Nematode Assemblages Research Articles

The Influential Role of the Habitat on the Diversity Patterns of Free-Living Aquatic Nematode Assemblages in the Cuban Archipelago

Free living nematodes are the most abundant and diverse metazoans in aquatic sediments. We used a framework of habitat types to reveal quantitative patterns in species richness (SR), β-diversity, and biological traits (BT). Meiofauna was quantitatively collected from 60 sites within nine habitat types and 24,736 nematodes were identified to species level. We reported a regional richness of 410 ± 12 species for the Cuban archipelago; however, caves and deep waters need to be sampled more intensively. Relationships between SR and abundance supported the dynamic equilibrium model with habitats ordered across gradients of resource availability and physical disturbance. Seagrass meadows were the most specious and freshwater/anchihaline caves the least diverse habitats. Differences in β-diversity likely were due to habitat heterogeneity and limitations for dispersal. The assemblage composition was unique in some habitats likely reflecting the effects of habitat filtering. However, coastal habitats shared many species reflecting high connectivity and dispersal capability of nematodes due to hydrodynamics. The BTs “life strategy”, “trophic group”, and “tail shape” reflected ecological adaptations; but “amphidial fovea” and “cuticle”, likely reflected phylogenetic signatures from families/genera living in different habitats. Habitat type played an influential role in the diversity patterns of aquatic nematodes from taxonomic and functional points of view.

Soil nematodes in the rhizosphere of a metal accumulating plant in a pollution gradient from a non-ferrous metal factory in Bulgaria

Nematodes were studied at sites with low, medium and high level of soil metal contamination in the area of a non-ferrous metal plant. Soil total metal concentrations ranged from values below their maximum permissible concentrations (MPC) in soil to 48, 44, 16 and 4 times higher than the MPC for Cd, Pb, Zn and Cu, respectively. Nematodes were isolated from uncultivated, monoculture stands of the metal accumulating mustard weed (Lepidium draba L., Brassicaceae) in April, May and June 2015. Overall, 55 nematode genera were identified during the investigation: 50 genera at low, 39 at medium, 37 at high levels of soil metal pollution. Several nematode diversity measures and the specific responses of some nematode genera differentiated the three investigated sites. Both nematode richness (S) and diversity (H') of genera correlated negatively with the soil metal concentrations in the following order: Cd>Pb>Zn>Cu. Several genera (Alaimus, Cylindrolaimus, Paramphidelus, Scutylenchus, Steinernema) were common at the least contaminated site and were either rare or not found at the rest of the sites. Some genera (Clarkus, Filenchus) were most abundant at the medium level of contamination. The abundance of eleven genera correlated negatively with the metal concentrations in the samples. Most of the negative correlations (Acrobeles, Coslenchus, Geomonhystera, Plectus) were in the following order: Cd>Zn>Pb>Cu. The abundance of nine genera correlated positively with the metal concentrations and most of their correlations were in the order: Cu>Pb>Zn>Cd. Faunal profile analyses of the free living nematode assemblages revealed higher values of Structure index (SI) at low (75–91%) and medium (77–87%) levels of contamination in comparison with the most polluted site (35–46%). Nematode structure metabolic footprints (SFP) at low and medium levels of contamination were much higher than at the high pollution level. Both SI and SFP at the medium level of metal contamination indicated low bioavailability and low toxicity of Pb (1290 mg kg-1soil), Cd (34 mg kg-1soil), Zn (1779 mg kg-1soil) and Cu (190 mg kg-1soil) for the free-living nematodes, isolated from the rhizosphere of the mustard weed at this site. The rhizosphere of the metal accumulating plant might be protective for these nematodes, providing conditions of reduced bioavailable metals in contaminated soil during the vegetation period of the plants.

Diversity and incidence of plant-parasitic nematodes associated with saffron (Crocus sativus L.) in Morocco and their relationship with soil physicochemical properties

Summary Saffron (Crocus sativus) fields in Morocco’s Taliouine and Taznakht regions were surveyed between January and April 2018 to study the diversity and incidence of plant-parasitic nematodes and assess the effects of soil physicochemical properties on the nematodes. Fourteen nematode genera were identified in soil and root samples collected from 66 saffron fields. The most common plant-parasitic nematodes in the Taliouine region were Pratylenchus spp. and Helicotylenchus spp. In the Taznakht region, the most common nematodes were Pratylenchus spp., Tylenchorhynchus spp. and Ditylenchus dipsaci. Nematodes, particularly Pratylenchus spp. and Ditylenchus spp., were abundant and frequent throughout the region. Several nematode genera were significantly associated with soil texture and mineral content, indicating that soil properties play an important role in plant-parasitic nematode communities. This description of plant-parasitic nematode assemblages associated with saffron fields in Morocco and their relationship with soil physicochemical properties provides a starting point from which appropriate nematode management strategies can be implemented.

Influence of Asari clam (<i>Ruditapes philippinarum</i>) abundance increase caused by cover-net on the nematode assemblages on a tidal flat

Influence of Asari clam (<i>Ruditapes philippinarum</i>) abundance increase caused by cover-net on the nematode assemblages on a tidal flat

Dominant plant species influence nematode richness by moderating understory diversity and microbial assemblages

Belowground assemblages are tightly linked to the aboveground vegetation, and often differ between plant species and vegetation types due to direct and indirect influences. However, the relative contribution of these direct and indirect influences of plants on belowground organisms differs among taxa and remains poorly understood. We established a plant removal experiment to better understand the effects of dominant plant species on nematode assemblages in an alpine meadow on the Tibetan plateau. We quantified plant community diversity, soil microbial assemblage richness and edaphic properties to explore how a dominant shrub and graminoids affect nematode assemblage structure and community-weighted mean (CWM) biomass using structural equation modelling (SEM). We found contrasting responses of nematode richness and CWM biomass of nematodes to the removal of shrubs and graminoids, including an intriguing interaction between them. The latter indicates that interactions between shrubs and graminoids modify nematode communities rather than their independent effects. Our results further suggest that dominant plants predominantly indirectly influence nematode richness through changes in biotic variables, specifically understory diversity, and bacterial and fungal richness. However, the dominant plants had no direct and limited indirect effects on CWM nematode biomass, which instead increased with soil nitrogen content, and decreased with soil pH, carbon and ammonium content. Our results provide insight into the relative role of direct and indirect influences on belowground assemblages and highlight the importance of dominant plants in maintaining belowground diversity. By contrast, edaphic properties appear more important to belowground biomass, likely reflecting longer term influences of the plant community on resource availability and quality. Vegetation changes in grassland, such as reduced dominance of shrubs and graminoids, might therefore reduce soil biodiversity relatively rapidly but contribute to longer term impacts through changes in biogeochemical cycles.

Effects of Mercury (Hg) on Soil Nematodes: A Microcosm Approach.

Mercury (Hg), one of the most toxic heavy metals, is commonly used in the gold extraction process in small-scale mining operations in many countries. Our previous field work on the impact of mining on soil nematode assemblages in a small-scale mining area in Sibutad, the Philippines, revealed no significant negative effects despite sometimes strongly elevated Hg concentrations. Using a microcosm approach, we now applied similar Hg concentrations as commonly found in these field sites (2.5, 5, and 10mg/kg Hg) and determined their impact on nematode assemblages from a different soil with different physicochemical soil attributes. Our results demonstrate (a) limited "bottling" effects (incubation effects) after a 45-day incubation period: a nematode abundance decrease of up to 37%, but absence of significant differences in diversity and nematode assemblage composition; (b) that total nematode abundance already decreased at Hg concentrations (2.5mg/kg), which did not yield significant impacts on other nematode assemblage descriptors, such as assemblage composition and different diversity indices; and (c) that the Hg concentrations found in the Sibutad field sites can be detrimental to soil nematode assemblages. The discrepancy between our microcosm and the field-based results is probably related to differences in physicochemical soil attributes (e.g., OM contents, soil pH), which suggests that nematode-based environmental assessments should be interpreted in a context-dependent manner.

A comparison of epiphytic nematode diversity and assemblages inCorallinaturves on British and South Korean coasts across hierarchical spatial scales

AbstractCosmopolitan habitat-forming taxa of algae such as the genusCorallinaprovide an opportunity to compare patterns of biodiversity over wide geographic scales. Nematode assemblages inhabitingCorallinaturves were compared between the south coasts of the British Isles and South Korea. A fully nested design was used with three regions in each country, two shores in each region and replicate samples taken from three patches on each shore to compare differences in the taxonomic and biological trait composition of nematode assemblages across scales. A biological traits approach, based on functional diversity of nematodes, was used to make comparisons between countries, among regions, between shores and among patches. The taxonomic and biological trait compositions of nematode assemblages were significantly different across all spatial scales (patches, shores, regions and countries). There is greater variation amongst nematode assemblages at the scale of shore than at other spatial scales. Nematode assemblage structure and functional traits are influenced by the local environmental factors on each shore including sea-surface temperature, the amount of sediment trapped inCorallinaspp. and tidal range. The sea-surface temperature and the amount of sediment trapped inCorallinaspp. were the predominant factors determining nematode abundance and composition of assemblages and their functional diversity.

ВІЛЬНОЖИВУЧІ МОРСЬКІ НЕМАТОДИ ПРИБЕРЕЖНОЇ ЗОНИ О. ЗМІЇНИЙ УКРАЇНСЬКОГО ШЕЛЬФУ ЧОРНОГО МОРЯ

The species diversity, quantitative parameters and spatial distribution of the free-living marine nematodes in the meiobenthic community of the coastal zone area near the Snake Island, Black Sea, Ukraine shelf, have been studied for the first time. In total of 47 species from 5 orders, 14 families and 31 genera were registered. The representatives of orders Monhysterida and Enoplida were most abundant. The results of the comparative analysis of nematode assemblage in dependence of the substrate type are described. The percentage of nematodes in total meiobenthos in piers fouling consisted of 16% only, but on silt bottoms it reached 60.8%. The species diversity also increases on silt bottoms. Four nematode species are registered in piers fouling, but 36 on silts. The omnivores-carnivores consisted of 50% of the nematode assemblage in piers fouling. On silts, the percentage of non-selective deposit feeders reached 47%, but epistrate feeders decreased up to 14%.

Trichinella pseudospiralis in a wolverine (Gulo gulo) from the Canadian North.

Species of Trichinella are a globally distributed assemblage of nematodes, often with distinct host ranges, which include people, domestic, and wild animals. Trichinella spp. are important in northern Canada, where dietary habits of people and methods of meat preparation (drying, smoking, fermenting as well as raw) increase the risk posed by these foodborne zoonotic parasites. Outbreaks in the arctic and subarctic regions of Canada and the United States are generally attributed to T. nativa (T2) or the T6 genotype, when genetic characterization is performed. We report the discovery of Trichinella pseudospiralis (T4), a non-encapsulated species, in a wolverine (Gulo gulo) from the Northwest Territories of Canada. This parasite has been previously reported elsewhere from both mammals and carnivorous birds, but our findings represent new host and geographic records for T. pseudospiralis. Multiplex PCR and sequencing of fragments of Cytochrome Oxidase Subunit I (COI) and D3 rDNA confirmed the identification. Phylogenetically, Canadian isolates linked with each other and others derived from Palearctic or Neotropical regions, but not elsewhere in the Nearctic (continental USA). We suggest that migratory birds might have played a role in the dispersal of this pathogen 1000's of km to northwestern Canada. Wolverines are not typically consumed by humans, and thus should not pose a direct food safety risk for trichinellosis. However, the current finding suggests that they may serve as an indicator of a broader distribution for T. pseudospiralis. Along with infection risk already recognized for T. nativa and Trichinella T6, our observations emphasize the need for further studies using molecular diagnostics and alternative methods to clarify if this is a solitary case, or if T. pseudospiralis and other freeze susceptible species of Trichinella (such as T. spiralis) circulate more broadly in wildlife in Canada, and elsewhere.

Bioindicators or sediment relationships: Evaluating ecological responses from sandy beach nematodes

Sandy beaches from tropical countries are currently facing many challenges due to rapid urban development and its impacts on coastal areas. Despite their aesthetic, recreational and ecological importance, these environments are neglected when it comes to assessment and conservation measures, which can be done in several ways, including biomonitoring. Nematodes are amongst the most suitable organisms to be used as ecological indicators in sandy beaches due to their high abundance on marine sediments and its rapid responses to different sorts of impacts. We analyzed the nematode assemblages and the environmental variables from seven sandy beaches under different types of pressure from Rio de Janeiro state, in Brazil, and applied the biological indexes that use nematodes as bioindicators in order to evaluate differences on the ecological status of these beaches. Sampling took place in the summer of 2015, during the spring low tide. Physicochemical characteristics, microbiology and granulometry were measured alongside human density on each of the beaches and linked to nematode distribution found on the intertidal zone. Botafogo beach, already known for being highly affected by sewage disposal, showed high values for organic matter content and the least diverse assemblage, with high dominance from genus Chromadorita. Despite the higher human density, most urban and touristic beaches (Barra da Tijuca and Copacabana) did not show distinct values for the diversity measures when compared to the most preserved beaches (Restinga da Marambaia and Fora - Urca). While the applied biological indexes did not show clear answers concerning the ecological health of the studied sites; the sediment sorting coefficient was the variable that best explained the nematode distribution and some genera are associated to certain spectrums with this variable. For instance, opportunist genera such as Daptonema and Theristus were found on broader spectrums of sorting coefficient while predators with bigger body diameters showed a more restricted distribution. As the mean grain size is still considered the main variable on nematode distribution for sandy beaches, this study reveals that the sorting coefficient also gives important answers for the nematode distribution.

Spatial scale influences diversity patterns of free-living nematode assemblages in coral degradation zones from the Caribbean Sea

Diversity of marine nematodes in coral degradation zones (CDZs) has been poorly studied despite of its contribution to global coral reef diversity; additionally, effects of spatial scales on nematode assemblages are also largely unknown. To fill this gap, we studied the marine nematode assemblages in CDZs from two coral reefs in the Caribbean Sea to describe the diversity, test the effects of spatial scales, and explore if there were adaptive biological trait combinations. We sampled 2 reefs (Ballenatos and Punta Frances), 6 sites, and 20 dead coral piles in a fully nested design identifying the nematodes to species level. CDZs harbored a diverse nematode assemblage of 112 species with large spatial turnover. Differences between reefs in abundance and species density were probably related to differential energy availability, with Punta Frances receiving larger input of material and energy from land. The spatial scale had a significant effect on the species richness, whereas differences in species composition were mainly driven by the scale at which ecological drivers operated (10−1 m for interstitial heterogeneity vs. 105 m for dispersal). Geographical distances in the order of 180 km likely constituted barriers to nematode dispersal and as such promoted assemblage dissimilarity. Our evidence indicated that a particular set of biological traits favored the adaptation of nematodes to CDZs, namely a distinctive combination of armed stoma, ornamented cuticle, and conical tail.

Effects of the water-soluble fraction of a crude oil on freshwater meiofauna and nematode assemblages

Oil water-soluble fractions (WSFs) compounds have low persistence in water; evaporating in a matter of hours to days. Nonetheless, they pose high toxicity to exposed biota. Their effects may be instantaneous or delayed, affecting, respectively, mainly survival vs growth and reproduction. We investigated the effects of crude oil WSFs on freshwater meiobenthos, with a focus on nematode assemblages, in community microcosm experiments lasting 15 weeks. Treatments consisted of the application of different concentrations of oil WSFs, i.e. high (100%) medium (50%) and low (10%), and effects were assessed one, three, nine and 15 weeks after contamination, allowing us to detect both short-term and lasting effects of oil-WSF. Additionally, we compared the effects of a single contamination event with those of a so-called ‘constant’ oil-WSF contamination where we replenished evaporated water with water containing the medium concentration of oil WSF. Next to nematodes, the most abundant meiofaunal taxa were rotifers, gastrotrichs, oligochaetes and tardigrades. Total abundance, different diversity indices, the composition of feeding-types and the age structure were investigated in the assessment of direct oil effects on the structure of nematode assemblages. Limited immediate effects were observed, except for a significant decrease of the index of taxonomic distinctness, which already appeared in the first week. Significant impacts on total nematode abundance, diversity and species composition only became apparent after 9–15 weeks of incubation, indicating that delayed effects of a single exposure are far more pronounced than instantaneous effects. Moreover, for most response variables, the strongest impacts were not observed in the highest-concentration treatment, but in a medium-concentration treatment with regular replenishment of oil WSF, suggesting that internal exposure may be important in generating effects. Furthermore, the predictability of the sensitivity of individual species was sometimes poor, which may not only result from these species' sensitivities, but also from alterations in interspecific interactions in polluted communities. Further toxicity tests should be carried out in order to unravel the main modes of action of crude oil WSF which lead to the observed long-term sublethal effects on nematode communities.

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

Effects of long-term tillage on carbon partitioning of nematode metabolism in a Black soil of Northeast China

Conservation tillage is one of the major strategies for maintaining agricultural sustainability and has significant beneficial effects on soil organic carbon (C) retention and soil organism diversity. However, how changes in soil organism populations and/or community structure under different tillage practices contribute to C sequestration in soil is not well documented. In this paper, soil nematode assemblages were used as a model to quantify C allocation in production and respiration of soil organisms in a long-term tillage trial initiated in 2001 on a Black soil (Typic Hapludoll) of Northeastern China. Soils were sampled from no tillage (NT), ridge tillage (RT) and conventional tillage (CT) practices in the soybean (Glycine max Merr.) phase of the maize (Zea mays L.) -soybean rotation. In comparison with CT, RT and NT significantly increased production and respiration C of nematodes as a consequence of more basal C flowing into soil food web. The significantly increased bacterivore metabolic C in both production and respiration under RT and NT suggests that a bacterial-channel was the predominant pathway for C entering the food web. However, the efficiency of C allocation into soil nematodes, as indicated by the ratio of respiration C to production C (R/P), varied widely between RT and NT. NT significantly improved the C storage capacity of almost all nematode trophic groups while RT predominantly promoted the C storage capacity of bacterivores. Our results suggest that NT is more favorable than RT for allocating C into soil organisms under long-term application in the Black soil of Northeast China.

Nematode communities differ in Hopi landrace maize and commercial maize

Selection pressures of crop breeding in varying abiotic contexts may produce cultivars differing in their relationships with belowground organisms. Nematode assemblages associated with a Hopi maize (Zea mays L.) landrace and two commercial maize varieties were examined at three traditional farms (two irrigated, one dry-farmed) near the village of Moenkopi on the Hopi Reservation in Arizona, U.S.A. At each farm, the landrace and one commercial maize variety were cultivated in close proximity. Within the two irrigated farms, densities of free-living nematodes, but not plant parasitic nematodes, were higher in landrace plots compared to commercial variety plots; however, at the dry-farmed site the nematode assemblages associated with the two maize varieties did not differ. Nonmetric multidimensional scaling (NMDS) and multiple response permutation procedure (MRPP) showed that at the irrigated farms, nematode assemblages associated with landrace maize differed significantly from those associated with commercial maize in analyses based on functional guilds, feeding groups and non-phytoparasitic c-p groups. Assemblages at the dry-farmed site were different from those at the irrigated sites in community composition based on morphotypes, functional guilds, and feeding groups, but were similar to the irrigated commercial variety plots based on c-p groups. Nematode abundances were likely constrained by water availability at the dry-farmed site, but at the irrigated sites, nematode community dissimilarities between the landrace and the commercial maize variety may have resulted from differences in plant-soil microbe interactions for the two crop varieties. Selection pressures associated with Hopi agroecosystems might have produced landraces with different belowground allocation strategies than commercial crop varieties selected under high resource conditions.

Role of spatial scales and environmental drivers in shaping nematode communities in the Blanes Canyon and its adjacent slope

Understanding community assembly and processes driving diversity in deep-sea environments is a major challenge in marine ecosystems. In this paper, we investigated the importance of environmental gradients at different spatial scales in structuring deep-sea canyon and continental slope meiobenthic nematode communities in the NW Mediterranean Sea. Three scales were investigated 1) Ecosystem: Blanes Canyon vs. adjacent open slope; 2) Water-depth within each ecosystem: 1500, 1750 and 2000 m; and 3) Vertical profile (three layers within the first 5 cm of sediment). Nematode communities were analysed in terms of density, biomass, diversity and community structure. Grain size, Chl a, Chl a: phaeopigments, CPE, organic carbon and total nitrogen were measured to assess the relationships with nematode assemblages. Blanes Canyon harbours more abundant and diverse assemblages than the slope, particularly at 1750 m and 2000 m depth respectively. The higher canyon values may be related to the higher food availability there, which can be a consequence of the so-called “canyon effect”. Slope assemblages were overall more uniform than those in the canyon, where there were greater bathymetrical differences in community structure. Densities in the canyon peaked at 1750 m depth, which did not correspond with the bathymetric gradient in food availability. The deepest canyon station was the most similar to the slope stations in terms of both environmental conditions and nematode communities, suggesting it lie outside the canyon influence. The higher habitat heterogeneity of the canyon (indicated by its greater vertical sediment and water depth differences) played a key role in structuring nematode spatial distribution. Independently of the ecosystem, however, the vertical sediment profile was the most determinative factor for density, community structure, and diversity.

Comparison of nematode assemblages associated with Sargassum muticum in its native range in South Korea and as an invasive species in the English Channel

Canopy-forming algae are important habitat providers in coastal ecosystems. Several canopy-forming species have spread outside their native geographic range. We investigated the role that these invasive non-native algae play in providing habitat for meiofaunal species. Sargassum muticum is a native species in East Asia and has been a successful invasive species of North American and European coasts. The nematode assemblages living in intertidal S. muticum on the English Channel coast in Europe, where it is an invasive species, were compared to those within its native range on the southern coasts of Korea. Nematode assemblages were sampled using a nested survey design (replicates nested within patches within shores within regions within coastlines in each country). Significant differences between countries were found in nematode assemblages in terms of both taxonomic composition and functional traits. Despite differences in assemblage structures between countries, some cosmopolitan nematode species were present in both countries. These nematode species may possibly have come from Asia to Europe with S. muticum.

Dune soil communities primarily associated with climate factors, not exotic plant presence

Soil communities are shaped by multiple biotic and environmental components. We assessed the role of multiple factors in shaping soil bacterial and nematode communities in an ongoing plant invasion in western Michigan sand dunes. We aimed to determine which factors were important for structuring soil communities. We surveyed seven sites containing the exotic plant, Leymus arenarius, in western Michigan, USA sand dunes. We sampled the plant community and collected soil cores to assess bacterial and nematode communities. We assessed bacterial functional diversity using Biolog Ecoplates. Nematode communities were assessed based on morphological identification. Temperature was a strong determinant of bacterial functional diversity and community composition. Precipitation and Ammophila density were also correlated with bacterial function composition. Nematode communities were shaped by a combination of temperature, precipitation, Ammophila density, and to a lesser degree soil organic matter and Leymus density. Soil bacteria and bacterivorous nematode assemblages were not significantly associated in their responses to the environment. Soil communities of bacteria and nematodes in this early successional dune system are affected strongly by changes in climatic factors, rather than exotic plant presence.

Plant and soil microfaunal biodiversity across the borders between arable and forest ecosystems in a Mediterranean landscape

The distribution of organisms across ecosystem borders can be indicative of trophic interactions, food-web dynamics, and the potential for recovery after disturbance. Yet relatively little is known regarding patterns and ecology of belowground organisms across borders. Our hypothesis was that incremental zonation of vegetation and soil properties at the interface between cultivated fields and forests may facilitate the recolonization of a more complex soil faunal assemblage after disturbance ceases. Vegetation, soil characteristics, and soil nematodes (indicators of disturbance) were studied at the interface between arable and natural ecosystems (oak forest and maquis shrubland) in southwestern France. Sampling was along 23-m long transects, at six positions (center and edge of grain fields, both sides of field borders, and bands of shrub and forest vegetation) at four sites. Plant functional groups changed more markedly than species richness. Total soil carbon (C) and nematode biomass were 3.5 and 6 times higher in the forest than in the center of the cultivated fields. The nematode Structure Index gradually increased from fields to forests, along with higher total and labile soil C pools, litter, root C, and root C:N, and more negative root δ15N. Microbivore nematodes were related to labile and total soil C. Structural equation modeling indicated that nematode predators and prey were both affected by total soil C, but proximity to the forest was important for predators, whereas plant community complexity was important for prey (i.e., microbivorous nematodes). The forested borders had minor effects on zonation of nematode assemblages and soil ecosystem services within the fields, yet woody vegetation may have facilitated recolonization by plants and soil fauna after tillage ceased and probably provided benefits for production of livestock (i.e., shade and erosion reduction) that were not measured. During plant succession, litter C and N apparently decomposed slowly into active forms in the soil, creating habitats for more K-selected, larger-bodied nematodes. Due to less cultivation and higher C inputs during the past 50 years, the more homogeneous landscape may promote more complex soil food webs, but less total agrobiodiversity, compared to the mosaic of diverse ecosystems that occurred in the ancient cultural landscape of the past.

How does an invasive Heracleum sosnowskyi affect soil nematode communities in natural conditions?

Summary We analysed the effect of the invasive perennial plant Heracleum sosnowskyi on soil nematode communities and diversity, and plant species composition, by comparing invaded and non-invaded (control) areas in natural conditions. Invasion of H. sosnowskyi caused significant shifts in plant species composition, which subsequently modified nematode assemblages. Stress-sensitive omnivores, fungivores and root-biomass-dependent obligate plant parasites best reflected changes in soil nematode communities under the influence of H. sosnowskyi invasion. The negative effect of H. sosnowskyi was most evident on Aphelenchus, Tylencholaimus, Geocenamus, Helicotylenchus, Pratylenchus, Tylenchorhynchus and Aporcelaimellus. Our results indicate that significant changes in the herbaceous layer after H. sosnowskyi invasion in ecosystems where H. sosnowskyi eventually became dominant impacted soil nematode communities but did not affect nematode diversity. This was in contrast to the habitats where a solitary plant of H. sosnowskyi grew and no significant changes in nematode communities were observed.