GRASSLAND-INVERTEBRATE INTERACTIONS: PLANT PRODUCTIVITY, RESILIENCE AND COMMUNITY DYNAMICS EDITED BY : Ivan Hiltpold and Michael Rostás PUBLISHED IN : Frontiers in Plant Science and Frontiers in Ecology and Evolution 1 October 2017 | G rassland-Invertebrate Interactions Frontiers Copyright Statement © Copyright 2007-2017 Frontiers Media SA. All rights reserved. All content included on this site, such as text, graphics, logos, button icons, images, video/audio clips, downloads, data compilations and software, is the property of or is licensed to Frontiers Media SA (“Frontiers”) or its licensees and/or subcontractors. The copyright in the text of individual articles is the property of their respective authors, subject to a license granted to Frontiers. The compilation of articles constituting this e-book, wherever published, as well as the compilation of all other content on this site, is the exclusive property of Frontiers. 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For the full conditions see the Conditions for Authors and the Conditions for Website Use. ISSN 1664-8714 ISBN 978-2-88945-290-3 DOI 10.3389/978-2-88945-290-3 About Frontiers Frontiers is more than just an open-access publisher of scholarly articles: it is a pioneering approach to the world of academia, radically improving the way scholarly research is managed. The grand vision of Frontiers is a world where all people have an equal opportunity to seek, share and generate knowledge. Frontiers provides immediate and permanent online open access to all its publications, but this alone is not enough to realize our grand goals. Frontiers Journal Series The Frontiers Journal Series is a multi-tier and interdisciplinary set of open-access, online journals, promising a paradigm shift from the current review, selection and dissemination processes in academic publishing. 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Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: researchtopics@frontiersin.org 2 October 2017 | G rassland-Invertebrate Interactions GRASSLAND-INVERTEBRATE INTERACTIONS: PLANT PRODUCTIVITY, RESILIENCE AND COMMUNITY DYNAMICS Topic Editors: Ivan Hiltpold, University of Delaware, United States Michael Rostás, Lincoln University, New Zealand Natural and anthropogenic grasslands such as prairies, meadows, rangelands, and pastures cover more than 40% of the planet’s surface and provide a wealth of ecological services. Grasslands alone store one third of the global carbon stocks and grass roots, through their specific architectures, ensure water cycling and prevent the erosion of fertile topsoil. In addition, grasslands are of vital importance for human food production as vast areas of rangelands and pastures provide feed for livestock. Pastoral legumes mobilize atmos- pheric nitrogen and improve fertility of arable soils. Not least, grasslands are an essential genetic resource. The three major crop species that feed half of the global population have been bred from wild grasses. Ancestors of our contemporary turf cultivars, common components of urban land- scapes and recreation spaces, originated from wild grasslands. Although natural and managed grasslands repre- sent pivotal ecosystems, many aspects of how they function are poorly understood. To date, most attention has focused on grassland primary producers (i.e. forage plants) and mammalian grazers but invertebrates are likely to play an equally, if not more important role in grassland ecosystem functioning. In Australian pastures, for example, the biomass of root-feeding scarab beetles can often exceed that of sheep and plant damage caused by invertebrates is sometimes equivalent to an average dairy cow’s grass consumption. Indeed, grasslands are one of the most densely populated ecosystems with invertebrates being probably the most important engineers that shape both plant communities and the grassland as a whole. In a rapidly changing world with increasing anthropogenic pressure on grasslands, this Research Topic focuses on: 1. How grassland habitats shape invertebrate biodiversity 2. Impacts of climate change on grassland-invertebrate interactions Ryegrass Credit: Mohammad Mohammadi 3 October 2017 | G rassland-Invertebrate Interactions 3. Plant and invertebrate pest monitoring and management 4. Plant-mediated multitrophic interactions and biological control in grasslands 5. Land use and grassland invertebrates 6. Plant resistance to invertebrate pests Given the increasing demand for food and land for human habitation, unprecedented threats to grasslands are anticipated. Resilient to some extent, these key ecosystems need to be better comprehended to guarantee their sustainable management and ecosystem services. Citation: Hiltpold, I., Rostás, M., eds. (2017). Grassland-Invertebrate Interactions: Plant Productivity, Resilience and Community Dynamics. Lausanne: Frontiers Media. doi: 10.3389/978-2-88945-290-3 4 October 2017 | G rassland-Invertebrate Interactions Table of Contents 07 Editorial: Grassland-Invertebrate Interactions: Plant Productivity, Resilience and Community Dynamics Michael Rostás and Ivan Hiltpold CHAPTER 1 - What drives the diversity and distribution of grassland invertebrates and what role do agricultural management practices play? 10 The Abundance, Diversity, and Metabolic Footprint of Soil Nematodes Is Highest in High Elevation Alpine Grasslands Alan Kergunteuil, Raquel Campos-Herrera, Sara Sánchez-Moreno, Pascal Vittoz and Sergio Rasmann 22 The Distribution of Soil Insects across Three Spatial Scales in Agricultural Grassland Carly M. Benefer, Karzan S. D’Ahmed, Rod P . Blackshaw, Hadewij M. Sint and Phil J. Murray 31 Multiple Assembly Rules Drive the Co-occurrence of Orthopteran and Plant Species in Grasslands: Combining Network, Functional and Phylogenetic Approaches Bertrand Fournier, Arnaud Mouly and François Gillet 43 Impact of Grassland Reseeding, Herbicide Spraying and Ploughing on Diversity and Abundance of Soil Arthropods Wei Liu, Junling Zhang, Stuart L. Norris and Philip J. Murray 52 Detection of Invertebrate Suppressive Soils, and Identification of a Possible Biological Control Agent for Meloidogyne Nematodes Using High Resolution Rhizosphere Microbial Community Analysis Nigel L. Bell, Katharine H. Adam, Rhys J. Jones, Richard D. Johnson, Yeukai F . Mtandavari, Gabriela Burch, Vanessa Cave, Catherine Cameron, Paul Maclean, Alison J. Popay and Damien Fleetwood CHAPTER 2 - What are the cascading effects of climate change on invertebrate communities in semi-natural and improved grasslands? 67 Grasslands, Invertebrates, and Precipitation: A Review of the Effects of Climate Change Kirk L. Barnett and Sarah L. Facey 75 The Importance of Testing Multiple Environmental Factors in Legume–Insect Research: Replication, Reviewers, and Rebuttal Scott N. Johnson, Andrew N. Gherlenda, Adam Frew and James M. W. Ryalls 5 October 2017 | G rassland-Invertebrate Interactions 79 DRI-Grass: A New Experimental Platform for Addressing Grassland Ecosystem Responses to Future Precipitation Scenarios in South-East Australia Sally A. Power, Kirk L. Barnett, Raul Ochoa-Hueso, Sarah L. Facey, Eleanor V. J. Gibson-Forty, Susan E. Hartley, Uffe N. Nielsen, David T. Tissue and Scott N. Johnson 93 Altered Precipitation Impacts on Above- and Below-Ground Grassland Invertebrates: Summer Drought Leads to Outbreaks in Spring Marcel D. Torode, Kirk L. Barnett, Sarah L. Facey, Uffe N. Nielsen, Sally A. Power and Scott N. Johnson 105 Above–Belowground Herbivore Interactions in Mixed Plant Communities Are Influenced by Altered Precipitation Patterns James M. W. Ryalls, Ben D. Moore, Markus Riegler and Scott N. Johnson CHAPTER 3 - How do invasive invertebrates affect grassland diversity and functioning, and how can these invaders be sustainably managed to mitigate their impact on grasslands? 119 Belowground Ecology of Scarabs Feeding on Grass Roots: Current Knowledge and Future Directions for Management in Australasia Adam Frew, Kirk Barnett, Uffe N. Nielsen, Markus Riegler and Scott N. Johnson 134 Dispersal of the Invasive Pasture Pest Heteronychus arator into Areas of Low Population Density: Effects of Sex and Season, and Implications for Pest Management Sarah Mansfield, Philippa J. Gerard, Mark R. H. Hurst, Richard J. Townsend, Derrick J. Wilson and Chikako van Koten 142 Novel In vitro Procedures for Rearing a Root-Feeding Pest ( Heteronychus arator ) of Grasslands Ivan Hiltpold, Ben D. Moore and Scott N. Johnson 149 A Review of Perennial Ryegrass Endophytes and Their Potential Use in the Management of African Black Beetle in Perennial Grazing Systems in Australia Mijail Karpyn Esqueda, Alan L. Yen, Simone Rochfort, Kathryn M. Guthridge, Kevin S. Powell, Jacqueline Edwards and German C. Spangenberg 170 Temperature and Plant Genotype Alter Alkaloid Concentrations in Ryegrass Infected with an Epichloë Endophyte and This Affects an Insect Herbivore Louise M. Hennessy, Alison J. Popay, Sarah C. Finch, Michael J. Clearwater and Vanessa M. Cave 180 Aploneura lentisci (Homoptera: Aphididae) and Its Interactions with Fungal Endophytes in Perennial Ryegrass ( Lolium perenne ) Alison J. Popay and Neil R. Cox 194 Does White Clover ( Trifolium repens ) Abundance in Temperate Pastures Determine Sitona obsoletus (Coleoptera: Curculionidae) Larval Populations? Mark R. McNeill, Chikako van Koten, Vanessa M. Cave, David Chapman and Hamish Hodgson 205 Apparent Acquired Resistance by a Weevil to Its Parasitoid Is Influenced by Host Plant Stephen L. Goldson and Federico Tomasetto 213 Is the Invasive Species Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae) (Argentine Stem Weevil) a Threat to New Zealand Natural Grassland Ecosystems? Barbara. P . Barratt, Diane M. Barton, Bruce A. Philip, Colin M. Ferguson and Stephen L. Goldson 6 October 2017 | G rassland-Invertebrate Interactions 221 Evolution of Specialization of Cassida rubiginosa on Cirsium arvense (Compositae, Cardueae) Michael G. Cripps, Sarah D. Jackman, Cristina Roquet, Chikako van Koten, Michael Rostás, Graeme W. Bourdôt and Alfonso Susanna CHAPTER 4 - What makes grasslands resilient to invertebrate threats and community changes? 231 Get Tough, Get Toxic, or Get a Bodyguard: Identifying Candidate Traits Conferring Belowground Resistance to Herbivores in Grasses Ben D. Moore and Scott N. Johnson 247 Invertebrate Biosecurity Challenges in High-Productivity Grassland: The New Zealand Example Stephen L. Goldson, Barbara P . Barratt and Karen F . Armstrong EDITORIAL published: 15 August 2017 doi: 10.3389/fpls.2017.01413 Frontiers in Plant Science | www.frontiersin.org August 2017 | Volume 8 | Article 1413 | Edited and reviewed by: Klaus Birkhofer, Brandenburg University of Technology, Germany *Correspondence: Michael Rostás michael.rostas@lincoln.ac.nz Specialty section: This article was submitted to Agroecology and Land Use Systems, a section of the journal Frontiers in Plant Science Received: 19 June 2017 Accepted: 31 July 2017 Published: 15 August 2017 Citation: Rostás M and Hiltpold I (2017) Editorial: Grassland-Invertebrate Interactions: Plant Productivity, Resilience and Community Dynamics. Front. Plant Sci. 8:1413. doi: 10.3389/fpls.2017.01413 Editorial: Grassland-Invertebrate Interactions: Plant Productivity, Resilience and Community Dynamics Michael Rostás 1 * and Ivan Hiltpold 2, 3 1 Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand, 2 Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia, 3 College of Agriculture and Natural Resources, University of Delaware, Newark, NJ, United States Keywords: biological control, biosecurity, climate change, community ecology, pests Editorial on the Research Topic Grassland-Invertebrate Interactions: Plant Productivity, Resilience and Community Dynamics Grasslands are plant communities dominated by non-woody vegetation, in particular species of the Poaceae family. Such communities occur naturally from the tropics to the tundra in areas of low rainfall where soils do not hold enough moisture to support forest growth. Where climatic conditions fail to support natural grasslands, however, they exist due to more or less intensive farming practices and are known as unimproved ( = semi-natural) or improved grasslands (Curry, 1994). Grassland types differ significantly in biodiversity and productivity (Kruess and Tscharntke, 2002); the latter being characterized by intensive management, including reseeding, fertilization, and irrigation to encourage the growth of only few plant species with particular value for grazing livestock. Natural and semi-natural grasslands, on the other hand, are often habitats to many rare plant and invertebrate species that depend on no or low-intensity farming, respectively. Natural and anthropogenic grasslands cover more than a quarter of the earth’s surface and provide a wealth of ecological services. Grassland ecosystems store a third of the global carbon stocks, ensure water cycling, and are vital for human food production (Gibson, 2009). Invertebrates play major roles in such ecosystems as they contribute to soil fertility, plant growth, pollination, and biological control on the one hand but cause considerable economic loss through herbivory on the other. This research topic reports new findings and concepts on grassland–invertebrate interactions in semi-natural and improved grasslands with emphasis on the effects of climate change, invasive species, and sustainable control methods of invasive pests. Five reviews, one opinion paper, two methods, and fourteen research articles explore the influence of biotic and environmental factors and management practices on the communities of invertebrates and their relationships with plants and natural enemies. The majority of contributions is dedicated to Australian and New Zealand grassland systems resulting from an invitation to the participants of the ninth Australasian Conference on Grassland Invertebrate Ecology held in Sydney in April 2016. Several studies on invertebrate communities in European grasslands complement our Topic. What drives the diversity and distribution of grassland invertebrates and what role do agricultural management practices play? This question is explored in a number of papers such as the one by Kergunteuil et al. who investigate the nematode fauna in Swiss alpine meadows. Surprisingly, and in contrast to aboveground ecosystems, the study shows that the abundance and diversity of nematodes increases along an elevation gradient, which suggests a more important role for nematodes in the functioning of high-altitude alpine grasslands than previously anticipated. The distribution of soil invertebrates is also the focus of Benefer et al. albeit in low-land permanent pastures dominated by perennial ryegrass ( Lolium perenne L.). Their work demonstrates that spatial 7 Rostás and Hiltpold Grassland-Invertebrate Interactions scale is an important factor in describing species distribution. Focussing on the aboveground community of invertebrates, Fournier et al. analyse the rules that determine the co-occurrence network of orthopterans (grasshoppers and crickets) and plants in semi-natural grasslands of the French Jura Mountains. Such networks have a modular structure and the distribution of orthopterans into modules results from trophic and other interactions with plants. The presented models are valuable for biodiversity conservation and will allow for predictions on how such networks will be affected by changes in agricultural practices. Impacts of such practices on grassland invertebrate communities are the focus of a study by Liu et al. who show that herbicide spraying, plowing, and reseeding of permanent grassland can have opposing effects. While herbicide treatment tends to increase soil invertebrates, in particular decomposers due to enhanced food supply, a decrease in abundance can be found after plowing, which constitutes a significant disturbance. Interestingly, most populations were able to recover over a period as short as 1 year after reseeding. What are the cascading effects of climate change on invertebrate communities in semi-natural and improved grasslands? In addition to agricultural intensification, grasslands, and their invertebrate communities need to cope with rising CO 2 levels, temperature, and changes in precipitation. How prognosed precipitation patterns affect grassland insects is reviewed for the first time by Barnett and Facey. The authors constitute that overall the effects on invertebrates, caused indirectly by changes in plant biomass and diversity, are highly idiosyncratic and dependent on the grassland ecosystem under scrutiny. This conclusion comes with a recommendation for further experiments in this under-studied area of research, which should consider multiple climate factors at the same time, thus reflecting the complex reality of climate change. This notion is reiterated in an Opinion paper by Johnson et al. which furthermore analyses the inherent problem of pseudoreplication in climate change experiments and offers advice on how this can be dealt with. Better results from climate change studies was also the motivation for designing an improved experimental platform to examine ecosystem responses to drought and root herbivory. The so-called DRI-Grass ( D rought and R oot Herbivore I nteractions in a Grass land) system described by Powers et al. consists of rain-exclusion shelters with a sophisticated irrigation system that measures local rainfall and responds by delivering water in specific proportions of the actual amount with the effect of realistically mimicking natural precipitation patterns. Using the DRI-Grass platform, Torode et al. take a close look at plant and invertebrate community responses, above- and belowground and across a range of expected rainfall scenarios. Their findings suggest that summer drought, in particular, may favor outbreaks of sucking herbivores, probably followed by a density-dependent response in parasitoid abundance. Ryalls et al., in a similar setting, aim at teasing apart the complex interactions between above- and belowground herbivores in a grass-legume model system when exposed to altered precipitation patterns. Interestingly, in this case drought and root damage by weevils lead to decreases in aphid numbers, thus underpinning Barnett and Facey’s conclusions about the idiosyncratic and system-specific nature of such interactions. How do invasive invertebrates affect grassland diversity and functioning, and how can these invaders be sustainably managed to mitigate their impact on grasslands? This topic is covered by a third series of papers which focuses in particular on management strategies involving biotic resistance factors. To start with, Frew et al. give an overview of economically important pest species of the Scarab family in Australasia. Their timely review presents basic information on a group of beetles, whose larvae (grubs) cause significant damage by feeding on the roots of pasture plants. A range of abiotic and biotic soil factors as well as plant traits are explored that influence oviposition by adult beetles, larval behavior and survival, and ultimately population dynamics. Three further scarab papers discuss only a single species, the African black beetle Heteronychus arator , an invasive grub which is of particular concern to farmers in several countries. Mansfield et al. focus on the dispersal behavior of H. arator and address the question why control measures such as insecticide treatment have failed to reduce population levels. Their findings support the hypothesis that African black beetles re-colonize areas of low density by walking and pitfall traps are confirmed as a valuable monitoring tool. An improved method for rearing H. arator in the laboratory is presented by Hiltpold et al. which allows H. arator to be reared from egg to adult. The protocol may also be useful as a template for rearing other root herbivores, thus facilitating future studies in this important area as research of root–herbivore interactions is often hampered by the availability of the herbivore. Karpyn Esqueda et al. finally give us a broad historical account of improved grassland development in Australia, the establishment of H. arator as a major pest and discuss the use of endophytic fungi that produce insect-deterring toxins, as a control method. Hennessy et al. focus on such grass endophytes (i.e., symbiotic fungi in the genus Epichloë ) and the impact on insect herbivores. Their chemo-ecological study demonstrates the anti-feedant effect of fungally produced epoxy-janthitrems against caterpillars of Wiseana spp. and assesses the role of temperature on the production of these secondary metabolites. Studying several endophyte strains with different metabolic profiles, Popay and Cox confirm the beneficial effects of epoxy-janthitrem producing Epichloë festucae Tul. & Tul. against root aphids. Novel endophyte technology, which is based on using selected strains with specific metabolite profiles, is a sustainable control method against insect pests that is well-established in New Zealand and Australia. Bell et al. also highlight the importance of fungi as natural enemies of pasture pests. Using a combination of next- generation sequencing and bioassays, root nematode catching Orbiliomycetes fungi were identified as potential biocontrol agents from suppressive soils. Studies as the above are promising and will ultimately lead to better control of hard-to-tackle soil herbivores. Adults and larvae of weevils (Curculionidae) are major pasture pests that can feed above- and belowground. In a multi- year study by McNeill et al., the question is raised whether abundance of the host plant Trifolium repens L. determines population density of the weevil Sitona obsoletus Gmelin. While Frontiers in Plant Science | www.frontiersin.org August 2017 | Volume 8 | Article 1413 | 8 Rostás and Hiltpold Grassland-Invertebrate Interactions such a correlation is absent, mortality caused by introduced parasitoids seems to regulate weevil populations. In another weevil study Goldson and Tomasetto aim at elucidating the mechanism behind the observed decline in the initially successful biological control of Listronotus bonariensis Kuschel by its parasitoid Microctonus hyperodae Loan (Tomasetto et al., 2017). Their laboratory study suggests that the weevil has acquired host plant dependent resistance against its natural enemy, leading to the conclusion that low plant and enemy diversity in agriculture may facilitate the evolution of host resistance. Barratt et al., on the other hand, assess the potential impact of L. bonariensis , a pest of improved grasslands, on natural grassland ecosystems and are able to show that the weevil, although present, is not a significant threat to native grass species. Apart from insects, invasive plants also pose a serious threat to natural and agricultural grasslands, and in many cases specialized herbivorous arthropods such as the thistle leaf beetle, Cassida rubiginosa Müller , have been introduced as weed control agents. Cripps et al. examine the evolution of host plant specialization in this beetle and present work that uses a quantitative measure of evolutionary separation between hosts to predict herbivore performance. Studies like these contribute to our understanding of contemporary evolution in novel environments and will aid in predicting non-target risks and host range expansion of biological control agents. What makes grasslands resilient to invertebrate threats and community changes? Two review papers finally highlight the capacity and need for resilience in grassland ecosystems. Moore and Johnson present a thorough survey of the many physical and chemical resistance mechanisms that grasses have evolved against insects and draw our attention to the roots as little is known of belowground defenses in grasses. Strengthening these plant resistance mechanisms in order to deal with new invasive pests is also one of the main recommendations by Goldson et al. Their analysis on pasture biosecurity in New Zealand comes to this conclusion because pre-border controls are deemed less effective for pastures compared with other agricultural sectors due to a range of inherent constraints. In this Research Topic, we have covered a broad range of themes with an emphasis on the invertebrate fauna of managed but also semi-natural grasslands, the abiotic and biotic factors that affect their dynamics, and some of the control measures that have the potential to provide ecologically and economically sustainable plant protection. Although grasslands are pivotal ecosystems, several aspects of their ecology are still elusive. With increasing anthropogenic pressure on fragile natural and semi- natural grasslands and the need for sustainable management of improved grassland systems, it is of paramount importance to better comprehend their complexity and functioning in order to conserve these resources. We are confident this compilation of papers will be a valuable resource for researchers and others interested in grassland ecology. AUTHOR CONTRIBUTIONS MR wrote the first draft with substantial contributions from IH. Both authors jointly edited successive versions and approved it for publication. ACKNOWLEDGMENTS We thank all authors, reviewers, and editors for their excellent and varied contributions. We would also like to acknowledge the Australasian Congress of Grassland Invertebrate Ecology and the Hawkesbury Institute for the Environment, Western Sydney University who provided financial assistance for open access publication fees. REFERENCES Curry, J. P. (1994). Grassland Invertebrates: Ecology, Influence on Soil Fertility and effects on Plant Growth . London: Chapman & Hall. Gibson, D. J. (2009). Grasses and Grassland Ecology . Oxford: Oxford University Press. Kruess, A., and Tscharntke, T. (2002). Grazing intensity and the diversity of grasshoppers, butterflies, and trap-nesting bees and wasps. Conserv. Biol. 16, 1570–1580. doi: 10.1046/j.1523-1739.2002.01334.x Tomasetto, F., Tylianakis, J. M., Reale, M., Wratten, S., and Goldson, S. L. (2017). Intensified agriculture favors evolved resistance to biological control. Proc. Natl. Acad. Sci. U.S.A. 114, 3885–3890. doi: 10.1073/pnas.1618416114 Conflict of Interest Statement: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Copyright © 2017 Rostás and Hiltpold. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Frontiers in Plant Science | www.frontiersin.org August 2017 | Volume 8 | Article 1413 | 9 ORIGINAL RESEARCH published: 19 July 2016 doi: 10.3389/fevo.2016.00084 Frontiers in Ecology and Evolution | www.frontiersin.org July 2016 | Volume 4 | Article 84 | Edited by: Ivan Hiltpold, Western Sydney University, Australia Reviewed by: Jared Gregory Ali, Cornell University, USA Luis Sampedro, Spanish National Research Council, Spain *Correspondence: Alan Kergunteuil alan.kergunteuil@unine.ch Specialty section: This article was submitted to Agroecology and Land Use Systems, a section of the journal Frontiers in Ecology and Evolution Received: 12 May 2016 Accepted: 06 July 2016 Published: 19 July 2016 Citation: Kergunteuil A, Campos-Herrera R, Sánchez-Moreno S, Vittoz P and Rasmann S (2016) The Abundance, Diversity, and Metabolic Footprint of Soil Nematodes Is Highest in High Elevation Alpine Grasslands. Front. Ecol. Evol. 4:84. doi: 10.3389/fevo.2016.00084 The Abundance, Diversity, and Metabolic Footprint of Soil Nematodes Is Highest in High Elevation Alpine Grasslands Alan Kergunteuil 1 *, Raquel Campos-Herrera 2 , Sara Sánchez-Moreno 3 , Pascal Vittoz 4 and Sergio Rasmann 1 1 Functional Ecology laboratory, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland, 2 Centro Para os Recursos Biológicos e Alimentos Mediterrânicos (MeditBio), Faculdade de Ciências e Tecnologia, Universidade do Algarve, Faro, Portugal, 3 Plant Protection Products Unit (DTEVPF), National Institute for Agricultural and Food Research and Technology, Madrid, Spain, 4 Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland Nematodes are key components of soil biodiversity and represent valuable bio-indicators of soil food webs. Numerous community indices have been developed in order to track variations in nematode-mediate soil ecosystem processes, but their use is mainly restricted to anthropogenic stresses. In this study, we propose to expand the use of nematodes’ derived ecological indices in order to shed light on variations of soil food webs in natural systems distributed along elevation gradients. For this purpose, we aimed at determining how elevation affects the community structure and the trophic diversity by studying the abundance, the composition and the functional diversity of nematode communities. Nematode communities were sampled every 200 m across five transects that span about 2000 m in elevation in the Alps. To understand the underlying ecological parameters driving these patterns we studied both abiotic factors (soil properties) and biotic factors (trophic links, relationships with plant diversity). We found that (1) nematode abundance increases with elevation of lowland forests and alpine meadows; (2) differences in nematodes communities rely on habitat-specific functional diversity (e.g., tolerance to harsh environments, “colonizer/persister” status) while most trophic groups are ubiquitous; and (3) the metabolic footprint of the complete nematode community increases with elevation. We thus conclude that the contribution of soil dwelling nematodes to belowground ecosystem processes, including carbon and energy flow, is stronger at high elevation. The resulting cascading effects on the soil food web structure are discussed from an ecosystem functioning perspective. Overall, this study highlights the importance of nematodes in soil ecosystems and brings insights on their functional role along ecological gradients. Keywords: elevation gradient, entomopathogenic nematodes, nematophagous fungi, plant-herbivore interaction, soil ecosystem functioning 10 Kergunteuil et al. Nematode Communities along Elevation Gradients INTRODUCTION It has been estimated that under the earth’s surface, the myriad of soil habitats shelter about 25% of the worldwide described species, thus providing crucial reservoirs of biodiversity and subsequent ecosystem functioning (Fitter et al., 2005; Decaëns, 2010; Bardgett and van der Putten, 2014). While research on soil biota continues to bear inherent challenges, the combination of traditional research with genomic tools has accelerated the exploration of soil diversity and our understanding of ecosystem dynamics (Johnson et al., 2007). In addition, numerous studies have become increasingly focused on replacing soil diversity within trophic interactions for unraveling soil ecosystem processes (Bardgett and van der Putten, 2014). Indeed, soil fauna is essential for ecosystem functioning through different processes, such as primary production and nutrient cycling of carbon, phosphorous, or nitrogen (Brussaard, 1997). The role of soil functional diversity in the decomposition of organic matter and, more importantly, in the assimilation of carbon in food webs, governs energy flows worldwide (Hunt and Wall, 2002; Krumins et al., 2013). Several groups of soil-dwelling organisms (e.g., bacteria, fungi, protists, collembolan, enchytraeid worms or earthworms) can partition their task in order to optimize trophic interactions and energy flow. In addition, among soil inhabitants, the group of roundworms (i.e., nematodes; phylum Nematoda) is a key component of the belowground living mosaic. Indeed, nematodes, with more than 14,000 described species, are distributed in almost every habitat on Earth, and represent more than 80% of metazoan taxonomic and functional diversity in soils (Bongers and Bongers, 1998; Hodda et al., 2009). Nematodes can be assigned to basically all functional trophic guilds, and span the whole gamut of ecological adaptations, ranging from “colonizer” (r strategists) to “persister” (K strategists) along a colonizer- persister (“cp”) scale (Bongers, 1990). Besides the diversity in life history traits, nematodes sustain a large range of trophic groups and eight feeding types have been described: herbivore, fungivore, bacterivore, substrate ingester, predator of animals, unicellular eukaryote feeder, parasites, and omnivore (Yeates et al., 1993). The combination of both cp groups and feeding habits provides a wide diversity of functional guilds. In addition, nematodes occupy a central position in soil food-webs by linking microbial communities with macrofauna. Hence, nematodes are widely used as appropriate bioindicators to track changes in the environment and the resulting cascading effects on soil food- web structure (Sochová et al., 2006; Wilson and Kakouli-Duarte, 2009). Several community and metabolic footprints indices have been developed in order to assess how nematode communities affect (or are affected by) soil quality (Bongers and Ferris, 1999; Ferris et al., 2001; Ferris, 2010), although such studies remain mostly restricted to anthropogenic systems (Salamún et al., 2014; Zhao et al., 2015). Here, we propose to expand the use of nematodes’ derived ecological indices for increasing our understanding soil-driven ecosystem functioning along natural ecological gradients. Studying the causes and consequences of species abundance and distribution along environmental clines remains crucial for providing insights into community assembly and ecosystem functioning (Gaston, 2000; Doherty et al., 2011; Oliver et al., 2015). In this context, ecological gradients act as potent environmental filters and thus provide powerful tools for dissecting biotic and abiotic factors driving species diversity and ecosystem dynamics. For instance, elevation gradients have been classically used to develop key ecological concepts such as the niche theory or the species-energy hypothesis (Grinell, 1917; Brown, 1971; Lomolino, 2001). More recently, various authors have considered elevation gradients as promising “natural experiments” to test evolutionary hypotheses in species niche- breadth or predict plant adaptation to changing environment (Körner, 2007; Alexander et al., 2015; Rasmann and Pellissier, 2015). Indeed, mountain slopes present strong variation in both biotic and abiotic factors that can to alter ecological niches, abundance in species population, or community assemblage (Hodkinson, 2005). In addition, biotic variations occur over short distances, thereby limiting the confounding effect of phylogeography when studying inter-specific interactions from a comparative ecology approach (Rasmann et al., 2014). While, numerous studies have demonstrated the ability of nematodes to colonize the harshest environments, such as the polar regions (Loof, 1971; Yeates, 2010), only few studies have been interested in studying their distribution along elevation, and to our knowledge, none of them have assessed changes in nematode communities along continuous elevation gradients (Hoschitz and Kaufmann, 2004). With the present work, we aimed at unraveling the community ecology of soil-dwelling nematodes along steep elevation gradients, from the colline regions up to the Alpine grasslands. Specifically, we hypothesized: (1) a decrease in nematode abundance at high elevation following classic views on biodiversity gradients (McCain and Grytnes, 2010); (2) changes in the nematode communities’ structures according to variations of ecological niches along the gradient; and (3) changes in the nematode-mediated metabolic footprint indices along the elevation gradient of the Alps. MATERIALS AND METHODS Study Site To dissect nematode food web structure along elevation gradients, between July and August 2013, we sampled soils ranging from 700 m above sea level (asl) up to 2700 m asl across five transects in the Swiss Alps (Figure S1). The five transects were collected over 130 km in order to assess variations in nematode communities over a large scale in Alpine systems. Along each elevational transect, sampling sites of 2 × 2 m were chosen approximately separated from each other by an elevation of 200 m asl ( n = 48 sites, Table S1). As we aimed to measure soil diversity in the most pristine conditions, we sampled within the climacic vegetation at each site (Delarze et al., 2015). In lowlands, soil samples were predominantly collected within Fagus sylvatica , Quercus spp., or Castanea sativa dominated forests. Sites in the mountain and the subalpine belts were mainly collected in F. sylvatica , Pinus sylvestris , Abies alba, or Picea abies dominated Frontiers in Ecology and Evolution | www.frontiersin.org July 2016 | Volume 4 | Article