Nematode Community Research Articles

Subtropical benthic freshwater nematode response to Low versus High water level alteration

Quantitative and qualitative responses of subtropical benthic freshwater nematodes to changing water levels (low versus high) have not been considered before. Three distinct locations with different depths in two freshwater channels (Rowaina and Shalma) of the northern Nile delta had been chosen for this purpose. Low and High-water levels (LWL & HWL) were in January and July 2019 respectively. Nematode abundance and diversity were significantly different between water levels, locations, and their interactions. They were categorized into six feeding groups in both water levels, locations and channels (bacterivores, plant ectoparasites, fungivores, Nematovorous, omnivorous, and predators). However, bacterivorous and omnivorous disappeared during HWL in Rowaina channel. The relative dominance of the feeding groups differed between water levels, localities, and channels. Dominancy was generally higher in Shalma. Diversity pattern in Rowaina contrasted that of Shalma. Environmental variables differently influenced nematode community. It could be concluded that water level fluctuation was not the only factor determining benthic nematode abundance, diversity, and trophic categorization. Specific water body conditions affect benthic nematode community structure. Nematode communities are environmentally sensitive agent. Furthermore, the current findings might improve our understanding of aquaculture, as water level fluctuations affect benthic nematodes, which directly or indirectly affect the reared organisms.

Soil nematode trophic structure and biochar addition in recently converted boreal lands

Context Climate change facilitated expansion of agriculture into northern regions increases the amount of Podzol dominated farmland. Biochar can improve poor growing conditions in soils. There are no universally accepted soil quality indicators for assessing the sustainability of expanding and intensifying boreal farming. Changes in the soil community structure can inform on soil functional status and the impact of management. Aims We assessed the impacts of biochar added to recently converted agricultural land on soil nematodes. We hypothesised that biochar addition would increase soil pH, correlate with total nematode abundance, and favour bacterivores over fungivores. Methods Biochar was added to soil at 10–80 Mg C ha−1 rates. Physicochemical soil properties, crop yields, nematode community trophic composition, trophic group ratios, and diversity indices were assessed. Key results Soil quality and fertility were improved with biochar, critically through increasing pH from 4.8 to 5.5. The interactions between pH, available metals, and micro-nutrients were related to biochar rate. Biochar was associated with increased bacterivore abundance (CI90 of 328 ± 132 vs 618 ± 50 individuals) indicating accelerated SOM degradation, and increased omnivore abundance (CI90 of 13 ± 17 vs 33 ± 7 individuals) indicating a more resilient community. Changes to Podzol quality may be most reliably indicated by bacterivore abundance and community complexity than by ratios and diversity indices. Conclusions Biochar application improved soil quality as suggested by nematode community structure. Implications Biochar application may be recommended to improve Podzol quality and fertility. Soil nematodes can indicate relative changes to Podzol quality.

Infaunal community structure, diversity, and function in Pacific-Arctic shelf sediments: a comparison of meiofaunal- and macrofaunal-sized nematodes

Meiofauna, and nematodes in particular, perform essential roles in benthic ecosystems and serve as bioindicators of disturbance and environmental change. In the Pacific Arctic, a region experiencing rapid environmental change, this component of the fauna has received little attention, and the role of meiofauna in ecosystem processes is poorly understood. We collected multi-core samples at 10 stations in the northern Bering and southern Chukchi Seas in June 2018 and characterized the sedimentary environment. We also assessed meiofauna community structure and abundance at higher taxonomic levels and evaluated genus-level nematode composition in meiofaunal (63-500 µm) and macrofaunal (>500 µm) size fractions. Nematodes were classified by feeding type and life-history strategies. Total meiofauna abundance and biomass varied greatly, with 1449-12875 ind. 10 cm-2 and 373-2325 µg dry weight 10 cm-2 for the upper 5 cm of sediment. Estimated production of meiofaunal-sized nematodes was 5-28 g C m-2 yr-1. Four distinct communities of meiofaunal-sized nematodes were identified in different sub-regions reflecting food availability and substrate type. The meiofaunal- and macrofaunal-sized nematodes represented 2 distinct communities. The unique taxonomic composition and large standing stock of the macrofaunal-sized nematodes (22 ± 15% of total nematode biomass) suggest they are critical components of the infauna and merit further research to assess their role in critical ecosystem functions. This study provides the first genus-level characterization of nematodes and some of the first measurements of meiofauna standing stock in the region, contributing important data for assessing ecosystem function in a rapidly changing Arctic.

Metabarcoding of nematode communities associated with Ananas comosus L. (Pineapple)

Metabarcoding of nematode communities associated with Ananas comosus L. (Pineapple)

Leaf phenology rather than mycorrhizal type regulates soil nematode abundance, but collectively affects nematode diversity in seven common subtropical tree species

The underlying mechanisms of the relationships between tree species and the soil micro-food web in forest ecosystems remain uncertain, primarily ascribed to an insufficient understanding on how tree functional traits drive soil nematode communities, including in subtropical forests. We investigated the impacts of seven subtropical tree species (evergreen: Pinus massoniana, Mytilaria laosensis, Ilex chinensis, Michelia macclurei; and deciduous: Liquidambar formosana, Quercus acutissima, and Betula luminifera) on the soil nematode communities. We found that the abundance of soil nematodes was not affected by mycorrhizal types, but it was around 83% higher under the deciduous trees than the evergreen trees, indicating the importance of leaf phenology to the abundance of soil nematodes. Nonetheless, both the evergreen and the arbuscular mycorrhizal trees increased soil nematode diversity, resulting from changes in root traits and soil properties. Furthermore, root traits (root C, root N, and root C:N ratio), and soil properties (total C, total N, moisture content, and bulk density) were the best predictors of the community composition of soil nematodes, indicating a key role of resource quality and soil microhabitat in regulating soil nematodes. In contrast, the ectomycorrhizal trees had lower plant parasite and Wasilewska indices, and evenness, whereas the evergreen trees slightly improved the evenness of soil nematodes. This study suggests that tree species affect the soil food web through changes in soil conditions and plant functional traits in subtropical forests.

Impacts of the first deep-sea seafloor massive sulfide mining excavation tests on benthic communities

Japan undertook the first ever tests of deep-sea seafloor massive sulfide (SMS) excavation in 2017 in the Okinawa Trough. This study examines infauna from several nearby stations before and up to 3 yr after disturbance. Distance from excavation, current direction, seafloor topography, and modeled and observed deposition were used to classify the level of impact of each station. Metal concentrations were analyzed, as were nanofauna (2-32 µm), meiofauna (32-300 µm), and macrofauna (>300 µm). Elevated Cd, Pb, Hg, Zn, Fe, and Cu were confirmed as indicators of sedimentation from the SMS extraction. Benthic communities appeared altered by the disturbance test, with different size classes showing different levels of response and recovery. Nanofaunal and meiofaunal abundances appeared to take several weeks to show impacts from the disturbance and may have returned to pre-test levels within 1 yr, but changes to nematode community structure persisted longer. In contrast, macrofaunal abundances and diversity appeared to decrease immediately, and possibly remained depressed compared to pre-test levels at impacted sites at least 3 yr later. In addition, meiofaunal nematode:copepod ratio and macrofaunal percent composition of polychaetes, along with several nematode taxa, may serve as useful bioindicators of SMS mining. The small scale of disturbance requires caution when extrapolating to full-scale mining, but these results suggest current direction and topography greatly influence the extent of mining impacts; in addition, several metals may be useful for identifying the mining footprint. Biological results indicate that larger macroinfauna may be less resistant and resilient to mining impacts than smaller meiofauna and impacts from even small-scale mining activities may persist for at least 3 yr.

Effect of Brassicaceae Waste Application on Soil Nematode Community

Brassicaceae are known to contain compounds that are biofumigants. This study aimed to determine the effect of Brassicaceae waste application on soil nematode community. Broccoli leaves and stems (Brassica oleracea var. italic), cabbage leaves and stems (B. oleracea var. capitate), kailan stems (B. oleracea var. alboglabra), radish leaves (Raphanus sativus), and leaves of kamanilan weed (Rorippa indica) were tested in this study. The total glucosinolate content of Brassicaceae waste was estimated using the palladium method with a modified spectrophotometer. The experiment was carried out in polybags containing 500 grams of soil-infested nematodes. Brassicaceae waste (15 grams/polybag) was chopped and mixed into the soil, watered, and polybags were tightly closed for 14 days. The experiment was arranged in a completely randomized design with nine treatments and five replications. The results of the total glucosinolate analysis showed that broccoli, radish, and kamanilan leaves fall into the high category (144.7-185.2 µmol/g); cabbage leaves, cabbage stems, and kailan stems fall into the medium category (52.0-56.0 µmol/g); and broccoli stems fall into the low category (35.4 µmol/g). There was no correlation between total glucosinolate contents and their effect on suppressing soil nematode communities at the applied effluent dose. The population of bacterivorous nematodes increased in each waste treatment, especially in kamanilan leaf treatment (R. indica) which reached 13,008 individuals. These results indicate that kamanilan weed has good potential to improve soil health. The treatment of Brassicaceae waste against soil nematode communities showed a low diversity index, an uneven evenness index, and a high dominance index.

Legume biological nitrogen fixation improves but chemical nitrogen fertilizer suppresses soil nematode communities in a Camellia oleifera plantation

AbstractLegume intercropping by biological nitrogen (N) fixation is supposed as a more sustainable way than chemical N addition to enhance soil N availability in agronomy, however, the effects of the two types of N input on soil food web are scarcely determined. To fill the knowledge gap, we conducted a field experiment with randomized block design in an oil‐tea (Camellia oleifera) plantation, which included five N manipulation treatment: legume intercropping (Arachis hypogaea and Cassia tora), chemical N fertilizer application (84 and 168 kg N ha−1 yr−1), and the control (no N addition). The soil nematode communities and physicochemical properties were monitored in the seedling, heading, and mature stages of the legumes respectively. The results showed that the legume intercropping significantly increased the abundances of bacterivores and omnivore‐predators compared with the N fertilizations. Weighted nematode fauna analysis showed that N fertilization treatments were mainly located in the degraded plot (quadrat IV), and legume treatments were located in the structure plot (quadrat III). Structural equation model revealed that the legume intercropping positively correlated with the abundance of bacterivores and omnivore‐predators while N fertilization rate negatively correlated with the abundance of bacterivores and fungivores. Our results suggest that the legume biological N fixation was more conducive to providing N sources to soil organisms than the chemical N fertilizer, which resulted in an enhanced and a degraded soil food web respectively. Thus, legume intercropping is a more sustainable N management practice for the cultivation of C. oleifera plantations.

Changes in diversity patterns and assembly processes of soil nematode communities during forest secondary succession on the Loess Plateau

The secondary succession of plant communities involves considerable changes in belowground communities of microbes and animals. Nematodes are the most abundant animals in soil and play a vital role in maintaining soil biodiversity and functions. Exploring the ecological processes that drive soil nematode diversity and community assembly during secondary succession can help to gain a predictive and mechanistic understanding of soil biodiversity maintenance and ecosystem recovery. In this study, based on the investigation of soil nematode community composition and structure, we examined the changes in nematode α- and β-diversity along forest secondary succession and disentangled the contributions of different community assembly processes (deterministic and stochastic processes) in each successional stage on the Loess Plateau, a key region of ecological restoration in China. The results showed that: (1) Abundances of plant-parasitic and bacterial-feeding nematodes were lower in the pioneer and climax forest stages than in the grassland and shrub stages. Meanwhile, nematode community composition considerably changed, with the dominant trophic group changing from plant-parasitic (grassland stage: 35.48%) and bacterial-feeding (shrub stage: 35.63%) to fungal-feeding (pioneer and climax forest stages: 30.65–36.44%). These changes might be associated with higher carbon-to-nitrogen ratios of fine roots and litters, as well as higher litter phosphorus content (LTP), in pioneer and climax forests; (2) Nematode α-diversity and β-diversity peaked in the shrub stage and decreased substantially in the climax forest stage, but β-diversity differed more significantly between successional stages than α-diversity. Fine root biomass, root carbon to nitrogen ratio, and litter phosphorus content were the main predictors of nematode α- and β-diversity, while geographic distance positively affected nematode β-diversity; (3) In the grassland and climax forest stages, deterministic processes dominated nematode community assembly, probably due to the strong influence of environmental factors such as the quantity or quality of plant resources. Especially, in the climax forest stage, the low quality of plant resources might be responsible for the low nematode diversity and network complexity. In the shrub and pioneer forest stages, the contribution of stochastic processes gradually increased, and nematode networks became more complex. Taken together, our results emphasize the importance of litter and root quality in regulating nematode diversity and community assembly, especially in the late successional stage, which provides insights into forest restoration and sustainable management in the Loess Plateau and other similar arid and semiarid regions.

Change in land-use from natural forest impacts functional composition and metabolic footprint of soil nematode community in Western Himalayas

Change in aboveground land-use confer many alterations in belowground soil ecology, which is a growing concern for the loss of biodiversity and the functioning of terrestrial ecosystems. Here, we studied nematodes - a key component and bioindicators of soil biodiversity in native temperate forests and its derived land-use (scrubland; SL, grassland; GL, cropland; CL) in western Himalayas. Five composite soil samples as replicates were collected from each land-use for analysis of soil properties and nematodes. Land-use change reduced the total nematode abundance. Contrary to our expectations, higher level of diversity was found in soils of SL while GL and CL had an overall lower level of diversity. Sigma maturity index and soil faunal profile suggested that replacement of natural forest with GL and CL was accompanied by disturbance, with lesser food web complexity and stability in the belowground soil food web. Metabolic footprint contributed through the structural component of nematode community decreased in GL and CL. Functional and trophic shifts in nematode metabolic footprint were recorded. Overall, we demonstrated that conversion lowered soil nematode abundance, altered soil nematode community structure, changed their stability and function and lowered their diversity. Moreover, this study have advantages for the sustainable management and restoration of native temperate forests in the region for the conservation of belowground biodiversity.

Litter Additions Reduce the Side Effects of Biocides on Soil Nematode Communities in Illicium Verum Forest.

The application of biocides may create unintended consequences on soil biota and ecosystem stability. The inputs of organic matter can increase biocides adsorption and reduction of non-target organisms influence. A field experiment was conducted to study the changes of soil abiotic and nematode communities resulting from biocides application in non-litter-added and litter-added soils in Illicium verum forest. Our results showed that litter addition could change the responses of soil nematodes to biocides. The influence of fungicide was evident mainly in litter-added plots in which it increased nematode abundance. Insecticide and its interaction with fungicide significantly decreased the diversity index and the abundance of omnivores-predators and herbivores in non-litter-added plots. While, insecticide had little effect on nematode diversity and abundance in litter-added plots. Litter addition may help to maintain the structure and stability of soil food web and result in bacteria dominant decomposition pathway. Our results suggest that litter addition may be a critical factor for maintaining soil ecosystem stability when biocides are applied in Illicium verum forest.

Post-Fire Recovery of Soil Nematode Communities Depends on Fire Severity

Following the creation of a new organic layer after a forest fire, there is an initial build-up phase of overall biota. We studied soil nematode community development in a chronosequence of post-fire coniferous forest sites in relation to different fire severity. The taxonomic and functional composition of the soil nematode community was analyzed to detect immediate changes and levels of post-fire recovery in soil food web structures, i.e., 0, 1, 4, 8, 14, 20, 45, and 110 years after the event. Unburned forest sites served as controls. With small exceptions recorded immediately after the burn (mean nematode abundance, total biomass), the low severe wildfires had no impacts on the structures of nematode communities. The structures of nematode communities were found to be stable on sites affected by low severe wildfires, without considerable fluctuations in comparison to the unburned sites during chronosequence. On the contrary, nematode communities responded considerably to fires of high severity. The significant changes, i.e., a decrease of mean nematode abundance, plant parasites, omnivores and predators, species number, and nematode diversity, the values of CI, SI, MI, but an increase in the number of bacterivores and EI were recorded immediately after the fire. Such status, one year after a fire of high severity, has been observed. Full recovery of nematode communities 14 years after the disruption was found. Overall, our results showed that fire severity was a considerable element affecting soil nematode communities immediately after events, as well as the time needed to recover communities’ structure during post-fire chronosequence.

Accelerated temporal turnover of the soil nematode community under alpine grassland degradation

AbstractSoil nematodes play pivotal roles in the soil food web. However, the trophic regulation on nematodes in the soil micro‐food web and its temporal dynamics are less explored. Here, we investigated the seasonal dynamics of soil nematode community in an alpine grassland on the Qinghai–Tibet Plateau at non‐degraded (ND), moderately degraded (MD) and severely degraded (SD) stages, either under open‐top chamber warming (W) or not (NW). Nematode richness was higher in SD than in MD and ND that did not differ, accompanied by a clear shift from the bottom‐up regulation via belowground productivity in ND to the top‐down regulation via omnivore and predator nematodes in SD. The intensified top‐down regulation in SD was explained by increased proportions of predator and omnivore nematodes, likely induced by the expanded soil pore size in SD. As a result, accelerated temporal turnover of nematode community was observed under grassland degradation, which were 0.006 (slope, p = 0.78), 0.045 (p = 0.07), and 0.077 (p = 0.001) in ND, MD, and SD, respectively. Moreover, grassland degradation strengthened the association between nematode density and ecosystem respiration, whose slope was higher in SD (0.0025, p < 0.05) than in MD (0.0008, p < 0.01) or ND (insignificant). In contrast, warming did not affect the temporal turnover of the nematode community, richness, nor its role in ecosystem respiration. Overall, we revealed the accelerated temporal turnover of nematode community and its strengthened role in determining ecosystem respiration under alpine grassland degradation, suggesting that trophic cascade changes under ecosystem degradation may alter the ecosystem functioning.

Characteristics and pollution risks of potentially toxic elements and nematode community structure on farm soil near coal mines.

As one of the most important coal-producing provinces of China, Shanxi Province has been concerned about soil potentially toxic elements (PTEs) contamination in recent years. The study aimed to determine the status and sources of PTEs contamination and evaluate the quality of the soil ecology. This study investigated the degree of 13 PTEs contamination. The sources and contributions of PTEs were traced by the absolute principal component score followed by a multiple linear regression model (APCS-MLR). And the status of the soil ecosystem was verified by evaluating the soil nematode community around the coal mining areas in Jinzhong. The results showed that the mean PTEs concentration of 5 trace elements were higher than the background values of Shanxi, and safe to considerable was indicated by the pollution and ecological risk values. Soil Hg was the most contaminated element, followed by Cd. The distribution of PTEs was determined by coal mining activities (44.72%) followed by agricultural practice (32.37%) and coal transportation (21.37%). The nematode genera Acrobeloides (4.01%), Aphelenchus (20.30%), Meloidogyne (11.95%) and Aporcelaimus (2.74%) could be regarded as bioindicators of soil PTEs contamination by their tolerance. Concentrations of soil Cr, Mn, Ti and Cd showed remarkable influences on the total nematode abundance, maturity index, enrichment index, structural index, Shannon-Wiener diversity index and Pielou index of soil nematode. It is an appropriate method to evaluate the status of soil PTEs contamination combining the response of a single nematode genus and the nematode community evaluation index.

Soil nematode abundances drive agroecosystem multifunctionality under short-term elevated CO2 and O3.

The response of soil biotas to climate change has the potential to regulate multiple ecosystem functions. However, it is still challenging to accurately predict how multiple climate change factors will affect multiple ecosystem functions. Here, we assessed the short-term responses of agroecosystem multifunctionality to a factorial combination of elevated CO2 (+200 ppm) and O3 (+40 ppb) and identified the key soil biotas (i.e., bacteria, fungi, protists, and nematodes) concerning the changes in the multiple ecosystem functions for two rice varieties (Japonica, Nanjing 5055 vs. Wuyujing 3). We provided strong evidence that combined treatment rather than individual treatments of short-term elevated CO2 and O3 significantly increased the agroecosystem multifunctionality index by 32.3% in the Wuyujing 3 variety, but not in the Nanjing 5055 variety. Soil biotas exhibited an important role in regulating multifunctionality under short-term elevated CO2 and O3 , with soil nematode abundances better explaining the changes in ecosystem multifunctionality than soil biota diversity. Furthermore, the higher trophic groups of nematodes, omnivores-predators served as the principal predictor of agroecosystem multifunctionality. These results provide unprecedented new evidence that short-term elevated CO2 and O3 can potentially affect agroecosystem multifunctionality through soil nematode abundances, especially omnivores-predators. Our study demonstrates that high trophic groups were specifically beneficial for regulating multiple ecosystem functions and highlights the importance of soil nematode communities for the maintenance of agroecosystem functions and health under climate change in the future.

Both alpha and beta diversity of nematode declines in response to moso bamboo expansion in south China

Establishment of invasive plants in natural forest ecosystems can deplete forest vegetation and significantly affect soil biodiversity. However, its effects on the alpha and beta diversity of soil nematode are inadequately documented and remain poorly understood. We collected 810 soil samples from three forest types (broadleaf forest, mixed bamboo forest, and homogeneous moso bamboo forest) at three locations in southern China. High-throughput sequencing technology was applied to explore the impact of moso bamboo (Phyllostachys edulis) invasion on nematode alpha and beta diversity as well as soil properties. Moso bamboo invasion was associated with lower levels of total organic carbon, total nitrogen, and available potassium, as well as increased soil pH. Both alpha and beta diversity of nematodes showed a gradual decline from broadleaf forest to bamboo forest (Ace index from 109.47 to 79.53 and Bray-Curtis index from 0.825 to 0.785). Forest type and site significantly affected nematode communities (P < 0.001). Our findings highlight the importance of protecting forest vegetation diversity from invasive plants, thus helping preserve soil biodiversity and its underlying ecosystem services along with habitat complexity.

Effects of management intensity, soil properties and region on the nematode communities in temperate forests in Germany

A key to forest productivity is structure and function of the biotic microbiome in the soil, which determines nutrient mineralisation and consequently tree growth and fitness. Soil nematodes are a dominant part of these assemblages, with an important role in the associated micro-food web. However, nothing is known about how forest management and soil properties affect soil nematodes. This study investigated the nematode communities in the organic layer and mineral soil of 150 forests located in three different German regions. Fifty forest stands each were studied in Schwäbische Alb (ALB), Hainch-Dün (HAI) and Schorfheide-Chorin (SCH). The effect of forest management (forest management index – ForMI, silvicultural management intensity indicator – SMI), soil properties (total C, N, S, P, organic C, inorganic C, pH, water content) and microbial food source (phospholipid fatty acids - PLFA) on nematode density, community and ecological indices were assessed.The nematode density in the organic layer of the forests was with a mean of 290 individuals g−1 DW comparable across all three regions, while in the mineral soil nematode density was significant lower in SCH. Here, dry sandy soils are frequently stocked with intensively managed pine forests, and the associated fungal-based decomposition is reflected in a greater proportion of fungal-feeding nematodes and a higher Channel Index. Effects of region and soil layer were mirrored by the structure of the nematode community. Organic layer and mineral soil differed distinctly, while in the latter SCH separated from ALB and HAI. The nematode community was predominantly affected by region, soil properties and resources, with microbial diet as driving factor in the organic layer, whereas soil parameters were more important in mineral soil. In comparison, the influence of forest management was low, with ForMI and SIM together explaining 8% (organic layer) and 4% (mineral soil) of the overall variation. Most remarkable, the nematode community in HAI, a region dominated by broad-leaf forests, was resilient to management intensity in the organic layer. On the other hand, management practice had family-specific impact: In the organic layer of ALB, the density of the bacterial-feeding Teratocephalidae and the fungal-feeding Aphelenchoididae increased with higher Inonat (indicates non-natural tree species) and higher SMIr (addresses stand age and species selection related to the risk of stand loss). In sum, the structure and function of nematode communities were driven by both, biotic factors such food source (i.e. the soil layer inhabited) and abiotic factors such as soil type and climate (i.e. region). Furthermore, forest management can affect nematode communities, mainly by the selected tree species, but also by stand age and density.

Plant diversity effects on herbivory are related to soil biodiversity and plant chemistry

Abstract Insect herbivory is a key process in ecosystem functioning. While theory predicts that plant diversity modulates herbivory, the mechanistic links remain unclear. We postulated that the plant metabolome mechanistically links plant diversity and herbivory. In late summer and in spring, we assessed individual plant above‐ground herbivory rates and metabolomes of seven plant species in experimental plant communities varying in plant species diversity and resource acquisition strategies. In the same communities, we also measured plant individual biomass as well as soil microbial and nematode community composition. Herbivory rates decreased with increasing plant species richness. Path modelling revealed that plant species richness and community resource acquisition strategy correlated with soil community composition. In particular, changes in nematode community composition were related to plant metabolome composition and thereby herbivory rates. Synthesis. These results suggest that soil community composition plays an important role in reducing herbivory rates with increasing plant diversity by changing plant metabolomes.

Effects of long-term fertilization with contemporary Danish human urine, composted household waste and sewage sludge on soil nematode abundance and community structure

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health.Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure.At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding.Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2–5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments.We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

Life in a Contaminated Environment: How Soil Nematodes Can Indicate Long-Term Heavy-Metal Pollution.

We investigated the genera, trophic groups, and functional guilds of soil nematodes at five alluvial meadows along the Litavka River in the Czech Republic to assess their usefulness as indicators of heavy metal pollution in soils. The Litavka River flows around the waste-sedimentation pond of a smelter in the city of Příbram in the Central Bohemian Region. Lead, zinc, and arsenic are the main pollutants in the soils in the vicinity of the smelter. The alluvial meadows closest to the pond and mine waste were the most heavily polluted sites, and contamination decreased downstream along the river with increasing distance from the sources of pollution. The nematode communities were sensitive to pollution, with the most contaminated sites having considerably fewer nematode individuals, fewer genera, and a less diverse and more degraded food web with less nematode biomass. Arsenic, lead, and zinc contents were significantly negatively correlated with the numbers of bacterivores, predators, omnivores, plant parasites, and fungivores, which were significantly less abundant at highly polluted sites. This correlation suggests that nematode groups with higher c-p values, and those with c-p 1 and 2 designations, can be useful indicators of high heavy-metal contamination in areas polluted for a long time. In contrast, the abundance of c-p 3 plant parasitic nematodes was positively correlated with copper, nickel, and zinc contents and with soil-moisture content in the alluvial meadows. Maturity index (MI) and MI2-5 were the most sensitive indices of the degree of disturbance of the soil ecosystem, with enrichment index, structure index, and basal index indicating the altered decomposition channels and diminished structure of the food web.