Search

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]

More diverse plant communities are generally more productive than monocultures. This benefit of species diversity is supposed to stem from resource partitioning of species in mixtures where different species use the resources spatially, temporally, or chemically in distinct ways. With respect to water, the simultaneous cultivation of crops with distinct water uptake patterns might reduce niche overlaps and thus result in higher productivity. However, little is known about whether and how spatial water uptake patterns of crop species differ among different planting arrangements and whether these changes result in increased niche partitioning and explain overyielding in mixtures.Stable isotopes of water and a Bayesian model were used to investigate the spatial water uptake patterns of six different crop species and how these patterns change depending on the planting arrangement (monocultures vs mixtures). Niche overlaps and niche widths in spatial water uptake were compared among the different crop diversity levels and linked to productivity. Furthermore, spatial water uptake was related to competition intensity and overyielding in mixtures.We found evidence for increased niche partitioning in spatial water uptake, and therefore complementary spatial root distributions of crop species, and higher expected productivity in mixtures compared to expected productivity in monocultures both due to inherent species‐level differences in water uptake and plasticity in the water uptake pattern of species. We also found a significant relationship of competition and overyielding with observed patterns in spatial water uptake. These results suggest that competition was most intense in shallow soil layers and enhanced overyielding was related to a gradual increase of water uptake in deeper soil layers. Thus, overyielding might be related to a more complete spatial exploitation of available water sources.Synthesis. Differences in spatial water uptake and niche partitioning of intercropped species, driven most likely by a complementary spatial root distribution, might explain why mixtures outperform monocultures. These findings underpin the potential of intercropping systems for a more sustainable agriculture with a more efficient use of soil resources and hence reduced input demands. [ABSTRACT FROM AUTHOR]

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

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

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

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

Facilitation is known as the positive effect of one species (benefactor) on associated neighbouring species (beneficiaries). Although the beneficial part of this interaction has received considerable research interest, there is a gap of knowledge on the bidirectional nature of these interactions; in particular, the physiological and fitness consequences for both beneficiaries and benefactors., Alpine cushion plants are generally strong benefactors, increasing species richness and abundance on a global scale, and provide a suitable system to study the physiological effects of bidirectional interactions and its consequences for reproduction. Current knowledge suggests that species improve their fitness when associated to a benefactor cushion species, whereas cushions may receive predominantly negative feedbacks., We measured physiological and reproductive traits of the cushion species Arenaria tetraquetra ssp. amabilis and three other forbs ( Eryngium glaciale, Lotus corniculatus ssp. glacialis and Plantago nivalis) in the dry Sierra Nevada Mountains, southern Spain. All four species were studied either when growing alone or when the three forbs were associated with the cushion plant., The three forb species improved their water status when associated with the cushion, and Lotus and Plantago significantly increased their seed set. In contrast, Arenaria showed poorer water status and reduced flower density and seed set with increasing cover of beneficiary species. There was a clear relationship between physiological and reproductive traits in Arenaria growing without beneficiaries but not in Arenaria with beneficiaries. Control cushions (without beneficiary species) showed increased seed set and seed mass with increasing photosynthetic and water use efficiencies, respectively, the latter being positively related to leaf nitrogen content. In contrast, cushions with a large cover of beneficiary species did not show such relations. The missing relationship between physiological and reproductive traits for these facilitating cushions indicates that reproductive output in heavily colonized cushions may not be directly related to the plant physiological status and the availability of resources., Our results revealed the antagonistic behaviour underlying the interaction between beneficiary species and facilitating cushion plants, similar to parasitic interactions. They also provide indications for changes in cushions' resource allocation pattern in response to colonization by beneficiaries. [ABSTRACT FROM AUTHOR]

Facilitative interactions are defined as positive effects of one species on another, but bidirectional feedbacks may be positive, neutral, or negative. Understanding the bidirectional nature of these interactions is a fundamental prerequisite for the assessment of the potential evolutionary consequences of facilitation., In a global study combining observational and experimental approaches, we quantified the impact of the cover and richness of species associated with alpine cushion plants on reproductive traits of the benefactor cushions., We found a decline in cushion seed production with increasing cover of cushion-associated species, indicating that being a benefactor came at an overall cost. The effect of cushion-associated species was negative for flower density and seed set of cushions, but not for fruit set and seed quality. Richness of cushion-associated species had positive effects on seed density and modulated the effects of their abundance on flower density and fruit set, indicating that the costs and benefits of harboring associated species depend on the composition of the plant assemblage., Our study demonstrates 'parasitic' interactions among plants over a wide range of species and environments in alpine systems, and we consider their implications for the possible selective effects of interactions between benefactor and beneficiary species. [ABSTRACT FROM AUTHOR]

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

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

Abstract: The impact of plant–plant interactions on species diversity patterns has been broadly addressed in stressful environments, such as alpine ecosystems, where foundation species promote species richness by creating habitat for other species. However, foundation species with contrasting phenotypes might modify the microhabitat differently, which would alter the subordinate community composition, and coincide with distinct feedback effects of those subordinate species on the foundation species. However, the precise interaction mechanisms that facilitate species are not fully understood, especially the relative contribution of above‐ and below‐ground compartments of foundation species to subordinate species and the potential feedbacks they receive. We explored whether two contrasted canopy phenotypes (tight and loose) of the shrub Cytisus galianoi differed in their effects on the microhabitat and on subordinate plant community composition in a dry subalpine system. We also experimentally distinguished the relative contribution of above‐ (canopy) and below‐ground (soil) effects of C. galianoi on the most frequent subordinate species, Festuca indigesta, as well as the reciprocal effects of F. indigesta on C. galianoi. We performed observational and manipulative experiments to assess the influence of phenotypic differences of the shrub on understorey microhabitat and subordinate plant community composition. Reciprocal effects were assessed by removing either F. indigesta from the understorey of the two shrub phenotypes or the C. galianoi canopy from the immediate vicinity of F. indigesta. The two C. galianoi phenotypes differed in mean values of functional traits (like stem density or plant height), modified their understorey microhabitats differently and hosted distinct subordinate communities. Loose phenotypes had more positive effects on community composition and diversity than tight phenotypes. In addition, tight phenotypes simultaneously showed both more positive above‐ground and more negative below‐ground effects on F. indigesta than loose phenotypes. There were no significant feedback effects of F. indigesta on C. galianoi. The two phenotypes of the foundation species C. galianoi showed contrasting effects on the subordinate plant community: Compared to the tight phenotype, the loose phenotype had higher associated species diversity and reduced reciprocal interaction intensities above‐ and below‐ground with the subordinate species F. indigesta. This highlights the impact of phenotypic variation for plant interactions and community‐level diversity. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

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

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

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

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

Understanding the mechanisms of community assembly may provide evidence to improve crop management, and in particular how weeds impact on crop yields. Focussing on plant functional traits and their diversity, we analysed a crop–weed interaction study with different levels of weed species and barley cultivar diversity to assess how weed species and barley cultivars respond to competition. Pre-emption of light resources by the taller barley did not impact on the weeds, with both weeds and barley showing similar order of magnitude shifts in height, specific leaf area and leaf dry matter content in response to crop–weed competition. These shifts were to a more conservative growth pattern, and suggest in this study a greater importance of below- than above-ground interactions in driving trait responses. The mixture of barley cultivars shifted the weeds to a more conservative growth pattern compared to the cultivar monocultures. The results indicate that cultivar mixtures could result in less need for weed control in arable fields, and possibly that the development of complementary cultivar mixtures could reinforce this effect. This confirms the results of other studies which show that mixtures either improve yields or make yields less variable in response to weed competition. [ABSTRACT FROM AUTHOR]

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