Relationships between species richness and biomass production are context dependent in grasslands differing in land-use and seed addition.

Despite evidence from grasslands experiments suggesting that plant species loss reduces biomass production, the strength of biodiversity-ecosystem functioning relationships in managed grasslands is still debated. High land-use intensity and reduced species pools are often suggested to make relationships between biodiversity and productivity less positive or even negative, but concrete evidence is still scarce. We investigated biodiversity-productivity relationships over two years in 150 managed grasslands in Germany. Specifically, we distinguished between relationships of biodiversity and biomass production in managed grasslands (1) varying in land-use intensity (e.g. of mowing, grazing and/or fertilization), (2) where land-use intensity is experimentally reduced, and (3) where additionally to land-use reductions, species pools are enlarged by seed addition. Among grasslands varying in land-use intensity, we found negative biodiversity-productivity relationships. Land-use reduction weakened these relationships, towards neutral, and sometimes, even positive relationships. Seed addition reduced species pool limitations, but this did not strengthen biodiversity-productivity relationships. Our findings indicate that land-use intensity is an important factor explaining the predominantly negative biodiversity-productivity relationships in managed grasslands. While we did not find that species pool limitations weakened biodiversity-productivity relationships, our results are based on a two-year-old experiment, possibly such effects are only visible in the long-term. Ultimately, advancing insights on biodiversity-ecosystem functioning relationships helps us to understand under which conditions agricultural production may benefit from promoting biodiversity.

Artificial light at night decreases plant diversity and performance in experimental grassland communities.

Artificial light at night (ALAN) affects many areas of the world and is increasing globally. To date, there has been limited and inconsistent evidence regarding the consequences of ALAN for plant communities, as well as for the fitness of their constituent species. ALAN could be beneficial for plants as they need light as energy source, but they also need darkness for regeneration and growth. We created model communities composed of 16 plant species sown, exposed to a gradient of ALAN ranging from 'moonlight only' to conditions like situations typically found directly underneath a streetlamp. We measured plant community composition and its production (biomass), as well as functional traits of three plant species from different functional groups (grasses, herbs, legumes) in two separate harvests. We found that biomass was reduced by 33% in the highest ALAN treatment compared to the control, Shannon diversity decreased by 43% and evenness by 34% in the first harvest. Some species failed to establish in the second harvest. Specific leaf area, leaf dry matter content and leaf hairiness responded to ALAN. These responses suggest that plant communities will be sensitive to increasing ALAN, and they flag a need for plant conservation activities that consider impending ALAN scenarios. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Ecosystem consequences of invertebrate decline.

Human activities cause substantial changes in biodiversity.1,2 Despite ongoing concern about the implications of invertebrate decline,3,4,5,6,7 few empirical studies have examined the ecosystem consequences of invertebrate biomass loss. Here, we test the responses of six ecosystem services informed by 30 above- and belowground ecosystem variables to three levels of aboveground (i.e., vegetation associated) invertebrate community biomass (100%, 36%, and 0% of ambient biomass) in experimental grassland mesocosms in a controlled Ecotron facility. In line with recent reports on invertebrate biomass loss over the last decade, our 36% biomass treatment also represented a decrease in invertebrate abundance (-70%) and richness (-44%). Moreover, we simulated the pronounced change in invertebrate biomass and turnover in community composition across the season. We found that the loss of invertebrate biomass decreases ecosystem multifunctionality, including two critical ecosystem services, aboveground pest control and belowground decomposition, while harvested plant biomass increases, likely because less energy was channeled up the food chain. Moreover, communities and ecosystem functions become decoupled with a lower biomass of invertebrates. Our study shows that invertebrate loss threatens the integrity of grasslands by decoupling ecosystem processes and decreasing ecosystem-service supply.

Responses of rhizosphere fungi to the root economics space in grassland monocultures of different age.

Recent studies on root traits have shown that there are two axes explaining trait variation belowground: the collaboration axis with mycorrhizal partners and the conservation ('fast - slow') axis. However, it is yet unknown whether these trait axes affect the assembly of soilborne fungi. We expect saprotrophic fungi to link to the conservation axis of root traits, whereas pathogenic and arbuscular mycorrhizal fungi link to the collaboration axis, but in opposite directions, as arbuscular mycorrhizal fungi might provide pathogen protection. To test these hypotheses, we sequenced rhizosphere fungal communities and measured root traits in monocultures of 25 grassland plant species, differing in age. Within the fungal guilds, we evaluated fungal species richness, relative abundance and community composition. Contrary to our hypotheses, fungal diversity and relative abundance were not strongly related to the root trait axes. However, saprotrophic fungal community composition was affected by the conservation gradient and pathogenic community composition by the collaboration gradient. The rhizosphere AMF community composition did not change along the collaboration gradient, even though the root trait axis was in line with the root mycorrhizal colonization rate. Overall, our results indicate that in the long term, the root trait axes are linked with fungal community composition.

Putting conservation gardening into practice.

Conservation gardening (CG) represents a socio-ecological approach to address the decline of native plant species and transform the gardening industry into an innovative conservation tool. However, essential information regarding amenable plants, their ecological requirements for gardening, and commercial availability remains limited and not readily available. In this study, we present a workflow using Germany as a case study to bridge this knowledge gap. We synthesized the Red Lists of all 16 federal states in Germany, and text-mined a comprehensive platform for garden plants, as well as multiple German producers of native plants. To provide accessible information, we developed a user-friendly app ( https://conservation-gardening.shinyapps.io/app-en/ ) that offers region-specific lists of CG plants, along with practical guidance for planting and purchasing. Our findings reveal that a median of 845 plant species are red-listed across federal states (ranging from 515 to 1123), with 41% of these species amenable to gardening (ranging from 29 to 53%), resulting in a total of 988 CG species. Notably, 66% of these species (650) are already available for purchase. Additionally, we observed that many CG plants exhibit drought tolerance and require less fertilizer on average, with implications for long-term urban planning and climate adaptation. Collaborating with gardening experts, we present a selection of purchasable CG balcony plants for each federal state, highlighting the feasibility of CG even for individuals without gardens. With a multitude of declining plants amenable to gardening and the vital role of gardens as refuges and green corridors, CG holds substantial potential to catalyze transformative change in bending the curve of biodiversity loss.

Biomass removal promotes plant diversity after short-term de-intensification of managed grasslands.

Land-use intensification is one of the main drivers threatening biodiversity in managed grasslands. Despite multiple studies investigating the effect of different land-use components in driving changes in plant biodiversity, their effects are usually studied in isolation. Here, we establish a full factorial design crossing fertilization with a combined treatment of biomass removal, on 16 managed grasslands spanning a gradient in land-use intensity, across three regions in Germany. Specifically, we investigate the interactive effects of different land-use components on plant composition and diversity using structural equation modelling. We hypothesize that fertilization and biomass removal alter plant biodiversity, directly and indirectly, mediated through changes in light availability. We found that, direct and indirect effects of biomass removal on plant biodiversity were larger than effects of fertilization, yet significantly differed between season. Furthermore, we found that indirect effects of biomass removal on plant biodiversity were mediated through changes in light availability, but also by changes in soil moisture. Our analysis thus supports previous findings, that soil moisture may operate as an alternative indirect mechanism by which biomass removal may affect plant biodiversity. Most importantly, our findings highlight that in the short-term biomass removal can partly compensate the negative effects of fertilization on plant biodiversity in managed grasslands. By studying the interactive nature of different land-use drivers we advance our understanding of the complex mechanisms controlling plant biodiversity in managed grasslands, which ultimately may help to maintain higher levels of biodiversity in grassland ecosystems.

The structure of root-associated fungal communities is related to the long-term effects of plant diversity on productivity.

Root-associated fungi could play a role in determining both the positive relationship between plant diversity and productivity in experimental grasslands, and its strengthening over time. This hypothesis assumes that specialized pathogenic and mutualistic fungal communities gradually assemble over time, enhancing plant growth more in species-rich than in species-poor plots. To test this hypothesis, we used high-throughput amplicon sequencing to characterize root-associated fungal communities in experimental grasslands of 1 and 15 years of age with varying levels of plant species richness. Specifically, we tested whether the relationship between fungal communities and plant richness and productivity becomes stronger with the age of the experimental plots. Our results showed that fungal diversity increased with plant diversity, but this relationship weakened rather than strengthened over the two time points. Contrastingly, fungal community composition showed increasing associations with plant diversity over time, suggesting a gradual build-up of specific fungal assemblages. Analyses of different fungal guilds showed that these changes were particularly marked in pathogenic fungi, whose shifts in relative abundance are consistent with the pathogen dilution hypothesis in diverse plant communities. Our results suggest that root-associated fungal pathogens play more specific roles in determining the diversity-productivity relationship than other root-associated plant symbionts.

Biodiversity-stability relationships strengthen over time in a long-term grassland experiment.

Numerous studies have demonstrated that biodiversity drives ecosystem functioning, yet how biodiversity loss alters ecosystems functioning and stability in the long-term lacks experimental evidence. We report temporal effects of species richness on community productivity, stability, species asynchrony, and complementarity, and how the relationships among them change over 17 years in a grassland biodiversity experiment. Productivity declined more rapidly in less diverse communities resulting in temporally strengthening positive effects of richness on productivity, complementarity, and stability. In later years asynchrony played a more important role in increasing community stability as the negative effect of richness on population stability diminished. Only during later years did species complementarity relate to species asynchrony. These results show that species complementarity and asynchrony can take more than a decade to develop strong stabilizing effects on ecosystem functioning in diverse plant communities. Thus, the mechanisms stabilizing ecosystem functioning change with community age.

Drought-exposure history increases complementarity between plant species in response to a subsequent drought.

Growing threats from extreme climatic events and biodiversity loss have raised concerns about their interactive consequences for ecosystem functioning. Evidence suggests biodiversity can buffer ecosystem functioning during such climatic events. However, whether exposure to extreme climatic events will strengthen the biodiversity-dependent buffering effects for future generations remains elusive. We assess such transgenerational effects by exposing experimental grassland communities to eight recurrent summer droughts versus ambient conditions in the field. Seed offspring of 12 species are then subjected to a subsequent drought event in the glasshouse, grown individually, in monocultures or in 2-species mixtures. Comparing productivity between mixtures and monocultures, drought-selected plants show greater between-species complementarity than ambient-selected plants when recovering from the subsequent drought, causing stronger biodiversity effects on productivity and better recovery of drought-selected mixtures after the drought. These findings suggest exposure to recurrent climatic events can improve ecosystem responses to future events through transgenerational reinforcement of species complementarity.

Ecosystem effects of environmental extremes.

A large-scale experimental facility reveals tropical rainforest responses to drought.

The iDiv Ecotron-A flexible research platform for multitrophic biodiversity research.

Across the globe, ecological communities are confronted with multiple global environmental change drivers, and they are responding in complex ways ranging from behavioral, physiological, and morphological changes within populations to changes in community composition and food web structure with consequences for ecosystem functioning. A better understanding of global change-induced alterations of multitrophic biodiversity and the ecosystem-level responses in terrestrial ecosystems requires holistic and integrative experimental approaches to manipulate and study complex communities and processes above and below the ground. We argue that mesocosm experiments fill a critical gap in this context, especially when based on ecological theory and coupled with microcosm experiments, field experiments, and observational studies of macroecological patterns. We describe the design and specifications of a novel terrestrial mesocosm facility, the iDiv Ecotron. It was developed to allow the setup and maintenance of complex communities and the manipulation of several abiotic factors in a near-natural way, while simultaneously measuring multiple ecosystem functions. To demonstrate the capabilities of the facility, we provide a case study. This study shows that changes in aboveground multitrophic interactions caused by decreased predator densities can have cascading effects on the composition of belowground communities. The iDiv Ecotrons technical features, which allow for the assembly of an endless spectrum of ecosystem components, create the opportunity for collaboration among researchers with an equally broad spectrum of expertise. In the last part, we outline some of such components that will be implemented in future ecological experiments to be realized in the iDiv Ecotron.

A starting guide to root ecology: strengthening ecological concepts and standardising root classification, sampling, processing and trait measurements.

In the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting-edge, meaningful and integrated knowledge. Consideration of the below-ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below-ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from the literature to provide key background knowledge useful for: (1) defining below-ground plant entities and giving keys for their meaningful dissection, classification and naming beyond the classical fine-root vs coarse-root approach; (2) considering the specificity of root research to produce sound laboratory and field data; (3) describing typical, but overlooked steps for studying roots (e.g. root handling, cleaning and storage); and (4) gathering metadata necessary for the interpretation of results and their reuse. Most importantly, all root traits have been introduced with some degree of ecological context that will be a foundation for understanding their ecological meaning, their typical use and uncertainties, and some methodological and conceptual perspectives for future research. Considering all of this, we urge readers not to solely extract protocol recommendations for trait measurements from this work, but to take a moment to read and reflect on the extensive information contained in this broader guide to root ecology, including sections I-VII and the many introductions to each section and root trait description. Finally, it is critical to understand that a major aim of this guide is to help break down barriers between the many subdisciplines of root ecology and ecophysiology, broaden researchers' views on the multiple aspects of root study and create favourable conditions for the inception of comprehensive experiments on the role of roots in plant and ecosystem functioning.

An integrated framework of plant form and function: the belowground perspective.

Plant trait variation drives plant function, community composition and ecosystem processes. However, our current understanding of trait variation disproportionately relies on aboveground observations. Here we integrate root traits into the global framework of plant form and function. We developed and tested an overarching conceptual framework that integrates two recently identified root trait gradients with a well-established aboveground plant trait framework. We confronted our novel framework with published relationships between above- and belowground trait analogues and with multivariate analyses of above- and belowground traits of 2510 species. Our traits represent the leaf and root conservation gradients (specific leaf area, leaf and root nitrogen concentration, and root tissue density), the root collaboration gradient (root diameter and specific root length) and the plant size gradient (plant height and rooting depth). We found that an integrated, whole-plant trait space required as much as four axes. The two main axes represented the fast-slow 'conservation' gradient on which leaf and fine-root traits were well aligned, and the 'collaboration' gradient in roots. The two additional axes were separate, orthogonal plant size axes for height and rooting depth. This perspective on the multidimensional nature of plant trait variation better encompasses plant function and influence on the surrounding environment.

Root traits explain plant species distributions along climatic gradients yet challenge the nature of ecological trade-offs.

Ecological theory is built on trade-offs, where trait differences among species evolved as adaptations to different environments. Trade-offs are often assumed to be bidirectional, where opposite ends of a gradient in trait values confer advantages in different environments. However, unidirectional benefits could be widespread if extreme trait values confer advantages at one end of an environmental gradient, whereas a wide range of trait values are equally beneficial at the other end. Here, we show that root traits explain species occurrences along broad gradients of temperature and water availability, but model predictions only resembled trade-offs in two out of 24 models. Forest species with low specific root length and high root tissue density (RTD) were more likely to occur in warm climates but species with high specific root length and low RTD were more likely to occur in cold climates. Unidirectional benefits were more prevalent than trade-offs: for example, species with large-diameter roots and high RTD were more commonly associated with dry climates, but species with the opposite trait values were not associated with wet climates. Directional selection for traits consistently occurred in cold or dry climates, whereas a diversity of root trait values were equally viable in warm or wet climates. Explicit integration of unidirectional benefits into ecological theory is needed to advance our understanding of the consequences of trait variation on species responses to environmental change.

Incorporation of mineral nitrogen into the soil food web as affected by plant community composition.

Although nitrogen (N) deposition is increasing globally, N availability still limits many organisms, such as microorganisms and mesofauna. However, little is known to which extent soil organisms rely on mineral-derived N and whether plant community composition modifies its incorporation into soil food webs. More diverse plant communities more effectively compete with microorganisms for mineral N likely reducing the incorporation of mineral-derived N into soil food webs. We set up a field experiment in experimental grasslands with different levels of plant species and functional group richness. We labeled soil with 15NH4 15NO3 and analyzed the incorporation of mineral-derived 15N into soil microorganisms and mesofauna over 3 months. Mineral-derived N incorporation decreased over time in all investigated organisms. Plant species richness and presence of legumes reduced the uptake of mineral-derived N into microorganisms. In parallel, the incorporation of mineral-derived 15N into mesofauna species declined with time and decreased with increasing plant species richness in the secondary decomposer springtail Ceratophysella sp. Effects of both plant species richness and functional group richness on other mesofauna species varied with time. The presence of grasses increased the 15N incorporation into Ceratophysella sp., but decreased it in the primary decomposer oribatid mite Tectocepheus velatus sarekensis. The results highlight that mineral N is quickly channeled into soil animal food webs via microorganisms irrespective of plant diversity. The amount of mineral-derived N incorporated into soil animals, and the plant community properties affecting this incorporation, differed markedly between soil animal taxa, reflecting species-specific use of food resources. Our results highlight that plant diversity and community composition alter the competition for N in soil and change the transfer of N across trophic levels in soil food webs, potentially leading to changes in soil animal population dynamics and community composition. Sustaining high plant diversity may buffer detrimental effects of elevated N deposition on soil biota.