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Recent demonstrations of the role of plant–soil biota interactions have challenged the conventional view that vegetation changes are mainly driven by changing abiotic conditions. However, while this concept has been validated under natural conditions, our understanding of the long-term consequences of plant–soil interactions for above-belowground community assembly is restricted to mathematical and conceptual model projections. Here, we demonstrate experimentally that one-time additions of soil biota and plant seeds alter soil-borne nematode and plant community composition in semi-natural grassland for 20 years. Over time, aboveground and belowground community composition became increasingly correlated, suggesting an increasing connectedness of soil biota and plants. We conclude that the initial composition of not only plant communities, but also soil communities has a long-lasting impact on the trajectory of community assembly.

1. Belowground nematodes are important for soil functioning, as they are ubiquitous and operate at various trophic levels in the soil food web. However, morphological nematode community analysis is time consuming and requires ample training. qPCR-based nematode identification techniques are well available, but high throughput sequencing (HTS) might be more suitable for non-targeted nematode community analysis. 2. We compared effectiveness of qPCR and HTS-based approaches with morphological nematode identification while examining how climate warming-induced plant range expansion may influence belowground nematode assemblages. We extracted nematodes from soil of Centaurea stoebe and C. jacea populations in Slovenia, where both plant species are native, and Germany, where C. stoebe is range expander and C. jacea is native. Half of each nematode sample was identified morphologically and the other half was analysed using targeted qPCR and a novel HTS approach. 3. HTS produced the highest taxonomic resolution of the nematode community. Nematode taxa abundances correlated between the methods. Therefore, especially relative HTS and relative morphological data revealed nearly identical ecological patterns. All methods showed lower numbers of plant feeding nematodes in rhizosphere soils of C. stoebe compared to C. jacea. However, a profound difference was observed between absolute and relative abundance data; both sampling origin and plant species affected relative abundances of bacterivorous nematodes, whereas there was no effect on absolute abundances. 4. Taken together, as HTS correlates with relative analyses of soil nematode communities, while providing highest taxonomic resolution and sample throughput, we propose a combination of HTS with microscopic counting to supplement important quantitative data on soil nematode communities. This provides the most cost-effective, in-depths methodology to study soil nematode community responses to changes in the environment. This m

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid-and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.

Plant diversity is known to influence the abundance and diversity of belowground biota; however, patterns are not well predictable and there is still much unknown about the driving mechanisms. We analyzed changes in soil nematode community composition as affected by long-term manipulations of plant species and functional group diversity in a field experiment with plant species diversity controlled by sowing a range of 1-60 species mixtures and controlling non-sown species by hand weeding. Nematode communities contain a variety of species feeding on bacteria, fungi, plants, invertebrates, while some are omnivorous. We analyzed responses of nematode abundance and diversity to plant species and functional diversity, and used structural equation modeling (SEM) to explore the possible mechanisms underlying the observed patterns. The abundance of individuals of all nematode feeding types, except for predatory nematodes, increased with both plant species and plant functional group diversity. The abundance of microbial-feeding nematodes was related positively to aboveground plant community biomass, whereas abundance of plant-feeding nematodes was related positively to shoot C:N ratio. The abundance of predatory nematodes, in turn, was positively related to numbers of plant-feeding nematodes, but not to the abundance of microbial feeders. Interestingly, the numbers of plant-feeding nematodes per unit root mass were lowest in the high-diversity plant communities, pointing at reduced exposure to belowground herbivores when plants grow in species-diverse communities. Taxon richness of plant-feeding and microbialfeeding nematodes increased with plant species and plant functional group diversity. Increasing plant functional group diversity also enhanced taxon richness of predatory nematodes. The SEM suggests that bottom-up control effects of plant species and plant functional group diversity on abundance of nematodes in the various feeding types predominantly involve mechanistic

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.

Aboveground herbivores have strong effects on grassland nitrogen (N) cycling. They can accelerate or slow down soil net N mineralization depending on ecosystem productivity and grazing intensity. Yet, most studies only consider either ungulates or invertebrate herbivores, but not the combined effect of several functionally different vertebrate and invertebrate herbivore species or guilds. We assessed how a diverse herbivore community affects net N mineralization in subalpine grasslands. By using size-selective fences, we progressively excluded large, medium, and small mammals, as well as invertebrates from two vegetation types, and assessed how the exclosure types (ET) affected net N mineralization. The two vegetation types differed in long-term management (centuries), forage quality, and grazing history and intensity. To gain a more mechanistic understanding of how herbivores affect net N mineralization, we linked mineralization to soil abiotic (temperature; moisture; NO3?, NH4+, and total inorganic N concentrations/pools; C, N, P concentrations; pH; bulk density), soil biotic (microbial biomass; abundance of collembolans, mites, and nematodes) and plant (shoot and root biomass; consumption; plant C, N, and fiber content; plant N pool) properties. Net N mineralization differed between ET, but not between vegetation types. Thus, short-term changes in herbivore community composition and, therefore, in grazing intensity had a stronger effect on net N mineralization than long-term management and grazing history. We found highest N mineralization values when only invertebrates were present, suggesting that mammals had a negative effect on net N mineralization. Of the variables included in our analyses, only mite abundance and aboveground plant biomass explained variation in net N mineralization among ET. Abundances of both mites and leaf-sucking invertebrates were positively correlated with aboveground plant biomass, and biomass increased with progressive exclusion. The

Aims Coastal sand dunes have a well-established abiotic gradient from beach to land and a corresponding spatial gradient of plant species representing succession in time. Here, we relate the distribution of plant-feeding nematodes with dominant plant species in the field to host specialization and impacts on plant species under controlled greenhouse conditions. Methods We assessed plant-feeding nematodes in soil and roots of six plant species that dominate the vegetation at successional positions along the gradient. In controlled conditions, we determined performance of all plant-feeding nematodes on each plant species and their effects on plant biomass. Results Specialist feeding type nematodes were confined to plant species in either foredunes or landward dunes. Generalist feeding type nematodes were found in highest numbers in the landward dunes. Most tested nematode species decreased root, but not shoot or rhizome biomass. Conclusions Host plant suitability determined occurrence of some plant-feeding nematodes in dunes, but abiotic and biotic soil conditions may play a role as well. Generalist feeding type nematodes were able to reproduce on all plant species. Feeding specialists, which are more protected by plant roots, might prefer host plants in the foredunes for the same reason as their host plants: to escape from natural enemies.

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 sa