Plant–soil feedback of native and range-expanding plant species is insensitive to temperature

Temperature change affects many aboveground and belowground ecosystem processes. Here we investigate the effect of a 5°C temperature increase on plant–soil feedback. We compare plant species from a temperate climate region with immigrant plants that originate from warmer regions and have recently shifted their range polewards. We tested whether the magnitude of plant–soil feedback is affected by ambient temperature and whether the effect of temperature differs between these groups of plant species. Six European/Eurasian plant species that recently colonized the Netherlands (non-natives), and six related species (natives) from the Netherlands were selected. Plant–soil feedback of these species was determined by comparing performance in conspecific and heterospecific soils. In order to test the effect of temperature on these plant–soil feedback interactions, the experiments were performed at two greenhouse temperatures of 20/15°C and 25/20°C, respectively. Inoculation with unconditioned soil had the same effect on natives and non-natives. However, the effect of conspecific conditioned soil was negative compared to heterospecific soil for natives, but was positive for non-natives. In both cases, plant–soil interactions were not affected by temperature. Therefore, we conclude that the temperature component of climate change does not affect the direction, or strength of plant–soil feedback, neither for native nor for non-native plant species. However, as the non-natives have a more positive soil feedback than natives, climate warming may introduce new plant species in temperate regions that have less soil-borne control of abundance

Plant–soil feedbacks of exotic plant species across life forms: a meta-analysis

Invasive exotic plant species effects on soil biota and processes in their new range can promote or counteract invasions via changed plant–soil feedback interactions to themselves or to native plant species. Recent meta-analyses reveale that soil influenced by native and exotic plant species is affecting growth and performance of natives more strongly than exotics. However, the question is how uniform these responses are across contrasting life forms. Here, we test the hypothesis that life form matters for effects on soil and plant–soil feedback. In a meta-analysis we show that exotics enhanced C cycling, numbers of meso-invertebrates and nematodes, while having variable effects on other soil biota and processes. Plant effects on soil biota and processes were not dependent on life form, but patterns in feedback effects of natives and exotics were dependent on life form. Native grasses and forbs caused changes in soil that subsequently negatively affected their biomass, whereas native trees caused changes in soil that subsequently positively affected their biomass. Most exotics had neutral feedback effects, although exotic forbs had positive feedback effects. Effects of exotics on natives differed among plant life forms. Native trees were inhibited in soils conditioned by exotics, whereas native grasses were positively influenced in soil conditioned by exotics. We conclude that plant life form matters when comparing plant–soil feedback effects both within and between natives and exotics. We propose that impact analyses of exotic plant species on the performance of native plant species can be improved by comparing responses within plant life form

Testing the paradox of enrichment along a land use gradient in a multitrophic aboveground and belowground community

In the light of ongoing land use changes, it is important to understand how multitrophic communities perform at different land use intensities. The paradox of enrichment predicts that fertilization leads to destabilization and extinction of predator-prey systems. We tested this prediction for a land use intensity gradient from natural to highly fertilized agricultural ecosystems. We included multiple aboveground and belowground trophic levels and land use-dependent searching efficiencies of insects. To overcome logistic constraints of field experiments, we used a successfully validated simulation model to investigate plant responses to removal of herbivores and their enemies. Consistent with our predictions, instability measured by herbivore-induced plant mortality increased with increasing land use intensity. Simultaneously, the balance between herbivores and natural enemies turned increasingly towards herbivore dominance and natural enemy failure. Under natural conditions, there were more frequently significant effects of belowground herbivores and their natural enemies on plant performance, whereas there were more aboveground effects in agroecosystems. This result was partly due to the “boom-bust” behavior of the shoot herbivore population. Plant responses to herbivore or natural enemy removal were much more abrupt than the imposed smooth land use intensity gradient. This may be due to the presence of multiple trophic levels aboveground and belowground. Our model suggests that destabilization and extinction are more likely to occur in agroecosystems than in natural communities, but the shape of the relationship is nonlinear under the influence of multiple trophic interactions.

Specific bottom–up effects of arbuscular mycorrhizal fungi across a plant–herbivore–parasitoid system

The majority of plants are involved in symbioses with arbuscular mycorrhizal fungi (AMF), and these associations are known to have a strong influence on the performance of both plants and insect herbivores. Little is known about the impact of AMF on complex trophic chains, although such effects are conceivable. In a greenhouse study we examined the effects of two AMF species, Glomus intraradices and G. mosseae on trophic interactions between the grass Phleum pratense, the aphid Rhopalosiphum padi, and the parasitic wasp Aphidius rhopalosiphi. Inoculation with AMF in our study system generally enhanced plant biomass (+5.2%) and decreased aphid population growth (−47%), but there were no fungal species-specific effects. When plants were infested with G. intraradices, the rate of parasitism in aphids increased by 140% relative to the G. mosseae and control treatment. When plants were associated with AMF, the developmental time of the parasitoids decreased by 4.3% and weight at eclosion increased by 23.8%. There were no clear effects of AMF on the concentration of nitrogen and phosphorus in plant foliage. Our study demonstrates that the effects of AMF go beyond a simple amelioration of the plants’ nutritional status and involve rather more complex species-specific cascading effects of AMF in the food chain that have a strong impact not only on the performance of plants but also on higher trophic levels, such as herbivores and parasitoids

Impact of foliar herbivory on the development of a root-feeding insect and its parasitoid

The majority of studies exploring interactions between above- and below-ground biota have been focused on the effects of root-associated organisms on foliar herbivorous insects. This study examined the effects of foliar herbivory by Pieris brassicae L. (Lepidoptera: Pieridae) on the performance of the root herbivore Delia radicum L. (Diptera: Anthomyiidae) and its parasitoid Trybliographa rapae (Westwood) (Hymenoptera: Figitidae), mediated through a shared host plant Brassica nigra L. (Brassicaceae). In the presence of foliar herbivory, the survival of D. radicum and T. rapae decreased significantly by more than 50%. In addition, newly emerged adults of both root herbivores and parasitoids were significantly smaller on plants that had been exposed to foliar herbivory than on control plants. To determine what factor(s) may have accounted for the observed results, we examined the effects of foliar herbivory on root quantity and quality. No significant differences in root biomass were found between plants with and without shoot herbivore damage. Moreover, concentrations of nitrogen in root tissues were also unaffected by shoot damage by P. brassicae larvae. However, higher levels of indole glucosinolates were measured in roots of plants exposed to foliar herbivory, suggesting that the development of the root herbivore and its parasitoid may be, at least partly, negatively affected by increased levels of these allelochemicals in root tissues. Our results show that foliar herbivores can affect the development not only of root-feeding insects but also their natural enemies. We argue that such indirect interactions between above- and below-ground biota may play an important role in the structuring and functioning of communities

Large grazers modify effects of aboveground–belowground interactions on small-scale plant community composition

Aboveground and belowground organisms influence plant community composition by local interactions, and their scale of impact may vary from millimeters belowground to kilometers aboveground. However, it still poorly understood how large grazers that select their forage on large spatial scales interact with small-scale aboveground–belowground interactions on plant community heterogeneity. Here, we investigate how cattle (Bos taurus) modify the effects of interactions between yellow meadow ants (Lasius flavus) and European brown hares (Lepus europaeus) on the formation of small-scale heterogeneity in vegetation composition. In the absence of cattle, hares selectively foraged on ant mounds, while under combined grazing by hares and cattle, vertebrate grazing pressure was similar on and off mounds. Ant mounds that were grazed by only hares had a different plant community composition compared to their surroundings: the cover of the grazing-intolerant grass Elytrigia atherica was reduced on ant mounds, whereas the relative cover of the more grazing-tolerant and palatable grass Festuca rubra was enhanced. Combined grazing by hares and cattle, resulted in homogenization of plant community composition on and off ant mounds, with high overall cover of F. rubra. We conclude that hares can respond to local ant–soil–vegetation interactions, because they are small, selective herbivores that make their foraging decisions on a local scale. This results in small-scale plant patches on mounds of yellow meadow ants. In the presence of cattle, which are less selective aboveground herbivores, local plant community patterns triggered by small-scale aboveground–belowground interactions can disappear. Therefore, cattle modify the consequences of aboveground–belowground interactions for small-scale plant community composition

Plant Diversity Surpasses Plant Functional Groups and Plant Productivity as Driver of Soil Biota in the Long Term

One of the most significant consequences of contemporary global change is the rapid decline of biodiversity in many ecosystems. Knowledge of the consequences of biodiversity loss in terrestrial ecosystems is largely restricted to single ecosystem functions. Impacts of key plant functional groups on soil biota are considered to be more important than those of plant diversity; however, current knowledge mainly relies on short-term experiments.We studied changes in the impacts of plant diversity and presence of key functional groups on soil biota by investigating the performance of soil microorganisms and soil fauna two, four and six years after the establishment of model grasslands. The results indicate that temporal changes of plant community effects depend on the trophic affiliation of soil animals: plant diversity effects on decomposers only occurred after six years, changed little in herbivores, but occurred in predators after two years. The results suggest that plant diversity, in terms of species and functional group richness, is the most important plant community property affecting soil biota, exceeding the relevance of plant above- and belowground productivity and the presence of key plant functional groups, i.e. grasses and legumes, with the relevance of the latter decreasing in time.Plant diversity effects on biota are not only due to the presence of key plant functional groups or plant productivity highlighting the importance of diverse and high-quality plant derived resources, and supporting the validity of the singular hypothesis for soil biota. Our results demonstrate that in the long term plant diversity essentially drives the performance of soil biota questioning the paradigm that belowground communities are not affected by plant diversity and reinforcing the importance of biodiversity for ecosystem functioning

Decomposers and root feeders interactively affect plant defence in Sinapis alba

Aboveground herbivory is well known to change plant growth and defence. In contrast, effects of soil organisms, acting alone or in concert, on allocation patterns are less well understood. We investigated separate and combined effects of the endogeic earthworm species Aporrectodea caliginosa and the root feeding nematode species Pratylenchus penetrans and Meloidogyne incognita on plant responses including growth and defence metabolite concentrations in leaves of white mustard, Sinapis alba. Soil biota had a strong impact on plant traits, with the intensity varying due to species combinations. Nematode infestation reduced shoot biomass and nitrogen concentration but only in the absence of earthworms. Earthworms likely counteracted the negative effects of nematodes. Infestation with the migratory lesion-nematode P. penetrans combined with earthworms led to increased root length. Earthworm biomass increased in the presence of this species, indicating that these nematodes increased the food resources of earthworms—presumably dead and decaying roots. Nitrogen-based defence compounds, i.e. glucosinolates, did not correlate with nitrogen levels. In the presence of earthworms, concentrations of aromatic glucosinolates in leaves were significantly increased. In contrast, infection with P. penetrans strongly decreased concentrations of glucosinolates (up to 81%). Infestation with the sedentary nematode M. incognita induced aromatic glucosinolates by more than 50% but only when earthworms were also present. Myrosinase activities, glucosinolate-hydrolysing enzymes, were unaffected by nematodes but reduced in the presence of earthworms. Our results document that root-feeding nematodes elicit systemic plant responses in defence metabolites, with the responses varying drastically with nematode species of different functional groups. Furthermore, systemic plant responses are also altered by decomposer animals, such as earthworms, challenging the assumption that induction of plant responses including defence traits is restricted to herbivores. Soil animals even interact and modulate the individual effects on plant growth and plant defence, thereby likely also influencing shoot herbivore attack