Mycorrhiza in tree diversity-ecosystem function relationships: conceptual framework and experimental implementation

Mycorrhizal type and tree diversity affect foliar elemental pools and stoichiometry

Species-specific differences in nutrient acquisition strategies allow for complementary use of resources among plants in mixtures, which may be further shaped by mycorrhizal associations. However, empirical evidence of this potential role of mycorrhizae is scarce, particularly for tree communities. We investigated the impact of tree species richness and mycorrhizal types, arbuscular mycorrhizal fungi (AM) and ectomycorrhizal fungi (EM), on above- and belowground carbon (C), nitrogen (N), and phosphorus (P) dynamics. Soil and soil microbial biomass elemental dynamics showed weak responses to tree species richness and none to mycorrhizal type. However, foliar elemental concentrations, stoichiometry, and pools were significantly affected by both treatments. Tree species richness increased foliar C and P pools but not N pools. Additive partitioning analyses showed that net biodiversity effects of foliar C, N, P pools in EM tree communities were driven by selection effects, but in mixtures of both mycorrhizal types by complementarity effects. Furthermore, increased tree species richness reduced soil nitrate availability, over 2 yr. Our results indicate that positive effects of tree diversity on aboveground nutrient storage are mediated by complementary mycorrhizal strategies and highlight the importance of using mixtures composed of tree species with different types of mycorrhizae to achieve more multifunctional afforestation.

Tree diversity increases productivity through enhancing structural complexity across mycorrhizal types

Tree species diversity and mycorrhizal associations play a central role for forest productivity, but factors driving positive biodiversity-productivity relationships remain poorly understood. In a biodiversity experiment manipulating tree diversity and mycorrhizal associations, we examined the roles of above- and belowground processes in modulating wood productivity in young temperate tree communities and potential underlying mechanisms. We found that tree species richness, but not mycorrhizal associations, increased forest productivity by enhancing aboveground structural complexity within communities. Structurally complex communities were almost twice as productive as structurally simple stands, particularly when light interception was high. We further demonstrate that overyielding was largely explained by positive net biodiversity effects on structural complexity with functional variation in shade tolerance and taxonomic diversity being key drivers of structural complexity in mixtures. Consideration of stand structural complexity appears to be a crucial element in predicting carbon sequestration in the early successional stages of mixed-species forests.

Temporal variation of mycorrhization rates in a tree diversity experiment

While mycorrhization rates have been studied in different contexts, not much is known about their temporal patterns across seasons. Here, we asked how mycorrhization rates of 10 deciduous trees assessed by microscopy changed from winter to spring to early summer. We made use of a tree diversity experiment on nutrient-rich soil (former farmland) in Central Germany. In the experiment, saplings of host species with a preference for either arbuscular mycorrhiza (AM) or ectomycorrhiza (EM) were planted in monocultures, two-species, and four-species mixtures. In addition, mixtures were composed of tree species of only one mycorrhizal type or by AM/EM trees. For almost all species, with the exception of Aesculus hippocastanum and Acer pseudoplatanus (only AM), dual mycorrhization with both types (AM and EM) was found at every sampling time (December, March, and May), although the expected preferences for certain mycorrhizal types were confirmed. The sampling date had a significant influence on mycorrhization rates of both EM and AM tree species. Frequencies of EM and AM were lowest in May, but there were no differences between December and March. The causes of this seasonal variation may be associated with climate-induced differences in carbon allocation to mycorrhizal tree roots in the temperate climate. Within individual trees, mycorrhization rates by AM and EM fungi were not correlated over time, pointing to asynchronous variation between both types and to independent drivers for AM and EM mycorrhization. At the community level, mycorrhiza frequency of either of the two types became more asynchronous from two-species to four-species mixtures. Thus, increased community asynchrony in mycorrhization could be another important mechanism in biodiversity-ecosystem functioning relationships.

Higher productivity in forests with mixed mycorrhizal strategies

Decades of theory and empirical studies have demonstrated links between biodiversity and ecosystem functioning, yet the putative processes that underlie these patterns remain elusive. This is especially true for forest ecosystems, where the functional traits of plant species are challenging to quantify. We analyzed 74,563 forest inventory plots that span 35 ecoregions in the contiguous USA and found that in ~77% of the ecoregions mixed mycorrhizal plots were more productive than plots where either arbuscular or ectomycorrhizal fungal-associated tree species were dominant. Moreover, the positive effects of mixing mycorrhizal strategies on forest productivity were more pronounced at low than high tree species richness. We conclude that at low richness different mycorrhizal strategies may allow tree species to partition nutrient uptake and thus can increase community productivity, whereas at high richness other dimensions of functional diversity can enhance resource partitioning and community productivity. Our findings highlight the importance of mixed mycorrhizal strategies, in addition to that of taxonomic diversity in general, for maintaining ecosystem functioning in forests.

Exclosure (or what we risk losing)

This is a story of becoming. In this creative non-fiction essay, I share a case study of an informal science program for high school aged youth that took place over 5-weeks one summer in an urban park in Pittsburgh, PA, USA. I conducted observations, interviews, and artifact analysis to explore how youth environmental interest and identity developed through relational processes between human and more-than-human beings. As a participant-observer, I tried to focus my attention on learning about learning. But I kept getting pulled from my research to something bigger, something messier. In my essay, I reflect on what it meant for our small group to become naturalists together, juxtaposing the diversity of our human cultures/histories/languages/selves with the diversity of the park, from the soil to the tree canopy. I then draw intimate connections between the twin losses of biological and cultural diversity. By using narrative storytelling, I invite the reader to come on a journey with me through the story of my own ideas, the ideas of the youth and educators I worked with, and the story of the land itself.

Tree diversity effects on productivity depend on mycorrhizae and life strategies in a temperate forest experiment

Tree species are known to predominantly interact either with arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. However, there is a knowledge gap regarding whether these mycorrhizae differently influence biodiversity-ecosystem functioning (BEF) relationships and whether a combination of both can increase community productivity. In 2015, we established a tree-diversity experiment by growing tree communities with varying species richness levels (one, two, or four species) and either with AM or EM tree species or a combination of both. We investigated basal area and annual basal area increment from 2015 to 2020 as proxies for community productivity. We found significant positive relationships between tree species richness and community productivity, which strengthened over time. Further, AM and EM tree species differently influenced productivity; however, there was no overyielding when AM and EM trees grew together. EM tree communities were characterized by low productivity in the beginning but an increase of increment over time and showed overall strong biodiversity effects. For AM tree communities the opposite was true. Although young trees did not benefit from the presence of the other mycorrhizal type, dissimilar mechanisms underlying BEF relationships in AM and EM trees indicate that maximizing tree and mycorrhizal diversity may increase ecosystem functioning in the long run.

Differences in Density Dependence among Tree Mycorrhizal Types Affect Tree Species Diversity and Relative Growth Rates

Conspecific negative density dependence (CNDD) may vary by tree mycorrhizal type. However, whether arbuscular mycorrhizal (AM)-associated tree species suffer from stronger CNDD than ectomycorrhizal (EcM) and ericoid mycorrhizal (ErM)-associated tree species at different tree life stages, and whether EcM tree species can promote AM and ErM saplings and adults growth, remain to be studied. Based on the subtropical evergreen broad-leaved forest data in eastern China, the generalized linear mixed-effects model was used to analyze the effects of the conspecific density and heterospecific density grouped by symbiont mycorrhizal type on different tree life stages of different tree mycorrhizal types. The results showed that compared to other tree mycorrhizal types at the same growth stage, EcM saplings and AM adults experienced stronger CNDD. Heterospecific EcM density had a stronger positive effect on AM and ErM individuals. Species diversity and average relative growth rate (RGR) first increased and then decreased with increasing basal area (BA) ratios of EcM to AM tree species. These results suggested that the stronger CNDD of EcM saplings and AM adults favored local species diversity over other tree mycorrhizal types. The EcM tree species better facilitated the growth of AM and ErM tree species in the neighborhood, increasing the forest carbon sink rate. Interestingly, species diversity and average RGR decreased when EcM or AM tree species predominated. Therefore, our study highlights that manipulating the BA ratio of EcM to AM tree species will play a nonnegligible role in maintaining biodiversity and increasing forest carbon sink rates.

Biotic Interactions as Mediators of Context-Dependent Biodiversity-Ecosystem Functioning Relationships

Biodiversity drives the maintenance and stability of ecosystem functioning as well as many of nature’s benefits to people, yet people cause substantial biodiversity change. Despite broad consensus about a positive relationship between biodiversity and ecosystem functioning (BEF), the underlying mechanisms and their context-dependencies are not well understood. This proposal, submitted to the European Research Council (ERC), aims at filling this knowledge gap by providing a novel conceptual framework for integrating biotic interactions across guilds of organisms, i.e. plants and mycorrhizal fungi, to explain the ecosystem consequences of biodiversity change. The overarching hypothesis is that EF increases when more tree species associate with functionally dissimilar mycorrhizal fungi. Taking a whole-ecosystem perspective, we propose to explore the role of tree-mycorrhiza interactions in driving BEF across environmental contexts and how this relates to nutrient dynamics. Given the significant role that mycorrhizae play in soil nutrient and water uptake, BEF relationships will be investigated under normal and drought conditions. Resulting ecosystem consequences will be explored by studying main energy channels and ecosystem multifunctionality using food web energy fluxes and by assessing carbon storage. Synthesising drivers of biotic interactions will allow us to understand context-dependent BEF relationships. This interdisciplinary and integrative project spans the whole gradient from local-scale process assessments to global relationships by building on unique experimental infrastructures like the MyDiv Experiment, iDiv Ecotron and the global network TreeDivNet, to link ecological mechanisms to reforestation initiatives. This innovative combination of basic scientific research with real-world interventions links trait-based community ecology, global change research and ecosystem ecology, pioneering a new generation of BEF research and represents a significant step towards implementing BEF theory for human needs.

Coupling of plant and mycorrhizal fungal diversity: its occurrence, relevance, and possible implications under global change

First principles predict that diversity at one trophic level often begets diversity at other levels, suggesting plant and mycorrhizal fungal diversity should be coupled. Local-scale studies have shown positive coupling between the two, but the association is less consistent when extended to larger spatial and temporal scales. These inconsistencies are likely due to divergent relationships of different mycorrhizal fungal guilds to plant diversity, scale dependency, and a lack of coordinated sampling efforts. Given that mycorrhizal fungi play a central role in plant productivity and nutrient cycling, as well as ecosystem responses to global change, an improved understanding of the coupling between plant and mycorrhizal fungal diversity across scales will reduce uncertainties in predicting the ecosystem consequences of species gains and losses.

Advanced research tools for fungal diversity and its impact on forest ecosystem

Fungi are dominant ecological participants in the forest ecosystems, which play a major role in recycling organic matter and channeling nutrients across trophic levels. Fungal populations are shaped by plant communities and environmental parameters, and in turn, fungal communities also impact the forest ecosystem through intrinsic participation of different fungal guilds. Mycorrhizal fungi result in conservation and stability of forest ecosystem, while pathogenic fungi can bring change in forest ecosystem, by replacing the dominant plant species with new or exotic plant species. Saprotrophic fungi, being ecological regulators in the forest ecosystem, convert dead tree logs into reusable constituents and complete the ecological cycles of nitrogen and carbon. However, fungal communities have not been studied in-depth with respect to functional, spatiotemporal, or environmental parameters. Previously, fungal diversity and its role in shaping the forest ecosystem were studied by traditional and laborious cultural methods, which were unable to achieve real-time results and draw a conclusive picture of fungal communities. This review highlights the latest advances in biological methods such as next-generation sequencing and meta'omics for observing fungal diversity in the forest ecosystem, the role of different fungal groups in shaping forest ecosystem, forest productivity, and nutrient cycling at global scales.

Tree species rather than type of mycorrhizal association drive inorganic and organic nitrogen acquisition in tree-tree interactions

Mycorrhizal fungi play an important role for the nitrogen (N) supply of trees. The influence of different mycorrhizal types on N acquisition in tree-tree interactions is, however, not well understood, particularly with regard to the competition for growth-limiting N. We studied the effect of competition between temperate forest tree species on their inorganic and organic N acquisition in relation to their mycorrhizal type (i.e., arbuscular mycorrhiza or ectomycorrhiza). In a field experiment, we quantified net N uptake capacity from inorganic and organic N sources using 15N/13C stable isotopes for arbuscular mycorrhizal tree species (i.e., Acer pseudoplatanus L., Fraxinus excelsior L., and Prunus avium L.) as well as ectomycorrhizal tree species (i.e., Carpinus betulus L., Fagus sylvatica L., and Tilia platyphyllos Scop.). All species were grown in intra- and interspecific competition (i.e., monoculture or mixture). Our results showed that N sources were not used complementarily depending on a species' mycorrhizal association, but their uptake rather depended on the competitor, indicating species-specific effects. Generally, ammonium was preferred over glutamine and glutamine over nitrate. In conclusion, our findings suggest that the inorganic and organic N acquisition of the studied temperate tree species is less regulated by mycorrhizal association but rather by the availability of specific N sources in the soil as well as the competitive environment of different tree species.

Nutrient status not secondary metabolites drives herbivory and pathogen infestation across differently mycorrhized tree monocultures and mixtures

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Research on tree diversity and antagonists often neglects plant complementarity.

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We studied species richness/mycorrhizal type effects on leaf herbivory/pathogens.

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Mycorrhizal type had different effects on herbivory and pathogen infestation.

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Elemental not metabolite concentrations determined leaf damage.ld.

Research aimed at understanding the mechanisms underlying the relationship between tree diversity and antagonist infestation is often neglecting resource-use complementarity among plant species. We investigated the effects of tree species identity, species richness, and mycorrhizal type on leaf herbivory and pathogen infestation. We used a tree sapling experiment manipulating the two most common mycorrhizal types, arbuscular mycorrhiza and ectomycorrhiza, via respective tree species in monocultures and two-species mixtures. We visually assessed leaf herbivory and pathogen infestation rates, and measured concentrations of a suite of plant metabolites (amino acids, sugars, and phenolics), leaf elemental concentrations (carbon, nitrogen, and phosphorus), and tree biomass. Tree species and mycorrhizal richness had no significant effect on herbivory and pathogen infestation, whereas species identity and mycorrhizal type had. Damage rates were higher in arbuscular mycorrhizal (AM) than in ectomycorrhizal (EM) trees. Our structural equation model (SEM) indicated that elemental, but not metabolite concentrations, determined herbivory and pathogen infestation, suggesting that the investigated chemical defence strategies may not have been involved in the effects found in our study with tree saplings. Other chemical and physical defence strategies as well as species identity as its determinant may have played a more crucial role in the studied saplings. Furthermore, the SEM indicated a direct positive effect of AM trees on herbivory rates, suggesting that other dominant mechanisms, not considered here, were involved as well. We found differences in the attribution of elemental concentrations between the two rates. This points to the fact that herbivory and pathogen infestation are driven by distinct mechanisms. Our study highlights the importance of biotic contexts for understanding the mechanisms underlying the effects of biodiversity on tree-antagonist interactions.

Distinct effects of host and neighbour tree identity on arbuscular and ectomycorrhizal fungi along a tree diversity gradient

Plant diversity and plant-related ecosystem functions have been important in biodiversity-ecosystem functioning studies. However, biotic interactions with mycorrhizal fungi have been understudied although they are crucial for plant-resource acquisition. Here, we investigated the effects of tree species richness and tree mycorrhizal type on arbuscular (AMF) and ectomycorrhizal fungal (EMF) communities. We aimed to understand how dissimilarities in taxa composition and beta-diversity are related to target trees and neighbours of the same or different mycorrhizal type. We sampled a tree diversity experiment with saplings (~7 years old), where tree species richness (monocultures, 2-species, and 4-species mixtures) and mycorrhizal type were manipulated. AMF and EMF richness significantly increased with increasing tree species richness. AMF richness of mixture plots resembled that of the sum of the respective monocultures, whereas EMF richness of mixture plots was lower compared to the sum of the respective monocultures. Specialisation scores revealed significantly more specialised AMF than EMF suggesting that, in contrast to previous studies, AMF were more specialised, whereas EMF were not. We further found that AMF communities were little driven by the surrounding trees, whereas EMF communities were. Our study revealed drivers of mycorrhizal fungal communities and further highlights the distinct strategies of AMF and EMF.

Mixing tree species associated with arbuscular or ectotrophic mycorrhizae reveals dual mycorrhization and interactive effects on the fungal partners

Recent studies found that the majority of shrub and tree species are associated with both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. However, our knowledge on how different mycorrhizal types interact with each other is still limited. We asked whether the combination of hosts with a preferred association with either AM or EM fungi increases the host tree roots' mycorrhization rate and affects AM and EM fungal richness and community composition.We established a tree diversity experiment, where five tree species of each of the two mycorrhiza types were planted in monocultures, two-species and four-species mixtures. We applied morphological assessment to estimate mycorrhization rates and next-generation molecular sequencing to quantify mycobiont richness.Both the morphological and molecular assessment revealed dual-mycorrhizal colonization in 79% and 100% of the samples, respectively. OTU community composition strongly differed between AM and EM trees. While host tree species richness did not affect mycorrhization rates, we observed significant effects of mixing AM- and EM-associated hosts in AM mycorrhization rate. Glomeromycota richness was larger in monotypic AM tree combinations than in AM-EM mixtures, pointing to a dilution or suppression effect of AM by EM trees. We found a strong match between morphological quantification of AM mycorrhization rate and Glomeromycota richness. Synthesis. We provide evidence that the combination of hosts differing in their preferred mycorrhiza association affects the host's fungal community composition, thus revealing important biotic interactions among trees and their associated fungi.

Fungal guilds and soil functionality respond to tree community traits rather than to tree diversity in European forests

At the global scale, most forest research on biodiversity focuses on aboveground organisms. However, understanding the structural associations between aboveground and belowground communities provides relevant information about important functions linked to biogeochemical cycles. Microorganisms such as soil fungi are known to be closely coupled to the dominant tree vegetation, and we hypothesize that tree traits affect fungal guilds and soil functionality in multiple ways. By analysing fungal diversity of 64 plots from four European forest types using Illumina DNA sequencing, we show that soil fungal communities respond to tree community traits rather than to tree species diversity. To explain changes in fungal community structure and measured soil enzymatic activities, we used a trait-based ecological approach and community-weighted means of tree traits to define 'fast' (acquisitive) versus 'slow' (conservative) tree communities. We found specific tree trait effects on different soil fungal guilds and soil enzymatic activities: tree traits associated with litter and absorptive roots correlated with fungal, especially pathogen diversity, and influenced community composition of soil fungi. Relative abundance of the symbiotrophic and saprotrophic guilds mirrored the litter quality, while the root traits of fast tree communities enhanced symbiotrophic abundance. We found that forest types of higher latitudes, which are dominated by fast tree communities, correlated with high carbon-cycling enzymatic activities. In contrast, Mediterranean forests with slow tree communities showed high enzymatic activities related to nitrogen and phosphorous. Our findings highlight that tree trait effects of either 'fast' or 'slow' tree communities drive different fungal guilds and influence biogeochemical cycles.

Science-Driven Societal Transformation, Part I: Worldview

Humanity faces serious social and environmental problems, including climate change and biodiversity loss. Increasingly, scientists, global policy experts, and the general public conclude that incremental approaches to reduce risk are insufficient and transformative change is needed across all sectors of society. However, the meaning of transformation is still unsettled in the literature, as is the proper role of science in fostering it. This paper is the first in a three-part series that adds to the discussion by proposing a novel science-driven research-and-development program aimed at societal transformation. More than a proposal, it offers a perspective and conceptual framework from which societal transformation might be approached. As part of this, it advances a formal mechanics with which to model and understand self-organizing societies of individuals. While acknowledging the necessity of reform to existing societal systems (e.g., governance, economic, and financial systems), the focus of the series is on transformation understood as systems change or systems migration—the de novo development of and migration to new societal systems. The series provides definitions, aims, reasoning, worldview, and a theory of change, and discusses fitness metrics and design principles for new systems. This first paper proposes a worldview, built using ideas from evolutionary biology, complex systems science, cognitive sciences, and information theory, which is intended to serve as the foundation for the R&D program. Subsequent papers in the series build on the worldview to address fitness metrics, system design, and other topics.

Unique and common traits in mycorrhizal symbioses

Mycorrhizas are among the most important biological interkingdom interactions, as they involve ~340,000 land plants and ~50,000 taxa of soil fungi. In these mutually beneficial interactions, fungi receive photosynthesis-derived carbon and provide the host plant with mineral nutrients such as phosphorus and nitrogen in exchange. More than 150 years of research on mycorrhizas has raised awareness of their biology, biodiversity and ecological impact. In this Review, we focus on recent phylogenomic, molecular and cell biology studies to present the current state of knowledge of the origin of mycorrhizal fungi and the evolutionary history of their relationship with land plants. As mycorrhizas feature a variety of phenotypes, depending on partner taxonomy, physiology and cellular interactions, we explore similarities and differences between mycorrhizal types. During evolution, mycorrhizal fungi have refined their biotrophic capabilities to take advantage of their hosts as food sources and protective niches, while plants have developed multiple strategies to accommodate diverse fungal symbionts. Intimate associations with pervasive ecological success have originated at the crossroads between these two evolutionary pathways. Our understanding of the biological processes underlying these symbioses, where fungi act as biofertilizers and bioprotectors, provides the tools to design biotechnological applications addressing environmental and agricultural challenges.

How to estimate complementarity and selection effects from an incomplete sample of species

Declines in global biodiversity have inspired a generation of studies that seek to characterize relationships between biodiversity and ecosystem functioning. The metrics for complementarity and selection effects derived by Loreau and Hector in 2001 remain some of the most influential and widely used statistics for studying these relationships. These metrics quantify the degree to which the effect of biodiversity on a given ecosystem function depends on only a few species that perform well in monoculture and in mixture (the selection effect) or if the effect of biodiversity on a given ecosystem function is independent of monoculture performance (the complementarity effect). This distinction may be useful in determining the consequences of the loss of rare versus common or dominant species in natural systems. However, because these metrics require observations of all species in a community in monoculture, applications in natural systems have been limited.Here, we derive a statistical augmentation of the original partition, which can be applied to incomplete random samples of species drawn from a larger pool. This augmentation controls for the bias introduced by using only a subsample of species in monocultures rather than having monocultures of all species.Using simulated and empirical examples, we demonstrate the robustness of these metrics, and provide source code for calculating them. We find that these augmentations provide a reliable estimate of complementarity and selection effects as long as approximately 50% of the species present in mixture are present in monoculture and these species represent a random subset of the mixture.We foresee two primary applications for this method: (a) estimating complementarity and selection effects for experimentally assembled communities where monoculture data are lacking for some species, and (b) extrapolating results from biodiversity experiments to diverse natural systems.

Biotic interactions, community assembly, and eco-evolutionary dynamics as drivers of long-term biodiversity–ecosystem functioning relationships

The functioning and service provisioning of ecosystems in the face of anthropogenic environmental and biodiversity change is a cornerstone of ecological research. The last three decades of biodiversity–ecosystem functioning (BEF) research have provided compelling evidence for the significant positive role of biodiversity in the functioning of many ecosystems. Despite broad consensus of this relationship, the underlying ecological and evolutionary mechanisms have not been well understood. This complicates the transition from a description of patterns to a predictive science. The proposed Research Unit aims at filling this gap of knowledge by applying novel experimental and analytical approaches in one of the longest-running biodiversity experiments in the world: the Jena Experiment. The central aim of the Research Unit is to uncover the mechanisms that determine BEF relationships in the short- and in the long-term. Increasing BEF relationships with time in long-term experiments do not only call for a paradigm shift in the appreciation of the relevance of biodiversity change, they likely are key to understanding the mechanisms of BEF relationships in general. The subprojects of the proposed Research Unit fall into two tightly linked main categories with two research areas each that aim at exploring variation in community assembly processes and resulting differences in biotic interactions as determinants of the long-term BEF relationship. Subprojects under “Microbial community assembly” and “Assembly and functions of animal communities” mostly focus on plant diversity effects on the assembly of communities and their feedback effects on biotic interactions and ecosystem functions. Subprojects under “Mediators of plant-biotic interactions” and “Intraspecific diversity and micro-evolutionary changes” mostly focus on plant diversity effects on plant trait expression and micro-evolutionary adaptation, and subsequent feedback effects on biotic interactions and ecosystem functions. This unification of evolutionary and ecosystem processes requires collaboration across the proposed subprojects in targeted plant and soil history experiments using cutting-edge technology and will produce significant synergies and novel mechanistic insights into BEF relationships. The Research Unit of the Jena Experiment is uniquely positioned in this context by taking an interdisciplinary and integrative approach to capture whole-ecosystem responses to changes in biodiversity and to advance a vibrant research field.

A multitrophic perspective on biodiversity-ecosystem functioning research

Concern about the functional consequences of unprecedented loss in biodiversity has prompted biodiversity-ecosystem functioning (BEF) research to become one of the most active fields of ecological research in the past 25 years. Hundreds of experiments have manipulated biodiversity as an independent variable and found compelling support that the functioning of ecosystems increases with the diversity of their ecological communities. This research has also identified some of the mechanisms underlying BEF relationships, some context-dependencies of the strength of relationships, as well as implications for various ecosystem services that mankind depends upon. In this paper, we argue that a multitrophic perspective of biotic interactions in random and non-random biodiversity change scenarios is key to advance future BEF research and to address some of its most important remaining challenges. We discuss that the study and the quantification of multitrophic interactions in space and time facilitates scaling up from small-scale biodiversity manipulations and ecosystem function assessments to management-relevant spatial scales across ecosystem boundaries. We specifically consider multitrophic conceptual frameworks to understand and predict the context-dependency of BEF relationships. Moreover, we highlight the importance of the eco-evolutionary underpinnings of multitrophic BEF relationships. We outline that FAIR data (meeting the standards of findability, accessibility, interoperability, and reusability) and reproducible processing will be key to advance this field of research by making it more integrative. Finally, we show how these BEF insights may be implemented for ecosystem management, society, and policy. Given that human well-being critically depends on the multiple services provided by diverse, multitrophic communities, integrating the approaches of evolutionary ecology, community ecology, and ecosystem ecology in future BEF research will be key to refine conservation targets and develop sustainable management strategies.

Mycorrhizal types differ in ecophysiology and alter plant nutrition and soil processes

Mycorrhizal fungi benefit plants by improved mineral nutrition and protection against stress, yet information about fundamental differences among mycorrhizal types in fungi and trees and their relative importance in biogeochemical processes is only beginning to accumulate. We critically review and synthesize the ecophysiological differences in ectomycorrhizal, ericoid mycorrhizal and arbuscular mycorrhizal symbioses and the effect of these mycorrhizal types on soil processes from local to global scales. We demonstrate that guilds of mycorrhizal fungi display substantial differences in genome-encoded capacity for mineral nutrition, particularly acquisition of nitrogen and phosphorus from organic material. Mycorrhizal associations alter the trade-off between allocation to roots or mycelium, ecophysiological traits such as root exudation, weathering, enzyme production, plant protection, and community assembly as well as response to climate change. Mycorrhizal types exhibit differential effects on ecosystem carbon and nutrient cycling that affect global elemental fluxes and may mediate biome shifts in response to global change. We also note that most studies performed to date have not been properly replicated and collectively suffer from strong geographical sampling bias towards temperate biomes. We advocate that combining carefully replicated field experiments and controlled laboratory experiments with isotope labelling and -omics techniques offers great promise towards understanding differences in ecophysiology and ecosystem services among mycorrhizal types.

Growing Research Networks on Mycorrhizae for Mutual Benefits

Research on mycorrhizal interactions has traditionally developed into separate disciplines addressing different organizational levels. This separation has led to an incomplete understanding of mycorrhizal functioning. Integration of mycorrhiza research at different scales is needed to understand the mechanisms underlying the context dependency of mycorrhizal associations, and to use mycorrhizae for solving environmental issues. Here, we provide a road map for the integration of mycorrhiza research into a unique framework that spans genes to ecosystems. Using two key topics, we identify parallels in mycorrhiza research at different organizational levels. Based on two current projects, we show how scientific integration creates synergies, and discuss future directions. Only by overcoming disciplinary boundaries, we will achieve a more comprehensive understanding of the functioning of mycorrhizal associations.