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This article discusses the concept of ecological intensification of agriculture through biodiversity management. It explains that humans have been able to achieve higher population densities than other animals due to the invention of agriculture, which allows for the conversion of biomass into food. However, modern industrial agriculture has led to negative effects on the environment, such as pollution, soil fertility loss, and biodiversity loss. The article highlights the positive relationship between biodiversity and plant biomass production in agroecosystems and explores various applications of biodiversity in agriculture, including genetic diversity within crops, mixed cropping, and field border plant diversity. It also discusses obstacles to implementing ecological intensification, such as lack of knowledge and inappropriate incentives. The article concludes by providing a list of literature reviews that readers can use as a starting point for further research on the topic. [Extracted from the article]

Inspired by grassland biodiversity experiments studying the impact of plant diversity on primary productivity, the Crop Diversity Experiment setup in 2018 aimed at testing whether these biodiversity benefits also hold for annual crop systems and whether crop mixtures also achieved transgressive overyielding, i.e. yield in mixture that was higher than the most productive monoculture. The first 3 years of the experiment demonstrated that crop mixtures do not only increase yield compared with an average monoculture but often also compared with the highest yielding monoculture. The crop diversity effects were stronger under more stressful environmental conditions and were often achieved in mixtures with legume crops. However, we observed transgressive overyielding also under favorable conditions and in mixtures without legumes. With our investigation of the underlying mechanisms of the yield benefits we found both direct complementarities between crop species and indirect effects via other organisms. The former included chemical, spatial and temporal complementarity in N uptake, complementary root distribution leading to complementary water uptake, as well as spatial and temporal complementarity in light use. Among the indirect mechanisms we identified complementary suppression of weeds and more abundant plant growth-promoting microbes in crop mixtures, apart from complementarity in pest and disease suppression not yet studied in the Crop Diversity Experiment but demonstrated elsewhere. In consequence, the Crop Diversity Experiment supports not only the assumption that the ecological processes identified in biodiversity experiments also hold in crop systems, but that diversification of arable crop systems provides a valuable tool to sustainably produce food. [ABSTRACT FROM AUTHOR]

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Increasing plant diversity in agricultural systems provides promising solutions for sustainably increasing crop yield. It remains unclear; however, how plant–plant interactions in diverse systems are mediated by plant genetic variation. We conducted a greenhouse experiment in which we grew three varieties of common beans with three companion plant species (chickpeas, sorghum, and sunflower) in different combinations (crop mixtures, bean cultivar mixtures, and monocultures), with and without drought stress. We hypothesized that under drought stress, the effect of companion plant species on bean yield would be mediated by the drought tolerance potential of the species. We further hypothesized that this effect would vary across different bean cultivars. Overall, we show that the effect of companion plant species on bean yield was not influenced by drought stress; instead, it was dependent on the identity of the bean variety. This could partially be explained by variation in growth rate between bean varieties, where the fastest growing variety recorded the highest yield increase in plant mixtures. The effect of companion plant species on chickpea biomass, however, was potentially influenced by chickpea drought tolerance potential; chickpea biomass was recorded to be higher in plant mixtures than in its monoculture under drought conditions. Our study highlights that to develop plant mixtures, it is not only important to consider the functional traits of the interacting plant species, but also those of the different plant varieties. We further suggest that stress tolerance can be a useful trait for initial selection of plant varieties when developing crop mixtures. [ABSTRACT FROM AUTHOR]

Enhancing diversity within crop systems can have benefits including increased resource use efficiency and productivity, and increased control of weeds, pests and diseases. Some benefits are expected to operate through biodiversity-driven insurance effects, whereby enhanced diversity increases the chance that a system component can compensate for the impacts of adverse environmental conditions. Studies of insurance effects in natural and agricultural systems have provided equivocal results. As insurance effects are expected to play a key role in helping to maintain crop production in more variable future climates (for example under periodic drought), it is essential to know when and how they operate and interact with other potentially beneficial biodiversity-function effects. Using barley as a model crop, and pot-based plant communities, we studied the interactive effects of barley cultivar diversity and drought stress on plant productivity and the response of agricultural weeds, fungal disease, and aphids. Drought reduced barley and weed biomass, but there were no interactive effects of drought and cultivar diversity on plant productivity. Increased cultivar diversity enhanced weed suppression, potentially as a result of reduced functional space availability, and reduced disease severity on a susceptible cultivar; these effects were consistent irrespective of drought. Aphid responses were more complex, with idiosyncratic response patterns on individual cultivars. Overall, we found no evidence of an insurance effect of enhanced cultivar diversity for the negative impact of drought on crop productivity, but our results indicate that other positive biodiversity effects (weed and disease suppression) are maintained under drought. However, it is clear that not all potentially-beneficial biodiversity effects respond in the same manner. Field trials are now needed to explore whether a range of responses also occur in crop field settings, whether these can be expected to occur predictably under a range of environmental conditions, and how these then impact on crop production. [ABSTRACT FROM AUTHOR]

• High-elevation environments in the Himalayas are stressful for plant life. • Himalayan endemic Berberis angulosa is a nurse shrub that facilitates beneficiary species. • Facilitation by Berberis shrubs promotes plant diversity, and protects high-value and threatened medicinal species. • The nurse shrub plays a critical role in structuring plant communities in high-elevation Himalayas. Facilitation is a global phenomenon that occurs when one species promotes the growth, survival, or reproduction of another species, mostly in stressful environments. However, the importance of facilitation by shrubs in maintaining plant community diversity is not well evaluated in the Himalayas, especially for the richness and conservation of medicinal and human-valued species. Therefore, we aimed to explore the facilitative role of a dwarf shrub species, Berberis angulosa , in maintaining plant composition and richness of human-valued species in the Langtang valley of Nepal's Himalayas. We censused plant species in open patches and beneath Berberis during monsoon and post-monsoon (dry) seasons at three elevations. Total species richness and richness of human-valued species were significantly higher inside the Berberis canopy than in gaps; the former being 39% and the latter 46% greater under shrubs than in open sites. Facilitation by Berberis shrubs promoted plant community diversity irrespective of season and elevation; however, higher differences in mean species richness for both total plant species and human-valued species during the dry season and at high elevation indicated increased facilitation intensity under more stressful conditions. The facilitative effect of Berberis shrubs increased, combining both seasons, overall plant diversity by 19% (total=105), and human-valued species by 16% (total=56). Our results show the importance of facilitation by nurse shrubs in structuring plant communities and protecting medicinal and socio-ecologically important plants, thus enriching ecosystem services in the Himalayas. These results suggest nurse plant species should be incorporated into conservation policies and management strategies for effective biodiversity conservation and sustainability, especially in the face of climate change. [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]

Intensive agriculture has major negative impacts on ecosystem diversity and functioning, including that of soils. The associated reduction of soil biodiversity and essential soil functions, such as nutrient cycling, can restrict plant growth and crop yield. By increasing plant diversity in agricultural systems, intercropping could be a promising way to foster soil microbial diversity and functioning. However, plant–microbe interactions and the extent to which they influence crop yield under field conditions are still poorly understood. In this study, we performed an extensive intercropping experiment using eight crop species and 40 different crop mixtures to investigate how crop diversity affects soil microbial diversity and activity, and whether these changes subsequently affect crop yield. Experiments were carried out in mesocosms under natural conditions in Switzerland and in Spain, two countries with drastically different soils and climate, and our crop communities included either one, two or four species. We sampled and sequenced soil microbial DNA to assess soil microbial diversity, and measured soil basal respiration as a proxy for soil activity. Results indicate that in Switzerland, increasing crop diversity led to shifts in soil microbial community composition, and in particular to an increase of several plant-growth promoting microbes, such as members of the bacterial phylum Actinobacteria. These shifts in community composition subsequently led to a 15 and 35% increase in crop yield in 2 and 4-species mixtures, respectively. This suggests that the positive effects of crop diversity on crop productivity can partially be explained by changes in soil microbial composition. However, the effects of crop diversity on soil microbes were relatively small compared to the effects of abiotic factors such as fertilization (three times larger) or soil moisture (three times larger). Furthermore, these processes were context-dependent: in Spain, where resources were limited, soil microbial communities did not respond to crop diversity, and their effect on crop yield was less strong. This research highlights the potential beneficial role of soil microbial communities in intercropping systems, while also reflecting on the relative importance of crop diversity compared to abiotic drivers of microbiomes and emphasizing the context-dependence of crop–microbe relationships. [ABSTRACT FROM AUTHOR]

Biological diversity depends on multiple, cooccurring ecological interactions. However, most studies focus on one interaction type at a time, leaving community ecologists unsure of how positive and negative associations among species combine to influence biodiversity patterns. Using surveys of plant populations in alpine communities worldwide, we explore patterns of positive and negative associations among triads of species (modules) and their relationship to local biodiversity. Three modules, each incorporating both positive and negative associations, were overrepresented, thus acting as "network motifs." Furthermore, the overrepresentation of these network motifs is positively linked to species diversity globally. A theoretical model illustrates that these network motifs, based on competition between facilitated species or facilitation between inferior competitors, increase local persistence. Our findings suggest that the interplay of competition and facilitation is crucial for maintaining biodiversity. [ABSTRACT FROM AUTHOR]

Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant–insect interaction analysis and variance partitioning of biodiversity effects. We present a case‐study experiment in which facilitation by a cushion‐plant species and a dwarf‐shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects. [ABSTRACT FROM AUTHOR]

Plant diversity fosters productivity in natural ecosystems. Biodiversity effects might increase agricultural yields at no cost in additional inputs. However, the effects of diversity on crop assemblages are inconsistent, probably because crops and wild plants differ in a range of traits relevant to plant–plant interactions. We tested whether domestication has changed the potential of crop mixtures to over‐yield by comparing the performance and traits of major crop species and those of their wild progenitors under varying levels of diversity. We found stronger biodiversity effects in mixtures of wild progenitors, due to larger selection effects. Variation in selection effects was partly explained by within‐mixture differences in leaf size. Our results indicate that domestication might disrupt the ability of crops to benefit from diverse neighbourhoods via reduced trait variance. These results highlight potential limitations of current crop mixtures to over‐yield and the potential of breeding to re‐establish variance and increase mixture performance. [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]

Arenaria polytrichoides (Caryophyllaceae) is a common cushion plant occurring at high elevations in the Himalaya-Hengduan Mountains, SW China. It frequently has other non-cushion species growing within its canopy, forming a contrast with the surrounding areas because it creates patches of higher diversity and greater biomass. In this study, we examined the relationship between the cushions and associated noncushion species along a gradient of cushion size. A total of 200 A. polytrichoides individuals were selected to fit four size classes. Field measurements were carried out to assess canopy structure, functional traits relevant to growth and reproduction, and soil quality below cushions along the size gradient. Furthermore, the size effect of cushions on the richness and abundance of species and biomass production was also examined. All the morphological variables examined exhibited a positive correlation with cushion size, as did the nutrients under cushions. Large and compact cushions were associated with higher soil nutrient contents compared with small and loose cushions. As a result of these biogenic environmental changes, there was a stronger facilitation effect performed by large cushions. Data pertaining to functional traits revealed that large cushions benefit from the enhanced resources within their compact structure and exhibit greater fitness and a higher reproductive output than small cushions. Our data indicated that interactions occur between cushion species and other plants depending on the size of the cushions, probably because of the greater heterogeneity of conditions beneath larger cushions. These findings provide a clear demonstration of the generally overlooked importance of the traits of nurse plants, such as size and age, in terms of their facilitative effects. [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]

In alpine environments facilitator species buffer environmental extremes while building up soil resources above that of open areas. These modulating effects are critical for the persistence of species out of their optimal range and contribute to increase community-level plant species richness and phylogenetic diversity. We analyzed the effects of seven potential facilitator species with contrasting morphologies on subordinate plant species along a crossed environmental gradient, linking such effects to canopy effects. We also used these patches consisting of multiple shrub species to evaluate the effects of the whole shrub community on species richness and phylogenetic diversity, and whether such shrub community effects differed along the gradient. We used ecological and phylogenetic data of alpine plant communities along two altitudinal gradients on opposing aspects of the Sierra Nevada Mountains (Spain). As expected, shrubs buffered harsh abiotic conditions by decreasing mean temperatures and increasing relative humidity with regard to open areas. Composition of subordinate plant communities differed among shrubs and among sites, and correlated with relative humidity along the gradient pointing to the dependence of subordinate species on micro-environments created by shrubs. There were a variety of shrub effects on overall plant abundance and richness depending on shrub identity. In the most extreme sites we recorded generally positive effects of the shrub community, which promoted whole-community species richness and phylogenetic diversity despite species-specific effects ranging from clearly negative to positive. Our data therefore show that the effect of different shrub species on plant community richness and phylogenetic diversity is not redundant, as every shrub species may host unique communities, thereby affecting the structure and composition of the whole community. [ABSTRACT FROM AUTHOR]

Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a 'safety net' sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change. [ABSTRACT FROM AUTHOR]

By capitalising on positive biodiversity--productivity relationships, intercropping provides opportunities to improve agricultural sustainability. Intercropping is generally implemented using commercial seeds that were bred for maximal productivity in monocultures, thereby ignoring the ability of plants to adapt over generations to the surrounding neighbourhood, notably through increased complementarity, that is reduced competition or increased facilitation. This is why using monoculture- adapted seeds for intercropping might limit the benefits of crop diversity on yield. However, the adaptation potential of crops and the corresponding changes in complementarity have not been explored in annual crop systems. Here we show that plant--plant interactions among annual crops shifted towards reduced competition and/or increased facilitation when the plants were growing in the same community type as their parents did in the previous two generations. Total yield did not respond to this common coexistence history, but in fertilized conditions, we observed increased overyielding in mixtures with a common coexistence history. Surprisingly, we observed character convergence between species sharing the same coexistence history for two generations, in monocultures but also in mixtures: the six crop species tested converged towards taller phenotypes with lower leaf dry matter content. This study provides the first empirical evidence for the potential of parental diversity affecting plant--plant interactions, species complementarity and therefore potentially ecosystem functioning of the following generations in annual cropping systems. Although further studies are required to assess the context--dependence of these results, our findings may still have important implications for diversified agriculture as they illustrate the potential of targeted cultivars to increase complementarity of species in intercropping, which could be achieved through specific breeding for mixtures. [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]