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Societal Impact Statement: Forests worldwide face significant challenges due to climate change, impacting their health and productivity. In this study, we examined how European beech and Scots pine influence each other's phenology and growth in mixed forests. Our findings indicate that mixing these complementary tree species can increase resource efficiency within forest ecosystems. By leveraging informed species selection, this research highlights the potential for developing knowledge‐based, resource‐efficient forests. These insights are invaluable for policymakers and forest managers in designing forests that are not only productive but also sustainable and adaptable to evolving environmental conditions. Summary: We investigated the effects of interspecific neighbors on crown morphology and growth efficiency in European temperate forests, specifically focusing on European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). Our goal was to determine whether the previously reported overyielding in this mixture is primarily due to improved space‐use efficiency and packing density or enhanced resource‐use efficiency.Our methodology involved a detailed analysis of 128 individual felled trees. We assessed the effect of intraspecific and interspecific neighbors on stem volume growth, the allometric relationships of tree crowns and their components, and the allocation of branch and leaf biomass along the trees' vertical structure.Our findings demonstrate that interspecific neighbors significantly influence the allometric relationships of tree crowns, especially altering the vertical biomass distribution in European beech. Additionally, we found that interspecific neighbors can significantly enhance the growth efficiency of European beech but not for Scots pine.This research provides valuable insights for enhancing forest growth models and guiding forest management practices. By understanding the critical role of crown biomass allocation and growth efficiency in mixed‐species stands, policymakers and forest managers can design forests that are both productive and adaptable to changing environmental conditions. This study emphasizes the importance of species interactions in forest dynamics and bridges theoretical concepts with practical applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Plant–plant interactions are major determinants of the dynamics of terrestrial ecosystems. There is a long tradition in the study of these interactions, their mechanisms and their consequences using experimental, observational and theoretical approaches. Empirical studies overwhelmingly focus at the level of species pairs or small sets of species. Although empirical data on these interactions at the community level are scarce, such studies have gained pace in the last decade. Studying plant–plant interactions at the community level requires knowledge of which species interact with which others, so an ecological networks approach must be incorporated into the basic toolbox of plant community ecology. The concept of recruitment networks (RNs) provides an integrative framework and new insights for many topics in the field of plant community ecology. RNs synthesise the set of canopy–recruit interactions in a local plant assemblage. Canopy–recruit interactions describe which (“canopy”) species allow the recruitment of other species in their vicinity and how. Here we critically review basic concepts of ecological network theory as they apply to RNs. We use RecruitNet, a recently published worldwide data set of canopy–recruit interactions, to describe RN patterns emerging at the interaction, species, and community levels, and relate them to different abiotic gradients. Our results show that RNs can be sampled with high accuracy. The studies included in RecruitNet show a very high mean network completeness (95%), indicating that undetected canopy–recruit pairs must be few and occur very infrequently. Across 351,064 canopy–recruit pairs analysed, the effect of the interaction on recruitment was neutral in an average of 69% of the interactions per community, but the remaining interactions were positive (i.e. facilitative) five times more often than negative (i.e. competitive), and positive interactions had twice the strength of negative ones. Moreover, the frequency and strength of facilitation increases along a climatic aridity gradient worldwide, so the demography of plant communities is increasingly strongly dependent on facilitation as aridity increases. At network level, species can be ascribed to four functional types depending on their position in the network: core, satellite, strict transients and disturbance‐dependent transients. This functional structure can allow a rough estimation of which species are more likely to persist. In RecruitNet communities, this functional structure most often departs from random null model expectation and could allow on average the persistence of 77% of the species in a local community. The functional structure of RNs also varies along the aridity gradient, but differently in shrubland than in forest communities. This variation suggests an increase in the probability of species persistence with aridity in forests, while such probability remains roughly constant along the gradient in shrublands. The different functional structure of RNs between forests and shrublands could contribute to explaining their co‐occurrence as alternative stable states of the vegetation under the same climatic conditions. This review is not exhaustive of all the topics that can be addressed using the framework of RNs, but instead aims to present some of the interesting insights that it can bring to the field of plant community ecology. [ABSTRACT FROM AUTHOR]

Pollinator‐mediated reproductive interactions among co‐flowering plant species provide a canonical example of how biotic factors may contribute to species coexistence, yet we lack understanding of the exact mechanisms. Flowering‐dominant and unusually attractive "magnet species" with disproportionate contributions to pollination may play key roles in such reproductive interactions, but their relative roles within the same community have rarely been assessed. We experimentally removed either a flowering‐dominant or a highly attractive magnet species and compared effects on visitation frequency, pollinator richness, and seed set of co‐flowering plants. Removal of either the flowering‐dominant species or the magnet species reduced community‐level pollinator visitation. Removal of the magnet species had the most consistent effect, including reduced pollinator visitation and richness, and reduced seed set of most co‐flowering plants. These results suggest that the magnet species, which interacts with a wider range of pollinator species than does the dominant species, promotes the visitation and reproductive fitness of most other species. Removal of the flowering‐dominant species affected only certain species, perhaps because these plants had floral traits similar to the dominant species. Our results highlight the role of attractive magnet species within a community in structuring reproductive interactions and identify potential mechanisms involved in coexistence facilitated by reproductive interactions. [ABSTRACT FROM AUTHOR]

Interactions among plants are changing across the globe resulting from a multitude of changes in the environment. Obtaining accurate predictions of plant species' range dynamics requires us to account for plant–plant interactions, but this remains challenging using the existing species distribution modelling (SDM) techniques.Advanced SDM techniques facilitate the integration of plant species interactions based on species‐to‐species associations. However, for uncharted environmental conditions in which the formerly derived species' correlations potentially no longer hold, a more process‐based alternative is expected to become increasingly relevant.We first review the most common SDM techniques that integrate plant–plant interactions and then present the concept for a novel map product: a spatial plant–plant interaction index (PII) depicting the link between a focal species' performance and the trait signature of the interacting vegetation. The latest developments in remote sensing and the increasing availability of vegetation plot data facilitate PII mapping based on vegetation trait–environment relationships.Synthesis: PII mapping holds the potential to advance next‐generation biogeographical analyses as it can serve as a pivotal missing covariate layer necessary for the integration of plant–plant interactions into SDM applications. This data product adds flexibility to the ecologists' toolbox to analyse species range shifts and the formation of novel communities as a response to multiple environmental changes. [ABSTRACT FROM AUTHOR]

Background and aims: N enrichment is a major driver of plant species loss worldwide. Nevertheless, its impacts on local species assemblages (i.e., β-diversity), another essential but often overlooked index of biodiversity, remain uncertain. Moreover, whether or how C input changes the effects of N enrichment on plant biodiversity are poorly understood. Methods: We addressed the questions using location test of continuous input of a gradient of both N (n = 5) and labile C (n = 3) in a semi-arid grassland, conducted a five-year survey of plants biodiversity in each plot annually, and analyzed their variations and correlations. Results: N enrichment made plant α-diversity lose and plant production increase, which enhanced over time. The responses of different species varied, and plant communities shifted from stochastic to deterministic assembly during the five-year survey. The effects of N enrichment on plant biodiversity could be significantly relieved by a lower rate of labile C input. In this case, a lower rate of labile C enhanced coexistence of plant species (based on data of number and height), especially for certain taller species; but a higher rate of labile C input was opposite. Conclusion: A lower labile C treatments under N enrichment alleviated the negative responses of plant biodiversity over time. Plant species that could adjust their height strategically may better adapt to varied N and C addition and play important roles in plant communities assembly. All provided novel prospects in prediction and prevention of biodiversity reduction in semi-arid grasslands. [ABSTRACT FROM AUTHOR]

Context: Although shrub encroachment is a common phenomenon in grasslands, which often suppress co-existing herbaceous plants, little is known about how encroaching native shrubs affect endemic and threatened orchid species. Aims: We assessed the effect of the native dwarf shrub Helichrysum species on orchid species in a protected mountainous grassland system in Tanzania. Methods: We selected five Helichrysum shrub-dominated blocks and applied four treatments in each, i.e. no or low encroachment (<20% Helichrysum cover; 'low cover'), high encroachment (>50% Helichrysum cover; 'high cover'), cutting all stems of Helichrysum shrubs to ground level ('stem cut') and removing both stems and roots of all Helichrysum shrubs ('uprooted'). We then compared orchid species diversity, abundance and functional traits by using a mixed linear model across treatments. Key results: Orchid species diversity and abundance were significantly lower in 'high cover' plots than in other treatments. In 'high cover' plots, orchid species such as Disa robusta, Satyrium acutirostrum , and S. sphaeranthum had a significantly lower chlorophyll content than they did in 'low cover' plots. The 'uprooting' treatment showed significantly higher orchid species diversity in the second field season. Conclusion: The expansion of Helichrysum shrubs adversely affected orchid abundance, diversity, and individual vigour, which in turn affected the regenerative ability of orchids. Implications: We suggest that management should focus on shrub removal, because only 'cutting' had a beneficial effect on orchids. Shrub removal should be focused on areas of high shrub cover to promote further orchid species growth in this mountainous grassland of Tanzania. Five blocks dominated with Helichrysum splendidum were identified and, in each block, four plots were established by cutting and in other plot cutting and uprooting the stems of H. splendidum. High abundance of orchids was found in plots with a low Helichrysum cover. The orchids had physiological differences across the plots. Photograph by Christopher Mgimba. [ABSTRACT FROM AUTHOR]

Maritime Antarctica's harsh abiotic conditions forged simple terrestrial ecosystems, mostly constituted of bryophytes, lichens, and vascular plants. Though biotic interactions are, together with abiotic factors, thought to help shape this ecosystem, influencing species' distribution and, indirectly, mediating their response to climate, the importance of these interactions is still fairly unknown. We modeled current and future abundance patterns of bryophytes, lichens, and vascular plants, accounting for biotic interactions and abiotic drivers, along a climatic gradient in maritime Antarctica. The influence of regional climate and other drivers was modeled using structural equation models, with and without biotic interactions. Models with biotic interactions performed better; the one offering higher ecological support was used to estimate current and future spatial distributions of vegetation. Results suggest that plants are confined to lower elevations, negatively impacting bryophytes and lichens, whereas at higher elevations both climate and other drivers influence bryophytes and lichens. Our findings strongly support the use of biotic interactions to predict the spatial distribution of Antarctic vegetation. [Display omitted] • Bryophytes, lichens, and plants constitute the bulk of Maritime Antarctic vegetation • Abiotic drivers only partially explained Antarctic vegetation abundance • Biotic interactions were key to further explain vegetation abundance patterns • These findings boost our understanding of climate change impact in Antarctica There is an urgent need to improve predictive ecological models of climate change effects in maritime Antarctic vegetation. Rocha et al. uncovered that the inclusion of biotic interactions is a vital step to better explain and predict vegetation abundance patterns. These findings contribute toward building better conservation tools for the region. [ABSTRACT FROM AUTHOR]

Plant resource allocation strategies are thought to be largely a consequence of changing abiotic conditions and evolutionary history. However, biotic interactions also influence how a plant allocates resources. As a result, plants mediate indirect interactions between organisms above‐ and belowground through resource allocation. Neighboring plants can influence plant fitness directly through competition for resources, and indirectly by altering associated community interactions (associational effects), such as pollination, herbivory, and a suite of belowground interactions. Given the importance of community interactions for plant success, and the known ability for plant neighbors to change these interactions, the goal of this "pandemic project" was to understand how heterospecific plant neighbors alter plant resource allocation, whether this occurred through above‐ or belowground mechanisms, and whether this in turn alters biotic interactions and the relationship between a focal plant and its herbivore and soil community interactions. To do so, we established a common garden experiment, manipulating plant neighbor identity and the extent of interaction among neighbors (aboveground only, vs. above‐ and belowground interactions, using customized pot types), and measured changes to a focal plant and its biotic interactions over two growing seasons. We found evidence of both neighbor effects and pot type, showing that neighbor interactions affect a focal plant through both above‐ and belowground processes, and how the focal plant is affected depends on neighbor identity. Though neighbors did not directly alter herbivory or most soil microbial interactions, they did alter the relationship between belowground microbial communities and a plant response trait (specific leaf area). Plant resource allocation responses were reduced with time, showing the importance of extending experiments beyond a single growing season, and are an important consideration when making predictions about plant responses to changing conditions. This study contributes to a growing body of work showing how community contexts affect the above‐ and belowground interactions of a plant through plant resource allocation strategies. [ABSTRACT FROM AUTHOR]

Cloud forests figure as one of the most diverse ecosystems, accounting not only for a high number of plant species but also with a great variety of interactions among them. A common interaction in these forests is the one between vascular epiphytes and their hosts. However, few studies have used the network approach to analyze them. Here, we analyze the horizontal and vertical structure of the vascular epiphyte – host network in a cloud forest in central Mexico. We quantified the number of epiphyte stands on each host both total and per-stratum. Complete network, group, and species metrics were estimated at both levels of analysis. The host – epiphyte networks had relatively low network size but were highly connected; moderately nested, with low specialization, and modularity; but higher vulnerability than generality, and high niche overlap. The community was composed by a high number of generalist species. To our knowledge this is the first study in which network analyses are conducted with standardized data and including all host and epiphyte species in the community. The analyses suggest that the networks are robust, and that functional redundancy might be probable, two advantageous characteristics in a very fragmented and threatened cloud forest. [ABSTRACT FROM AUTHOR]

Plants infected by parasitic species might be further stressed by climate warming as both factors can influence the host plant's nutrient acquisition and growth. The root economics space, defined by root functional traits, reflects a plant's nutrient acquisition strategy. However, the combined effects of warming and parasitism on root functional traits and their positions within the root economics space have not been extensively studies.We grew soybean plants in pot cultures outdoor in the absence or presence of parasitism by Cuscuta gronovii and with or without simulated climate warming using infrared heater lamps. We measured various root functional traits of soybean, including root morphological traits, symbiosis with arbuscular mycorrhizal fungi (AMF) and rhizobia and enzyme activity. Correlations among these traits were analysed, and principal component analysis was used to determine the position of the plants in the root economics space.Parasitism significantly reduced AMF colonization rate, nodule biomass, root tissue density (RTD) and phosphatase activity in the rhizosheath, while increasing root nitrogen concentration (RN). Nodule biomass was positively correlated with AMF colonization, indicating an 'outsourcing' strategy for nutrient foraging. Parasitized soybeans occupied a trait space with higher RN and lower RTD, indicative of a 'fast' nutrient acquisition strategy. Warming did not significantly affect root functional traits or the plants' positions in the root economics space, regardless of parasitism presence.This study is the first to demonstrate that rhizobial colonization, similar to AMF colonization, is part of the 'outsourcing' strategy and that parasitism shifts host plants from a 'slow' to a 'fast' nutrient uptake strategy. These findings provide new insights into plant below‐ground strategies under warming and parasitism. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Introduction: Rhizosphere bacterial community as a valuable indicator of soil quality and function, has been widespread studied. However, little knowledge is about the response of bacterial communities to plant–plant interaction and different fertilizers during secondary forest succession. Methods: We conducted a field pot experiment applying organic and inorganic fertilizers to monocultures and mixed cultures of dominant plant species from mid- to late-successional stages (Salix oritrepha, Betula albosinensis, and Picea asperata), and investigated the responses of plant growth and rhizosphere bacterial communities. Results and discussion: Results indicated that growth rate of plant height varied among plant species, but no significant differences were observed in soil bacterial diversity and composition among plant species or inter-specific interactions under control. Compared to control, inorganic fertilizer resulted in increases in plant growth and the relative abundance of Proteobacteria, Patescibacteria, Bacteroidetes and Gemmatimonadetes, while simultaneously leading to decrease in the relative abundance of Acidobacteria, Actinobacteria, Chloroflexi, Rokubacteria and Planctomycetes. When grown with other species, the bacterial communities in the mixture resembled those of S. oritrepha in singular monoculture under inorganic fertilizer treatment, but plant growth was not affected by interspecific interaction. Unlike inorganic fertilizer, organic fertilizer significantly affected bacterial communities and increased bacterial diversity, but did not alter the effects of plant–plant interactions on bacterial communities. It was also observed that organic fertilizer facilitated later successional species’ growth (P. asperata and B. albosinensis) by the mid-successional species (S. oritrepha), ultimately facilitating secondary forest succession. In addition, plants at different successional stages harbor specific bacterial communities to affect their growth, and the bacterial communities contributed more than soil properties to the variations in the plant growth of S. oritrepha and P. asperata though the bacterial communities were regulated by soil factors. This finding highlights the significance of the rhizosphere bacteria on plant growth and plant community succession. It also emphasize the importance of considering both plant–plant interactions and diverse fertilizer types in forest restoration efforts and provide valuable insights into optimizing agronomic practices for secondary forest succession. [ABSTRACT FROM AUTHOR]

Summary Cuscuta campestris, a stem parasitic plant, has served as a valuable model plant for the exploration of plant–plant interactions and molecular trafficking. However, a major barrier to C. campestris research is that a method to generate stable transgenic plants has not yet been developed. Here, we describe the development of a Cuscuta transformation protocol using various reporter genes (GFP, GUS, or RUBY) and morphogenic genes (CcWUS2 and CcGRF/GIF), leading to a robust protocol for Agrobacterium‐mediated C. campestris transformation. The stably transformed and regenerated RUBY C. campestris plants produced haustoria, the signature organ of parasitic plants, and these were functional in forming host attachments. The locations of T‐DNA integration in the parasite genome were confirmed through TAIL‐PCR. Transformed C. campestris also produced flowers and viable transgenic seeds exhibiting betalain pigment, providing proof of germline transmission of the RUBY transgene. Furthermore, RUBY is not only a useful selectable marker for the Agrobacterium‐mediated transformation, but may also provide insight into the movement of molecules from C. campestris to the host during parasitism. Thus, the protocol for transformation of C. campestris reported here overcomes a major obstacle to Cuscuta research and opens new possibilities for studying parasitic plants and their interactions with hosts. [ABSTRACT FROM AUTHOR]

In arid ecosystems, vegetation patches promote biological activity and ecosystem functioning through species interactions that mitigate adverse environmental impacts. However, overgrazing disrupts those interactions, contributing to desertification. We investigated livestock influence on spatial vegetation patterns through the modification of the frequency and type of associations (i.e. number of associated species within a vegetation patch) among types of successional species (i.e. early, intermediate, and late). We studied vegetation in nine rangelands with varying stocking rates (treatments) within the Monte Desert region. We postulated three hypotheses: (1) Grazing simplifies community structure, increasing the frequency of isolated individuals and reducing the association diversity among plant species; (2) competition between plants favors the associations among species with different ecological niche requirements, reducing competition, enhancing facilitation, and regulating the association frequency among species; (3) grazing modifies plant competition and patterns of association among species. We found that with increasing stocking rates, the frequency of isolated individuals increased while association diversity declined. Associations between species with dissimilar niche requirements (e.g. early–late) were more frequent than those with similar needs (e.g. early–early). Livestock grazing modified plant competition, leading to an increased frequency of associations among species with similar requirements. Therefore, the association frequency among types of species in these drylands clearly reflected the degradation process along a grazing gradient, aiding in understanding plant ecological interactions. The association frequency could be implemented as an indicator in diagnostic and monitoring stages of restoration processes. [ABSTRACT FROM AUTHOR]

The elemental allelopathy hypothesis states that the metal‐rich litter of hyper‐accumulating species may have a detrimental impact on neighbouring plants giving a competitive advantage to hyper‐accumulators. Here, we aim to specify the conditions of application of this hypothesis in realistic field conditions, and its relative importance compared to other positive effects found in metalliferous systems.We disentangled the litter‐induced elemental allelopathy and canopy effects of two metallophyte species (Arenaria multicaulis and Hutchinsia alpina) with different levels of leaf Zn and Cd accumulation on two ecotypes of Agrostis capillaris with different levels of metal tolerance. The experiment was conducted in two habitats with contrasting pollution levels in a former mining valley in the Pyrenees (France).The metallophyte species that accumulates more metals (Hutchinsia alpina) showed a strong elemental allelopathy effect on the target with lower metal tolerance in the habitat with lower pollution level, while the metallophyte species that accumulates less metals (Arenaria multicaulis) had no litter effect. Both metallophyte species had positive canopy effects likely due to improvement of micro‐climatic conditions. The drought that occurred during the experiment may have influenced these canopy effects, increasing their importance during the course of the study. For Hutchinsia alpina, the positive canopy effects were stronger than the negative litter effects, resulting in overall positive effects on both target ecotypes.Synthesis. Our results brought a better understanding of the occurrence of elemental allelopathy in metallophyte communities and its relative importance as compared to micro‐climatic facilitation in a global warming context. [ABSTRACT FROM AUTHOR]

Plant–plant interactions regulate plant community structure and function. Shifts in these interactions due to global climate change, mediated through disproportional increases of certain species or functional groups, may strongly affect plant community properties. Still, we lack knowledge of community‐level effects of climate‐driven changes in biotic interactions. We examined plant community interactions by experimentally removing a dominant functional group, graminoids, in semi‐natural grasslands in Southern Norway. To test whether the effect of graminoid removal varied with climate, the experiment was replicated across broad‐scale temperature and precipitation gradients. To quantify community‐level interactions across sites, we tested for changes in the remaining vascular community (i.e. forbs) cover, richness, evenness, and functional traits reflecting leaf‐economic investment and plant size over five years. The effect of graminoid removal on forb community structure and functioning varied over time, and along the climate gradients. Forb cover increased in response to graminoid removal, especially at warmer sites. Species richness increased following removal irrespective of climate, whilst evenness increased under warmer and wetter conditions irrespective of removal. No climate or removal effect was found for species turnover. Functional trait responses varied along the precipitation gradient – compared to controls, forb mean SLA decreased in drier conditions after graminoid removal. Leaf thickness increased under cooler and drier conditions irrespective of removal. These community structure alterations demonstrate stronger competitive interactions between forbs and graminoids under warmer conditions, whilst functional trait responses indicate a facilitative effect of graminoids under drier conditions. This indicates that both competition and facilitation regulate plant communities, suggesting complexity when scaling from populations to communities. Finally, both temperature and precipitation determine the direction and intensity of biotic interactions, with ecosystem‐wide implications for forb persistence and ecosystem functioning under future climates. Further work is needed to generalise the role of changing interactions in mediating community responses to climate change. [ABSTRACT FROM AUTHOR]

Belowground plant competition has been shown to induce varying responses, from increases to decreases in root biomass allocation or in directional root placement. Such inconsistencies could result from the fact that root allocation and directional growth were seldom studied together, even though they might represent different strategies. Moreover, variations in belowground responses might be due to different size hierarchies between plants, but this hypothesis has not been studied previously. In a greenhouse rhizobox experiment, we examined the way both root allocation and directional root placement of Pisum sativum are affected by the size and density of Festuca glauca neighbours, and by nutrient distribution. We found that root allocation of P. sativum increased with the density and size of F. glauca. By contrast, directional root placement was unaffected by neighbour size and increased either towards or away from neighbours when nutrients were patchily or uniformly distributed, respectively. These results demonstrate that directional root placement under competition is contingent on the distribution of soil resources. Interestingly, our results suggest that root allocation and directional placement might be uncoupled strategies that simultaneously provide stress tolerance and spatial responsiveness to neighbours, thus highlighting the importance of measuring both when studying belowground plant competition. [ABSTRACT FROM AUTHOR]

Lianas, or woody vines, are key components of many tropical forests and can have substantial impacts on the dynamics and functioning of these important ecosystems. Their competition with trees for resources, in particular light, can hamper the recovery of forests from disturbances. Yet, it is unclear how forest disturbance interacts with liana–tree ratio (LTR), topography and soil properties to shape tree dynamics and the trajectories of forest succession.Using temporal data from the Kilombero Valley and the Udzungwa Mountains of Tanzania, we demonstrate how the dynamics of tree stems and biomass vary between secondary and old‐growth forests with changes in the dominance of lianas and environmental gradients.Greater tree recruitment and mortality in secondary forests compared with old‐growth forests suggested rapid regeneration processes and faster turnover. However, no significant differences were found in the net annual changes in the number or biomass of trees between secondary and old‐growth forests.Our findings also showed that higher LTRs were positively associated with stem mortality but also with tree biomass growth, indicating a nuanced ecological role of lianas in forest ecosystems, which warrants further investigation to fully understand the causal factors at play.Net changes in tree stem numbers decreased significantly with elevation, implying climatic constraints on forest regeneration at higher elevations. Soil cation exchange capacity and organic carbon were found to significantly influence tree stem recruitment and net change in abundance, although their effects on biomass remained unclear.Synthesis: Our findings indicate that the recovery of tropical forests from disturbance in terms of the number and biomass of tree stems may be predictable along environmental gradients. These insights have the potential to broaden our capacity to develop more nuanced strategies that identify when and where tropical forests may require restoration interventions, with a focus on structural recovery. [ABSTRACT FROM AUTHOR]

Epiphytism is an example of an obligate interspecific interaction between plants, where a plant species grows on another plant species for physical support. In epiphytic orchids that rely on suitable host tree species (phorophytes) and mycorrhizal fungi for germination and growth, a distinct preference has been observed for particular host tree species. However, the factors driving this host preference remain unclear.In this study, we investigated whether mycorrhizal fungi that promote seedling development determine the preference of phorophytes in the epiphytic orchid Dendrobium wangliangii. First, we identified the preferred host tree species for this orchid. Next, in vitro and in situ germination experiments were conducted to identify potential fungi that promote seed germination. Finally, high‐throughput sequencing was used to assess the distribution of these fungi on both colonized host trees and potential host trees, including individual trees of the host species not yet colonized by the orchid and trees of another species growing in the vicinity of a colonized tree.Dendrobium wangliangii exhibited a preference for trees within the Fagaceae family. Two Fusarium species from the bark of host trees were identified as the primary fungi that promote seed germination. Successful protocorm formation and seedling development were observed exclusively on preferred phorophytes. Fungal community analyses further indicated that both Fusarium spp. occurred on all potential host trees, suggesting that the host preference of this epiphytic orchid is not constrained by the distribution of suitable mycorrhizal fungi.Synthesis: Regarding the epiphytes that depend on mycorrhizal fungi for successful seedling recruitment, we conclude that strong epiphyte–phorophyte associations do not arise from the limited distribution of mycorrhizal fungi but are more likely the result of other factors inherent in the phorophyte environment. [ABSTRACT FROM AUTHOR]

Positive plant–plant interactions (facilitation) may enhance the recruitment and establishment of species less adapted to local macroclimatic conditions. A major cause of this effect is climatic buffering, which implies an increased mismatch between the macroclimatic conditions and the climatic requirements of the existing community – climatic disequilibrium – of plants living under canopies. Here we explore the effect of drought‐induced defoliation of Mediterranean shrubland canopy on the recruitment of woody species. We analyzed the differences in the climatic disequilibrium across different categories of canopy defoliation and plant–plant interactions: facilitation, neutral and inhibition. Climatic disequilibrium was estimated as the Euclidean distance in the multivariate environmental space between observed macroclimate and community inferred climate. The inferred climate was calculated by averaging the coordinates of the species' climatic niche centroids, obtained from species distribution, weighted by the species' relative abundances in each community. We found that the recruiting community growing under canopy showed higher climatic disequilibrium than the community growing in the gaps. The facilitated recruiting community growing under dead and living canopy showed the highest disequilibrium, followed by the community growing under mid‐affected canopy. The climatic disequilibrium of the recruiting communities experiencing neutral and inhibited interaction was not affected by canopy defoliation. These findings indicate that the climatic disequilibrium of the recruiting community is determined by the facilitation–competition balance. Living canopy provides climatic buffering, but it also implies competition, while dead canopy may provide some structural climatic buffering, without implying competition for resources. These results highlight the relevance of incorporating plant–plant interactions, particularly facilitation, to better forecast plant community responses to extreme climate events and climate change. [ABSTRACT FROM AUTHOR]

Understanding how plant fitness varies along natural gradients is critical for predicting responses to environmental change. However, individual vital rates are often used as fitness proxies without knowing how other vital rates vary along the same gradients.We investigated how canopy cover, plant–plant interactions, water availability and soil properties influenced the emergence, survival, seed production and population growth rates of eight annual plant species in semi‐arid Western Australia. We sowed seeds into sun‐exposed and shaded blocks across a reserve, removed all neighbouring plants from half of the interaction neighbourhoods, and used rainout shelters to reduce and increase precipitation relative to ambient plots.Canopy cover had strong negative effects on emergence, but few direct impacts on other vital rates and population growth rates. Direct competitive effects on survival and seed production were rare, although evident for population growth rate for 3/8 species. Competition was stronger in open than shaded plots for half of the species. Canopy cover also interacted with the watering treatment to influence survival of half of the species, but watering alone had few direct impacts on species' vital and population growth rates. We found only positive significant correlations between pairs of rates, and survival and seed production were far more frequently correlated with population growth rate than emergence.Synthesis. Our study illustrates that vital rates can respond to the same local‐scale environmental variation in different ways that are likely not driven by life history trade‐offs. We caution against using emergence as a proxy for population growth rate and emphasise that no single vital rate was a reliable fitness proxy overall. Interactions among abiotic and biotic factors were important drivers of vital and population growth rates for some species, highlighting the need to account for plant–plant interactions when predicting population responses to environmental change. [ABSTRACT FROM AUTHOR]

Summary: Greenbeards are selfish genetic elements that make their bearers behave either altruistically towards individuals bearing similar greenbeard copies or harmfully towards individuals bearing different copies. They were first proposed by W. D. Hamilton over 50 yr ago, to illustrate that kin selection may operate at the level of single genes. Examples of greenbeards have now been reported in a wide range of taxa, but they remain undocumented in plants. In this paper, we discuss the theoretical likelihood of greenbeard existence in plants. We then question why the greenbeard concept has never been applied to plants and speculate on how hypothetical greenbeards could affect plant–plant interactions. Finally, we point to different research directions to improve our knowledge of greenbeards in plants. [ABSTRACT FROM AUTHOR]

The study of tree species coexistence is crucial to understand the assembly of forest communities. In this context, trees adjust their traits in response to the interactions with other trees and, specifically, as a result of the competition for resources. Further, mycorrhizal fungal diversity and associations are important drivers of ecosystem functioning in forests, but their role as drivers of intraspecific trait variation has been disregarded. Here, we studied intraspecific trait variation of trees in response to tree and mycorrhizal fungal diversity.We sampled 3200 leaves from 640 trees belonging to 10 native, deciduous species in a tree diversity experiment in Central Germany. This experiment relies on the combination of gradients of tree richness and mycorrhizal associations. To handle large amounts of leaf samples, we acquired leaf‐level spectral data and used deep learning to predict values for five leaf traits from the leaf economics spectrum (LES): specific leaf area, leaf dry matter content, carbon to nitrogen ratio, carbon content and phosphorus content. For every tree, we calculated the mean value for every trait and two multi‐trait functional indices (functional richness and functional dispersion) based on values for individual leaves. Finally, we used sequencing‐based data to assess the richness of mycorrhizal fungi associated with the trees.We found that tree and mycorrhizal fungi richness had an effect on different leaf functional traits. Specifically, tree richness positively affected specific leaf area and, additionally, had a negative effect on the functional indicies, which revealed that the phenotypic diversity within the tree crown decreased with tree species richness. In addition, leaf carbon to nitrogen ratio decreased with increasing arbuscular mycorrhizal fungal richness in both arbuscular and ectomycorrhizal tree species. Finally, we did not find differences between arbuscular and ectomycorrhizal trees regarding their location within the LES.Our results suggest that trees modify their strategy in response to local tree diversity, not only by shifting trait values but also by shifting the variability intraindividually. In addition, higher mycorrhizal fungal diversity does not seem to lead to higher complementarity, but instead, tree and mycorrhizal fungi affect different aspects of leaf traits. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

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1. Co-flowering plant species often interact through shared pollinators, with effects ranging from positive (facilitation) to negative (competition). It remains unclear how this variation relates to variation in floral density, floral trait distinctiveness, and local environmental conditions. We studied the effect of grazer exclusion, a proposed local management strategy, on pollinator-mediated plant-plant interactions in heavily degraded alpine meadows of the Qinghai-Tibet Plateau. 2. We studied the effect of experimental grazer exclusion on plant reproduction and pollinator-mediated reproductive interactions quantified through pollen transfer networks. We also explored potential mechanisms of pollinator-mediated interspecific pollen transfer and its effect on plant reproductive fitness, including local floral abundance and floral trait distinctiveness among co-flowering species. 3. Grazer exclusion led to greater pollen deposition onto stigmas. The overall quantitative effects of pollinator-mediated interspecific interactions on the receptor species were mainly positive (facilitative) or neutral (with no detectable effect). The frequency of positive relative to negative quantitative effects for pairwise donor-receptor pairs tended to increase after grazer exclusion. Plants with floral traits similar to those of local 'hub species' appeared to benefit from pollinator-mediated interactions. 4. Our results suggest an overall positive effect of excluding grazers during the plant growing season on plant reproduction. Facilitative species interactions predominate in harsh environments such as the alpine, and the benefits of pollinator-mediated interactions among plants seemed to exceed the cost of conspecific pollen loss associated with pollinator sharing. This suggest that species invasions into alpine plant communities, an expected consequence of climate change, may not necessarily have negative effects on the reproduction of resident plant species. [ABSTRACT FROM AUTHOR]

Growing crops in more diverse crop systems (i.e., intercropping) is one way to produce food more sustainably. Even though intercropping, compared to average monocultures, is generally more productive, the full yield potential of intercropping might not yet have been achieved as modern crop cultivars are bred to be grown in monoculture. Breeding plants for more familiarity in mixtures, i.e., plants that are adapted to more diverse communities (i.e., adaptation) or even to coexist with each other (i.e., coadaptation) might have the potential to sustainably enhance productivity. In this study, the productivity benefits of familiarity through evolutionary adaptation and coevolutionary coadaptation were disentangled in a crop system through an extensive common garden experiment. Furthermore, evolutionary and coevolutionary effects on species-level and community-level productivity were linked to corresponding changes in functional traits. We found evidence for higher productivity and trait convergence with increasing familiarity with the plant communities. Furthermore, our results provide evidence for the coevolution of plants in mixtures leading to higher productivity of coadapted species. However, with the functional traits measured in our study, we could not fully explain the productivity benefits found upon coevolution. Our study investigated coevolution among randomly interacting plants and was able to demonstrate that coadaptation through coevolution of coexisting species in mixtures occurs and promotes ecosystem functioning (i.e., higher productivity). This result is particularly relevant for the diversification of agricultural and forest ecosystems, demonstrating the added value of artificially selecting plants for the communities they are familiar with. [ABSTRACT FROM AUTHOR]

Phyllosphere fungal communities participate in multiple ecological functions (litter decomposition, disease‐causing, plant defence). However, there is a lack of knowledge on whether and how these functions contribute to plant community dynamics under natural conditions. One of the aspects of plant dynamics in which these fungi can most clearly affect is recruitment, since the success of newly germinated plants can be seriously compromised by pathogenic activity or the absence of mutualistic interactions. To determine the relationship between phyllosphere fungal communities and plant recruitment, we combined published information on the frequency of plant–plant recruitment interactions and phyllosphere fungal communities in 38 woody species from two mixed forests in southern Spain. Our results indicate that phyllosphere pathogens and saprotrophs have a negative effect on canopy–recruit interactions, while epiphytic fungi have a positive effect. Additionally, the presence of canopy species hosting high richness of epiphytes or counting with a high diversity of saprotrophic fungi favours the formation of an abundant sapling bank. Synthesis. Our results suggest that phyllosphere fungi play a relevant role in the assembly of the sapling bank in forest communities, thus, potentially influencing plant community dynamics. Beyond the well‐known negative effect of pathogenic fungi on recruitment, our results show the mutualistic effect of fungal epiphytes and a dual role of saprotrophs as antagonistic, decreasing recruitment of certain species, or mutualistic, enhancing recruitment in the sapling bank. [ABSTRACT FROM AUTHOR]

Plants interact in complex networks but how network structure depends on resources, natural enemies and species resource‐use strategy remains poorly understood. Here, we quantified competition networks among 18 plants varying in fast–slow strategy, by testing how increased nutrient availability and reduced foliar pathogens affected intra‐ and inter‐specific interactions. Our results show that nitrogen and pathogens altered several aspects of network structure, often in unexpected ways due to fast and slow growing species responding differently. Nitrogen addition increased competition asymmetry in slow growing networks, as expected, but decreased it in fast growing networks. Pathogen reduction made networks more even and less skewed because pathogens targeted weaker competitors. Surprisingly, pathogens and nitrogen dampened each other's effect. Our results show that plant growth strategy is key to understand how competition respond to resources and enemies, a prediction from classic theories which has rarely been tested by linking functional traits to competition networks. [ABSTRACT FROM AUTHOR]

Interactions between two plant species can be influenced by the presence of other plant species and such an effect may change as the diversity of the other species increases. To test these hypotheses, we first constructed aquatic communities consisting of 1, 2 and 4 emergent plant species and then grew ramets of Lemna minor only, ramets of Spirodela polyrhiza only or ramets of both L. minor and S. polyrhiza within these aquatic communities. We also included controls with ramets of L. minor , S. polyrhiza or both but without any emergent plants. Biomass and number of ramets of L. minor and S. polyrhiza were significantly smaller with than without the emergent plants, but they did not differ among the three richness levels. The presence of S. polyrhiza did not significantly affect the growth of L. minor , and such an effect was not dependent on the richness of the emergent plant species. Without the emergent plant species, the presence of L. minor markedly reduced biomass (−92%) and number of ramets (−88%) of S. polyrhiza. However, such a competitive effect of L. minor on S. polyrhiza became much weaker in the presence of one emergent plant species (−46% biomass and −39% number of ramets) and completely disappeared in the presence of two or four emergent plant species. Therefore, both the presence and richness of emergent plant species can alter competitive interactions between the two duckweed species. These findings highlight the importance of species diversity in regulating plant–plant interactions. [ABSTRACT FROM AUTHOR]

Plant neighbors in arid environments can ameliorate abiotic stress by reducing insolation, but they also attract herbivores and pathogens, especially when neighbors are close relatives that share similar antagonists. Plants' metabolic profiles provide a chemical fingerprint of the physiological processes behind plant responses to different environmental stresses. For example, abscisic acid and proline, mainly involved in stomatal closure and osmotic adjustment, can induce plant responses to abiotic stress, while jasmonic acid and salicylic acid primarily regulate plant defense to herbivory or pathogens. Neighbor plants can generate contrasting ecological contexts, modulating plant responses to abiotic and biotic stresses. We hypothesize that plant metabolic profile is modulated by its neighbors in a vegetation patch, expecting a higher investment in metabolites related to biotic-stress tolerance (i.e., herbivory or pathogens) when growing associated with other plants, especially to phylogenetically close relatives, compared to plants growing alone. We show that plants from five species growing with neighbors invest more in biotic-stress tolerance while their conspecifics, growing alone, invest more in abiotic-stress tolerance. This tendency in plants' metabolic profiles was not affected by the phylogenetic diversity of their neighborhood. Linking physiological snapshots with community processes can contribute to elucidating metabolic profiles derived from plant-plant interactions. [ABSTRACT FROM AUTHOR]

Mixed‐species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. In particular, the trait‐based mechanisms driving the role of tree diversity under drought remain elusive.Using tree cores from a large‐scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; δ13C) to changes in climate‐induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought‐tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases δ13C and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterised the biotic context using drought‐tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance versus resource acquisition and stomatal control.Tree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species‐rich neighbourhoods. The effects of neighbourhood species richness and climate on growth and δ13C were modulated by the traits of focal trees and the traits of their neighbours. At either end of each drought‐tolerance gradient, species responded in opposing directions during dry and wet years.We show that species' drought‐tolerance traits can explain the strength and nature of biodiversity–ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress. [ABSTRACT FROM AUTHOR]

The rhizosphere is a complex physical and chemical interface between plants and their underground environment, both biotic and abiotic. Plants exude a large number of chemicals into the rhizosphere in order to manipulate these biotic and abiotic components. Among such chemicals are strigolactones, ancient signalling molecules that in flowering plants act as both internal hormones and external rhizosphere signals. Plants exude strigolactones to communicate with their preferred symbiotic partners and neighbouring plants, but at least some classes of parasitic organisms are able to 'crack' these private messages and eavesdrop on the signals. In this review, we examine the intentional consequences of strigolactone exudation, and also the unintentional consequences caused by eavesdroppers. We examine the molecular mechanisms by which strigolactones act within the rhizosphere, and attempt to understand the enigma of the strigolactone molecular diversity synthesized and exuded into the rhizosphere by plants. We conclude by looking at the prospects of using improved understanding of strigolactones in agricultural contexts. [ABSTRACT FROM AUTHOR]

Summary: Understanding and predicting recruitment in species‐rich plant communities requires identifying functional determinants of both density‐independent performance and interactions.In a common‐garden field experiment with 25 species of the woody plant genus Protea, we varied the initial spatial and taxonomic arrangement of seedlings and followed their survival and growth during recruitment. Neighbourhood models quantified how six key functional traits affect density‐independent performance, interaction effects and responses.Trait‐based neighbourhood models accurately predicted individual survival and growth from the initial spatial and functional composition of species‐rich experimental communities. Functional variation among species caused substantial variation in density‐independent survival and growth that was not correlated with interaction effects and responses. Interactions were spatially restricted but had important, predominantly competitive, effects on recruitment. Traits increasing the acquisition of limiting resources (water for survival and soil P for growth) mediated trade‐offs between interaction effects and responses. Moreover, resprouting species had higher survival but reduced growth, likely reinforcing the survival–growth trade‐off in adult plants.Resource acquisition of juvenile plants shapes Protea community dynamics with acquisitive species with strong competitive effects suffering more from competition. Together with functional determinants of density‐independent performance, this makes recruitment remarkably predictable, which is critical for efficient restoration and near‐term ecological forecasts of species‐rich communities. [ABSTRACT FROM AUTHOR]

Importance of nurse plants structuring plant communities is well‐appreciated at local scales, yet the effect of a single nurse on large scales has been neglected in analyses. So far, studies only use environmental gradients within one type of ecosystem and tend to generalize the nurse effects.To assess how the effect of a single nurse species is modulated by different environmental settings, interactions between the shrub Vachellia caven and the surrounding plant communities were evaluated at 481 paired plots (outside vs. underneath the plant crown), in 39 sites across two distribution ranges, the Mediterranean west and the mostly subtropical east of the Andes Mountains (covering ca. 2 × 106 km2).Cover, abundance and richness of perennial plants underneath and outside V. caven were used as response variables to estimate an index indicative of plant interactions (relative interaction index [RII]) and tested how this was affected by the rainfall gradient and distribution range.Overall, RII responses to rainfall gradients had low conditional R2 (~0.25) in this large scale of analysis, but were significantly different between ranges: the RII followed a quadratic trend across the rainfall gradient in the western range, while this relationship was positive and close to linear at the eastern range.Then, by projecting the RII models (i.e. for abundance, cover and richness) spatially through a consensus map, we show that most positive effects of V. caven are geographically found in dissimilar areas: the central part of Chile (western range) and across the Paraná River (eastern range).When local fine‐scale predictors (i.e. annual herbs' cover and height, and herbivores' faeces cover) were used to model each response variable at the plot level (underneath or outside V. caven), we observed similar trends as when we considered only the large‐scale predictors.Synthesis. Here, we show that the effect of the same nurse species on neighbouring plant communities can be very different depending on ranges of distribution, stressing that its ecological function cannot be generalized and not only depends on local factors but also is large‐scale context‐dependent. [ABSTRACT FROM AUTHOR]

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

Plants transmit ecologically relevant messages to neighbouring plants through chemical cues. For instance, insect herbivory triggers the production of herbivore‐induced plant volatiles (HIPVs), which can enhance neighbouring plant defences. HIPVs are emitted from directly damaged plant tissues and from systemic, nondamaged tissues. Although volatile‐mediated interplant interactions have been observed both above‐ and belowground, it remains unknown whether belowground herbivory induces systemic HIPVs aboveground that influence neighbouring plants. To explore how belowground herbivory affects interplant interactions aboveground, we characterised systemic HIPVs from squash induced by belowground striped cucumber beetle (Acalymma vittatum) larval herbivory. We exposed squash 'receiver plants' to systemic HIPVs or volatiles from nondamaged plants. We then measured herbivore resistance by challenging 'receiver plants' with aboveground‐feeding herbivores: adult beetles (A. vittatum) or squash bugs (Anasa tristis). We discovered belowground‐damaged plants emitted more (E)‐β‐ocimene, a key volatile from the systemic HIPV blend, than nondamaged controls, and that exposure to systemic HIPVs enhanced neighbouring plant resistance to aboveground squash bugs, but not adult beetles. Further investigations into the mechanism of interplant interaction revealed β‐ocimene alone can elicit plant resistance against squash bugs. Overall, our findings reveal a novel form of volatile‐mediated interactions between plants spanning across aboveground–belowground plant systems. Summary Statement: Belowground insect herbivory alters aboveground volatiles emitted by squash plants. Exposing neighbouring plants to these volatiles enhances plant resistance to an aboveground heterospecific insect herbivore, but not aboveground conspecifics. [ABSTRACT FROM AUTHOR]

Studies of drivers shaping forest communities frequently include abiotic or biotic factors, while their interactive effects remain understudied. Here, we combined data on two prominent abiotic gradients, climatic moisture deficit and wildfire probability, along with tree functional neighbourhoods (i.e. trait differences of close neighbours) to assess variation in survival and growth of 56 tree species in the northwestern US.We asked two questions: (1) How does functional neighbourhood dissimilarity vary with environmental gradients? and (2) How do demographic rates of tree species in the northwestern United States vary with the interactive effects of environmental gradients and functional neighbourhood? We expected functional neighbourhoods to become more similar as environmental stress increased, due to a convergence of species towards an optimum stress tolerance strategy. We also predicted the interactive effects of abiotic and biotic factors on tree demography and high variation in species‐specific responses to these interactive effects due to divergent species life history strategies.Functional neighbourhoods defined by dissimilarities in stem conductivity, litter decomposition, resprouting ability and specific leaf area changed with climate, shifting to more diverse neighbourhoods as climatic moisture deficit and wildfire probability increased. Results supported interactive effects of the functional neighbourhood and climatic moisture deficit or wildfire probability on tree demography, but only when the identity of dominant species was considered. Species‐specific responses were highly variable in their direction and magnitude and often demonstrated opposing effects of climate and the functional neighbourhood and climatic moisture deficit on tree demography.Synthesis. Our findings show that climate and tree neighbourhood functional dissimilarity jointly impact tree demography; however, the effects are species‐specific. Results of this study highlight the need to consider the interactive effects of abiotic and biotic contexts and individual species responses to their environment to adequately understand tree persistence under current and future climate conditions. [ABSTRACT FROM AUTHOR]

Fluctuating resource availability plays a critical role in determining non‐native plant invasions through mediating the competitive balance between non‐native and native species. However, the impact of fluctuating resource availability on interactions among non‐native species remains largely unknown. This represents a barrier to understanding invasion mechanisms, particularly in habitats that harbor multiple non‐native species with different responses to fluctuating resource availability. To examine the responses of non‐native plant species to nutrient fluctuations, we compared the growth of each of 12 non‐native species found to be common in local natural areas to nutrients supplied at a constant rate or supplied as a single large pulse in a pot experiment. We found that seven species produced more biomass with pulsed nutrients compared to constant nutrients (hereafter "benefitting species"), while the other five species did not differ between nutrient enrichment treatments (hereafter "non‐benefitting species"). To investigate how nutrient fluctuations influence the interactions among non‐native plant species, we established experimental non‐native communities in the field with two benefitting and two non‐benefitting non‐native species. Compared with constant nutrient supply, the single large pulse of nutrient did not influence community biomass, but strongly increased the biomass and cover of the benefitting species and decreased those of the non‐benefitting species. Furthermore, the benefitting species had higher leaf N content and greater plant height when nutrients were supplied as a single large pulse than at a constant rate, whereas the non‐benefitting species showed no differences in leaf N content and were shorter when nutrients were supplied as a single large pulse than at a constant rate. Our results add to the growing evidence that the individual responses of non‐native species to nutrient fluctuation are species‐specific. More importantly, benefitting species were favored by nutrients coming in a pulse, while non‐benefitting ones were favored by nutrients coming constantly when they grew together. This suggests that nutrient fluctuations can mediate the competitive balance among non‐native plants and may thus determine their invasion success in a community harboring multiple non‐native plant species. [ABSTRACT FROM AUTHOR]

Background: Understanding the role of species identity in interactions among individuals is crucial for assessing the productivity and stability of mixed forests over time. However, there is limited knowledge concerning the variation in competitive effect and response of different species along climatic gradients. In this study, we investigated the importance of climate, tree size, and competition on the growth of three tree species: spruce (Picea abies), fir (Abies alba), and beech (Fagus sylvatica), and examined their competitive response and effect along a climatic gradient. Methods: We selected 39 plots distributed across the European mountains with records of the position and growth of 5,759 individuals. For each target species, models relating tree growth to tree size, climate and competition were proposed. Competition was modelled using a neighbourhood competition index that considered the effects of inter- and intraspecific competition on target trees. Competitive responses and effects were related to climate. Likelihood methods and information theory were used to select the best model. Results: Our findings revealed that competition had a greater impact on target species growth than tree size or climate. Climate did influence the competitive effects of neighbouring species, but it did not affect the target species' response to competition. The strength of competitive effects varied along the gradient, contingent on the identity of the interacting species. When the target species exhibited an intermediate competitive effect relative to neighbouring species, both higher inter- than intraspecific competitive effects and competition reduction occurred along the gradient. Notably, species competitive effects were most pronounced when the target species' growth was at its peak and weakest when growing conditions were far from their maximum. Conclusions: Climate modulates the effects of competition from neighbouring trees on the target tree and not the susceptibility of the target tree to competition. The modelling approach should be useful in future research to expand our knowledge of how competition modulates forest communities across environmental gradients. [ABSTRACT FROM AUTHOR]

Summary: Controlled experiments at the level of individual plants show that legume species use different strategies for the regulation of symbiotic dinitrogen fixation in response to nitrogen availability. These strategies were suggested to improve legume fitness in the context of the plant community, although rarely studied at this level. We evaluated how nitrogen availability and conspecific vs heterospecific interactions influenced the strategy of regulation of nitrogen fixation.We grew two species of herbaceous legumes representing two different strategies of regulation without interaction, under treatments of deficient and sufficient nitrogen availability, with conspecific or heterospecific interaction.We found that Hymenocarpus circinnatus maintained a facultative strategy of downregulating nitrogen fixation when nitrogen was available under both con‐ and heterospecific interactions, as was also found for this species when grown alone. Vicia palaestina also downregulated nitrogen fixation under both con‐ and heterospecific interactions but did not regulate fixation when grown alone. Our results showed that under nitrogen limitation, interaction with a neighboring plant reduced fitness, reflecting a competitive effect.Our findings suggest that when interacting with other plants, downregulation of nitrogen fixation is more likely, therefore reducing the energetic cost of fixation, and improving plant performance in competitive ecological communities, especially when nitrogen is available. [ABSTRACT FROM AUTHOR]

Viscum combreticola Engl., an evergreen semi-parasitic mistletoe plant, is utilized in herbal medicines. Herein, a UHPLC-q-TOF-MS profiling and molecular networking approach were used to investigate the chemical interactions between V. combreticola and two of its host plants, Combretum erythrophyllum and Pseudolachnostylis maprouneifolia Pax. Moreover, in vitro grown V. combreticola seedlings were used to explore the host independence of the phytochemistry of these plants. The phytochemistry of V. combreticola was found to be independent and distinct from that of the host plants. Moreover, both mature V. combreticola and in vitro seedlings displayed diverse polyphenolic compounds but exhibited distinct metabolic profiles. Notably, the esterification of phenolic acids (hydroxycinnamic and benzoic acids) to quinic acid was a unique chemistry that was observed in both mature and in vitro grown V. combreticola. Beyond providing metabolic fingerprints of the studied samples, the UHPLC-q-TOF-MS and molecular networking effectively visualized plant-plant chemical relationships at a metabolite level. [ABSTRACT FROM AUTHOR]

In agricultural production, intercropping is a widely used system with many benefits. Lupin (Lupinus angustifolius L.) is a legume that contains a large variety of plant secondary metabolites, which have multiple functions in the plant, e.g. signalling, nodulation and stress response. An untargeted metabolomics approach was applied to investigate how the metabolome of lupin was affected by intercropped barley (Hordeum vulgare L.). The only primary metabolite of lupin affected by intercropping was tryptophan. Several secondary metabolites were affected by intercropping in lupin, and five flavonoids were annotated hereof. The flavonoid levels were increased, and tryptophan levels decreased in lupin when intercropped. Two flavonoids are prenylated, and prenylated flavonoids are believed to play a role in the plant's stress response. Furthermore, flavonoids are involved in plant defence and the nodulation process. Thus the present flavonoids may affect regulation of lupin N2-fixation activity. Highlights Intercropping caused a change in the secondary metabolites of Lupinus angustifolius L. Prenylated flavonoids were generated in Lupinus angustifolius L. as a response to intercropping Tryptophan was the only identified primary metabolite affected by intercropping [ABSTRACT FROM AUTHOR]

Volatiles emitted by herbivore-attacked plants (senders) can enhance defenses in neighboring plants (receivers), however, the temporal dynamics of this phenomenon remain poorly studied. Using a custom-built, high-throughput proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) system, we explored temporal patterns of volatile transfer and responses between herbivore-attacked and undamaged maize plants. We found that continuous exposure to natural blends of herbivore-induced volatiles results in clocked temporal response patterns in neighboring plants, characterized by an induced terpene burst at the onset of the second day of exposure. This delayed burst is not explained by terpene accumulation during the night, but coincides with delayed jasmonate accumulation in receiver plants. The delayed burst occurs independent of day:night light transitions and cannot be fully explained by sender volatile dynamics. Instead, it is the result of a stress memory from volatile exposure during the first day and secondary exposure to bioactive volatiles on the second day. Our study reveals that prolonged exposure to natural blends of stress-induced volatiles results in a response that integrates priming and direct induction into a distinct and predictable temporal response pattern. This provides an answer to the long-standing question of whether stress volatiles predominantly induce or prime plant defenses in neighboring plants, by revealing that they can do both in sequence.

Despite their low contribution to forest carbon stocks, lianas (woody vines) play an important role in the carbon dynamics of tropical forests. As structural parasites, they hinder tree survival, growth and fecundity; hence, they negatively impact net ecosystem productivity and long-term carbon sequestration.Competition (for water and light) drives various forest processes and depends on the local abundance of resources over time. However, evaluating the relative role of resource availability on the interactions between lianas and trees from empirical observations is particularly challenging. Previous approaches have used labour-intensive and ecosystem-scale manipulation experiments, which are infeasible in most situations.We propose to circumvent this challenge by evaluating the uncertainty of water and light capture processes of a process-based vegetation model (ED2) including the liana growth form. We further developed the liana plant functional type in ED2 to mechanistically simulate water uptake and transport from roots to leaves, and start the model from prescribed initial conditions. We then used the PEcAn bioinformatics platform to constrain liana parameters and run uncertainty analyses.Baseline runs successfully reproduced ecosystem gas exchange fluxes (gross primary productivity and latent heat) and forest structural features (leaf area index, aboveground biomass) in two sites (Barro Colorado Island, Panama and Paracou, French Guiana) characterized by different rainfall regimes and levels of liana abundance.Model uncertainty analyses revealed that water limitation was the factor driving the competition between trees and lianas at the drier site (BCI), and during the relatively short dry season of the wetter site (Paracou). In young patches, light competition dominated in Paracou but alternated with water competition between the wet and the dry season on BCI according to the model simulations.The modelling workflow also identified key liana traits (photosynthetic quantum efficiency, stomatal regulation parameters, allometric relationships) and processes (water use, respiration, climbing) driving the model uncertainty. They should be considered as priorities for future data acquisition and model development to improve predictions of the carbon dynamics of liana-infested forests. Synthesis. Competition for water plays a larger role in the interaction between lianas and trees than previously hypothesized, as demonstrated by simulations from a process-based vegetation model.

Positive plant–plant interactions are thought to drive vegetation patterns in harsh environments, such as semi-arid areas. According to the stress-gradient hypothesis (SGH), the role of positive interactions between species (facilitation) is expected to increase with harshness, predicting associated variation in species composition along environmental gradients. However, the relation between stress and facilitation along environmental gradients is debated. Furthermore, differentiating facilitative interactions from other underlying mechanisms, such as microtopographic heterogeneity, is not trivial. We analysed the spatial co-occurrence relationships of vascular plant species that form patchy vegetation in arid lapilli fields (tephra) from recent volcanic eruptions on La Palma, Canary Islands. Assuming a harshness gradient negatively correlated with elevation because the lower elevations are more arid and water availability is considered the most limiting resource, and that an outcome of facilitation is plants co-occurring in the same patch, from the SGH we expected a greater degree of co-occurrence at lower elevation. We tested this at both the species and the individual plant level. We analysed the species composition of 1277 shrubby vegetation patches at 64 different sampling points, ranging from the coast to around 700 m a.s.l. Patch morphology and microtopographic heterogeneity variables were also measured, to account for their potential effects on the species composition of patches. We used generalized linear models and generalized mixed-effects models to analyse species richness, number of individuals in patches and percentage of patches with positive co-occurrences, and a pairwise co-occurrence analysis combined with a graphical network analysis to reveal positive links between 13 of the species. We found that the percentage of patches with positive co-occurrences increased at higher elevations, in contrast to the predictions of the SGH, but in accordance with a refined stress-gradient hypothesis for arid sites, in which characteristics of the interacting species are incorporated.

Summary: Covariation of plant functional traits, that is, phenotypic integration, might constrain their variability. This was observed for inter‐ and intraspecific variation, but there is no evidence of a relationship between phenotypic integration and the functional variation within single plants (within‐individual trait variation; WTV), which could be key to understand the extent of WTV in contexts like plant–plant interactions.We studied the relationship between WTV and phenotypic integration in c. 500 trees of 21 species in planted forest patches varying in species richness in subtropical China. Using visible and near‐infrared spectroscopy (Vis‐NIRS), we measured nine leaf morphological and chemical traits. For each tree, we assessed metrics of single and multitrait variation to assess WTV, and we used plant trait network properties based on trait correlations to quantify phenotypic integration.Against expectations, strong phenotypic integration within a tree led to greater variation across leaves. Not only this was true for single traits, but also the dispersion in a tree's multitrait hypervolume was positively associated with tree's phenotypic integration. Surprisingly, we only detected weak influence of the surrounding tree‐species diversity on these relationships.Our study suggests that integrated phenotypes allow the variability of leaf phenotypes within the organism and supports that phenotypic integration prevents maladaptive variation. [ABSTRACT FROM AUTHOR]

As biological invasions increasingly threaten biodiversity, the removal of invasive nonnative species emerges as a possibility to recover the structure and function of native communities. Yet, we have limited knowledge of how communities assemble after nonnative removals. Since most ecosystems are invaded by multiple nonnative species, the impact of their removal likely depends on the interactions among nonnative species which, in turn, are contingent on the environmental context in which they occur.We evaluated the community assembly after the targeted removal of two highly invasive shrubs, Sweetbriar rose (Rosa rubiginosa) and Scotch broom (Cytisus scoparius). The removal was performed at two different times in the growing season (early or late removal) in field and mesocosm communities. In search of general patterns across species, we modelled species responses as a function of their origin (i.e. native/nonnative) and functional traits.We found evidence for negative and asymmetric interactions between dominant invasive species that translated into changes in the abundances of the rest of the species in the community. Depending on the identity of the removed species, the removal of invasive species affected community assembly by promoting other nonnative species or hindering the performance of native species. These effects were modulated by the timing of removal and did not depend on leaf or seed traits.Synthesis. Accounting for nonnative interactions and their temporal dependency should improve our inferences about assembly processes and the effectiveness of nonnative removal aimed at reducing the accumulation of nonnatives. [ABSTRACT FROM AUTHOR]

The ability of native communities to maintain invasion resistance in the face of environmental changes is crucial for biodiversity conservation. However, previous studies have primarily focused on the inhibitive effects experienced by invaders, providing limited insights into the ultimate outcome of resistance.In this study, we integrated modern coexistence theory into biotic resistance research to investigate the impact of nutrient enrichment on the resistance of Phragmites australis marshes to Spartina alterniflora invasion in the Yangtze estuary saltmarshes of China.Our results demonstrated that under non‐enriched conditions, successful invasion resistance was facilitated by stable coexistence between native and invasive species in the field. This prediction of invasion resistance aligned with the distribution dynamics of the two species in the Yangtze estuary saltmarshes over the past two decades. However, nutrient enrichment was likely to lead to a fundamental shift in their coexistence and ultimately, the failure of resistance.Synthesis and applications. Integrating modern coexistence theory into biotic resistance studies advances the assessment of invasion resistance by shifting from quantifying relative strength to predicting explicit resistance outcomes. Ecosystem managers can draw explicit conclusions about the potential establishment and impact of invaders by analysing observational or experimental data within the framework of modern coexistence theory. This information aids in identifying the most efficient strategies for addressing invasive species. [ABSTRACT FROM AUTHOR]

Forest stand densities are increasing in the boreal and temperate biomes, suggesting that tree‐tree competition is intensifying. Anticipating the consequences of this intensified competition is difficult because competition‐induced mortality may depend not only on the occurrence of extreme climatic events such as drought, but also on stand composition, since tree species differ in their ability to compete and tolerate competition. A better understanding of the effects of stand composition and drought on competition‐induced mortality would help to anticipate future changes in forest ecosystems.We studied the tree‐level probability of competition‐induced mortality using National Forest Inventory data from three European countries (Finland, France and Germany), covering a latitudinal gradient from the Mediterranean to the Arctic. We investigated how (i) the proportion of conspecifics, (ii) the shade tolerance (ST) of the focal tree and its competitors and (iii) drought events modify the effect of competition on tree mortality. We used a generalized linear mixed model on a dataset of 461,109 trees representing 39 species on 48,088 individual plots.Competition, measured as the basal area of larger trees, was a stronger driver of background mortality (BM) than tree size and climate. A higher proportion of conspecifics increased the competition effect on mortality, showing that conspecific individuals had a higher competitive effect compared to heterospecific individuals. The competition effect on mortality also increased as a function of the ST of neighbouring trees, suggesting an increased shading effect. A higher ST of a focal tree decreased the competition effect on mortality. Drought anomalies increased the competition effect, resulting in a higher mortality probability for the most suppressed trees.Synthesis. Competition was the main driver of background mortality. Increasing stand density increased competition‐induced tree mortality in both monospecific and mixed stands, but to different extents depending on the proportion of conspecifics and tree species shade tolerance (ST). Drought periods increase mortality, especially among the most suppressed trees, suggesting an interaction between competitive status and drought. Incorporating more detailed information on stand composition and tree species ST into tree mortality models will improve our understanding of forest dynamics in a changing climate. [ABSTRACT FROM AUTHOR]

The plant economics spectrum (PES) drives nutrient cycling through effects on soil decomposers. However, dead phytomass may remain standing or unshed (marcescent), hardly accessible to decomposers and be photodegraded. In arid zones, the significant part of marcescent phytomass can be decomposed without touching the ground. In temperate zones, photodegradation of marcescent phytomass is low but prompts important chemical changes, which affect its subsequent decomposability in the soil and alters the surrounding environment. It is unknown, however, how common marcescence is among different taxa and in which habitats, and how it is coordinated by PES traits.We sampled standing (marcescent) and lying (shed) dead phytomass from a broad spectrum of 127 herbaceous temperate species in a common garden experiment and related these parameters to PES traits, species ecological preferences and phylogeny.Nearly all species (97%) kept their phytomass marcescent. Tall species with a small leaf area and high leaf carbon had a high level of marcescence. Marcescent species also preferred sites affected by severe (but not necessarily frequent) disturbance. The degree of marcescence was considerably conserved in phylogeny.Synthesis. Marcescence extends PES trait effects on ecosystems, particularly in immature habitats, being a common but overlooked phenomenon of the temperate flora. [ABSTRACT FROM AUTHOR]