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Summary Soils and their microbiomes are now recognized as key components of plant health, but how to steer those microbiomes to obtain their beneficial functions is still unknown. Here, we assess whether plant–soil feedbacks can be applied in a crop system to shape soil microbiomes that suppress herbivorous insects in above‐ground tissues.We used four grass and four forb species to condition living soil. Then we inoculated those soil microbiomes into sterilized soil and grew chrysanthemum as a focal plant. We evaluated the soil microbiome in the inocula and after chrysanthemum growth, as well as plant and herbivore parameters.We show that inocula and inoculated soil in which a focal plant had grown harbor remarkably different microbiomes, with the focal plant exerting a strong negative effect on fungi, especially arbuscular mycorrhizal fungi. Soil inoculation consistently induced resistance against the thrips Frankliniella occidentalis, but not against the mite Tetranychus urticae, when compared with sterilized soil. Additionally, plant species shaped distinct microbiomes that had different effects on thrips, chlorogenic acid concentrations in leaves and plant growth.This study provides a proof‐of‐concept that the plant–soil feedback concept can be applied to steer soil microbiomes with the goal of inducing resistance above ground against herbivorous insects.

Our findings highlight how soil fungal and bacterial communities respond to time, season, and plant species identity. We found that succession shapes the soil bacterial community, while plant species and the type of plant species that grows in the soil drive the assembly of soil fungal communities. Future research on the effects of plants on soil microbes should take into consideration the relative roles of both time and plant growth on creating soil legacies that impact future plants growing in the soil. Understanding the temporal (in)stability of microbial communities in soils will be crucial for predicting soil microbial composition and functioning, especially as plant species compositions will shift with global climatic changes and land-use alterations. As fungal and bacterial communities respond to different environmental cues, our study also highlights that the selection of study organisms to answer specific ecological questions is not trivial and that the timing of sampling can greatly affect the conclusions made from these studies., Microorganisms are found everywhere and have critical roles in most ecosystems, but compared to plants and animals, little is known about their temporal dynamics. Here, we investigated the temporal stability of bacterial and fungal communities in the soil and how their temporal variation varies between grasses and forb species. We established 30 outdoor mesocosms consisting of six plant monocultures and followed microbial communities for an entire year in these soils. We demonstrate that bacterial communities vary greatly over time and that turnover plays an important role in shaping microbial communities. We further show that bacterial communities rapidly shift from one state to another and that this is related to changes in the relative contribution of certain taxa rather than to extinction. Fungal soil communities are more stable over time, and a large part of the variation can be explained by plant species and by whether they are grasses or forbs. Our findings show that the soil bacterial community is shaped by time, while plant group and plant species-specific effects drive soil fungal communities. This has important implications for plant-soil research and highlights that temporal dynamics of soil communities cannot be ignored in studies on plant-soil feedback and microbial community composition and function.

Plant-soil feedbacks (PSFs) can influence plant performance in natural and agricultural systems but how PSF principles can be applied in agriculture is not well-studied. In a two-phase PSF experiment, we tested how inoculating soil conditioned by plants into live and sterilized commercial glasshouse soil influences the root-associated microbiome (bacteria and fungi) and biomass of the cut flower chrysanthemum. The conditioned soil inocula were obtained by growing eight grassland species and chrysanthemum individually in soil collected from a commercial chrysanthemum glasshouse, or in soil from a natural grassland. Inoculation of conditioned grassland soil into sterilized glasshouse soil led to higher plant biomass, to more complex and connected microbial networks and to a lower abundance of the pathogenic fungi Olpidium in chrysanthemum roots, than inoculation into live glasshouse soil or inoculation with conditioned live glasshouse soil. Biomass of chrysanthemum was highest in 100% sterilized soil, but in this soil the root-associated microbiome also contained the highest relative abundance of Olpidium. Glasshouse soils are frequently steam-sterilized and our results show that inoculating these soils with desired soil microbiomes can steer the root microbiome in this crop. However, our study also highlights that steering live glasshouse soil with a disease-related microbiome into a healthy state remains challenging.

Biochar has been explored as an organic amendment to improve soil quality and benefit plant growth. The overall positive effects of biochar on crop yields are generally attributed to abiotic changes, while the alternative causal pathway via changes in soil biota is unexplored. We compared plant growth effects of legumes in sterile soil inoculated with dilutions of soil and soil microbial suspensions to determine the direct effects of biochar-induced changes in soil biota on plant growth. Suspensions and soil were from soil amended with biochar and soil without biochar. By comparing consecutive plant growth phases on the same inoculated soils, we also determined the temporal effects of soil biota from biochar-amended and control soils. Biota from biochar-amended soil was less beneficial for Medicago sativa growth, especially with small amounts of inocula. Flowering was delayed in the presence of biota from biochar plots. Inoculum with either soil or soil suspension gave similar results for plant biomass, indicating that microorganisms play a major role. Vicia villosa growth did not respond to the various inocula, even though the inoculum quantity strongly affected nematode community composition and protozoan abundance. In a later growing phase the negative effect of biochar-associated biota on Medicago growth mostly disappeared, which leads to the conclusion that the benefits of biochar application via abiotic changes may outweigh the negative effects of biochar on soil biota.

Aims Plant damage inflicted by aboveground herbivores can occur at different stages of plant development and can induce plant responses that affect the growth of belowground herbivores. This study explores impacts of aboveground herbivory at different plant development stages on the population dynamics of root-feeding nematodes. Methods We simulated aboveground herbivory by clipping the foliage of the grass species Holcus lanatus, and tested how plant defoliation at different times (1, 4 or 7 weeks after nematode inoculation) influenced the population of two root-feeding nematode species: the endoparasitic Pratylenchus penetrans and the ectoparasitic Tylenchorhynchus dubius. Results Defoliation increased the total abundance of P. penetrans and the number per unit root mass (density) of both P. penetrans and T. dubius. Defoliation enhanced the density of P. penetrans, however, only when plants were defoliated early. Timing did not influence the density of T. dubius, although both abundance and density increased over time. Defoliation increased the nitrogen concentration of plant roots, but reduced root biomass. The strongest reduction of root biomass occurred after early defoliation. Conclusions Our study indicates that plant responses to aboveground herbivory and their effects on belowground herbivores can be influenced by the time when plants are defoliated, as well as by the belowground herbivore species and their interactions.

Above–belowground (AG–BG) studies typically focus on plant-mediated effects inflicted by living organisms. However, animal cadavers may also play an important role in AG–BG interactions. Here, we explore whether living and dead foliar-feeding and soil-dwelling invertebrates differentially affect plants and their associated AG and BG multitrophic communities. In a mesocosm study we separated effects of living and dead locusts (AG herbivores) and earthworms (BG detritivores) on experimental multitrophic communities consisting of eight plant species, an AG aphid and parasitoid community and a BG nematode community. We measured root and shoot biomass and determined plant community composition and densities of aphids, parasitoids and nematodes. Living locusts decreased total shoot and root biomass in the mesocosms, whereas living earthworms enhanced total root biomass. Cadavers of both invertebrates strongly increased total root and shoot biomass, and changed the plant community composition mainly via enhanced growth of grasses. Earthworm cadavers affected plant biomass and community composition more strongly than their living counterparts, while this was reversed for locusts. Structural equation models showed that aphids and parasitoids were influenced via changes in plant community composition. Nematode densities in the soil, especially those of bacterivorous and entomopathogenic nematodes, were strongly increased by dead invertebrates, but unaffected by living ones. We conclude that effects of invertebrates on plant growth and densities of AG and BG organisms strongly depend on whether the invertebrates are dead or alive. Remarkably, invertebrate cadavers may inflict even stronger effects than their living counterparts. Hence, our study reveals an important, but often neglected, role of animal cadavers in AG–BG studies.

Under natural conditions, aboveground herbivory and plant-soil feedbacks (PSFs) are omnipresent interactions strongly affecting individual plant performance. While recent research revealed that aboveground insect herbivory generally impacts the outcome of PSFs, no study tested to what extent the intensity of herbivory affects the outcome. This, however, is essential to estimate the contribution of PSFs to plant performance under natural conditions in the field. Here, we tested PSF effects both with and without exposure to aboveground herbivory for four common grass species in nine grasslands that formed a gradient of aboveground invertebrate herbivory. Without aboveground herbivores, PSFs for each of the four grass species were similar in each of the nine grasslands—both in direction and in magnitude. In the presence of herbivores, however, the PSFs differed from those measured under herbivory exclusion, and depended on the intensity of herbivory. At low levels of herbivory, PSFs were similar in the presence and absence of herbivores, but differed at high herbivory levels. While PSFs without herbivores remained similar along the gradient of herbivory intensity, increasing herbivory intensity mostly resulted in neutral PSFs in the presence of herbivores. This suggests that the relative importance of PSFs for plant-species performance in grassland communities decreases with increasing intensity of herbivory. Hence, PSFs might be more important for plant performance in ecosystems with low herbivore pressure than in ecosystems with large impacts of insect herbivores.

Plant–soil feedbacks (PSFs) involve changes to the soil wrought by plants, which change biotic and abiotic properties of the soil, affecting plants that grow in the soil at a later time. The importance of PSFs for understanding ecosystem functioning has been the focus of much recent research, for example, in predicting the consequences for agricultural production, biodiversity conservation, and plant population dynamics. Here, we describe an experiment designed to test PSFs left by plants with contrasting traits under field conditions. This is one of the first, large-scale field experiments of its kind. We removed the existent plant community and replaced it with target plant communities that conditioned the soil. These communities consisted of contrasting proportions of grass and forb cover and consisted of either fast- or slow-growing plants, in accordance with the plant economics spectrum. We chose this well-established paradigm because plants on opposite ends of this spectrum have developed contrasting strategies to cope with environmental conditions. This means they differ in their feedbacks with soil abiotic and biotic factors. The experimental procedure was repeated in two successive years in two different subplots in order to investigate temporal effects on soils that were conditioned by the same plant community. Our treatments were successful in creating plant communities that differed in their total percentage cover based on temporal conditioning, percentage of grasses versus forbs, and percentage of fast- versus slow-growing plants. As a result, we expect that the influence of these different plant communities will lead to different PSFs. The unique and novel design of this experiment allows us to simultaneously test for the impacts of temporal effects, plant community composition and plant growth strategy on PSFs. Here, we describe the experimental design and demonstrate why this effective design is ideal to advance our understanding of PSFs in the field.

Soil microbial community composition and litter quality are important drivers of litter decomposition, but how litter quality influences the soil microbial composition largely remains unknown. We conducted a microcosm experiment to examine the effects of changes in litter quality induced by long-term N deposition on soil microbial community composition. Mixed-species litter and single-species litter were collected from a field experiment with replicate plots exposed to long-term N-addition in a semiarid grassland in northern China. The litters were decomposed in a standard live soil after which the composition of the microbial community was determined by Illumina MiSeq Sequencing. Changes in litter stoichiometry induced by N-addition increased the diversity of the fungal community. The alpha-diversity of the fungal community was more sensitive to the type of litter (mixed- or single-species) than to the N-addition effects, with higher abundance of fungal OTUs and Shannon-diversity observed in soil with mixed-species litter. Moreover, the relative abundance of saprophytic fungi increased with increasing N-addition rates, which suggests that fungi play an important role in the initial stages of the decomposition process. Litter type and N addition did not significantly change the diversity of bacterial community. The relative abundance of ammonia-oxidizing bacteria was lower in high N-addition treatments than in those with lower N input, indicating that changes in litter stoichiometry could change ecosystem functioning via its effects on bacteria. Our results presented robust evidence for the plant-mediated pathways through which N-deposition affects the soil microbial community and biogeochemical cycling.

Background and aims: Current knowledge of soil heterogeneity-diversity relationships (HDR) is largely based on studies manipulating single factor, but the advancements in HDR may require a comprehensive experiment incorporating multiple factors. Methods: We conducted a three-year field experiment in which a seed mixture of 16 common grassland species was sown in plots with heterogeneous soils consisting of small (10 cm × 10 cm) or large patches (30 cm × 30 cm) of low and high nutrients or low and high pH, and homogeneous soils with an even mixture of low and high nutrient/pH soils. Soil nutrients and pH were manipulated in separate treatments. We determined plant species richness and diversity at two focal scales (40 cm × 40 cm plot-scale and 10 cm × 10 cm patch-scale). Results: Plot-scale richness and diversity were not influenced by soil heterogeneity, but patch-scale richness was lower in plots with heterogeneous nutrients than in plots where nutrients were distributed homogeneously. There was no difference between the two heterogeneous nutrient soils with different grain sizes. Patch-scale diversity was higher in heterogeneous pH soils of large patch size than in heterogeneous pH soils of small patch size or the homogeneous pH soil at the final harvest. Species richness and diversity quantified at both plot and patch scales declined in all soils over time. Conclusions: The influence of soil heterogeneity on plant species diversity depends on whether the soil varies in nutrients or pH, and on the temporal-spatial scale at which species diversity and soil heterogeneity are measured. These results indicate that soil heterogeneity has the potential to promote plant coexistence and future HDR studies should consider multiple soil factors at various temporal-spatial scales.

Grasslands are important ecosystems and make up 40% of the terrestrial ecosystems worldwide. The Inner Mongolia steppe is the main grassland region of China, and nitrogen (N) and water availability are two important factors that limit the productivity of these grasslands. We tested how N and water addition influence the composition of the microbial community in the soil using PLFA, and soil physical and chemical properties in two semiarid grassland sites in Inner Mongolia during two consecutive years. In both sites, a split-plot design was employed with two water treatments (natural precipitation, stimulated wet year precipitation) and three N treatments (0 kg N ha⁻¹, 25 kg N ha⁻¹, 50 kg N ha⁻¹). Water addition greatly increased soil fungi and decreased bacteria while N had opposite effects. Water addition resulted in a significant increase in soil pH and electric conductivity. N addition did not lead to consistent changes in soil characteristics. Multivariate analysis showed that PLFA composition varied between all treatments but was mainly influenced by water addition. This study provides insight into how climatic changes such as alternations in rainfall and N deposition shape the soil microbial communities in Inner Mongolia steppes.

Many studies have examined how human-induced atmospheric changes will influence ecosystems. The long-term consequences of human induced climate changes on terrestrial ecosystems may be determined to a large extend by how the belowground compartment will respond to these changes. In a free-air ozone enrichment experiment running for 5 years, we reciprocally transplanted soil cores from ambient and elevated ozone rings to test whether exposure to elevated ozone results in persistent changes in the soil biota when the plant and soil are no longer exposed to elevated ozone, and how these legacy effects of elevated ozone influenced plant growth as compared to current effects of elevated ozone. After one growing season, the current ozone treatment enhanced plant growth, but in soil with a historical legacy of elevated ozone the plant biomass in that soil was reduced compared to the cores originated from ambient rings. Current exposure to ozone increased the phospholipid fatty acids of actinomycetes and protozoa, however, it decreased dissolved organic carbon, bacterivorous and fungivorous nematodes. Interestingly, numbers of bacterivorous and fungivorous nematodes were enhanced when soils with a legacy of elevated ozone were placed under elevated ozone conditions. We conclude that exposure to elevated [O3] results in a legacy effect in soil. This legacy effect most likely influenced plant growth and soil characteristics via responses of bacteria and fungi, and nematodes that feed upon these microbes. These soil legacies induced by changes in soil biotic community after long-term exposure of elevated ozone can alter the responses of ecosystems to current climatic changes.

1. In natural ecosystems, plants containing hosts for parasitoids are often embedded within heterogeneous plant communities. These plant communities surrounding host-infested plants may influence the host-finding ability of parasitoids. 2. A release-recapture-approach was used to examine whether the diversity and structural complexity of the community surrounding a host-infested plant influences the aggregation behaviour of the leaf-miner parasitoid Dacnusa sibirica Telenga and naturally occurring local leaf-miner parasitoids. Released and locally present parasitoids were collected on potted Jacobaea vulgaris Gaertn.plants infested with the generalist leaf-miner Chromatomyia syngenesiae Hardy. The plants were placed in experimentally established plant communities differing in plant diversity (1–9 species) and habitat complexity (bare ground, mown vegetation, and tall vegetation). Additionally, parasitoids were reared out from host mines on the trap plants. 3. Plant diversity did not influence the mean number of recaptured D. sibirica or captures of other locally present parasitoids but the number of recaptured parasitoids was influenced by habitat complexity. No D. sibirica parasitoids were recaptured in the bare ground plots or plots with mown vegetation. The mean number of recaptured D. sibirica generally increased with increasing complexity of the plant community, whereas locally present parasitoids were captured more frequently in communities with more bare ground. There was a unimodal relationship between the number of reared out parasitoids and diversity of the surrounding vegetation with the highest density of emerged parasitoids at intermediate diversity levels. 4. The present study adds to the thus far limited body of literature examining the aggregation behaviour of parasitoids in the field and suggests that the preference of parasitoids to aggregate in complex versus simple vegetation is association specific and thus depends on the parasitoid species as well as the identity of the plant community.

Crop residue decomposition is a major component of carbon (C) cycling and provides energy and nutrients to the soil micro-food web. An in-situ field experiment was conducted to examine how exogenous organic C is incorporated into the soil micro-food web and how this is influenced by four different fertilization treatments: organic manure (M), urea fertilizer (U), the combined application of organic and urea fertilizer (MU) and unfertilized control. The amount of 13C-enriched maize remained was traced in microbial phospholipid fatty acids (PLFAs) and in different trophic groups of the soil nematode community after a 183-day decomposition period. The fertilization type influenced the incorporation of residue into the microbial community. Soil bacterial and fungal PLFAs utilized the least 13C-labeled crop residues in the U treatment. Both the nematode bacterial and the fungal pathways utilized more crop residues in the M treatment than in other treatments. Given the ecological services provided by the soil organisms, our results suggest that long-term manure application increases the soil C pool directly. This also leads to more C from crop residues utilized by the soil food web, which in turn, can benefit crop growth or C accumulation in agroecosystems.

Plants leave species-specific legacies in the soil they grow in that can represent changes in abiotic or biotic soil properties. It has been shown that such legacies can affect future plants that grow in the same soil (plant–soil feedback, PSF). Such processes have been studied in detail, but mostly on individual plants. Here, we study PSF effects at the community level and use a trait-based approach both in the conditioning phase and in the feedback phase to study how 12 individual soil legacies influence six plant communities that differ in root size. We tested if (1) grassland perennial species with large root systems would leave a stronger legacy than those with small root systems, (2) grass species would leave a more positive soil legacy than forbs, and (3) communities with large root systems would be more responsive than small-rooted communities. We also tested (4) whether a leaf-chewing herbivore and a phloem feeder were affected by soil legacy effects in a community framework. Our study shows that the six different plant communities that we used respond differently to soil legacies of 12 different plant species and their functional groups. Species with large root systems did not leave stronger legacies than species with small root systems, nor were communities with large root systems more responsive than communities with root systems. Moreover, we show that when communities are affected by soil legacies, these effects carry over to the chewing herbivore Mamestra brassicae (Lepidoptera: Noctuidae) through induced behavioural changes resulting in better performance of a chewing herbivore on forb-conditioned soils than on grass-conditioned soils, whereas performance of the phloem feeder Rhopalosiphum padi (Hemiptera: Aphididae) remained unaffected. Synthesis. The results of this study shed light on the variability of soil effects found in previous work on feedbacks in communities. Our study suggests that the composition of plant communities determines to a large part the response to soil legacies. Furthermore, the responses to soil legacies of herbivores feeding on the plant communities that we observed, suggests that in natural ecosystems, the vegetation history may also have an influence on contemporary herbivore assemblages. This opens up exciting new areas in plant–insect research and can have important implications for insect pest management.

PSF has been extensively studied in both agricultural and natural systems, with increased activity in recent years, but a framework for integrating the concepts and principles developed in these systems is lacking. Interactions between soil biota and plant leaf and root traits have become an important tool in understanding PSF in wild plants, but this understanding has not yet been utilized in agricultural crop rotations. Soil inoculations with microbial strains are increasingly being used for steering the soil microbiome in agriculture but might also offer a promising method of restoration of degraded systems, and for controlling the spread of invasive species. Increasing evidence shows that PSF can play important roles in mediating ecosystem responses to forecasted climate change and extreme weather events. In agricultural and natural systems researchers have demonstrated large effects of plant–soil feedback (PSF) on plant growth. However, the concepts and approaches used in these two types of systems have developed, for the most part, independently. Here, we present a conceptual framework that integrates knowledge and approaches from these two contrasting systems. We use this integrated framework to demonstrate (i) how knowledge from complex natural systems can be used to increase agricultural resource-use efficiency and productivity and (ii) how research in agricultural systems can be used to test hypotheses and approaches developed in natural systems. Using this framework, we discuss avenues for new research toward an ecologically sustainable and climate-smart future.

The effects of plants on soil vary greatly between plant species and in mixed plant communities this can lead to spatial variation in plant-soil feedback (PSF) effects. Such spatial effects are thought to influence plant species coexistence, but the empirical evidence for this hypothesis is limited. Here, we investigate how spatial heterogeneity in PSFs influences plant growth and competition. The experiment was carried out with high and low nutrient soils to examine how these effects depend on soil fertility. We collected soil from field plots planted for three years with monocultures of Anthoxanthum odoratum and Centaurea jacea and tested the performance of the two species in a greenhouse experiment in heterogeneous soils consisting of patches of “own” and “foreign” soils and in soils where the “own” and “foreign” soils were mixed homogeneously. In the test phase, plants were grown in monocultures and in 1:1 mixtures in live or sterilized soils. Overall, A. odoratum in monocultures produced less aboveground biomass in heterogeneous soils than in homogeneous soils. Centaurea jacea produced less belowground biomass in live heterogeneous soils than in live homogeneous soils, but there was no difference between sterile heterogeneous and homogeneous soils. The belowground biomass per patch varied more in pots with live heterogeneous soils than in pots with live homogeneous soils for both plant species, but there was no difference between pots with sterile heterogeneous and homogeneous soils. In pots with plant mixtures, the difference in aboveground biomass between the two competing species tended to be smaller in heterogeneous than in homogeneous soils. In pots with heterogeneous soils, both plant species grown in mixtures produced more aboveground biomass in “foreign” soil patches than in “own” soil patches. The responses of plants to heterogeneous PSFs were not different between low and high nutrient soils. Our results show that spatially heterogeneous PSFs can influence plant performance and competition via reducing the growth inequality between the two competing species by allowing selective growth in foreign soil patches, independent of initial soil nutrient availability. Such effect may slow down exclusion processes and thus promote the coexistence of competing species at the local scale in mixed plant communities. A plain language summary is available for this article.

Background and aims Intraspecific aggregation of plant individuals can promote species coexistence by delaying competitive exclusions. However, such impacts may differ among species with contrasting spatial architecture and rely on the spatial distribution of resources. Methods We grew a phalanx clonal plant Carex neurocarpa (with aggregated ramets) and a guerilla one Bolboschoenus planiculmis (with diffused ramets) in monocultures or in 1:1 mixtures with an even or a clustered distribution pattern of the two species in homogeneous or heterogeneous soils. Results After 16 months, shoot biomass and ramet number were greater in mixtures than in monocultures in C. neurocarpa, but smaller in B. planiculmis. However, the growth of neither C. neurocarpa nor B. planiculmis differed between even and clustered mixtures. Soil nutrient heterogeneity did not significantly affect the growth of either species, but increased relative yield of B. planiculmis and decreased that of C. neurocarpa. Conclusions The relative importance of intra- vs. interspecific competition depends on the spatial architecture of plants, and soil nutrient heterogeneity slows down competitive exclusion by decreasing differences in competitive ability between plants. However, our results do not support the idea that intraspecific aggregation of individuals alters competitive interactions between species.

Background and aims Most plant-soil feedback and inoculation studies are limited to one growth cycle. We examined the effects of inoculation with eight plant-conditioned soils on chrysanthemum during two sequential growth cycles. The plants were also exposed sequentially to soil diseases. Methods In cycle 1, plants were grown in sterile soil inoculated or not with plant-conditioned soils, and exposed or not to Pythium or root feeding nematodes. In cycle 2, new plants were grown in soil from cycle 1 or in new 100% sterile soil. Plants were exposed again to Pythium, or to soil with pathogens and nematodes collected from a commercial chrysanthemum greenhouse. Results After two cycles, effects of soil inoculation on plant growth were still present. Chrysanthemum exhibited a negative conspecific feedback response, but this was less strong in inoculated soils. Pythium or nematode addition did not affect plant growth. However, addition of pathogen-containing soil from the commercial greenhouse reduced plant growth in sterile soil but increased growth in plant-conditioned soils. Conclusions Inoculation with plant-conditioned soil can reduce the negative conspecific plant-soil feedback of chrysanthemum. Our study further advances our understanding of the temporal dynamics of conspecific and heterospecific plant-soil feedbacks, and how they interact with soil-borne diseases.

Most studies on plant‐soil feedback (PSF) and plant competition measure the feedback response at one moment only. However, PSFs and competition may both change over time, and how PSF and competition interact over time is unclear. We tested the temporal dynamics of PSF and interspecific competition for the forb Jacobaea vulgaris and the grass Holcus lanatus. We grew both species individually and in interspecific competition in soil that was first conditioned in the greenhouse by J. vulgaris, by H. lanatus or without plant growth. For a period of 11 weeks, we harvested plants twice a week and analysed the fungal and chemical composition of the different soils at the end of the first and second growth phase. During the second growth phase, when grown in isolation, both species produced more biomass in heterospecific conditioned soil than in conspecific conditioned soil. Young J. vulgaris exhibited a strong negative conspecific feedback, but this effect diminished over time and became neutral in older plants. In contrast, when grown in competition, the negative conspecific feedback of J. vulgaris exacerbated over time. Older H. lanatus plants benefited more from heterospecific conditioning when competing with J. vulgaris, then when grown isolated. Fungal community composition and soil chemistry differed significantly between soils but this was mainly driven by differences between plant‐conditioned and unconditioned soils. Remarkably, at the end of the second growth phase, fungal community composition was not explained by the legacy of the species that had been grown in the soil most recently, but still reflected the legacy of the first growth phase. We reexamined plant growth during a third growth phase. Biomass of J. vulgaris was still influenced by the treatments imposed during the first phase, while H. lanatus responded only to the plant growth treatments imposed during the second phase. Synthesis. Our study shows that the direction and magnitude of PSF depends on plant age and competition, and also on soil legacy effects of earlier plant growth. These results highlight the need to incorporate dynamic PSFs in research on plant populations and communities.

Aims Plants use different types of responses such as tolerance and induced defense to mitigate the effects of herbivores. The direction and magnitude of both these plant responses can vary with plant age. However, most studies have focused on aboveground herbivory, whereas important feeding occurs belowground. Here, we tested the hypothesis that plant tolerance and defense following shoot damage or root herbivory depends on plant age. Methods In order to test our hypothesis, we exposed the perennial grass species Holcus lanatus to defoliation and root nematode inoculation at three growth stages (young, intermediate and old plants), and examined responses of plant traits related to tolerance (regrowth following defoliation) and defense (leaf and root nitrogen and phenolics). Important Findings Defoliation overall reduced plant shoot and root biomass as well as foliar concentrations of phenolics regardless of plant age at defoliation. In contrast, defoliation increased foliar N concentrations, but only when defoliation occurred at intermediate and old plant age. Inoculation with root-feeding nematodes reduced root N concentrations after a prolonged period of growth, but only when nematodes had been inoculated when plants were young. The relative shoot regrowth rate of plants increased immediately after defoliation but this was independent of the plant age at which defoliation occurred, i.e. was not stronger in plants that were defoliated at a more advanced age, as hypothesized. Similarly, relative root growth rates increased shortly after defoliation, but this was only observed for plants defoliated when they were young. We conclude that plant responses to aboveground and belowground herbivory in traits related to both defense and tolerance are affected by plant age, but do not generally change with plant age.

1. Many studies that provided evidence for a positive relationship between plant diversity and productivity have proposed that this effect may be explained by complementarity among species in resources utilization, or selection of particularly productive species in high-diversity plant communities. Recent studies have related the higher productivity in diverse plant communities to suppression of pathogenic soil biota. If soil biota plays a role in diversity–productivity relationships, the question remains about how they may influence complementarity and selection effects. 2. Here we examine how complementarity and selection effects may depend on soil biota using a plant–soil feedback approach. We used monocultures and mixtures of early successional plant species, which are known to have mostly negative plant–soil feedback effects, and mid-successional plant species, which generally have neutral plant–soil feedback. 3. We found that plant–soil feedback effects differed between monocultures and mixed plant communities, as well as between early and mid-successional plants. This resulted in a significant interaction effect between diversity and successional stage. In monocultures, plant–soil feedback tended to be negative for early and positive for mid-successional plant species. Interestingly, the community feedback responses of the mixed communities were opposite, being positive for early and negative for mid-successional community. 4. Plant–soil feedback differentially affected complementarity and selection effects of early and mid-successional plant communities: it enhanced complementarity effects of early and decreased selection effects of mid-successional species. 5. Synthesis. Soil biota that drive plant–soil feedback effects can influence the diversity–productivity relationship not only through decreased biomass production in monocultures compared to mixtures, but also through influencing complementarity and selection effects among species in mixed plant communities. Our results reveal that biodiversity–productivity relationships depend on plant–soil feedback interactions, which depend on the successional position of the plant. We propose that including successional position and trait-based analyses of plant–soil feedback in diversity-functioning studies will enhance understanding consequences of biodiversity loss for productivity and other ecosystem processes.

Soil nematode communities can provide important information about soil food web structure and function. However, how soil nematode communities and their metabolic footprints change over time in temperate forests is not well known. We examined the changes in the composition, diversity and metabolic footprints of soil nematode communities in three differently-aged (young, mid and old) forests of the Changbai Mountains, China. Carbon flows through different nematode trophic groups were also quantified based on nematode biomasses. The results showed that the highest abundance and diversity of total nematodes was found in the mid forest. Nematode communities were characterized by the replenishment in abundance but not the replacement of dominant genera. A low enrichment footprint in the young forest suggests a decline in available prey, while a high enrichment footprint in the mid forest indicates an increase in resource entry into soil food web. The relationship between the carbon flows of omnivores-predators and fungivores was stronger than that among other trophic groups. Our study shows that bottom-up effects of the vegetation, the soil environment and the connectedness of nematode trophic groups are all important driving forces for nematode community structure in temperate forests.

There is considerable evidence that both plant diversity and plant identity can influence the level of predation and predator abundance aboveground. However, how the level of predation in the soil and the abundance of predatory soil fauna are related to plant diversity and identity remains largely unknown. In a biodiversity field experiment, we examined the effects of plant diversity and identity on the infectivity of entomopathogenic nematodes (EPNs, Heterorhabditis and Steinernema spp.), which prey on soil arthropods, and abundance of carnivorous non-EPNs, which are predators of other nematode groups. To obtain a comprehensive view of the potential prey/food availability, we also quantified the abundance of soil insects and nonpredatory nematodes and the root biomass in the experimental plots. We used structural equation modeling (SEM) to investigate possible pathways by which plant diversity and identity may affect EPN infectivity and the abundance of carnivorous non-EPNs. Heterorhabditis spp. infectivity and the abundance of carnivorous non-EPNs were not directly related to plant diversity or the proportion of legumes, grasses and forbs in the plant community. However, Steinernema spp. infectivity was higher in monocultures of Festuca rubra and Trifolium pratense than in monocultures of the other six plant species. SEM revealed that legumes positively affected Steinernema infectivity, whereas plant diversity indirectly affected the infectivity of Heterorhabditis EPNs via effects on the abundance of soil insects. The abundance of prey (soil insects and root-feeding, bacterivorous, and fungivorous nematodes) increased with higher plant diversity. The abundance of prey nematodes was also positively affected by legumes. These plant community effects could not be explained by changes in root biomass. Our results show that plant diversity and identity effects on belowground biota (particularly soil nematode community) can differ between organisms that belong to the same feeding guild and that generalizations about plant diversity effects on soil organisms should be made with great caution.

Neighboring plants can influence arthropods on a focal plant and this can result in associational resistance or associational susceptibility. These effects can be mediated by above- and belowground interactions between the neighbor and focal plant, but determining the relative contribution of the above- and belowground effects remains an open challenge. We performed a common garden experiment with a design that enabled us to disentangle the above- and belowground effects of five different plant species on the growth and chemistry of the focal plant ragwort (Jacobaea vulgaris), and the arthropod community associated to this plant. Aboveground effects of different neighboring plant species were more important for the growth and quality of J. vulgaris and for the arthropod abundance on this plant than belowground effects of neighbors. This remained true when only indirect neighbor effects (via affecting the biomass or quality of the focal plant) were considered. The aboveground neighbor effects on arthropod abundance on the focal plant were strongly negative. However, the magnitude of the effect depended on the identity of the neighboring species, and herbivore abundance on the focal plant was higher when surrounded by conspecific than by heterospecific plants. We also observed interactions between above- and belowground neighbor effects, indicating that these effects may be non-additive. We conclude that above- and belowground associational effects are not equally strong, and that neighbor effects on plant-arthropod interactions occur predominantly aboveground. Read More: http://www.esajournals.org/doi/abs/10.1890/14-0563.1?af=R

Model terrestrial ecosystems were set-up in the Ecotron controlled environment facility. The effects of elevated CO

Background and aimBiochar application to soil is widely claimed to increase plant productivity. However, the underlying mechanisms are still not conclusively described. Here, we aim to elucidate these mechanisms using stable isotope probing.Methods We conducted two experiments with uniquely double-labelled (15N and 13C) biochar and its feedstock (residue), applied separately at 15 Mg ha−1. Both experiments contained three treatments: biochar amendment (Biochar), unpyrolysed residue amendment (Residue) and a no addition control (Control). Experiment I was a 119 day pot experiment seeded with Lolium perenne. Experiment II was a 71 day incubation experiment without plants in which CO2 and N2O fluxes were measured.Results Both Biochar and Residue significantly increased aboveground productivity compared to Control (140% and 160%, respectively). Initial N immobilisation was stimulated in Residue, whereas not in Biochar. 13C–CO2 analysis confirmed that biochar was significantly more recalcitrant than residue. 15N analysis showed that 2% and 0.3% of grass N was derived from the amended material in Residue and Biochar, respectively.ConclusionsOur results suggest that biochar-induced yield increases derive from a combination of reduced N immobilization and a moderate N fertilization effect. Although in the short term biochar might offer benefits compared to residue incorporation, it is unlikely that biochar yield gains will be sustainable for the decades to centuries that biochar C can be expected to reside in soil.

1.Differences in litter quality and in soil microbial community composition can influence the litter decomposition and “home-field advantage” (HFA). However, our knowledge about the relative role of litter and soil characteristics on litter decomposition and HFA effects is still limited, especially under long-term N deposition. 2.We collected soil and two types of litter (monospecific and mixed species litter) from five replicate plots from a long-term N-deposition field experiment with seven N-addition treatments (0, 2, 5, 10, 15, 20, 50 g N m−2 yr−1). We examined the effects of N-addition on litter quality and soil characteristics. We then carried out a three-pronged microcosm decomposition experiment with (i) litter from different N-addition treatments decomposed on a standard field soil; (ii) standard litter decomposed on soils from the different N-addition treatments; and (iii) litter decomposed on soil from the same N-addition treatment plot. 3.Decomposition of litter on standard soil was influenced strongly by the N-addition treatment, but did not consistently decrease or increase with increasing N-addition rates. Instead, decomposition of standard litter on soils collected from different N-addition treatments decreased with increasing rates of N-addition. Decomposition of litter on soil collected from the same plot increased with increasing N-addition rates. Soil characteristics explained more of the variation in litter decomposition than litter characteristics. 4.There was a clear HFA effect for litter decomposition; both from a litter and from a soil perspective. HFA effects increased when the dissimilarity in litter quality (N content and C: N ratio) increase among the different N-addition treatments and the soil effect was strongest at high N-addition rates. 5.N-addition influenced litter decomposition by changing both litter and soil characteristics. Importantly, N-addition decreased the capability of soils to decompose litter and it increased the home-field advantage effect indicating that soils decomposed local litter better than other litter, due to specialization in soil communities. Nitrogen deposition is an important threat to ecosystems worldwide and our study emphasizes that ecosystem functions such as decomposition can be greatly influenced by these global changes.

Summary The diversity of the surrounding plant community can directly affect the abundance of insects on a focal plant as well as the size and quality of that focal plant. However, to what extent the effects of plant diversity on the arthropod community on a focal plant are mediated by host plant quality or by the diversity of the surrounding plants remains unresolved. In the field, we sampled arthropod communities on focal Jacobaea vulgaris plants growing in experimental plant communities that were maintained at different levels of diversity (one, two, four or nine species) for 3 years. Focal plants were also planted in plots without surrounding vegetation. We recorded the structural characteristics of each of the surrounding plant communities as well as the growth, and primary and secondary chemistry (pyrrolizidine alkaloids, PAs) of the focal plants to disentangle the potential mechanisms causing the diversity effects. Two years after planting, the abundance of arthropods on focal plants that were still in the vegetative stage decreased with increasing plant diversity, while the abundance of arthropods on reproductive focal plants was not significantly affected by the diversity of the neighbouring community. The size of both vegetative and reproductive focal plants was not significantly affected by the diversity of the neighbouring community, but the levels of PAs and the foliar N concentration of vegetative focal plants decreased with increasing plant diversity. Structural equation modelling revealed that the effects of plant diversity on the arthropod communities on focal plants were not mediated by changes in plant quality. Synthesis. Plant quality can greatly influence insect preference and performance. However, under natural conditions, the effects of the neighbouring plant community can overrule the plant quality effects of individual plants growing in those communities on the abundance of insects associated to this plant.

Summary Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change. Using a new conceptual model, we show how critical alterations in plant–soil feedback interactions can change the assemblage of plant communities. We highlight recent advances, define terms and identify future challenges in this area of research and discuss how variations in strengths and directions of plant–soil feedbacks can explain succession, invasion, response to climate warming and diversity-productivity relationships. While there has been a rapid increase in understanding the biological, chemical and physical mechanisms and their interdependencies underlying plant–soil feedback interactions, further progress is to be expected from applying new experimental techniques and technologies, linking empirical studies to modelling and field-based studies that can include plant–soil feedback interactions on longer time scales that also include long-term processes such as litter decomposition and mineralization. Significant progress has also been made in analysing consequences of plant–soil feedbacks for biodiversity-functioning relationships, plant fitness and selection. To further integrate plant–soil feedbacks into ecological theory, it will be important to determine where and how observed patterns may be generalized, and how they may influence evolution. Synthesis. Gaining a greater understanding of plant–soil feedbacks and underlying mechanisms is improving our ability to predict consequences of these interactions for plant community composition and productivity under a variety of conditions. Future research will enable better prediction and mitigation of the consequences of human-induced global changes, improve efforts of restoration and conservation and promote sustainable provision of ecosystem services in a rapidly changing world.

1.Feeding by insect herbivores can affect plant growth and the concentration of defense compounds in plant tissues. Since plants provide resources for soil organisms, herbivory can also influence the composition of the soil community via its effects on the plant. Soil organisms, in turn, are important for plant growth. We tested whether insect herbivores, via their effects on the soil microbial community, can influence plant-soil feedbacks. 2.We first examined the effects of above-ground (AG) and below-ground (B) insect herbivory on the composition of pyrrolizidine alkaloids (PAs) in roots and on soil fungi in roots and rhizosphere soil of ragwort (Jacobaea vulgaris). The composition of fungal communities in roots and rhizosphere soil was affected by both AG and BG herbivory, but fungal composition also differed considerably between roots and rhizosphere soil. The composition of PAs in roots was affected only by BG herbivory. 3.Thirteen different fungal species were detected in roots and rhizosphere soil. The presence of the potentially pathogenic fungus Fusarium oxysporum decreased and that of Phoma exigua increased in presence of BG herbivory, but only in soil samples. 4.We then grew new plants in the soils conditioned by plants exposed to the herbivore treatments and in unconditioned soil. A subset of the new plants was exposed to foliar insect herbivory. Plant-soil feedback was strongly negative, but the feedback effect was least negative in soil conditioned by plants that had been exposed to BG herbivory. There was a negative direct effect of foliar herbivory on plant biomass during the feedback phase, but this effect was far less strong when the soil was conditioned by plants exposed to AG herbivory. AG herbivory during the conditioning phase also caused a soil feedback effect on the PA concentration in the foliage of ragwort. 5.Synthesis. Our results illustrate how insect herbivory can affect interactions between plants and soil organisms, and via these effects how herbivory can alter the performance of late-growing plants. Plant-soil feedback is emerging as an important theme in ecology and these results highlight that plant-soil feedback should be considered from a multitrophic AG and BG perspective

Many natural ecosystems have been degraded because of human activities(1,2) and need to be restored so that biodiversity is protected. However, restoration can take decades and restoration activities are often unsuccessful(3) because of abiotic constraints (for example, eutrophication, acidification) and unfavourable biotic conditions (for example, competition or adverse soil community composition). A key question is what manageable factors prevent transition from degraded to restored ecosystems and what interventions are required for successful restoration(2,4). Experiments have shown that the soil community is an important driver of plant community development(5-8), suggesting that manipulation of the soil community is key to successful restoration of terrestrial ecosystems(3,9). Here we examine a large-scale, six-year-old field experiment on ex-arable land and show that application of soil inocula not only promotes ecosystem restoration, but that different origins of soil inocula can steer the plant community development towards different target communities, varying from grassland to heathland vegetation. The impact of soil inoculation on plant and soil community composition was most pronounced when the topsoil layer was removed, whereas effects were less strong, but still significant, when the soil inocula were introduced into intact topsoil. Therefore, soil inoculation is a powerful tool to both restore disturbed terrestrial ecosystems and steer plant community development.

We studied short- and long-term growth responses of Poa annua L. (Gramineae) at ambient and elevated (ambient +200 μmol mol−1) atmospheric CO2. In experiment 1 we compared plant growth during the early, vegetative and final, reproductive growth phases. Plant growth in elevated CO2 was significantly enhanced during the early phase, but this was reversed in the reproductive phase. Seed mass and percentage germination were significantly reduced in elevated CO2. Experiment 2 tested for the impact of transgenerational and nutrient effects on the response of Poa annua to elevated CO2. Plants were grown at ambient and elevated CO2 for one or two consecutive generations at three soil nutrient levels. Leaf photosynthesis was significantly higher at elevated CO2, but was also affected by both soil nutrient status and plant generation. Plants grown at elevated CO2 and under conditions of low nutrient availability showed photosynthetic acclimation after 12 weeks of growth but not after 6 weeks. First-generation growth remained unaffected by elevated CO2, while second-generation plants produced significantly more tillers and flowers when grown in elevated CO2 compared to ambient conditions. This effect was strongest at low nutrient availability. Average above- and belowground biomass after 12 weeks of growth was enhanced in elevated CO2 during both generations, but more so during plant generation 2. This study demonstrates the importance of temporal/maternal effects in plant responses to elevated CO2.

The diversity of plant community can greatly affect the abundance and diversity of arthropods associated to that community, but can also influence the composition or abundance of arthropods on individual plants growing in that community. We sampled arthropods and recorded plant size of individual ragwort, Jacobaea vulgaris Gaertner ssp. vulgaris [synonym Senecio jacobaea L. (Asteraceae)], plants transplanted into 70 experimental grassland plots that differed in plant diversity (1–9 species) or that were kept without vegetation. The arthropod fauna was dominated by the specialist aphid Aphis jacobaeae Schrank (Hemiptera: Aphididae). The abundance of aphids on ragwort plants decreased significantly with increasing plant diversity. The abundance of other arthropod species was not affected by the diversity of the surrounding plant community. Plant size was also not affected by the diversity of the surrounding plant community, but varied significantly among monocultures. Ragwort plants were largest in monocultures of legumes. Aphid abundance on ragwort plants, however, was not related to the size of the individual ragwort plants, but was high in monocultures consisting of Tanacetum vulgare L. (Asteraceae) plants. This plant is morphologically similar to ragwort. Even though we observed significant effects of plant diversity, ragwort plants were considerably larger – and the abundance of aphids and other arthropods on ragwort plants substantially higher – in plots without vegetation than in vegetated plots. Our results show that the presence and the diversity of neighbouring plants can provide associational resistance to focal plants growing in that community. We conclude that the surrounding plant community directly affects the abundance of arthropods on focal ragwort plants, and not via the effects of neighbouring plants on the performance of the focal plants.

Ecosystems consist of aboveground and belowground subsystems and the structure of their communities is known to change with distance. However, most of this knowledge originates from visible, aboveground components, whereas relatively little is known about how soil community structure varies with distance and if this variability depends on the group of organisms considered. In the present study, we analyzed 30 grasslands from three neighboring chalk hill ridges in southern UK to determine the effect of geographic distance (1–198 km) on the similarity of bacterial communities and of nematode communities in the soil. We found that for both groups, community similarity decayed with distance and that this spatial pattern was not related to changes either in plant community composition or soil chemistry. Site history may have contributed to the observed pattern in the case of nematodes, since the distance effect depended on the presence of different nematode taxa at one of the hill ridges. On the other hand, site-related differences in bacterial community composition alone could not explain the spatial turnover, suggesting that other factors, such as biotic gradients and local dispersal processes that we did not include in our analysis, may be involved in the observed pattern. We conclude that, independently of the variety of causal factors that may be involved, the decay in similarity with geographic distance is a characteristic feature of both communities of soil bacteria and nematodes.

1. Legacy effects of plant influences on abiotic and biotic soil properties can result in priority effects that influence the structure and composition of plant communities. To better understand the role of these plant–soil interactions, here we expand the concept of plant–soil feedbacks from a within-species approach (intraspecific plant–soil feedback) to a between-species approach (interspecific plant–soil interactions). 2. In a greenhouse experiment, we tested how the early successional Jacobaea vulgaris affects its own performance and the performance of 30 co-occurring plant species via changes in abiotic and biotic soil conditions. In addition, we examined the reciprocal effect of the co-occurring species on J. vulgaris. 3. Our study had three important results. First, J. vulgaris exhibits strong negative plant–soil feedback. Secondly, there were large differences among the co-occurring species in interspecific plant–soil effects on J. vulgaris growth. Approximately, half the species reduced J. vulgaris performance, whereas the other half had no effect. Thirdly, soil conditioned by J. vulgaris had a positive or neutral effect on the growth of the co-occurring species. 4. To test the soil effects of entire plant communities, in 10 old-fields that differed in time since abandonment we recorded the identity of all plants surrounding J. vulgaris individuals. We calculated the weighted soil effect of this community on J. vulgaris and the reciprocal effect of J. vulgaris on the community. There was a positive linear relationship between time since abandonment and the weighted feedback effect of J. vulgaris on the plant community. 5. We suggest three mechanisms how the legacy of plant–soil interactions may enhance the rate of succession through priority effects: early successional plant species exert negative plant–soil feedback; co-occurring plant species cause negative interspecific plant–soil effects to the early successional species; and the early successional species have overall positive interspecific plant–soil effects on the co-occurring plant species. 6.Synthesis. The performance of an early successional species can be reduced directly by the legacy effects of intraspecific plant–soil feedback, as well as indirectly by the legacy effects of both intra- and interspecific plant–soil interactions. These intra- and interspecific plant–soil interactions can prioritize transitions of plant species in plant communities.

Nutrient enrichment of habitats (eutrophication) is considered to be one of the main causes of plant diversity decline worldwide. Several experiments have shown a rapid loss of species in the first years after fertilization started. However, little is known about changes in species richness in the long term. Here, we use a 50-year-old field experiment with a range of fertilization treatments in grasslands that were mown twice each year in the center of The Netherlands. We show that species richness in all plots initially declined but started to recover after approximately 25 years of continued fertilization. This was also true for the heavily fertilized treatment (NPK). In NPK-fertilized plots, the decline was strongest and associated with a strong divergence of plant trait composition from the control, reflecting a shift to a plant community adapted to nutrient-rich conditions. During the subsequent period of increase in species richness, the trait composition remained stable. These results show that plant species richness can, at least partially, recover after an initial diversity decline caused by fertilization.

Plant–insect interactions occur in spatially heterogeneous habitats. Understanding how such interactions shape density distributions of herbivores requires knowledge on how variation in plant traits (e.g. nutritional quality) affects herbivore abundance through, for example, affecting movement rates and aggregation behaviour. We studied the effects of plant patch size and herbivore-induced differences in plant nutritional quality on local densities of insect herbivores for two Brassica oleracea cultivars, i.e. white cabbage and Brussels sprouts. Early season herbivory as a treatment resulted in measurable differences in glucosinolate concentrations in both cultivars throughout the season. Herbivore induction and patch size both influenced community composition of herbivores in both cultivars, but the effects differed between species. Flea beetles (Phyllotreta spp.) were more abundant in large than in small patches, and this patch response was more pronounced on white cabbage than on Brussels sprouts. Herbivore-induction increased densities in all patches. Thrips tabaci was also more abundant in large patches and densities of this species were higher on Brussels sprouts than on white cabbage. Thrips densities were lower on induced than on control plants of both cultivars and this negative effect of induction tended to be more pronounced in large than in small patches. Densities of the cabbage moth (Mamestra brassicae) were lower on Brussels sprouts than on white cabbage and lower on herbivore-induced than on uninduced plants, with no effect of patch size. No clear effects of patch size and induction were found for aphids. This study shows that constitutive and herbivore-induced differences in plant traits interact with patch responses of insect herbivores.

Climate warming causes range shifts of many species toward higher latitudes and altitudes. However, range shifts of host species do not necessarily proceed at the same rates as those of their enemies and symbionts. Here, we examined how a range shifting plant species performs in soil from its original range in comparison with soil from the expansion range. Tragopogon dubius is currently expanding from southern into north-western Europe and we examined how this plant species responds to soil communities from its original and expansion ranges. We compared the performance of T. dubius with that of the closely related Tragopogon pratensis, which has a natural occurrence along the entire latitudinal gradient. Inoculation with the rhizosphere soil from T. dubius populations of the original range had a more negative effect on plant biomass production than inoculation with rhizosphere soil from the expansion range. Interestingly, the nonrange expander T. pratensis experienced a net negative soil effect throughout this entire range. The effects observed in this species pair may be due to release from soil born enemies or accumulation of beneficial soil born organisms. If this phenomenon applies broadly to other species, then range expansion may enable plants species to show enhanced performance.

International audience; Organic farming may contribute substantially to future agricultural production worldwide by improving soil quality and pest control, thereby reducing environmental impacts of conventional farming. We investigated in a comprehensive way soil chemical, as well as below and aboveground biological parameters of two organic and two conventional wheat farming systems that primarily differed in fertilization and weed management strategies. Contrast analyses identified management related differences between “herbicide-free” bioorganic (BIOORG) and biodynamic (BIODYN) systems and conventional systems with (CONFYM) or without manure (CONMIN) and herbicide application within a long-term agricultural experiment (DOK trial, Switzerland). Soil carbon content was significantly higher in systems receiving farmyard manure and concomitantly microbial biomass (fungi and bacteria) was increased. Microbial activity parameters, such as microbial basal respiration and nitrogen mineralization, showed an opposite pattern, suggesting that soil carbon in the conventional system (CONFYM) was more easily accessible to microorganisms than in organic systems. Bacterivorous nematodes and earthworms were most abundant in systems that received farmyard manure, which is in line with the responses of their potential food sources (microbes and organic matter). Mineral fertilizer application detrimentally affected enchytraeids and Diptera larvae, whereas aphids benefited. Spider abundance was favoured by organic management, most likely a response to increased prey availability from the belowground subsystem or increased weed coverage. In contrast to most soil-based, bottom-up controlled interactions, the twofold higher abundance of this generalist predator group in organic systems likely contributed to the significantly lower abundance of aboveground herbivore pests (aphids) in these systems. Long-term organic farming and the application of farmyard manure promoted soil quality, microbial biomass and fostered natural enemies and ecosystem engineers, suggesting enhanced nutrient cycling and pest control. Mineral fertilizers and herbicide application, in contrast, affected the potential for top-down control of aboveground pests negatively and reduced the organic carbon levels. Our study indicates that the use of synthetic fertilizers and herbicide application changes interactions within and between below and aboveground components, ultimately promoting negative environmental impacts of agriculture by reducing internal biological cycles and pest control. On the contrary, organic farming fosters microbial and faunal decomposers and this propagates into the aboveground system via generalist predators thereby increasing conservation biological control. However, grain and straw yields were 23% higher in systems receiving mineral fertilizers and herbicides reflecting the trade-off between productivity and environmental responsibility.

Tropospheric ozone has been recognized as one of the most important air pollutants. Many studies have shown that elevated ozone negatively impacts yields of important crops such as wheat or rice, but how ozone influences soil ecosystems of these crops and plant growth in rotation systems is less well understood. Using soil collected from a free-air ozone enrichment experiment running for 5 years, we carried out a plant-soil feedback experiment under greenhouse conditions to evaluate the influence of wheat cultivars ( Triticum aestivum L.) with different ozone-tolerance on rice ( Oryza sativa L.) grown in soils with or without a history of ozone exposure. Our results indicate that there were interactive effects of wheat cultivar and history of ozone exposure on soil respiration and the abundance of fungivorous nematodes. Moreover, the soil microbial community and the abundance of omnivorours-predatory nematodes varied in different wheat cultivars. These differences in the soil, in turn, had feedback effects on the succeeding growth of rice. Rice grown in soil in which previously the ozone-sensitive wheat cultivars Yangmai 2 or Yangmai 19 had grown, had lower shoot biomass than rice grown in the ozone-tolerant wheat cultivars Yangmai 16 soil. However, these cultivar specific effects on rice growth were independent from the previous ozone exposure of the soil. Our results suggest that, in rice-wheat rotation systems, when selecting wheat cultivars to cope with changing climatic conditions, such as elevated ozone, growers should consider the soil-feedback effects of these cultivars on the succeeding crop.

Although the consequences of changes in microbial diversity have received increasing attention, our understanding of processes that drive spatial variation in microbial diversity remains limited. In this study, we sampled bacterial communities in early and late successional temperate forests in Northeast China, and used distance-based redundancy analysis to examine how different processes influence bacterial beta diversity and phylogeny-based beta diversity using the Bray–Curtis and UniFrac metrics, respectively. After controlling for sampling effects, bacterial beta diversity in both forests was higher than expected by chance, which indicates that the bacterial community showed strong intraspecific aggregation. Both environmental filtering and dispersal limitation contributed to bacterial beta diversity and phylogeny-based beta diversity in the two forests. However, the relative importance of these different processes varied between the two forests. In the early successional forest, dispersal limitation played a dominant role in structuring the bacterial community, whereas the effects of environmental filtering were more important in the late successional forest. Our study revealed that bacterial beta diversity and phylogeny-based beta diversity in forest communities from the same region are regulated by different forces and that the relative importance of different forces varies over succession.

The increase in atmospheric carbon dioxide (CO2) levels is predicted to stimulate plant carbon (C) fixation, potentially influencing the size, structure and function of micro- and mesofaunal communities inhabiting the rhizosphere. To assess the effects of increased atmospheric CO2 on bacterial, fungal and nematode communities in the rhizosphere, Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown in three dune soils under controlled soil temperature and moisture conditions, while subjecting the aboveground compartment to defined atmospheric conditions differing in CO2 concentrations (350 and 700lLL � 1 ). Real-time polymerase chain reaction (PCR) and PCR-denaturing gradient gel electrophoresis methods were used to examine effects on the size and structure of rhizosphere communities. Multivariate analysis of community profiles showed that bacteria were most affected by elevated CO2, and fungi and nematodes to a lesser extent. The influence of elevated CO2 was plant dependent, with the mycorrhizal plant (F. rubra) exerting a greater influence on bacterial and fungal communities. Biomarker data indicated that arbuscular mycorrhizal fungi (AMF) may play an important role in the observed soil community responses. Effects of elevated CO2 were also soil dependent, with greater influence observed in the more organic-rich soils, which also supported higher levels of AMF colonization. These results indicate that responses of soil-borne communities to elevated CO2 are different for bacteria, fungi and nematodes and dependent on the plant type and soil nutrient availability. Nomenclature

1. As a result of global warming, species may spread into previously cool regions. Species that disperse faster than their natural enemies may become released from top-down control. We investigated whether plants originating from southern Europe and recently established in north-western Europe experience less soil pathogen effects than native species. 2. We selected three plant species originating from southern Europe that have immigrated into the Netherlands and three similar native Dutch species. All six plant species were grown in sterilized soils with a soil inoculum collected from the rhizospheres of field populations. As a control we grew a series of all six plant species with a sterilized rhizosphere inoculum. 3. We harvested the plants, added the conditioned soil to sterilized soil and grew a second generation of all six plant species in order to test for each plant pair feedback effects from the conditioned soil communities to conspecifics and heterospecifics. 4. The effect of the soil community is dependent on plant species, and is dependent on soil fertility in only one of the three pairs. 5. Soil conditioning caused less biomass reduction to exotic plant species than to native species, suggesting that exotic immigrants are less exposed to soil pathogens than similar native plant species. 6. Our results suggest that plant species that expand their range as a result of climate change may become released from soil pathogenic activity. Whether the exotics are released from soil pathogens, or whether they experience enhanced benefit from mutualistic symbionts remains to be studied. We conclude that range expansion may result in enemy release patterns that are similar to artificially introduced invasive exotic plant species. 7. The escape from enemies through range shifts changes key biotic interactions and complicates predictions of future distribution and dominance.

Soil abiotic and biotic factors play key roles in plant community dynamics. However, little is known about how soil biota influence vegetation changes over time. Here, we show that the effects of soil organisms may depend on both the successional development of ecosystems and on the successional position of the plants involved. In model systems of plants and soils from different successional stages, we observed negative plant-soil feedback for early-successional plant species, neutral feedback for mid-successional species, and positive feedback for late-successional species. The negative feedback of early-successional plants was independent of soil origin, while late-successional plants performed best in late- and worst in early-successional soil. Increased performance of the subordinate, late-successional plants resulted in enhanced plant community diversity. Observed feedback effects were more related to soil biota than to abiotic conditions. Our results show that temporal variations in plant-soil interactions profoundly contribute to plant community assemblage and ecosystem development.

The effect of host deprivation and egg expenditure on egg load, realized fecundity, and parasitism of the ichneumonid Mastrus ridibundus, a gregarious parasitoid introduced for the control of codling moth in California, were investigated under laboratory conditions. Females deprived of hosts had a greater egg load than females provided with excess hosts and no egg resorption was observed, the results even suggesting that females continue to add reserves to eggs over time. Host-deprived females were able to immediately use the eggs stored in their ovarioles, even after 6 days of host deprivation, and egg laying peaked on the first day of host availability. However, beyond the first day of reproduction, both daily oviposition and host attack rates were reduced, and overall, host-deprived females had a lower lifetime fecundity and attacked a lower number of hosts compared to females that were provided with excess host since their emergence. The occurrence of a potential trade-off between early and late reproduction and between reproduction and survival was also investigated. Early oviposition did not affect future reproduction nor survival. These results are discussed in the context classical biological control, with the view to understand how to manipulate host availability during the pre-release period to increase the reproductive potential, and therefore the fitness and establishment potential of M. ridibundus.

Plants have a variety of chemical defenses that often increase in concentration following attack by herbivores. Such induced plant responses can occur aboveground, in the leaves, and also belowground in the roots. We show here that belowground organisms can also induce defense responses aboveground and vice versa. Indirect defenses are particularly sensitive to interference by induced feeding activities in the other compartment, and this can disrupt multitrophic interactions. Unravelling the involvement of induced plant responses in the interactions between aboveground and belowground communities associated with plants is likely to benefit from comprehensive metabolomic analyses. Such analyses are likely to contribute to a better understanding of the costs and benefits involved in the selection for induced responses in plants.

Koinobiont parasitoids develop in hosts that continue feeding and growing during the course of parasitism. Here, we compared development of a solitary koinobiont endoparasitoid, Meteorus pulchricornis Westmael (Hymenoptera: Braconidae), in second (L2) and fourth (L4) instars of three host species that are closely related (Lepidoptera: Noctuidae) but which exhibit large variation in growth potential. Two hosts, Mamestra brassicae L. and Spodoptera littoralis Boisduval, may reach 1 g or more when the caterpillars are fully mature, whereas Spodoptera exigua Hübner is much smaller with mature caterpillars rarely exceeding 200 mg. Parasitoid survival (to pupation) in the two host instars was much higher on the larger hosts than on S. exigua. However, other fitness correlates in M. pulchricornis were very similar in the three host species. Development time was fairly uniform in L2 and L4 hosts of the three host species, whereas wasps were larger in L4 than in L2 hosts. However, M. pulchricornis developmentally arrested each of the hosts differently. The mass of dying L2 and L4 hosts after parasitoid larval egression (i.e., when they emerge from the dying caterpillar) varied significantly, with S. littoralis being by far the largest and S. exigua the smallest. These results reveal that M. pulchricornis is able to adjust its own development in response to species-specific differences in host resources.

Biochar application to soil is currently widely advocated for a variety of reasons related to sustainability. Typically, soil amelioration with biochar is presented as a multiple-‘win’ strategy, although it is also associated with potential risks such as environmental contamination. The most often claimed benefits of biochar (i.e. the ‘wins’) include (i) carbon sequestration; (ii) soil fertility enhancement; (iii) biofuel/bioenergy production; (iv) pollutant immobilization; and (v) waste disposal. However, the vast majority of studies ignore possible trade-offs between them. For example, there is an obvious trade-off between maximizing biofuel production and maximizing biochar production. Also, relatively little attention has been paid to mechanisms, as opposed to systems impacts, behind observed biochar effects, often leaving open the question as to whether they reflect truly unique properties of biochar as opposed to being simply the short-term consequences of a fertilization or liming effect. Here, we provide an outline for the future of soil biochar research. We first identify possible trade-offs between the potential benefits. Second, to be able to better understand and quantify these trade-offs, we propose guidelines for robust experimental design and selection of appropriate controls that allow both mechanistic and systems assessment of biochar effects and trade-offs between the wins. Third, we offer a conceptual framework to guide future experiments and suggest guidelines for the standardized reporting of biochar experiments to allow effective between-site comparisons to quantify trade-offs. Such a mechanistic and systems framework is required to allow effective comparisons between experiments, across scales and locations, to guide policy and recommendations concerning biochar application to soil.

Competition and herbivory are two major factors that can influence plant growth and plant defence. Although these two factors are often studied separately, they do not operate independently. We examined how aboveground herbivory by beet armyworm larvae (Spodoptera exigua) and belowground herbivory by wireworms (Agriotes lineatus) influenced competition between the plant species Jacobaea vulgaris and Leucanthemum vulgare exposed to three competition levels (no, intra-, and interspecific competition). In addition, we studied the effects of herbivory and competition on pyrrolizidine alkaloid (PA) concentrations in leaves of J. vulgaris. For J. vulgaris, aboveground herbivory significantly reduced shoot biomass while belowground herbivory increased root biomass. Biomass of L. vulgare was not affected by herbivory. Competition caused a reduction in biomass for both plant species, but herbivory did not affect the outcome of the competition. However, competition significantly influenced the amount of leaf damage experienced by the plants. A L. vulgare plant had significantly less damage from aboveground herbivores when grown together with J. vulgaris than when grown alone or in intraspecific competition, while a J. vulgaris plant experienced lowest damage in conditions of intraspecific competition. The total PA concentration in J. vulgaris leaves was highest for plants exposed to interspecific competition. Root herbivory caused an increase in the relative concentration of N-oxides, the less toxic form of PAs, in leaves of plants that were grown without competition, but a decrease in plants exposed to competition. Our study shows that competition and herbivory but also the type of competition and whether herbivory occurs above- or belowground, all influence plant performance. However, overall, there was no evidence that herbivory affects plant–plant competition.