the context of supporting plant diversity and biomass production. [ABSTRACT FROM AUTHOR]

When foraging and competing for below‐ground resources, plants have to coordinate the behaviour of thousands of root tips in a manner similar to that of eusocial animal colonies. While well described in animals, we know little about the spatial behaviour of plants, particularly at the level of individual roots.Here, we employed statistical methods previously used to describe animal ranging behaviour to examine root system overlap and the efficiency of root positioning in eight grassland species grown in monocultures and mixtures along a gradient of neighbour densities.Species varied widely in their ability to distribute roots efficiently, with the majority of species showing significant root aggregation at very fine spatial scales. Extensive root system overlap was observed in species mixtures, indicating a lack of territoriality at the level of whole root systems. However, with increasing density of competitors, several species withdrew roots from the periphery of foraging ranges and increased intraplant root aggregation in the remaining area, which may indicate consolidation of foraging areas under competitive pressure.Several species exhibited responses consistent with resource contest in species mixtures where encounters with competitors' roots triggered increased root aggregation at the expense of foraging efficiency. Such responses only occurred in mixtures of species with comparable competitive abilities but were absent in asymmetric species combinations.Synthesis. Combining fine‐scale measurement of plant root distributions with spatial statistics yields new insights into plant behavioural strategies with significant potential to impact resource foraging efficiency and productivity. [ABSTRACT FROM AUTHOR]

Understanding the patterns of competitive and facilitative interactions within and among species in plant communities is a central goal of plant ecology, because these patterns determine species coexistence and community dynamics. Network theory provides tools that allow these patterns to be quantified, and can provide greater understanding of important community properties, including community stability, than can documenting pairwise species interactions.I characterized the interactions of multiple, co‐occurring invasive and native species in an old field woody plant community to build plant interaction networks at two different life stages. With the goal of identifying structural features that may operate to maintain species coexistence, I characterized the architecture of these networks at multiple scales: the entire network, the substructures that compose the network and species' roles within substructures.I found that species‐level pairwise interactions alone did not provide an accurate or sufficiently detailed picture of community structure. Rather, using a network approach, I identified substructures that have the potential to promote and hinder species coexistence in interactions among seedlings. Characterizing the nuances of network substructures was illuminating, as the size of the substructures and the pattern of interaction intensities within substructures influence the expected effects on species coexistence. Including interactions at multiple life stages was also important; the seedling species that benefited most from the nested structure of facilitative interactions with adults occupied subordinate roles in substructures with other seedlings. This role reversal at different life stages is a potential factor promoting coexistence in the community. Last, the network framework was useful for comparing species' roles between native and invasive members of the community, and the three invasive species in this system had different, life stage‐dependent strategies in interactions with co‐occurring plants.Synthesis. The interplay of network architecture and substructures within plant communities and among plants at different life stages is important for understanding species coexistence. In the plant community characterized in this study, there were several features that may promote coexistence, and these features were not observable in interactions within a single life stage or when considering pairwise interactions independently. [ABSTRACT FROM AUTHOR]

Indirect interactions mediated by shared enemies or mutualists (i.e. apparent competition) can influence whether invasive plants harm or benefit co‐occurring species. However, studies to date have largely examined single pairwise interactions, limiting our understanding of the interplay among different types of interactions and whether indirect impacts systematically favour native or exotic species. Predicting indirect interaction strength has also proven challenging, and it remains unclear whether the strengths of different indirect interactions are correlated.We conducted a field experiment in a grassland invaded by Scotch broom Cytisus scoparius to compare the strength of its indirect impacts, via both soil fungi and herbivores, on 21 native and exotic legume species growing in pots buried in the ground. Direct interactions of plants with soil fungi were controlled using nylon mesh pot windows of differing porosity (1 or 38 µm) to prevent or allow soil fungi hyphal growth. Arthropod herbivores were controlled through spraying pyrethrum pesticide. To assess indirect impacts, interactions were compared between plants adjacent to or 50 m away from an extensive Scotch broom invasion. We measured plant performance (survival, height and biomass), arthropod and hare herbivory, and rhizobia nodulation.Despite increasing arthropod herbivory of both native and exotic plant species, Scotch broom had a net positive impact on their survival and growth, through sheltering them from abiotic stress, and indirectly via beneficial soil fungi and release from hare browsing. Soil fungi also increased arthropod herbivory, decreased rhizobia nodulation and disproportionately promoted the growth of exotic plants. Overall, exotic plants experienced stronger interactions, which favoured them with beneficial soil fungi and rhizobia but not hare browsing. Finally, indirect interaction strength was not correlated among indirect interactions mediated by different interaction partners.Synthesis. We demonstrate that invaders affect their competitors through multiple interacting indirect pathways that were stronger than direct 'nurse plant' effects, emphasizing the importance of a community‐level approach to studying biological invasions. Exotic species experienced stronger positive and negative impacts than natives, but were facilitated overall, potentially contributing to exotic dominance in communities. [ABSTRACT FROM AUTHOR]

Roots are capable of strong plastic responses to environmental signals, but the extent of such responses in the field is essentially unknown. Here, we aimed to identify interspecific root aggregations and segregations as indicators of plastic responses to the presence of other species. Furthermore, we asked whether aggregations change with heterogeneity in overall root density along soil depth and whether root communities show any relationship to species' functional traits.We used quantitative real‐Time PCR to estimate root quantities of nine grassland species in soil blocks at a centimetre scale. We combined these estimates with fine‐scale recording of species' positions above‐ground. We used deviations between measured root density and that expected from the relationship to above‐ground species abundance to correct for different chances of individual species to meet due to the non‐random distribution of their individuals. This approach allows us to identify whether species associations below‐ground are due to plastic response of their roots.We showed that while there were signals of both interspecific aggregation and segregation, prevalence of aggregation over segregation strongly increased with increasing soil depth. In shallow layers, where root density is high and its heterogeneity low, roots are likely to respond to a number of signals which produce both interspecific aggregation and segregation. In contrast, in deeper layers, where root density is low and its heterogeneity high, root distribution is likely to be driven primarily by foraging for resources, producing aggregations. Species composition of the root community did not show any relationship to functional traits (SLA, shoot life span, spreading distance and rooting depth) of the examined species.Synthesis. The results imply that processes that determine interspecific root associations change at a scale of centimetres which is close to the scale of individual fine roots. They also imply that while root foraging might explain root co‐occurrence under low root density, very different processes determine it when root density is high. Our findings also support the notion that roots, while extremely plastic, may not receive sufficient signals to elicit a response in the field if overall root density is high and homogeneous. [ABSTRACT FROM AUTHOR]

Fine‐root traits show remarkable variation with plant community structure and environmental shifts, but there is limited understanding of how trait covariation that exists among fine‐root traits shifts among different communities, especially in forests. We explored links among the fine‐root traits of forest communities to determine whether community root traits shift predictably according to an economics framework along environmental gradients.Measurements of root morphology, nitrogen, phosphorus and carbon concentrations, and measures of standing root densities were collected on fine‐roots (diameter ≤ 2 mm) from 129 forest plots in five subalpine forests.This study demonstrates an existence of a community‐level fine‐root economics spectrum (REScom) in the subalpine forests, in which specific root length was strongly and positively related to root nitrogen and phosphorus contents, but negatively related to root diameter. Soil nutrient limitation was a major driver of the REScom as changes in soil [N], [P] and [C] contents were related to changes in SRL, root [N], root [P]. Variables related to standing fine‐root length and mass were independent of the REScom and were primarily related to forest community structure, particularly in tree closure and herbaceous plant mass.Synthesis. These results indicate two distinct functional dimensions of community fine‐root trait variation: resource‐use efficiency via changes in root structure and construction, and separately via changes in the standing root system. Identifying shifts in allocation to and investment in fine‐roots enhances our understanding of a root and whole‐plant economics spectrum and community functioning. [ABSTRACT FROM AUTHOR]

The fast–slow plant economics spectrum predicts that because of evolutionary and biophysical constraints, different plant organs must be coordinated to converge in a unique ecological strategy within a continuum that shifts from fast to slow resource acquisition and conservation. Therefore, along a gradient of aridity, taxa with different strategies will be expected to be successful because selection pressures for slow resource acquisition become stronger as the environment becomes drier. In extremely arid and seasonal environments, however, a slow strategy may become disadvantageous because slow traits are costly to maintain. Additionally, as the availability of water decreases, selection pressures increase, reducing the variation in ecological strategies.Using shrub assemblages along an aridity gradient in the Atacama Desert, we test the hypothesis that selection pressures imposed by hyper‐aridity act simultaneously on the variation and coordination of trait attributes, leading to an inverse pattern in the fast–slow plant economics spectrum, where strategies shift from slow to fast as the environment becomes drier.We established 20–22 plots at each of four sites along the gradient to estimate plant community structure and functional variation. For all species recorded, we quantified a set of leaf, stem, and root traits.Results revealed an inverse pattern of the fast–slow economics spectrum for leaf and stem traits, but not for root traits; that is, as aridity further increased, above‐ground traits exhibited a shift from a slow to a fast strategy with some level of coordination. Below‐ground traits, however, did not shift accordingly with our prediction, rather they showed more complex pattern of shift and coordination with above‐ground traits along the gradient. We also found that trait variation showed an idiosyncratic pattern of variation along the gradient, indicating that ecological strategies are driven by local processes within sites.Synthesis. Our results increase our understanding of the fast–slow plant economics spectrum by showing that environmental gradients, as well as local process can simultaneously shape different below‐ and above‐ground resource acquisition strategies in extremely poor resource environments. [ABSTRACT FROM AUTHOR]

Reliable predictions of population spread rates are essential to forecast biological invasions. Recent studies have shown that populations spreading through favourable habitat can rapidly evolve higher dispersal and reproductive rates at the expansion front, which accelerates spread velocity. However, spreading populations are likely to eventually encounter stressful conditions in the expanded range. How evolution during spread in favourable environments affects subsequent population growth in harsher environments is currently unknown.We examined evolutionary change in performance under drought, interspecific competition, and heat stress for populations of Arabidopsis thaliana that experienced six generations of spread through replicated experimental landscapes of favourable habitat. To quantify how population performance under stress differed between leading edge and founding populations, we combined individual tests of genotype performance under stress with knowledge of the genotype frequency changes that occurred over the replicate invasions.After spreading through favourable environments, the average silique production of individuals exposed to drought or interspecific competition was lower in leading edge than founding populations. This change was driven by the evolution of lower intrinsic silique production, which was correlated with increased seed size, a trait that evolved as populations spread. The ability of plants to tolerate drought or interspecific competition, however, did not change markedly during spread. Heat tolerance did increase in leading edge populations, and this trait was associated with the evolution of taller plants during spread through favourable habitat.Synthesis. We conclude that evolution during spread in favourable environments may affect the ability of populations to grow under stressful conditions as experienced in the expanded range, through changes in either intrinsic fecundity or stress tolerance. Thus, evolution during spread may constrain or extend the eventual range limit of nonnative species invasions. Spreading populations may rapidly evolve higher rates of dispersal and reproduction. However, they are likely to encounter stressful conditions in the expanded range. We found evolutionary changes in performance under stress for populations of Arabidopsis thaliana that invaded replicated experimental landscapes of favourable habitat. Our results suggest that evolution during spread may alter performance under stress, affecting further range expansion. [ABSTRACT FROM AUTHOR]

Determining how changes in abiotic conditions influence community interactions is a fundamental challenge in ecology. Meeting this challenge is increasingly imperative in the Anthropocene where climate change and exotic species introductions alter abiotic context and biotic composition to reshuffle natural systems., We created plant assemblages consisting of monocultures or equal abundance of the native community dominant bluebunch wheatgrass ( Pseudoroegneria spicata) and the exotic spotted knapweed ( Centaurea stoebe), a co-occurring invasive forb that has overtaken grasslands across the western United States. We subjected these composition treatments to drought (20% of average precipitation vs. average) and herbivory on C. stoebe by its biocontrol agent Cyphocleonus achates to explore how reduced precipitation might influence the effects of competition and biocontrol herbivory on C. stoebe's abundance., At the end of 7 years, C. stoebe dominated mixed-species plots under normal precipitation conditions, with biomass 50% greater than that of the native P. spicata. However, under drought stress, P. spicata's biomass was >200% greater than C. stoebe's. Interestingly, both species were impervious to drought in monoculture, indicating the importance of the drought by competition interaction. The biocontrol herbivore reduced C. stoebe abundance and indirectly increased P. spicata biomass in mixed-species drought plots, but these effects were only marginally significant and relatively weak. Overall, C. stoebe abundance was primarily driven by the drought by competition interaction, with negatively additive but weak effects of the drought by herbivory interaction., The response of the exotic to the treatments was driven by rapid changes in population density linked to its fast life-history strategy, while the native's response was driven by changes in per capita plant biomass linked to its slower life-history strategy. Individual plant performance metrics did not predict overall population responses for the invader, indicating the importance of longer term population measures., Synthesis. These results demonstrate that reduced precipitation inputs linked to climate change can dramatically shift the balance of plant competition, even toggling the advantage from exotic to native dominance. They also illustrate the importance of biotic interactions in predicting species responses to abiotic change. [ABSTRACT FROM AUTHOR]

Plant-soil feedbacks contribute to species invasions, the maintenance of biodiversity and climate change impacts on terrestrial ecosystems. Despite their far-reaching importance, we lack a general understanding of the ecological and evolutionary determinants of plant-soil feedbacks., We conducted a large-scale plant-soil feedback experiment using 49 co-occurring plant species from southern Ontario, Canada, representing a wide phylogenetic range. We tested whether the effects of soil conditioning vary among these species and whether different focal species respond similarly to the same soil conditioning. Next, we investigated whether plant traits and soil feedbacks depend on phylogenetic similarity and which plant traits affect plant-soil feedbacks between pairs of plant species. Finally, we used our experimental results to test whether soil feedbacks affect co-occurrence of species in the field., We found evidence of both strong positive and negative soil feedbacks between pairs of plant species. Our soil-conditioning treatment explained nearly 20% of the variation in focal species performance., Phylogenetic relatedness and phenotypic similarity between plant species were unrelated to the strength of their soil feedback. However, numerous plant traits of the conditioning species influenced the strength of soil feedbacks on focal species, including specific leaf area and total above-ground productivity. Trait differences between species were also predictive of plant-soil feedbacks, though for some pairs of species, increased trait differences were associated with positive plant-soil feedbacks and for others, trait differences were associated with negative plant-soil feedbacks., Plant species co-occurrence in the field was related to their experimentally determined soil feedbacks but only for particular plant species., Synthesis. Our results illustrate how evolutionary history and phenotypic variation shape plant-soil feedbacks and highlight the need for trait-based studies. Due to the unique evolutionary history of individual traits and the variability in their importance across all possible interacting species, we show that indices of overall phenotypic and phylogenetic relatedness are poor predictors of plant-soil feedbacks at large phylogenetic scales. We conclude that a detailed trait-based approach can be used to predict plant-soil feedbacks, and laboratory measures of soil feedbacks can explain patterns of co-occurrence in nature. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi ( AMF) are key regulators of ecosystem processes, yet how their biodiversity works in ecosystems remains poorly understood., We documented the extent to which taxonomic resolution influenced the effect of biodiversity of AMF taxa on plant performance (growth, nutrient uptake and stress tolerance) in a meta-analysis of 902 articles., We found that the effect of biodiversity of AMF taxa depended on taxonomic resolution. Plant performance was positively promoted by AMF family richness, while no effect was found for fungal species richness. In addition, negative effect was found between AMF phylogenetic diversity and plant growth. This pattern can be explained by functional conservatism within AMF families and functional differentiation among AMF families., Synthesis. Conservation of AMF communities to maintain a full complement of ecosystem functions requires the presence of diverse families and not simply diverse species within a family. This finding may be of key importance for the function of ecosystems under various environmental perturbations to which AMF families may respond differently. [ABSTRACT FROM AUTHOR]

The availability of water is often highly variable over the life of a plant in nature, and most plants experience episodic extremes in water scarcity and abundance. The importance of plant plasticity in coping with such experiences is widely recognized, but little is known about how plastic responses to current conditions are affected by prior environmental experiences., Our objectives were to investigate the effects of early inundation or drought on the subsequent responses of plant species to the same, opposite or more favourable conditions., To address these questions, we subjected four invasive and four native herbaceous perennial species from different habitats (xeric, mesic, hydric) to two rounds of hydrological treatments (drought, moderate water, inundation) and analysed the effects of the early treatments on survival and performance (total biomass and relative growth) of individuals in the later treatments., In general, (i) early drought reduced the performance of more species than did early inundation, and decreased the final total mass of all species; (ii) early inundation and early drought did not lead to lower survival immediately or later, but improved the relative growth of survivors across all late conditions; (iii) late drought resulted in the highest mortality and lowest performance after any early treatment., With respect to habitat of origin: (i) early inundation was more beneficial for species from wet habitats than for other species; (ii) species from xeric habitats had the strongest drought tolerance after early drought; (iii) mesic species were more likely to suffer reduced later growth after either inundation or drought experience. Invasive species benefitted more from early inundation than did native species, but native species grew better after experiencing early drought., Results indicate that early exposure to inundation or drought conditions alters how plants respond to later conditions and suggest that exposure to extreme events can induce physiological or morphological changes that improve tolerance for either extreme conditions later. This increased tolerance can be at the cost of poorer performance under more benign conditions., Synthesis. Early inundation or drought experience may be harmful immediately, but can be beneficial for the later growth of plants. The ability of species to utilize early hydrological experiences was associated with the water range of their habitats and whether the species is invasive or native. The ability to modulate future plastic responses may be as important as short-term plasticity in adapting to temporal environmental heterogeneity. Such 'metaplasticity' can optimize current performance, while avoiding the potential costs of maintaining a high degree of plasticity throughout life. [ABSTRACT FROM AUTHOR]

Plant-associated microbial communities are crucial for plant growth and play an important role in disease suppression. Community composition and function change upon pathogen attack, yet to date, we do not know whether these changes are a side effect of the infection or actively driven by the plant., Here, we used a split-root approach to test whether barley plants recruit bacteria carrying antifungal traits upon infestation with Fusarium graminearum. Split-root systems allow disentangling local infection effects, such as root damage, from systemic, plant-driven effects on microbiome functionality. We assessed the recruitment of fluorescent pseudomonads, a taxon correlated with disease suppression, and of two well-described antifungal genes ( phl D coding for 2,4- DAPG and hcn AB coding for HCN)., We show an enrichment of fluorescent pseudomonads, phl D and hcn AB, upon pathogen infection. This effect was only measurable in the uninfected root compartment. We link these effects to an increased chemotaxis of pseudomonads towards exudates of infected plants., Synthesis. We conclude that barley plants selectively recruited bacteria carrying antifungal traits upon pathogen attack and that the pathogen application locally interfered with this process. By disentangling these two effects, we set the base for enhancing strategies unravelling how pathogens and plant hosts jointly shape microbiome functionality. [ABSTRACT FROM AUTHOR]

Plant communities show two general responses to gradients of soil resources: a decrease in species richness at high levels of resource availability and an associated shift in species composition from small and slow-growing species to large and fast-growing species. Models attempting to explain these responses have usually focused on a single pattern and provided contradicting predictions concerning the underlying mechanisms., We use an extension of Tilman's resource competition model to investigate the hypothesis that both patterns may originate from the size-asymmetric nature of light exploitation by competing plants. The only mechanism producing changes in species richness and species composition in our model is mortality due to competition., Under the framework of the model, asymmetric light exploitation is a necessary and sufficient condition to obtain the empirically observed responses of species richness and species composition to soil resource gradients. This theoretical result is robust to relaxing the simplifying assumptions of the model., Our model shows that the traits enhancing competitive superiority depend on the mode of resource exploitation: under symmetric exploitation, competitive superiority is achieved by tolerance of low resource levels, while under asymmetric exploitation, it is achieved by the ability to grow fast and attain a large size. This result indicates that a long-standing debate concerning the traits that enhance competitive superiority in plant communities (the 'Grime-Tilman debate') can be reduced into a single parameter of our model - the degree of asymmetry in resource competition., The model also explains the observed shift from below-ground to above-ground competition with increasing productivity, the associated increase in the asymmetry of competitive interactions and the increasing likelihood of competitive exclusion under high levels of productivity. None of these patterns could be obtained under symmetric competition in our model., Synthesis. The ability of the model to explain a wide range of observed patterns and the robustness of these predictions to its simplifying assumptions suggest that the size asymmetry of competition for light is a fundamental factor in determining the structure and diversity of plant communities. [ABSTRACT FROM AUTHOR]

There is a fundamental trade-off between leaf traits associated with either resource acquisition or resource conservation. This gradient of trait variation, called the economics spectrum, also applies to fine roots, but whether it is consistent for coarse roots or at the plant community level remains untested., We measured a set of morphological and chemical root traits at a community level (functional parameters; FP) in 20 plant communities located along land-use intensity gradients and across three climatic zones (tropical, mediterranean and montane). We hypothesized (i) the existence of a root economics spectrum in plant communities consistent within root types (fine, < 2 mm; coarse, 2-5 mm), (ii) that variations in root FP occur with soil depths (top 20 cm of soil and 100-150 cm deep) and (iii) along land-use gradients., Root FP covaried, in line with the resource acquisition-conservation trade-off, from communities with root FP associated with resource acquisition (e.g. high specific root length, SRL; thin diameters and low root dry matter contents, RDMC) to root FP associated with resource conservation (e.g. low SRL, thick diameters and high RDMC). This pattern was consistent for both fine and coarse roots indicating a strong consistency of a trade-off between resource acquisition and conservation for plant roots., Roots had different suites of traits at different depths, suggesting a disparity in root function and exploitation capacities. Shallow, fine roots were thinner, richer in nitrogen and with lower lignin concentrations associated with greater exploitation capacities compared to deep, fine roots. Shallow, coarse roots were richer in nitrogen, carbon and soluble concentrations than deep, coarse roots., Fine root parameters of highly disturbed, herbaceous-dominated plant communities in poorer soils were associated with foraging strategies, that is greater SRL and lower RDMC and lignin concentration than those from less disturbed communities. Coarse roots, however, were less sensitive to the land-use gradient., Synthesis. This study demonstrates the existence of a general trade-off in root construction at a community level, which operates within all root types, suggesting that all plant tissues are controlled by the trade-off between resource acquisition and conservation. [ABSTRACT FROM AUTHOR]

1. Habitat patches that have been completely cleared of their original vegetation historically and subsequently recolonized naturally provide a useful study system to explore the importance of the processes involved in community assembly. Forests where the understorey vegetation is recovering from past agricultural land use form an iconic example of such a system. 2. The colonization capacity of forest plant species into post-agricultural forests has been related to dispersal traits in previous comparative analyses, demonstrating the significance of dispersal limitation. Yet, none of them has evaluated evidence for a phylogenetic signal in colonization capacity and, thus, explored the possibility that the dispersal traits are correlated with unmeasured establishment-related traits that are also shared through common ancestry. 3. Here, we analysed the colonization capacity of 330 species into post-agricultural forests across seven different landscapes in Europe and North America. With phylogenetic meta-analysis models, we quantified the phylogenetic signal in colonization capacity and tested whether the colonization - dispersal trait relationships are confounded by phylogenetic non-independence. 4. Closely related forest understorey species were more similar to one another in terms of their capacity to colonize post-agricultural forests than were more distantly related species. The correlations between dispersal traits and colonization were not independent from phylogeny. While we found some evidence of phylogenetic clustering of species' frequencies in post-agricultural communities, this was apparently not a result of strong filtering on dispersal traits. 5. Synthesis. Given the phylogenetic signal in plant colonization capacity, a multitude of conserved species characteristics may explain community assembly in forests. Earlier trait-based syntheses strongly emphasised dispersal, but the factors limiting establishment and persistence of forest herbs in post-agricultural forests may be more nuanced than generally appreciated. [ABSTRACT FROM AUTHOR]

A long-standing hypothesis in ecology and evolutionary biology is that closely related species are more ecologically similar to each other and therefore compete more strongly than distant relatives do. A recent hypothesis posits that evolutionary relatedness may also explain the prevalence of mutualisms, with facilitative interactions being more common among distantly related species. Despite the importance of these hypotheses for understanding the structure and function of ecological communities, experimental tests to determine how evolutionary relatedness influences competition and facilitation are still somewhat rare., Here, we report results of a laboratory experiment in which we assessed how competitive and facilitative interactions among eight species of freshwater green algae are influenced by their relatedness. We measured the prevalence of competition and facilitation among 28 pairs of freshwater green algal species that were chosen to span a large gradient of phylogenetic distances. For each species, we first measured its invasion success when introduced into a steady-state population of another resident species. Then, we compared its growth rate when grown alone in monoculture to its growth rate when introduced as an invader. The change in the species' population growth rate as an invader (sensitivity) is used as a measure of the strength of its interaction with the resident species. A reduced growth rate in the presence of another species indicates competition, whereas an increased growth rate indicates facilitation., Although competition between species was more frequent (75% of interactions), facilitation was common (the other 25% of interactions). We found no significant relationship between the phylogenetic distance separating two interacting species and the success of invasion, nor the prevalence or strength of either competition or facilitation. Interspecific interactions depended more on the identity of the species, with certain taxa consistently acting as good or bad competitors/facilitators. These species were not predictable a priori from their positions on a phylogeny., Synthesis. The phylogenetic relatedness of the green algae species used here did not predict the prevalence of competitive and facilitative interactions, rejecting the hypothesis that close relatives compete strongly and contesting recent evidence that facilitation is likely to occur between distant relatives. [ABSTRACT FROM AUTHOR]

Previous studies have concluded that spatial aggregation of conspecifics should benefit weak competitors and put stronger competitors at a disadvantage, thus promoting plant species coexistence. However, if competitive ability is viewed as a behavioural trait, it becomes evident that traits determining spatial patterns and competitive ability could co-evolve, resulting in greater dispersal in stronger competitors and reduced competitive ability in spatially aggregated species., To test this prediction, we combined spatial data from a field survey of seven temperate grassland communities with the results of a common-garden competition experiment involving 28 focal species., We found that species exhibiting strong conspecific aggregation and infrequent heterospecific encounters in the field maintained greater growth in competition with conspecifics than with heterospecifics. In contrast, species that mostly encountered heterospecific neighbours in the field achieved greater growth when surrounded by heterospecific than conspecific neighbours, indicating greater competitive ability. The observed patterns of conspecific aggregation were related to variation in clonal dispersal characteristics and there was a direct positive relationship between clonal dispersal distance and competitive ability., Synthesis. Our study demonstrates that viewing competitive ability as a behavioural trait that imposes different costs and benefits on an individual depending on the identity of its neighbours can provide new insights into the long-debated topic of mechanisms promoting plant species coexistence. [ABSTRACT FROM AUTHOR]

Both plant species diversity and genetic diversity within a plant species can affect community properties and ecosystem processes. However, the relative contribution of species diversity and genetic diversity to ecosystem functioning is poorly known. Furthermore, ecosystem processes may respond non-additively to interactions between species diversity and genetic diversity. If interactive effects exist, the impact of biodiversity loss may not be predictable from simple assessments of either species diversity or genetic diversity alone., Here, we addressed how plant species diversity and genetic diversity within a dominant species independently and interactively influenced plant community biomass in a Great Lakes sand dune ecosystem. To test the independent effects of diversity, we established two experiments. In one, we manipulated genetic diversity within the dominant dune species, Ammophila breviligulata. In the other, we manipulated the number of plant species, excluding A. breviligulata. Then, to test for interactive effects, we constructed communities that varied the number of species and levels of genetic diversity within A. breviligulata., Although there were no independent effects of either species diversity or genetic diversity within A. breviligulata on biomass production in this system, interactive effects of species diversity and genetic diversity significantly influenced overall above-ground biomass production of the plant communities. Specifically, as genetic diversity within the dominant species increased, the relationship between species diversity and community-level biomass shifted from negative to positive. Negative non-additive effects of diversity drove this pattern., Synthesis. These results show, for the first time, that interactions between plant species diversity and genetic diversity within a dominant species can alter biomass production, highlighting the importance of incorporating interactions between levels of biodiversity into our understanding of how biodiversity influences ecosystem function. [ABSTRACT FROM AUTHOR]