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

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

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]

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]

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]