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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]

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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]

Facilitation by nurse plants increases understorey diversity and supports ecological communities. In turn, biodiversity shapes ecological networks and enhances ecosystem functioning. However, whether and how facilitation and increased biodiversity jointly influence community structure and ecosystem functioning remains unclear.We performed a field experiment disentangling the relative contribution of nurse plants and increasing understorey plant diversity in driving pollination interactions. Both the presence of nurse shrubs and increased understorey plant diversity increased pollinator diversity and visitation rates. While nurse and understorey diversity effects on pollinator visitation rates did not interact, the effects of increasing understorey plant diversity on pollinator diversity were stronger in the absence than in the presence of shrubs, meaning that nurse shrubs attenuated the effects of high understorey diversity and buffered the effects of low understorey diversity.We also found positive complementarity effects among understorey species as well as complementarity between nurse plants and understorey species at high diversity. Results also indicate negative selection effects, suggesting that species with generally few pollinators benefit the most in the polyculture while a species (possibly the nurse plant) with generally lots of pollinators does not. The corresponding changes in pollination networks with the experimental treatments were due to both changes in the frequency of visits and turnover in pollinator community composition.Synthesis. Plant–plant facilitative systems, where a nurse plant increases understorey plant diversity, are common in stressful environments. Here, we show that these facilitative systems positively influence mutualistic interactions with pollinators via both direct nurse effects and indirect positive effects of increasing plant diversity. Conserving and supporting nurse plant systems is crucial not only for maintaining plant diversity but also for supporting ecosystem functions and services. [ABSTRACT FROM AUTHOR]

We review the need for increasing agricultural sustainability, how this can in part be delivered by positive biodiversity–ecosystem function (BEF) effects, the role within these of plant–plant facilitation, and how a better understanding of this role may help to deliver sustainable crop (particularly arable) production systems.Major challenges facing intensive arable production include overall declines in biodiversity, poor soil structure and health, nutrient and soil particle run‐off, high greenhouse gas emissions, and increasing costs of synthetic inputs including herbicides, pesticides and fertilisers.Biodiversity–ecosystem function effects have the potential to deliver win–wins for arable food production, whereby enhanced biodiversity is associated with 'good outcomes' for farming sustainability, albeit sometimes through negative BEF effects for some components of the system. Although it can be difficult to separate explicitly from niche differentiation, evidence indicates facilitation can be a key component of these BEF effects.Explicit recognition of facilitation's role brings benefits to developing sustainable crop systems. First, it allows us to link fundamental ecological studies on the evolution of facilitation to the selection of traits that can enhance functioning in crop mixtures. Second, it provides us with analytical frameworks which can be used to bring structure and testable hypotheses to data derived from multiple (often independent) crop trials.Before concrete guidance can be provided to the agricultural sector as to how facilitation might be enhanced in crop systems, challenges exist with respect to quantifying facilitation, understanding the traits that maximise facilitation and integrating these traits into breeding programmes, components of an approach we suggest could be termed 'Functional Ecological Selection'.Synthesis. Ultimately, better integration between ecologists and crop scientists will be essential in harnessing the benefits of ecological knowledge for developing more sustainable agriculture. We need to focus on understanding the mechanistic basis of strong facilitative interactions in crop systems and using this information to select and breed for improved combinations of genotypes and species as part of the Functional Ecological Selection approach. [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]