Bacterial-feeding Nematodes Research Articles

Sulfate fertilization supports growth of ryegrass in soil columns but changes microbial community structures and reduces abundances of nematodes and arbuscular mycorrhiza

The increased use of sulfate fertilizers to compensate for soil sulphur (S) limitation in agricultural soils may affect soil microbes and micro-fauna involved in S mobilization. Here, columns with podzolic soil material and ryegrass (Lolium perenne) were fertilized with 0, 5, 10 and 20 kg ha−1 (S0/S5/S10/S20) inorganic sulfate-S alongside a full complement of other nutrients. In the S10 and S20 columns, significantly higher amounts of sulfate were present in soil solution. After two grass cuts (14 weeks in total), there was a significant decrease in arylsulfatase activity, bacterial-feeding nematode abundances and mycorrhizal colonization in the S10 and S20 columns compared to the S0. Bacterial, fungal and AM community structures shifted significantly across the treatments. After final harvest, the S10 and S20 columns had significantly higher grass dry matter yield and uptake of S, N, K, Ca and Mg compared to the S0. While the overall bacterial diversity was reduced in the S20 treatment, abundance (asfA) and diversity (ssuD and atsA) of bacterial genes involved in S cycling were not significantly affected by one-time sulfate fertilization. These results indicate that short-term sulfate fertilization benefits to plant growth outweighed the negative feedback from parts of the soil biota. To improve nutrient use efficiencies in a sustainable manner, future studies should consider alternative S fertilizers which may be beneficial to both, the soil biota and plants in the long-term.

Interactions of bacterial-feeding nematodes and indole-3-acetic acid (IAA)-producing bacteria promotes growth of Arabidopsis thaliana by regulating soil auxin status

To clarify the ‘auxin-driven’ effect of bacterial-feeding nematodes on plant growth, the influence of an indole-3-acetic acid (IAA)-producing bacteria, Bacillus amyloliquefaciens, non-IAA-producing bacteria Variovorax sp., and two bacterial-feeding nematodes (Cephalobus sp. and Mesorhabditis sp.) on the growth of Arabidopsis thaliana after various exposure durations was investigated using a gnotobiotic microcosm incubation system. The nematodes, responses of soil chemistry (IAA and mineral nitrogen), plant growth (root architecture, shoot dry weight, and plant nitrogen), and the expression of two IAA-responsive genes, IAA3 and IAA13, were measured. Bacterial-feeding nematodes stimulated the activity of IAA-producing bacteria by grazing, and promoted the mineralization of nitrogen in the soil, thus increasing the soil IAA and nitrogen content and promoting shoot dry weight and plant nitrogen content. The A. thaliana root architecture consisted of a highly branched root system, with bigger surface area. The IAA3 and IAA13 genes in A. thaliana roots significantly increased and there were significant correlations with the soil IAA content. This study further confirms the existence of an auxin-driven effect that promotes A. thaliana growth by bacterial-feeding nematodes through changes in the expression of root genes.

Bacterial feeding nematodes ingest haemocytes in the haemocoel of the insect Galleria mellonella.

Insect parasitic nematodes have acquired mechanisms to evade their host immune response for successful parasitism. Despite the importance of understanding of the evolution of evasion mechanisms from host immunity, insect immune response against non-parasitic nematodes has not been well studied. In our previous study, we demonstrated that a non-insect parasitic nematode Caenorhabditis elegans was not encapsulated by haemocytes in the larvae of the greater wax moth Galleria mellonella. To understand how nematodes influence insect haemocytes to escape encapsulation, we examined the effect of C. elegans on haemocytes in the haemocoel of G. mellonella larvae. Injection of nematodes resulted in the decrease of haemocyte density while mortality and spreading ability of haemocytes, the haematopoietic organs were not affected. In vitro co-incubation of haemocytes with nematodes resulted in a decrease of haemocyte density and we observed feeding on haemocytes by nematodes. Injection of C. elegans feeding-delay mutants into insects did not cause the decrease of haemocyte density. The decrease of haemocyte density was due to the nematode's ingestion of haemocytes. Furthermore, an entomopathogenic nematode and other bacterial feeding nematodes also showed similar feeding behaviour. The nematode's ability to feed on haemocytes may have played an important role in the evolution of nematode parasitism in bacterial-feeding nematodes.

Whey: The Soil Bio-Community Enhancer That Selectively Controls Root-Knot Nematodes.

To date, it is mandatory for ecofriendly pest-management tools to be used in agriculture. Whey is a dairy-processing waste, a plant and soil chemical and fungicidal basic substance. The beneficial effect of whey on soil microorganisms, enzymatic activities, and free-living nematodes—combined with its toxic activity on the plant parasites—forms root knot nematodes. In this study, this finding is reported for the first time. A drip-irrigating tomato plant combined with whey in water at 3.125% (v/w) and 6.25% (v/w) dose dependently promoted Gram+ and Gram− bacteria, actinomycetes, and fungi biomass. Respectively, whey treatment and duration augmented the bacterial feeding nematodes along with the soil enzymatic activities, e.g., alkaline phosphatase, dehydrogenase, and urease. The counterpart for these soil organisms’ and enzymes’ functionality is the decomposition of organic matter, nutrient mineralization and cycling. Additionally, whey applied at 6.25% (v/w) every 10 days in a field experiment exhibited an efficacy of 70% on root knot nematodes. It is calculated that the EC50/3d value paralyzes in vitro Meloidogyne javanica, which was 3.2% (v/v). Conclusively, the soil application of whey could be a sustainable and ecofriendly method to combat the root knot nematodes and additionally to enhance soil biotic components.

Laboratory Rearing of Culicoides stellifer (Diptera: Ceratopogonidae), a Suspected Vector of Orbiviruses in the United States.

Laboratory rearing procedures of Culicoides stellifer Coquillett (Diptera: Ceratopogonidae) were evaluated with an aim towards colonization of this species. Eggs collected from field-collected gravid females were placed on 0.25% agar slants and given a diet of 1) nematodes (Panagrellus redivivus Linnaeus), 2) nematodes + lactalbumin and yeast (LY), 3) microbes from nematode medium, and 4) tap water (autoclaved). Complete larval development to adult stage occurred only in two treatments: 1) nematodes and 2) nematodes + LY. Culicoides stellifer larvae could not survive beyond 1 wk on a diet of microbes alone or in the sterile water treatment. Larval survival rates were high using nematode diet (79.2 ± 11.3% [mean ± SE]) but were slightly lower in the nematode + LY group (66.5 ± 19.6%). Larval stage lasted ~21 d in both treatments. Sex ratio of F1 adults was ~1:1 (M:F) using nematode diet but was male biased (~2:1) with nematode + LY diet. These findings collectively suggest that a microbial community is required for midge larvae, either to support invertebrate prey base or as a potential food source. But in the present study, the supplied microbes alone were not sufficient to support midge survival/development. It appears that other nutritional components may also be essential to support the larval survival/development of C. stellifer. Overall, a simple diet of bacterial feeding nematodes and their associated microorganisms can be used to rear C. stellifer larvae under laboratory conditions. However, captive mating in F1 adults poses a major obstacle for successful colonization of this species currently.

Earthworm mucus interfere in the behavior and physiology of bacterial-feeding nematodes

Earthworms naturally secrete substantial amounts of mucus (relative to their body size) from the cuticle when moving through the soil. However, how the metabolites in the epidermally derived mucus affect soil microfauna is largely unknown. The objective of this study was to determine how earthworm mucus affected the physiology of the model nematode Caenorhabditis elegans and that of two soil-dwelling bacterial-feeding nematodes: Mesorhabditis sp. and Protorhabditis sp. The traits examined included phobotaxis, reproduction, mortality, body size, feeding inhibition rate, and feeding preference. Two nematode species escaped from the earthworm mucus, whereas earthworm mucus reduced the reproduction of C. elegans and increased the mortality of C. elegans and Mesorhabditis sp. Moreover, earthworm mucus reduced the feeding rate of C. elegans and Protorhabditis sp. and changed the feeding preferences of all three species of nematodes. At 48 h, earthworm mucus increased feeding on Bacillus amyloliquefaciens JX1 for C. elegans and Protorhabditis sp. and reduced feeding on Escherichia coli OP50 for Mesorhabditis sp. These results suggest that earthworm mucus can be detrimental to bacterial-feeding nematodes and provide insights into the non-trophic interactions between earthworms and other soil biota.

Nematophagous Pleurotus Species Consume Some Nematode Species but Are Themselves Consumed by Others

Pleurotus species are said to be nematophagous because they paralyze and consume some bacterial-feeding nematodes. It has never been clear whether that means all nematodes. Here we tested thirteen bacterial-feeding nematode species: seven of family Rhabditidae, three of Cephalobidae (one with three populations), two of Panagrolaimidae, and one of Diplogastridae. Nematodes interacted on water agar with toxin-producing isolates of Pleurotus pulmonarius (Fr.) Quél. and Pleurotus ostreatus (Jacq.) P. Kumm. Of the thirteen species, nine were susceptible to P. pulmonarius (all individuals were paralyzed) but four (four populations of two cephalobid species, one rhabditid, and one panagrolaimid) survived exposure to P. pulmonarius. The resistant four species not only survived but multiplied their numbers by consuming P. pulmonarius. A similar trend was observed with nematodes interacting with P. ostreatus; however, six species were resistant to P. ostreatus. Interestingly, four of these six species were susceptible to P. pulmonarius, and interactions overall were differential. Pleurotus species are nematophagous toward some nematodes but are also consumed by others in three of the four families assayed. Species-specific interactions point to the need for studies of the host ranges of both “nematophagous” fungi and “fungivorous” nematodes, especially if they are to be used for biological control.

Prospects of using entomopathogenic fungus in development of a biopesticide product with nematicidal activity

Abstract Entomopathogenic and nematophagous fungi are the recourse for biological control of phytoparasitic insects or various stages of nematodes. The objective of this work was to evaluate the prospects of using an entomopathogenic fungus strain of Beauveria bassiana to develop a biological product, in native form and immobilized on a carrier, which would possess, among other characteristics, nematicide activity. In culture suspension based on a mixture of milk whey and brewing spent grain liquor, the product showed catalase and cellulolytic activity, as well as high yield of spore-bearing biomass. Insecticidal activity of the fungus has been determined relative to a test-organism - Drosophila melanogaster. Virulence was at 50% with the infective dose of 102 CFU. A method of fungus passaging through organism of an insect is proposed as a way of maintaining biological activity. We have found nematocidal activity of the strain of B.bassianа with regard to a test organism – bacterial-feeding nematodes of the Rhabditidae family. A correlation dependency has been revealed between biological activity in terms of motile stages of nematodes and the concentration of culture suspension containing enzymes, secondary metabolites and native (own) toxins of entomopathogenic fungus. Use of native, undiluted suspension based on the mixture of milk whey and brewing spent grain liquor ensured 100% death of the number of nematodes within 2 day of incubation. The suggested product is a biodegradable carrier-immobilized form of biopesticide developed using spent grain that ensured viability of infectious units of the strain after storage.

Effects of bacterial-feeding nematodes on soil microbial activity and the microbial community in oil-contaminated soil

Rapid economic development has caused an increase in serious pollution problems due to the ever-increasing use of oil and its products, thus making oil pollution control an urgent task. Studies have shown that large amounts of bacterial-feeding nematodes are present in oil-contaminated soil; their function is as yet unclear. In this experiment, different densities of Caenorhabditis elegans (C. elegans) were inoculated into artificially simulated oil-contaminated soil to examine their effects on microbial activity and the microbial community in oil-contaminated soil. Six treatments were investigated: sterilized oil-contaminated soil as control 1 (FSP), nematode-free soil as control 2 (S), oil-contaminated soil (SP), oil-contaminated soil + 5, 10 or 20 individual C. elegans per gram of dry soil (i.e., SPN5, SPN10, SPN20). Results showed that oil pollution significantly increased the soil basal respiration. However, C. elegans weakened the soil basal respiration to different degrees and soil microbial respiration entropy essentially changed in line with the soil basal respiration. Oil pollution and C. elegans boosted catalase activity in contaminated soil by approximately 64.2–145.1%. Soil urease activity of SPN5, SPN10 and SPN20 was 88.5%, 126.7% and 109.0% stronger, respectively, than that of SP. The inoculation of C. elegans changed the microbial phospholipid fatty acid content in the oil-contaminated soil, including soil bacteria, fungi, actinomycetes, Gram-positive bacteria (G+) and Gram-negative bacteria (G−). Therefore, this research demonstrates that C. elegans can stimulate microbial reproduction in oil-contaminated soil, enhance related soil enzyme activities and regulate soil microbial community structure and diversity, thereby improving the contaminated soil environment and promoting oil degradation.

The effect of fumigation on nematode communities in California almond orchards

Summary Fumigants, such as 1,3-dichloropropene and chloropicrin, have become key to pre-plant pest management in almond production. Whilst the use of these fumigants has become increasingly restricted due to human health concerns, less is known about their below-ground non-target effects in orchards and how nematode communities recover from fumigation over time. In this study, replicated trials compared 1,3-dichloropropene + chloropicrin to non-treated controls in two almond orchards in California, USA. Nematode communities, nematode indices and nematode metabolic footprints were quantified soon after fumigation and for 2 years afterwards. Fumigation reduced the Herbivore Metabolic Footprint in year 1, and populations of Pratylenchus vulnus in year 3. Fumigation also reduced populations of larger omnivores and predators, resulting in lower levels of the Structure Index at one site. Populations of fungal-feeding nematodes were more adversely affected by fumigation than bacterial-feeding nematode populations. At both sites, fumigation still influenced nematode community composition 2 years after treatment application.

Occurrence and abundance of nematodes on onion in Turkey and their relationship with soil physicochemical properties

Summary The distribution of plant-feeding and free-living nematodes in large scale onion production areas in five geographical regions in Turkey was investigated in 2016 and 2017. Ditylenchus spp. and Tylenchus spp. were widely distributed. The stem and bulb nematode, Ditylenchus dipsaci, was found in 48 locations from 13 provinces. Other plant-feeding nematode genera were Pratylenchus, Paratylenchus and Pratylenchoides. Pratylenchus thornei was the most widely distributed root-lesion nematode species in onion fields in 11 locations from seven provinces. Pratylenchus neglectus was present in three locations and P. vulnus was in four locations. Aphelenchus spp. and Aphelenchoides spp. were the principal fungal-feeding nematodes in onion-growing areas. The most abundant bacterial-feeding nematode genera were Acrobeloides, Cephalobus, Eucephalobus and Rhabditis. Acrobeles and Wilsonema genera were low in occurrence and abundance. Nematodes from Dorylaimida and predator nematodes, Mononchus spp., were also found. The numbers of Ditylenchus from plant samples were significantly correlated positively to silt content, and significantly correlated negatively to organic matter and calcium content.

Legacies of afforestation on soil nematode community composition, structure, and diversity in a northern Canadian prairie

We examined how legacies of afforestation affect soil food webs using the composition, structure, and diversity of soil nematode communities along a prairie restoration chronosequence. Vegetation and soil nematode surveys were conducted across a restoration chronosequence of tree removal (2, 5, and 20 years) in a former plantation in Riding Mountain National Park, Canada, established on a Great Plains rough fescue prairie. Nematodes were extracted using sugar-gradient centrifugation, counted and assigned to feeding groups. Remaining plantation and recently restored prairies were characterized by bacterial feeding nematodes whereas the oldest restored prairie and control prairie were dominated by plant-root feeders. Nematode diversity did not reach the level observed in the prairie even 20 years following the removal of trees. Nematode community diversity and structure was strongly correlated with the composition of restored plant communities. Invasion of restored prairies by exotic grasses corresponded with a strong decline in the diversity of plant-root feeders. Legacies of afforestation can impact prairie soils years after trees have been removed and can lead to shifts in feeding structure and a loss of diversity in the soil food web. As grasslands continue to decline globally, considering soil faunal communities may help evaluate the outcomes of ecosystem restoration and maintain their key functions.

Effects of bacterial-feeding nematodes and organic matter on microbial activity and oil degradation in contaminated soil.

Increasing rates of oil exploitation and utilization are associated with increasing rates of oil pollution in soil. Nematodes are abundant in soils with or without oil contamination, among which bacterial-feeding nematodes are the dominant group. However, their function in oil-contaminated soil is unclear. This study explores the effects of bacterial-feeding nematode and organic matter addition on microbial activity and oil degradation in contaminated soil. Experiments were conducted using six treatments of oil-contaminated soil: sterilized (Control), nematode-free (OC), nematode addition (OCN), nematode + wheat straw addition (OCNW), nematode + rapeseed cake addition (OCNR), and nematode + biochar addition (OCNB). At the end of a 168-day incubation experiment, the oil concentration of OCN soil was 26.77% lower than that of OC soil, and those of OCNW, OCNR, and OCNB were 12.83%, 27.81%, and 4.77% lower, respectively, than that of OCN soil. Over the experiment, soil microbial biomass carbon, fluorescein diacetate hydrolysis activity, and dehydrogenase activity increased by 4.35-382.30%, 1.75-302.22%, and - 2.73-224.55%, respectively, in oil-contaminated soils, with or without nematode and organic matter addition. These results suggest that the addition of organic matter and bacterial-feeding nematodes to oil-contaminated soil can promote the growth and activity of microorganisms that break down oil.

Bacterial preys and commensals condition the effects of bacteriovorus nematodes on Zea mays and Arabidopsis thaliana

In this study, we analyzed the nematode-bacteria-plant interaction by using bacteriovorus nematodes isolated from maize rhizosphere and plant growth promoting rhizobacteria to evaluate their effect on plant growth and root development of maize and Arabidopsis thaliana. Two bacterial feeding nematodes, identified as Oscheius tipulae and Mesorhabditis sp., displayed distinct attraction patterns for seven rhizosphere bacteria with a strong bias towards Rhizobium strains. We tested the effect of these two nematodes on both plant growth and root morphology using native Zea mays and found that the co-inoculation of Rhizobium phaseoli Ch24-10, a plant growth promoter, and maize rhizosphere nematodes, increased dry weight of corn plants compared to plants treated only with bacteria or the nematode. Additionally, we found that the nematodes reduced the weight and length of the primary root and increased the number of emerging lateral roots. We further analyzed the effect of nematodes and bacteria using the model plant A. thaliana and observed similar effects on roots as those found in native corn. Nematodes reduced the primary root growth and increased the number of emerging lateral roots. The model nematode Caenorhabditis elegans N2 alone had no effect on A. thaliana plants, it became capable of affecting root morphology when fed with Acinetobacter pittii, which was originally isolated from the maize rhizosphere nematodes. Our results suggest a synergistic effect of nematodes and their associated bacteria both in plant development and root morphology, highlighting the importance of nematode-bacteria interactions in shaping plant growth and root morphology. A model of nematodes as Trojan horses carrying bacteria is proposed.

Food familiarity does not change nematode feeding behavior

Ability to identify familiar foods is a major driver of animal feeding behavior. Animals show preference for familiar foods over novel ones, presumably to avoid poisonous substances and better support their growth and reproduction. However, we do not know how their feeding behavior is affected when the familiar food is inferior to a novel food with regards to its palatability and nutritional properties. We tested the hypothesis that feeding preference is determined by specific food characteristics rather than food familiarity with fast-growing soil-dwelling nematodes. Two sequential experiments were designed to test the feeding behavior of soil bacterial-feeding nematodes (Mesorhabditis sp. and Acrobeloides sp.) resulting from familiar food recognition, including a 6-months training period to develop their food familiarity and a feeding experiment to test their food preference for five bacterial species. Nematodes showed clear preference for specific food sources, which were not necessarily the familiar food. Their feeding behavior was not affected by food familiarity, but correlated highly with bacterial traits such as cell size, growth rates, and water content. We conclude that nematode feeding behavior was controlled by food specificity rather than familiarity. We further suggest that physiological factors, possibly the physical size and presence of chemical receptors in the buccal cavity, allow nematodes to rapidly assess their food supply and switch from a familiar food to a preferred, novel food that is easier to ingest and better suited to support their growth and reproduction.

Toxicity Assay for Citrinin, Zearalenone and Zearalenone-14-Sulfate Using the Nematode Caenorhabditis elegans as Model Organism.

To keep pace with the rising number of detected mycotoxins, there is a growing need for fast and reliable toxicity tests to assess potential threats to food safety. Toxicity tests with the bacterial-feeding nematode Caenorhabditis elegans as the model organism are well established. In this study the C. elegans wildtype strain N2 (var. Bristol) was used to investigate the toxic effects of the food-relevant mycotoxins citrinin (CIT) and zearalenone-14-sulfate (ZEA-14-S) and zearalenone (ZEA) on different life cycle parameters including reproduction, thermal and oxidative stress resistance and lifespan. The metabolization of the mycotoxins by the nematodes in vivo was investigated using HPLC-MS/MS. ZEA was metabolized in vivo to the reduced isomers α-zearalenol (α-ZEL) and β-ZEL. ZEA-14-S was reduced to α-/β-ZEL-14-sulfate and CIT was metabolized to mono-hydroxylated CIT. All mycotoxins tested led to a significant decrease in the number of nematode offspring produced. ZEA and CIT displayed negative effects on stress tolerance levels and for CIT an additional shortening of the mean lifespan was observed. In the case of ZEA-14-S, however, the mean lifespan was prolonged. The presented study shows the applicability of C. elegans for toxicity testing of emerging food mycotoxins for the purpose of assigning potential health threats.

Nutrient optimization of tree growth alters structure and function of boreal soil food webs

Nutrient optimization has been proposed as a way to increase boreal forest production, and involves chronic additions of liquid fertilizer with amounts of micro- and macro-nutrients adjusted annually to match tree nutritional requirements. We used a short-term (maintained since 2007) and a long-term (maintained since 1987) fertilization experiment in northern Sweden, in order to understand nutrient optimization effects on soil microbiota and mesofauna, and to explore the relationships between plant litter and microbial elemental stoichiometry. Soil microbes, soil fauna, and aboveground litter were collected from the control plots, and short- and long-term nutrient optimization plots. Correlation analyses revealed no relationships between microbial biomass and litter nutrient ratios. Litter C:N, C:P and N:P ratios declined in response to both optimization treatments; while only microbial C:P ratios declined in response to long-term nutrient optimization. Further, we found that both short- and long-term optimization treatments decreased total microbial, fungal, and bacterial PLFA biomass and shifted the microbial community structure towards a lower fungi:bacterial ratio. In contrast, abundances of most fungal- and bacterial-feeding soil biota were little affected by the nutrient optimization treatments. However, abundance of hemi-edaphic Collembola declined in response to the long-term nutrient optimization treatment. The relative abundances (%) of fungal-feeding and plant-feeding nematodes, respectively, declined and increased in response to both short-term and long-term treatments; bacterial-feeding nematodes increased relative to fungal feeders. Overall, our results demonstrate that long-term nutrient optimization aiming to increase forest production decreases litter C:N, C:P and N:P ratios, microbial C:P ratios and fungal biomass, whereas higher trophic levels are less affected.

Interactions among competing nematode species affect population growth rates.

Investigations of the interplay of organisms in an ecological community are a prerequisite to understanding the processes that shape the structures of those communities. Among several types of interactions, interest in the positive interactions of species that compete for the same resource has grown, as they may provide a mechanism enabling coexistence. In the laboratory experiment described herein, the effects of interspecific interaction on the population growth of two bacterial-feeding nematode species, Panagrolaimus cf. thienemanni and Poikilolaimus cf. regenfussi, were investigated. Specifically, we asked: (1) whether there is an interspecific interaction between organisms competing for a mutual resource and (2) whether these interactions are altered by the competitors' initial densities and (3) their variable growth rates (induced by different food supplies). Each treatment initially contained 48 nematode individuals, but at different species ratios (48:0; 32:16; 24:24; 16:32; 0:48). The populations were provided with three different bacterial densities (108, 109, and 1010cellsml-1) as food. The data were analyzed using a generalized linear mixed model. The best-fitting model revealed a significant decline in population growth rates with an increasing species ratio, but depending on the food density and species. These results provide strong evidence for positive interspecific interactions that vary with both species density and food-supply level. They also suggest important roles for positive interspecific interactions in habitat colonization and in maintaining the coexistence of species in the same trophic group.

Characterization of soil nematode communities in three cropping systems through morphological and DNA metabarcoding approaches

We used complementary morphological and DNA metabarcoding approaches to characterize soil nematode communities in three cropping systems, conventional till (CT), no-till (NT) and organic (ORG), from a long-term field experiment. We hypothesized that organic inputs to the ORG system would promote a more abundant nematode community, and that the NT system would show a more structured trophic system (higher Bongers MI) than CT due to decreased soil disturbance. The abundance of Tylenchidae and Cephalobidae both showed positive correlations to soil organic carbon and nitrogen, which were highest in the ORG system. The density of omnivore-predator and bacterial-feeding nematodes was reduced in NT soils compared to CT, while some plant-parasitic taxa increased. NT soils had similar Bongers MI values to CT, suggesting they contained nematode communities associated with soils experiencing comparable levels of disturbance. Metabarcoding revealed within-family differences in nematode diversity. Shannon and Simpson’s index values for the Tylenchidae and Rhabditidae were higher in the ORG system than CT. Compared to morphological analysis, metabarcoding over- or underestimated the prevalence of several nematode families and detected some families not observed based on morphology. Discrepancies between the techniques require further investigation to establish the accuracy of metabarcoding for characterization of soil nematode communities.

Soil biota in boreal urban greenspace: Responses to plant type and age

Plant functional type influences the abundance and distribution of soil biota. With time, as root systems develop, such effects become more apparent. The relationship of plant type and time with the structure and abundance of soil microbial and invertebrate communities has been widely investigated in a variety of systems. However, much less is known about long-term soil community dynamics within the context of urban environments. In this study, we investigated how soil microbes, nematodes and earthworms respond to different plant functional types (lawns only and lawns with deciduous or evergreen trees) and park age in 41 urban parks in southern Finland. As non-urban controls we included deciduous and evergreen trees in 5 forest sites. We expected that microbial biomass and the relative abundance of fungi over bacteria would increase with time. We also expected major differences in soil microbial and nematode communities depending on vegetation: we hypothesized that i) the presence of trees, and evergreens in particular, would support a greater abundance of fungi and fungal-feeding nematodes over bacteria and bacterial-feeding nematodes and ii) the fungi to bacteria ratio would be lowest in lawns, with deciduous trees showing intermediate values. In contrast to our predictions, we showed that old deciduous trees, rather than evergreens, supported the highest fungal abundances and fungal-feeding nematodes in the soil. Consistent with our predictions, microbial biomass in urban park soils tended to increase with time, whereas – in contrast to our hypotheses – fungal-feeding nematode abundance declined. Even in the oldest parks included in the current study, microbial biomass estimates never approximated those in the minimally managed natural forests, where biomass estimates were three times higher. Anecic earthworm abundance also increased with time in urban parks, whereas abundances of fungal-feeding, plant-feeding and omnivorous nematodes, as well as those of epigeic and endogeic earthworms remained constant with time and without any distinct differences between urban parks and the control forests. Our findings highlight that although urban park soils harbor diverse soil communities and considerable microbial biomass, they are distinct from adjacent natural sites in community composition and biomass.