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• Root-feeding herbivores can affect plant performance and the composition of natural plant communities, but there is little information about the mechanisms that control root herbivores in natural systems. This study explores the interactions between the pioneer dune grass Ammophila arenaria, arbuscular mycorrhizal fungi (AMF) and the root-feeding nematode Pratylenchus penetrans. • Our objectives were to determine whether AMF can suppress nematode infection and reproduction and to explore the mechanisms of nematode control by AMF. A sequential inoculation experiment and a split-root experiment were designed to analyse the importance of plant tolerance and resistance and of direct competition between AMF and P. penetrans for the root herbivore and the plant. • Root infection and multiplication of P. penetrans were significantly reduced by the native inoculum of AMF. Plant preinoculation with AMF further decreased nematode colonization and reproduction. Nematode suppression by AMF did not occur through a systemic plant response but through local mechanisms. • Our results suggest that AMF are crucial for the control of root-feeding nematodes in natural systems and illustrate that locally operating mechanisms are involved in this process.

Many plant species expand their range to higher latitudes in response to climate change. However, it is poorly understood how biotic interactions in the new range differ from interactions in the original range. Here, in a mesocosm experiment, we analyze nematode community responses in original and new range soils to plant communities with either (a) species native in both the original and new range, (b) range‐expanding species related to these natives (related range expanders), or (c) range expanders without native congeneric species in the new range (unrelated range expanders). We hypothesized that nematode community shifts between ranges are strongest for unrelated range expanders and minimal for plant species that are native in both ranges. As a part of these community shifts, we hypothesized that range expanders, but not natives, would accumulate fewer root‐feeding nematodes in their new range compared to their original range. Analyses of responses of nematodes from both original and new ranges and comparison between range expanders with and without close relatives have not been made before. Our study reveals that none of the plant communities experienced evident nematode community shifts between the original and new range. However, in soils from the new range, root‐feeding nematode communities of natives and related range expanders were more similar than in soils from the original range, whereas the nematode community of unrelated range expanders was distinct from the communities of natives and related range expanders in soils from both ranges. The abundances of root‐feeding nematodes were comparable between the original and new range for all plant communities. Unexpectedly, unrelated range expanders overall accumulated most root‐feeding nematodes, whereas related range expanders accumulated fewest. We conclude that nematode communities associated with native and range‐expanding plant species differ between the original and the new range, but that range‐expanding plant species do not accumulate fewer root‐feeding nematodes in their new than in their original range. We tested whether communities of climate change‐driven range‐expanding plant species accumulate different communities of nematodes in soils from their new range compared to soils from their original range. We examined plant communities that either consisted of range expanders with or range expanders without relatives in the native community, and the nematode responses to these native relatives were also examined. We did not find clear shifts in nematode community composition between original and new range soils, but found distinct responses to plant community type.

BACKGROUND AND AIMS: Daktulosphaira vitifoliae Fitch (grape phylloxera, Phylloxeridae) is one of the most devastating pests in viticulture, mainly because of their root feeding activity. Up to today fundamental relations between belowground habitat and population dynamics remain unclear. In this 2‐year study, we investigated the relations between grape phylloxera population and phenotypic traits of roots and feedings sites. METHODS AND RESULTS: We extracted root and soil samples frequently of two closely related mature rootstocks [Vitis berlandieri × V. riparia (cvs 5C and 125AA)]. We quantified and characterised larval population and crowding and assessed root gall pigmentation, root morphology and soil parameters. We identified and described three stages of seasonal population dynamics: reproduction, overwintering and declining. Further, we demonstrated a significant impact of root gall pigmentation and crowding on population dynamics. CONCLUSIONS: In temperate climates, grape phylloxera is able to overwinter at high density on roots of American rootstocks. Population dynamics are highly dependent on root gall development and the ability to crowd. SIGNIFICANCE OF THE STUDY: The results of our study are considered to have a significant impact on the development of management strategies for grape phylloxera.

413 I. 413 II. 414 III. 414 IV. 415 V. 416 VI. 417 VII. 417 417 References 417 SUMMARY: The distinctive ecology of root herbivores, the complexity and diversity of root–microbe interactions, and the physical nature of the soil matrix mean that plant responses to root herbivory extrapolate poorly from our understanding of responses to aboveground herbivores. For example, root attack induces different changes in phytohormones to those in damaged leaves, including a lower but more potent burst of jasmonates in several plant species. Root secondary metabolite responses also differ markedly, although patterns between roots and shoots are harder to discern. Root defences must therefore be investigated in their own ecophysiological and evolutionary context, specifically one which incorporates root microbial symbionts and antagonists, if we are to better understand the battle between plants and their hidden herbivores.

Plants influence the behavior of and modify community composition of soil-dwelling organisms through the exudation of organic molecules. Given the chemical complexity of the soil matrix, soil-dwelling organisms have evolved the ability to detect and respond to these cues for successful foraging. A key question is how specific these responses are and how they may evolve. Here, we review and discuss the ecology and evolution of chemotaxis of soil nematodes. Soil nematodes are a group of diverse functional and taxonomic types, which may reveal a variety of responses. We predicted that nematodes of different feeding guilds use host-specific cues for chemotaxis. However, the examination of a comprehensive nematode phylogeny revealed that distantly related nematodes, and nematodes from different feeding guilds, can exploit the same signals for positive orientation. Carbon dioxide (CO 2 ), which is ubiquitous in soil and indicates biological activity, is widely used as such a cue. The use of the same signals by a variety of species and species groups suggests that parts of the chemo-sensory machinery have remained highly conserved during the radiation of nematodes. However, besides CO 2 , many other chemical compounds, belonging to different chemical classes, have been shown to induce chemotaxis in nematodes. Plants surrounded by a complex nematode community, including beneficial entomopathogenic nematodes, plant-parasitic nematodes, as well as microbial feeders, are thus under diffuse selection for producing specific molecules in the rhizosphere that maximize their fitness. However, it is largely unknown how selection may operate and how belowground signaling may evolve. Given the paucity of data for certain groups of nematodes, future work is needed to better understand the evolutionary mechanisms of communication between plant roots and soil biota.

An increasing number of studies report plant range expansions to higher latitudes and altitudes in response to global warming. However, consequences for interactions with other species in the novel ranges are poorly understood. Here, we examine how range-expanding plant species interact with root-feeding nematodes from the new range. Root-feeding nematodes are ubiquitous belowground herbivores that may impact the structure and composition of natural vegetation. Because of their ecological novelty, we hypothesized that range-expanding plant species will be less suitable hosts for root-feeding nematodes than native congeneric plant species. In greenhouse and lab trials we compared nematode preference and performance of two root-feeding nematode species between range-expanding plant species and their congeneric natives. In order to understand differences in nematode preferences, we compared root volatile profiles of all range-expanders and congeneric natives. Nematode preferences and performances differed substantially among the pairs of range-expanders and natives. The range-expander that had the most unique volatile profile compared to its related native was unattractive and a poor host for nematodes. Other range-expanding plant species that differed less in root chemistry from native congeners, also differed less in nematode attraction and performance. We conclude that the three climate-driven range-expanding plant species studied varied considerably in their chemical novelty compared to their congeneric natives, and therefore affected native root-feeding nematodes in species-specific ways. Our data suggest that through variation in chemical novelty, range-expanding plant species may vary in their impacts on belowground herbivores in the new range.

Soilborne fungal and oomycete pathogens are the causal agents of several important plant diseases. Infection frequently co-occurs with herbivory by root-feeding insects, facilitating tripartite interactions that modify plant performance and mortality. In an agricultural context, interactions between pathogens, herbivores, and plants can have important consequences for yield protection. However, belowground interactions are inherently difficult to observe and are often overlooked. Here, we review the impact of direct and indirect interactions between root-associated insects, fungi, and oomycetes on the development of plant disease. We explore the relationship between insect feeding injury and pathogen infection, as well as the role of insects as vectors of fungal and oomycete pathogens. Synergistic interactions between insects and phytopathogens may be important in weed suppression, and we highlight several promising candidates for biocontrol. Bridging the gap between entomological and pathological research is a critical step in understanding how interactions between insects and microorganisms modify the community structure of the rhizosphere, and how this impacts plant functioning. Furthermore, the identification of belowground interactions is required to develop effective pest monitoring and management strategies.

Climate change causes species range expansions to higher latitudes and altitudes. It is expected that, due to differences in dispersal abilities between plants and soil biota, range-expanding plant species will become associated with a partly new belowground community in their expanded range. Theory on biological invasions predicts that outside their native range, range-expanding plant species may be released from specialist natural enemies, leading to the evolution of enhanced defence against generalist enemies. Here we tested the hypothesis that expanded range populations of the range-expanding plant species Centaurea stoebe accumulate fewer root-feeding nematodes than populations from the original range. Moreover, we examined whether Centaurea stoebe accumulates fewer root-feeding nematodes in expanded range soil than in original range soil. We grew plants from three expanded range and three original range populations of C. stoebe in soil from the original and from the new range. We compared nematode communities of C. stoebe with those of C. jacea, a congeneric species native to both ranges. Our results show that expanded range populations of C. stoebe did not accumulate fewer root-feeding nematodes than populations from the original range, but that C. stoebe, unlike C. jacea, accumulated fewest root-feeding nematodes in expanded range soil. Moreover, when we examined other nematode feeding groups, we found intra-specific plant population effects on all these groups. We conclude that range-expanding plant populations from the expanded range were not better defended against root-feeding nematodes than populations from the original range, but that C. stoebe might experience partial belowground enemy release.

Background The multitrophic interactions in plant rhizosphere and endosphere can be beneficial or deleterious for the plant health. The parasitism by root-feeding nematodes is on the negative end of the interaction spectrum, and may be very difficult to control. Biological agents are a promising alternative to the environmentally harmful nematicides; however, their efficiency in natural soil often seems to be low due to their limited establishment and dispersal. Thus, understanding how the introduced biological agents interact with nematodes and the surrounding microbiota is necessary to improve sustainable management of root-feeding nematodes. Here, we conducted two experiments to study the effects of Pseudomonas protegens strain CHA0 (CHA0) on the performance of the root-knot nematode Meloidogyne incognita . In the first experiment, we compared M. incognita performance in natural and sterilized soil in the presence and absence of CHA0. In the second experiment, we studied the composition of microbes in the rhizosphere and endosphere of tomato plants grown in native soil in response to M. incognita and CHA0. Results We found that nematode performance, especially nematode reproduction, was significantly increased in native soil amended with CHA0. In addition, we found the highest relative abundance of Pseudomonas in tomato endosphere in response to nematode co-inoculations with CHA0, which suggests that root wounding, caused by nematodes, increased the entrance of inoculated and/or native Pseudomonas spp. As many Pseudomonas spp. are plant growth promoting, this may explain that plant growth was highest in this treatment. Furthermore, the rhizosphere of nematode-inoculated plants was enriched with Flavobacterium , Hydrogenophaga and Variovorax , which are genera generally associated with nematode-suppressive soils. On the other hand, other known nematode-suppressive genera such as Bacillus , Lysobacter , Devosia and Rhizobium were depleted in plants where nematodes were co-inoculated with CHA0, which may explain the higher nematode performance when plants were co-inoculated with CHA0. Conclusions Our findings show that the effect of P. protegens strain CHA0 on M. incognita parasitism is influenced by the multitrophic interactions in the rhizosphere and endosphere of tomato plants. We must understand these interactions thoroughly to optimize sustainable means to mitigate the root-knot nematodes.

Several species of the flea beetles genus Longitarsus sequester pyrrolizidine alkaloids (PAs) from their host plants. Previous data demonstrated that PAs may be transferred from root-feeding larvae into the adult beetles. Here we compared the patterns and concentrations found in larvae and pupae of L. anchusae and L. echii with those of the roots of their respective hosts, Symphytum officinale and Echium vulgare (Boraginaceae). PA patterns and concentrations in the roots were complex and variable, whereas those in the larvae and pupae were simpler and more constant. In L. anchusae, intermedine and lycopsamine were the dominant PAs even if they could not be detected in the roots. In L. echii simpler, hydrolized PAs prevailed. Overall, the concentrations of total PAs of larvae and pupae were significantly higher than those of the roots the larvae had been feeding on. Larvae and pupae of both species also had considerably higher PA concentrations than determined previously for field collected beetles. Possibly the rather immobile juvenile stages enjoy a better protection by higher PA concentrations. On the other hand, we could not detect PAs in eggs of either species, indicating that transmission of appreciable amounts of PAs from mother to offspring does not occur.