Nematode Assemblages Research Articles

Effects of Plasticulture and Conservation Tillage on Nematode Assemblage and Their Relationships with Nitrous Oxide Emission following a Winter Cover Cropping and Vegetable Production System

Agriculture production emits significant amounts of nitrous oxide (N2O), a greenhouse gas with high global warming potential. The objectives of this study were to examine whether different husbandry practices (tillage and plasticulture) following winter cover cropping would influence soil food web structure and whether a change in the soil community could help mitigate N2O emission in vegetable plantings. Three consecutive field trials were conducted. A winter cover crop mix of forage radish (Raphanus sativus), crimson clover (Trifolium incarnatum) and cereal rye (Secale cereale) were planted in all plots. Winter cover crop was terminated by flail mowing followed by (1) conventional till without surface residues [Bare Ground (BG)], (2) conventional till with black plastic mulch (BP) without surface residues, (3) strip-till (ST) with partial surface residues, or (4) no-till (NT) with surface residues. The cash crop planted subsequently were eggplant (Solanum melongena) in 2012 and 2014 and sweet corn (Zea mays) in 2013. The soil food web structure was consistently disturbed in the BP compared to other treatments as indicated by a reduction in the abundance of predatory nematodes in 2012 and 2014, and nematode maturity index in 2013 in BP. Changes in soil food web structure in the conservation tillage (NT or ST) treatments based on the weight abundance of nematode community analysis were not consistent and did not improve over the 3-year study; but were consistently improved based on functional metabolic footprint calculation at termination of cover crops of 2013 and 2014. None-the-less, the N2O emissions increased as the abundance of fungivorous nematodes increased during all three trials. It was also found that improved soil food web structure [higher abundance of omnivorous in 2012 or predatory nematodes in 2013 and 2014, and structure index (SI) in all 3 years] reduced N2O emissions. These findings suggested that proper soil husbandry practices following winter cover cropping could mitigate N2O emissions over time.

Amazon River discharge impacts deep‐sea meiofauna

AbstractIn this study, we show that the deep‐sea meiofauna community at the Brazilian Equatorial Margin (BEM) is strongly influenced by the Amazon River. Our comparison across four deep ocean basins including Amazon, Pará‐Maranhão, Barreirinhas, and Ceará showed that the former supports a completely distinct meiofaunal community. Meiofaunal richness increased with increasing distance from the Amazon, reflecting changes in sediment proprieties among basins. Total phytopigment content at Amazon sediments was threefold higher than at other basins. The chlorophyll a/Phaeo mean ratio, however, was lower than 1, suggesting a predominant degraded bulk organic matter derived from the Amazon River discharge. Nematode assemblages from Amazon strongly differed from the other basins mostly due to higher genus richness, trophic diversity, and variations in the abundance of Sabatieria, which in turn led into higher dissimilarity values and turnover rate. Furthermore, the bathymetric distribution of nematode assemblages at Amazon and Ceará basins differed significantly among depth zones, especially due to the higher abundance and diversity at Amazon basin. Our findings show that the Amazon River plays a critical role in structuring and shaping the deep‐sea meiofauna and nematode biodiversity at the BEM. Increasing impacts on the Amazon rainforest will certainly affect the amount of freshwater discharge, and the quantity and quality of organic material transported to the Atlantic Ocean, which in turn will have effects on the deep‐sea communities.

A comparison of physical disturbance and pollution stressors in sandy beaches using nematode functional biological traits

Nematode functional traits and community structure approaches are receiving attention and being debated regarding the similarity in gained information. This work applied two nematode methods (i.e. functional traits, community structure) and sex ratios to investigate sandy beaches experiencing physical disturbances and anthropogenic stressors along the Alexandrian coast of Egypt. It is the first study to identify the Egyptian marine benthic nematodes to genus level yielding fourteen genera. This study addressed the following questions. (A) Which analyses of functional traits, community structure, or sex ratio could distinguish beaches experiencing natural disturbances from anthropogenic stressors? (B) What are the driving forces that govern nematode assemblages? Designated beaches were high pollution and energy (HPHE), high pollution but low energy (HPLE), and clean high energy (CHE). The study was conducted in March 2014, applying a stratified random sampling design and advanced multivariate analyses. Results revealed significant discrimination among and within beaches based on functional traits, community structure, and sex ratio. The functional traits (FBM) grouped data into two main groupings, predators and scavengers. Predators and cylindrical shape-tail types were found in high salinity moderately-sorted fine-grained sand dominant at HPHE and CHE. Scavengers and a variety of tail-shape types inhabited low saline water with well-sorted coarse sediment at HPLE. The community structure (CSM) revealed three groupings, as each beach had a specific assemblage based on its response to the measured physiochemical factors (salinity, pH, and temperature). Three genera were responsible for the high contribution across each beach Graphonema sp (HPHE), Enoplolaimus sp. (HPLE), and Oncholaimus sp. (CHE), as well as the co-sharing of Axnolaimus sp at HPLE. However, Axnolaimus sp and Oncholaimus sp showed the highest dissimilarity among beaches. The contribution of the measured factors was 53.8% (FBM) and 35.7% (CSM). Trophic guilds were anthropogenic stressors dependent and tail-shape type physically disturbing-related. However, nematode genera were species-specific to habitat type. The sex ratio was male-biased, and Juvenile-stages seemed to be temperature-dependent. The dissimilarity in the functional trait and community structure data recommend their application in biomonitoring and coastal restoration programs.

Nematode Assemblages Development Twenty-One Years after the Introduction of Meadow Soil into Bare Post Mining Spoil Heap

The revitalisation of soil fauna in post-mining soils is one of the ways in which we can slow down biodiversity loss. To investigate the effect of a meadow soil transplanted directly into the spoil substrate on the colonisation of a spoil heap, we used nematodes as a tool for an assessment of success in soil fauna recolonisation. Three blocks of meadow topsoil (10 × 3 × 0.4 m) were dug out and transported as intact as possible into a bare substrate of spoil heaps near Sokolov (Czech Republic). The soil samples were taken at the beginning of the experiment (1997) and then, after 19 years (2016), were transported into blocks (B) in their surroundings in a 2 m distance (I) and, finally, 30 m from the transported blocks as a control (C), to compare and assess the complexity of soil food web. Nematode total abundances were highest in B plots and lowest in the nearby I plots at the beginning, whereas later, their abundances were highest in I plots and lowest in the control (C) plots. However, due to the high variability, abundances were statistically insignificant. The trophic composition of I plots became similar to the composition in B plots in the late phase; however, the high occurrence of predators in C plots showed a running succession even after 19 years. Our results together with previous works from the same experiment support the findings that the level of soil development has a larger impact on recolonisation by soil fauna than the migration barrier itself.

Impact of Super-High Density Olive Orchard Management System on Soil Free-Living and Plant-Parasitic Nematodes in Central and South Italy.

Simple SummarySuper-high density olive orchards are spreading in Italy to reduce production costs and increase yields per hectare. The objective of this study was to assess the orchards’ effect on the soil nematode community in five sites located in the main Italian olive cultivation areas compared to the adjacent traditional olive orchard system. Super-high density olive orchard management combined with conventional tillage and mineral fertilization decreased total organic carbon compared to traditional management. The soil nematode community was affected by the depletion of organic matter, especially for plant-parasitic nematodes, which increased. Moreover, this investigation evidenced that the Super-high density olive orchard management system could change the soil plant-parasitic nematode composition of olive orchards. In fact, the families Telotylenchidae, Paratylenchidae, Meloidogynidae, and Criconematidae were favored in the Super-high density olive orchard system, while Longidoridae, Heteroderidae, and Pratylenchidae were disadvantaged. However, conservative and sustainable soil management might maintain or improve the soil nematode community functionality and reduce plant-parasitic nematodes.The soil nematode community plays an important role in ecosystem services. The objective of this study was to assess the effect of Super-high density (SHD) olive orchards on the nematode community in five sites with different soils, climates, and cultivars. At each site, the SHD management system was compared to the adjacent olive orchard traditional (TRAD) system, in which the same soil management and phytosanitary measures were applied. Soil management was assessed by total organic carbon content (TOC), while the soil nematode community was evaluated using the nematode taxa abundances and soil nematode indicators. TOC was significantly decreased in the SHD olive orchard system compared to TRAD in the sites characterized by conventional tillage and mineral fertilization. The two-way ANOSIM analysis on nematode abundance showed no difference between the two olive management methods, instead showing only a significant difference per site mainly due to variabilities in plant-parasitic nematode assemblage. However, a negative impact of SHD management was evident in environments stressed by summer droughts and conventional tillage: the ratio of obligate plant-parasites to bacterivores and fungivores (Pp/(B+F)) was significantly higher in SHD than in the TRAD olive orchard system, and the prey-to-predator θ mass ratio showed the lowest values in the sites under organic fertilization or green manure. The canonical correspondence analysis showed that the free-living nematodes were only slightly affected by SHD olive orchards; instead, the presence of plant-parasitic nematodes families such as Telotylenchidae, Paratylenchidae, Meloidogynidae, and Criconematidae was favored, in comparison to Longidoridae, Heteroderidae, and Pratylenchidae.

Nematode assemblages in conservation and conventional maize fields: a South African baseline study

Nematode assemblages in conservation and conventional maize fields: a South African baseline study

Cosmopolitism, rareness and endemism in deep-sea marine nematodes

Nematodes represent the most abundant benthic metazoan of all seas and oceans, and their relative importance increases with increasing water depth. Understanding the biodiversity patterns of this dominant phylum could be a critical step towards our comprehension of the evolutionary patterns across the largest biome of the biosphere. For instance, it has been assumed for a long time that nematodes are ubiquitous across depths, latitudes and biogeographic regions, but there is still little scientific evidence for this lack of endemism. The present study is based on a meta-analysis of nematode biodiversity data collected from 246 deep-sea sites of the Atlantic Ocean and Mediterranean Sea. We explored the cosmopolitanism, rareness and potential endemism of nematode genera in deep-sea sediments. The results of this analysis indicate that only one-third of nematode families are widely distributed and could potentially be cosmopolitan, whereas 94% of the nematode genera are linked to specific habitats or bathymetric ranges. Singleton nematode genera (i.e. genera presenting as a single individual only in one specific habitat) increased in importance with increasing water depth. We conclude that rareness and endemism may be a far more common feature than previously thought in deep-sea nematode assemblages and hypothesise that the deep ocean interior could be a huge reservoir of endemic nematode species.

Long-term cattle grazing shifts the ecological state of forest soils.

Cattle grazing profoundly affects abiotic and biotic characteristics of ecosystems. While most research has been performed on grasslands, the effect of large managed ungulates on forest ecosystems has largely been neglected. Compared to a baseline seminatural state, we investigated how long‐term cattle grazing of birch forest patches affected the abiotic state and the ecological community (microbes and invertebrates) of the soil subsystem. Grazing strongly modified the soil abiotic environment by increasing phosphorus content, pH, and bulk density, while reducing the C:N ratio. The reduced C:N ratio was strongly associated with a lower microbial biomass, mainly caused by a reduction of fungal biomass. This was linked to a decrease in fungivorous nematode abundance and the nematode channel index, indicating a relative uplift in the importance of the bacterial energy‐channel in the nematode assemblages. Cattle grazing highly modified invertebrate community composition producing distinct assemblages from the seminatural situation. Richness and abundance of microarthropods was consistently reduced by grazing (excepting collembolan richness) and grazing‐associated changes in soil pH, Olsen P, and reduced soil pore volume (bulk density) limiting niche space and refuge from physical disturbance. Anecic earthworm species predominated in grazed patches, but were absent from ungrazed forest, and may benefit from manure inputs, while their deep vertical burrowing behavior protects them from physical disturbance. Perturbation of birch forest habitat by long‐term ungulate grazing profoundly modified soil biodiversity, either directly through increased physical disturbance and manure input or indirectly by modifying soil abiotic conditions. Comparative analyses revealed the ecosystem engineering potential of large ungulate grazers in forest systems through major shifts in the composition and structure of microbial and invertebrate assemblages, including the potential for reduced energy flow through the fungal decomposition pathway. The precise consequences for species trophic interactions and biodiversity–ecosystem function relationships remain to be established, however.

Influence of salinity on the meiofaunal distribution in a hypersaline lake along the southeast coast of India.

The present study highlights that seasonal salinity variability plays a significant role in meiobenthic distribution with special reference to nematode assemblages. Sediment and water samples were collected from Pulicat Lake, a hypersaline lake along the southeast coast of India during two seasons (Southwest Monsoon (SWM) and Northeast Monsoon (NEM)). Based on the salinity distribution, the lake is categorized into four regions, viz., southern inlet, central region, middle inlet, and northern inlet. Meiobenthic abundance was higher during SWM (226-12,206 Ind/10 cm2) than in NEM (640-10,424 Ind/10 cm2). The meiofaunal abundance was high in the central region during both the seasons, followed by the southern, northern, and middle inlet. The nematode was the dominant meiobenthic group, followed by copepod, polychaete, and foraminifera. Due to high organic matter, the central region was dominated by deposit feeding nematode species like Halalaimus longicaudatus and Terschellingia longicaudata. The southern and northern regions were dominated by free-living nematodes Rhabditis olitoria, Mesorhabditis capitata, Mononochus bastian, Paramononchus sp., Piranchulus sp., and Diploscapter cylindricus. Oncholaimus sp., a hypersaline indicator species, was reported from the middle inlet location. Statistical analysis suggests salinity as a critical parameter for the distribution and diversity of nematodes.

Nematode community structure along elevation gradient in high altitude vegetation cover of Gangotri National Park (Uttarakhand), India

The study was undertaken to understand the dynamics of soil nematode communities association along elevation gradient and associated variables in high-altitude regions of Western Himalaya. The diversity and distribution pattern of soil nematodes were investigated at four elevation ranges (Elv1, Elv2, Elv3, and Elv4 each of 500 m class) along altitudinal gradient (3000–5000 m). The nematode community comprised 58 genera of which 37 genera showed sensitivity towards altitudinal variation and the community structure also varied among elevation classes. It was found that elevation significantly affect the nematodes trophic group, diversity composition, and the nematode indices. Nematode generic richness and evenness index indicated a relatively low biodiversity of soil nematodes is supported at higher altitudes. Moreover, maturity indices reflected lower sustenance of k-strategic nematodes at higher elevations. Structure index depicted fewer connections in the soil food web at higher elevations. Nematode faunal profile showed low nutrient and low disturbance in the region. Carbon footprint of the whole nematode assemblage declined along the elevation. Overall substantial differences in the nematode composition, abundance, trophic structure, and contribution to belowground carbon cycling were observed with change in elevation. These findings could be utilized as useful tool in the long-term monitoring and to understand the region's soil health.

Does pH variation influence the toxicity of organic contaminants in estuarine sediments? Effects of Irgarol on nematode assemblages

Natural pH values in coastal waters vary largely among locations, ecosystems, and time periods; still, there is an ongoing acidification trend. In this scenario, more acidic pH values can alter bioavailability of organic contaminants, to organisms. Despite this, interactive effects between pH and chemical substances are not usually considered in Ecological Risk Assessment protocols. This study investigated the effects of pH on the toxicity of a hydrophobic organic compound on a benthic community using a microcosm experiment setup to assess the response of nematode assemblages exposed to environmentally relevant concentrations of Irgarol at two natural pH conditions. Estuarine nematode assemblages were exposed to two concentrations of Irgarol at pH 7.0 and 8.0 for periods of 7 and 35 days. Lower diversity of nematode genera was observed at the highest tested Irgarol concentration (1281 ± 65 ng.g−1). The results showed that the effects of Irgarol contamination were independent of pH variation, indicating no influence of acidification within this range on the toxicity of Irgarol to benthic meiofauna. However, the results showed that estuarine nematode assemblages are impacted by long-term exposure to low (but naturally occurring) pHs. This indicates that estuarine organisms may be under naturally high physiological pressure and that permanent changes in the ecosystem's environmental factors, such as future coastal ocean acidification, may drive organisms closer to the edges of their tolerance windows.

Impact of crop management systems on soil nematode communities in South Brazil

The analysis of nematode communities allows inferring consequences of management practices on the soil food web. We studied the taxonomic structure of nematode communities in preserved areas of the Atlantic forest (native forest = NF) in Ponta Grossa, Paraná State, Brazil, and in three different agroecosystems in neighboring areas to assess the effect of agricultural land use on nematode assemblages. Agroecosystems were located in a red latosol cropped during 30 years under conventional tillage (CT), no-tillage (NT), and minimal tillage (MT). We collected ten composite soil samples in each area in the summer. Nematodes were extracted by Baermann funnel and fixed with formalin. Subsequently, individuals were classified into taxonomic groups and counted on a Peters slide to determine densities of each taxon. Plant-parasitic and free-living nematodes were classified at the genus level. Data were analyzed with the parameters abundance, Bray & Curtis, Shannon-Weaver, and Simpson indexes. We recorded 35 genera and abundance of nematodes in MT and NT areas was more similar. Higher richness was observed in NF in relation to cropped areas, especially under NT and CT. The PCA and clustering analyses from both nematode communities and soil chemical characteristics showed that MT and CT were more similar and NT was clustered near NF. The replacement of native vegetation by cropping systems caused a reduction of nematode diversity, demonstrating the influence of agricultural practices on nematode communities.

Impact of treated sewage on meiobenthic nematodes: a case study from the Tunisian Refining Industries Company

The main objective of the current study was to assess the impact of the water taken from the 'Tunisian Refining Industries Company' on meiobenthic nematodes, before and after a series of treatments in decantation basins followed by its discharge in Bizerte bay, Tunisia. The comparison of environmental parameters of the two types of water was clearly indicative of an improvement in the quality of treated waters after a significant reduction in their loads in hydrocarbons. Overall, the water retained a good quality after being treated by 'Tunisian Refining Industries Company' before discharge in the sea. At the end of the experiment, differential responses were observed according to the richness of sediment in organic matter and hydrocarbons. Thus, it was apparent that the nematode assemblage exposed to the treated waters was closer to controls and associated to higher values of abundance, than that under untreated ones. It was also assumed that the species Microlaimus honestus De Man, 1922, Paramonohystera proteus Wieser, 1956 and Cyartonema germanicum Juario, 1972 are sensitive bioindicators of bad environmental statues and of hydrocarbon presence in the environment. On the other hand, Metoncholaimus pristiurus (Zur Strassen, 1894) Filipjev, 1918 would rather be classified as a positive bioindicative species of this type of pollutants.

Assessment of Benthic Free-Living Nematode Assemblages Diversity in Kune – Vain Wetland (Adriatic Coast, Albania)

This work presents preliminary data on benthic free-living nematode assemblages from Kune-Vain Wetland Complex, situated in the northern part of the Adriatic coast in Albania. The study was carried out during a joint ecological approach, to collect chemical-physical and biological data of the wetland and evaluate the hydrological intervention in improving the environmental situation and increase resilience to climate change. The sampling was conducted bimonthly from July 2018 – July 2019, in three main water body component of Kune-Vain wetland, Ceka, Zaje and Merxhani. Nematode assemblages were analyzed in term of composition and structure, determining taxonomic composition up to genus level and biological traits. Nematodes were the dominant component of meiobenthos in all three water bodies, comprising 98-100%. Their taxonomic composition reflected the chemical features of transitional habitat dominated by brackish genera. Genera composition revealed different diversity patterns among water bodies. The most dominant genera were Sabatieria and Terschellingia, both deposit feeders and characteristic of bad ecological quality status.

High-throughput sequencing and conventional morphotyping show different soil nematode assemblages but similar community responses to altitudinal gradients on Mt. Ibuki, Japan

The progress of molecular techniques has provided opportunities to comprehensively understand the assemblage patterns of nematode communities in various natural ecosystems. However, we still do not clearly understand whether molecular techniques result in similar assemblage patterns for nematode communities as those generated by conventional morphological analyses. We compared the community structures of soil nematodes depicted by morphological and high-throughput sequencing (HTS) analyses at five different altitudes on Mt. Ibuki, central Japan. Diversity and community composition of soil nematodes were examined from soils in coniferous Japanese cedar (Cryptomeria japonica) forests at altitudes of 200 m, 500 m, and 800 m, in a broad-leaved Shirasawa maple (Acer shirasawanum) forest at an altitude of 1100 m, and in an alpine grassland (Boehmeria silvestrii and Cirsium sp.) at an altitude of 1350 m, by identification with morphotyping or Ion Torrent PGM sequencing. Seventy genera of nematodes were detected; 51 by the HTS method and 46 by the morphological method. Of these, only 27 genera (39 %) were commonly detected in both methods. In non-metric multidimensional scaling ordinations, the nematode communities derived from the two methods were distinctly segregated, but exhibited relatively similar distribution patterns according to environmental gradients within each method. The results indicated that HTS and conventional morphotyping could depict different nematode community structures, but similar community responses to environmental gradients. Thus, HTS analysis can be an effective tool to determine the nematode assemblages responding to environmental changes.

Nematode assemblages in four ecosystems of Parque Nacional del Agua, Costa Rica

The soil nematode fauna of five locations situated in Parque Nacional del Agua (PNA) in Costa Rica is characterized and analyzed. Four ecosystems were sampled in each location: primary (undisturbed) forest, secondary (naturally regenerated) forests, tree plantations (cleared and replanted with timber trees), and pastures (cleared of trees). Five soil samples of 100 g were analyzed in each location and ecosystem, resulting in a total of 100 samples. One hundred and thirty-one nematode genera were identified, and their abundance and biomass were estimated and analyzed by means of nonmetric multidimensional scaling (NMDS) and redundancy analysis (RDA). The observed nematode abundance was 1237 ± 520 specimens per soil sample for the whole survey, similar to previously reported from tropical soils. Dominance-diversity curves, based on nematode abundance, follow a similar ‘hollow curve’ pattern, with only 20 of the genera representing 84.6% of the total abundance, and only 12 of the genera representing 88% of the total biomass. Helicotylenchus, tylenchids, criconematids, Belondira, Longidorus, Xiphinema, Monotrichodorus, Prismatolaimus and Steinernema are important in the assemblages due their abundance or biomass in the different samples. Monotrichodorus and Discocriconemella appear related to undisturbed ecosystems, and they could have potential as disturbance indicators. Biomass-based dominance-diversity curves have similar qualitative and quantitative behavior to those observed in abundance distribution, but the dorylaims, Aporcelinus and Aporcelaimoides, which represented only the 0.35% of the abundance, having a major part of the total biomass (4.33%). NMDS analysis segregated locations into two groups, sampled sites were arranged according to the life zone where they belong. Ecosystems were segregated into natural ecosystems and plantations but having overlapping zones. Whereas RDA analysis indicated that organic matter and Cu are the most relevant edaphic variables for explaining the distribution of nematode assemblages, however few genera appear important in the ordination, Mesocriconema, Longidorus, Xiphinema and Belondira between them.

Substratum-dependent moss microhabitat types alter soil nematode community structure in the mixed coniferous forest of Dachigam National Park, Jammu and Kashmir

Mosses although lack a proper rhizosphere, and poorly exploit the substratum on which they grow, still play complex role in ecological processes by providing nutrients and shelter to various organisms. Among the moss fauna, nematodes are the most abundant inhabitants. Keeping this in mind, the present study investigates how nematode communities differ among substratum-dependent moss microhabitats from forest soil. For this, samples were collected from five different microhabitats (FS: forest soil, MS: mosses on soil, MR; mosses on rocks, MLT: mosses on lower tree trunk and MUT: mosses on upper part of tree trunk), from the mixed coniferous forest of Dachigam National Park, Srinagar, Jammu & Kashmir. Results showed that the distribution pattern of nematode assemblages mirror the variation of microclimate. Total nematode abundance, trophic abundance (bacterivores, fungivores, herbivores, predators) and diversity (Shannon index, Simpson index) were highest in FS and lowest in MUT. Maturity index indicated more stable nematode communities in forest soil compared to different moss microhabitats. Results from NMDS showed clear separation of samples between microhabitats forming isolated clusters. Enrichment index depicted more enriched condition in MUT and least in FS. In general, our findings provide insights that more abundant, diverse and stable nematode communities are supported in undisturbed forest soil compared to desiccation-prone moss microhabitats.

Impact of cage aquaculture of cobia (Rachycentron canadum) on nematode assemblages in the tropics

The increased demand for food for human consumption has led to an exponential growth of aquaculture in the marine environment. This growth has raised concerns about environmental health, as fish farming can cause organic enrichment and eutrophication in sediments and, consequently, alter the benthic biota. This study evaluated changes in the structure of nematode assemblages under the influence of a cobia farm sited on the shallow continental shelf in an oligotrophic area off northeastern Brazil. Two and eight months after the beginning of the 9-month fish rearing cycle (S1 and S2, respectively), and two months after harvest (S3), sediment and bottom water samples were taken at distances of 0, 30, 80 and 100 m away from the cages, and at a reference site 200 m from the cages. Univariate indexes for the nematode genera and multivariate structure of assemblages in spatial and temporal scales were investigated through PERMANOVAs. The temporal Beta diversity index was calculated comparing distances through time. Significant changes were found in the assemblages along the rearing cycle, namely increased abundance, low diversity, and evenness. Changes in dominance of the genus Chromaspirina on the Epsilonematidae and Draconematidae families and, changes in the dominant trophic group were observed between S1 and S2, the period when the largest amount of feed had been offered to the fish. No clear trend in spatial scale was revealed except by losses of genera below the cage and gains of genera in the furthest distance station between S1 and S2. Higher nitrogen content and pH values in S2 indicates that nutritional enrichment were the main drivers of change although a DistLM analysis evidenced low percentage of explanation of assemblage patterns by the measured environmental parameters. The fish farm in the oligotrophic and dynamic tropical region studied led to changes in nematode assemblages.

Abundance, diversity, and distribution of plant-parasitic nematodes in horticultural soils under different management systems in a tomato-producing area in Argentina

Summary Monitoring the diversity and structure of plant-parasitic nematode (PPN) communities together with developing appropriate control strategies can reduce the occurrence of these pathogens and other plant pests in horticultural crops. In this context a study of the abundance, frequency, diversity and distribution of PPN in horticultural soils under glasshouse conditions from the Green Belt of La Plata, Buenos Aires, Argentina, under different management systems was undertaken. Soil samples were collected from three horticultural areas with different tomato crop managements: agroecological crop (AC); organic crop with Brassicaceae soil amendments (OC); intensive conventional crop treated with methyl bromide (MeBr) (IC). The parameters evaluated were: nematode genera richness (G); Shannon-Wiener diversity index () (Hutcheson’s t-test was applied for this index); equitability index (E); abundance; and frequency of genera. ANOSIM and SIMPER statistical analyses were performed to find significant differences between the nematode assemblages from the different sites. A total of 14 genera of PPN were identified among the three crop sites. Members of the feeding habits categories ectoparasites, semi-endoparasites, migratory endoparasites and sedentary endoparasites were observed. Statistical analysis enabled us to characterise each site based on the composition of the nematode assemblages. Helicotylenchus, Tylenchus and Nacobbus were the most frequent and abundant genera. AC and OC showed similar values of richness and diversity; the crop treated with MeBr (IC) showed the lowest diversity of PPN.

Changes in Composition and Connectivity of Soil Nematode Assemblages under Different Mulching Systems in a Strawberry Field Experiment

Changes in Composition and Connectivity of Soil Nematode Assemblages under Different Mulching Systems in a Strawberry Field Experiment