Soil Nematode Community Structure Research Articles

The effect of anaerobic digestate as an organic soil fertilizer on the diversity and structure of the indigenous soil microbial and nematode communities.

Anaerobic digestate is a popular soil additive which can promote sustainability and transition toward a circular economy. This study addresses how anaerobic digestate modifies soil health when combined with a common chemical fertilizer. Attention was given to soil microbes and, a neglected but of paramount importance soil taxonomic group, soil nematodes. A mesocosm experiment was set up in order to assess the soil's microbial and nematode community. The results demonstrated that the microbial diversity was not affected by the different fertilization regimes, although species richness increased after digestate and mixed fertilization. The composition and abundance of nematode community did not respond to any treatment. Mixed fertilization notably increased potassium (K) and boron (B) levels, while nitrate (NO3-) levels were uniformly elevated across fertilized soils, despite variations in nitrogen input. Network analysis revealed that chemical fertilization led to a densely interconnected network with mainly mutualistic relationships which could cause ecosystem disruption, while digestate application formed a more complex community based on bacterial interactions. However, the combination of both orchestrated a more balanced and less complex community structure, which is more resilient to random disturbances, but on the downside, it is more likely to collapse under targeted perturbations.

Comparative analysis of soil nematode biodiversity from five different fruit orchards in Osmaneli district, Bilecik, Türkiye.

Nematode population densities were determined in 60 soil and root samples collected from 6 fruit orchards in the Bilecik province (western Turkey), between April 2022 and June 2022. The total number of identified nematodes have reached up to 2418 individuals (number of female: 1036; male: 154; and juvenile: 1228). They belong to 54 species, 54 genera, 33 families and 11 orders. Plant parasitic nematodes that were detected mostly are listed as follows: Helicotylenchus (6,12 %), Pratylenchus (5,74 %), Paratylenchus (4.83 %), Xiphinema (3,06 %), Tylenchorhynchus (2,19 %), Malenchus (1.94 %) and Tylenchus (1.19 %). According to the maturity index analysis, mean values showed the highest maturity level at peach trees (MI value: 3,52), followed by; walnut trees (MI value: 2.49), cherry trees (MI value: 2.15), nectarine trees (MI value: 1.86), plum trees (MI value: 1.57), and olive trees (MI value: 1.42). Mostly the diverse group in terms of species richness was within the order Dorylaimida. The nematodes associated with peach and walnut trees here showed the most stable environments in terms of soil nematode community structure.

Effect of Application Rates of N and P Fertilizers on Soil Nematode Community Structure in Mollisols

Long-term application of chemical fertilizer poses an environmental threat to belowground ecosystems. However, the impact of nitrogen (N) or phosphorus (P) fertilizers on soil biodiversity and the conditions of soil food web remains largely unknown. Soil nematodes are the most abundant multicellular soil animals and serve as excellent bioindicators of soil. Here, we investigated soil nematode communities and food web structure in a long-term experiment with different application rates of N and P fertilizers in northeast China. The application of N and P fertilizers increased the abundance of bacterivores but suppressed the abundance of omnivores and predators. The abundance of bacterivores exhibited an increasing trend, while that of omnivores and predators showed a decreasing trend with increasing rates of N and P fertilizers. Plant parasites displayed a decreasing trend in response to N fertilizer, but not to P fertilizer. N and P fertilizers also altered nematode functional guild composition, with N fertilizer increasing the abundance of Ba1, and P fertilizer increasing the abundance of Fu2 and Ba3. Nonmetric multidimensional scaling (NMDS) analysis revealed apparent successions of nematode communities from no fertilizer soils to high rates of N or P fertilizer soils at both the genus and functional guild levels. Furthermore, N and P fertilizers resulted in different nematode communities. In terms of nematode food web indices, N fertilizer increased the enrichment index (EI) but reduced the channel index (CI) and structure index (SI), whereas P fertilizer only reduced the SI value. High rates of N and P fertilizers increased the respired carbon of bacterivores but reduced the respired carbon of predators. Mantel tests revealed significant correlations between soil properties and the community composition of both fungivores and omnivores. Among all soil properties, available phosphorus (AP) had the greatest influence on the community structure of soil nematodes. Our findings indicate that N fertilizer has a powerful effect on nematode food web structure, while P fertilizer exerts a stronger effect on soil nematode community composition.

Effect of heavy metal contamination on soil nematode communities in urban brownfields

Heavy metal contamination in urban brownfields can pose serious threats to the soil ecosystem. Soil nematode communities can respond rapidly to minor alterations in the soil environment over brief time intervals and are extensively employed to track changes in the soil environment. Here, we investigated the impact of heavy metal contamination on soil nematode communities and assessed the ecological risks associated with brownfields. We analyzed heavy metal contamination and soil nematode community structure in a representative urban brownfield and its neighboring urban park. The results showed that the brownfield was predominantly impacted by chromium (Cr) contamination. Plant parasites served as the primary source for soil nematodes in the park, whereas bacterivores fulfilled this role in the brownfield. Omnivores-predators decrease or even disappear with the intensification of heavy metal contamination. Acrobeloides exhibited tolerance to heavy metal contamination. Based on life history strategy, nematode communities could be classified into five colonizer-persister (c-p) groups, and the c-p values were ranked from 1 (short generation time and high colonization ability and fecundity) to 5 (long generation time and low colonization ability and fecundity). Soil nematode communities with c-p values ranging from 1 to 3 exhibited a significant negative correlation with hexavalent chromium [Cr (VI)], while those with c-p values of 4 and 5 (representing high trophic level communities) showed a significant positive correlation. We postulate that bacterivores exhibit superior adaptations to heavy metal contamination. Specific nematode taxa can indicate the pollution status of elements. Soil nematode communities at high trophic levels are powerful indicators of response to Cr (VI) contamination.

Community structure and functional diversity of soil nematodes from Udupi district, Karnataka, India

Nematodes constitute the most significant, most numerous, and diversified set of multicellular organisms on the earth. They live in various environments and exhibit a wide range of behavioural patterns. In the soil food web, they can be found at various trophic levels as herbivores (plant parasitic nematodes), bacterivores, fungivores, omnivores, and predators. As there were fewer studies on nematode ecology in the Udupi region, the present study aims to study the community structure and functional diversity of soil nematodes. Soil samples were collected following opportunistic random sampling employing a soil auger and were stored at 40C until transported to the laboratory. Nematodes were isolated from soil, killed, fixed, dehydrated, and displayed on a glass slide after isolation. The standard keys were used to identify the individual to genera level. 62 genera of soil nematodes belonging to 26 families and 7 orders were identified. Predator were the most prevalent communities. Various statistical indices for assessing nematode population ecology and nematodes specific indices were also calculated and it indicated a significant abundance of large plant parasitic nematodes. The region exhibits low levels of labile organic carbon and nutrient enrichment (Enrichment Index (EI):14.06 to 21.22). Despite this, the soil food web in the region is well-structured, indicated by Structure Index (SI) (85.51 to 89.74). Prevalence of fungal decomposition dominance and the soil appears to be minimally disturbed, as indicated by high channel index values and low Basal Index (BI) values, respectively

Cover crop functional types alter soil nematode community composition and structure in dryland crop-fallow rotations

Increasing dryland cropping intensity by integrating cover crops into crop-fallow rotations can add diversity and alter soil ecosystem functions, including improvements in soil nutrient and water retention and cycling, and suppression of soil-borne pests. However, the use of cover crops can also carry the risk of increasing the abundance of plant-parasitic nematodes that could undermine system productivity. Here, we examined how the integration of diverse cover crops of different functional groups: Poaceae [forage oat (Avena sativa L.)]; Brassicaceae [forage rape (Brassica napus L.)]; and Fabaceae [common vetch (Vicia sativa subsp. sativa L. and fababean (Vicia faba L.) in monocultures and mixtures into a dryland crop-fallow rotation altered soil nematode community composition and structure relative to conventional fallows. We found that cover crop mixtures had greater diversity and complexity of free-living nematodes, indicating enhanced cycling of energy and nutrients (enrichment index >50 %) compared to monocultures. Furthermore, using a structural equation modelling approach, we showed the abundance of free-living nematodes is driven primarily by cover crop residue quality (C:N ratio, and cellulose content) and marginally by cover crop quantity (biomass). The grass-legume mixture had the highest abundance of plant-parasitic nematodes (Pratylenchus neglectus and Merlinius brevidens) but also fostered robust soil food webs with complex soil nematode trophic interactions, indicating promotion of soil ecosystem functions related to N and C cycling and overall improvement in soil health. The results indicate bottom-up effects of cover crops on soil nematode communities are modulated by cover crop functional type and mixture composition. Consequently, cover crops with appropriate traits must be selected if soil health is to be improved via suppression of plant-parasitic nematodes, promotion of free-living nematodes, and enhancement of soil food web complexity.

Effects of wild boar grubbing on the soil nematode community subject to seasonal variation in a broad-leaved Korean pine forest in Northeast China

Soil disturbances caused by large animals impact soil biodiversity and potentially alter forest ecosystem functioning and productivity. However, most studies have focused on the effects of wild boar infestations on above-ground vegetation and soil physical and chemical properties. Little is known about the influence of wild boar grubbing on the soil faunal community within forested ecosystems. To address this knowledge gap, we conducted a long-term (10-year) exclosure experiment to investigate the responses of soil nematode communities to wild boar grubbing and seasonal variations in a broad-leaved Korean pine forest in Changbai Mountain, China. The results indicated that wild boar grubbing did not significantly impact soil nematode abundance, genus richness, diversity indices (Shannon-Wiener diversity index, Simpson index, and evenness index), and ecological indices (enrichment index, channel index, structural index, and basal index). However, we observed that grubbing reduced the relative abundance of plant parasites while increased that of bacterivores and the maturity index (MI), leading to changes in nematode community composition. Notably, the influence of grubbing was more pronounced in the spring than in the autumn. Although season itself did not significantly affect soil nematode genus richness and diversity indices, it did affect soil nematode relative abundance, bacterivores, omnivores-predators, plant parasites, K-strategistis, r-strategistis, MI, enrichment index, and channel index. Long-term wild boar grubbing appeared to mitigate seasonal effects on soil nematode communities, resulting in higher MI and increased stability in nematode community abundance. Our findings suggest that changes in soil parameters, such as soil NH4+, soil pH, and soil NO3–, likely mediate the observed impact of wild boars on the soil nematode community. In summary, our study demonstrated that wild boar grubbing altered the structure of soil nematode communities, albeit with seasonal variations, indicating that the effects of wild boar activity on forest soil ecosystems influence biogeochemical cycles through changes in nematode community composition rather than nematode genera richness.

Plant diversity enhanced nematode-based soil quality indices and changed soil nematode community structure in intensively-managed agricultural grasslands

Plant productivity, decomposition and nutrient cycling are controlled by plant-soil-biota interactions. However, it remains poorly understood how plant species diversity impacts belowground communities that modulate these processes in intensively-managed grassland systems. In managed grassland communities comprising species selected for agronomic performance, we investigated how plant species diversity affected the soil nematode community and associated ecological indices with a focus on assessing aboveground-belowground interactions. A total of 27 nematode taxa were identified from 61 experimental field plots in which plant species diversity was systematically manipulated from a pool of six plant species within three functional groups (FGs; grasses, legumes, herbs). In general, there were strong effects of plant species identity on the nematode community; interspecific interaction effects did not consistently occur, but where they did were best related to plant community evenness. The equi-proportional six-species plant community had a significantly higher nematode diversity, maturity index (MI), structure index (SI) and proportion of sensitive taxa (omnivore and predators) but a lower enrichment index (EI) than the individual monocultures. The two legumes (Trifolium pratense and Trifolium repens) had the highest EI but lowest abundance of fungivores and channel index, indicating a bacterial-dominated decomposition pathway. Moreover, the community structure of nematodes in the equi-proportional six-species community was significantly different from that in the monocultures. This change in community structure was associated with factors highly correlated with plant diversity, including higher aboveground biomass yield and total nitrogen in harvested biomass as well as lower biomass of weed species. Overall, our results show that multi-species forage sward mixtures that include grasses, legumes, and herbs can have a positive effect on the soil nematode community and nematode-based soil quality indices. This is of practical relevance for farmers and for EU agricultural policy targeted at sustainability, soil health and farming for biodiversity benefits.

Dominant plants mediate effects of grazing on soil nematode traits in a wet meadow grassland

Grazing is an integral disturbance in grassland ecosystems, however, its effects on belowground ecosystems are poorly understood. As the extent and quality of grasslands continue to decline around the world, metrics are required to monitor the effects of grazing on the function of rangeland soils. Soil nematodes are an important group of soil biota used to understand soil function. However, traditional approaches that rely on indices based on life-history information of soil nematodes have been supplemented in recent literature with trait-based analyses. Here, we test how changes in the structure and composition of soil nematode communities relate to grazing. We collected and measured morphological and reproductive traits of dominant genera of soil nematodes in a wet meadow grassland in Manitoba, Canada, to test how grazing alters trait profiles of nematode communities. For ten genera of soil nematodes, representing 80 % of community abundance, we measured morphometric traits, including body length and mass and used published literature to collect data describing reproductive traits. Communities of free-living nematodes were dominated by bacteriovore and root feeding genera and grazing intensity decreased the richness, diversity, and evenness of soil nematode communities. However, we observed no significant differences in the feeding structure of nematode communities based on the timing or intensity of grazing and no effect of grazing on mean trait values of the most abundant genera of soil nematodes. In contrast, changes in the community weighted means of nematode traits were strongly related to the abundance of dominant vegetation. We discuss the potential effects of changes in soil nematode communities on the function of wet grassland soils. Results from our research indicate that sustainable management and restoration of wet meadow rangelands must consider the impacts of grazing intensity on soil function and that plants play a key role in structuring the soil nematode communities belowground.

Biocontrol-based strategies for improving soil health and managing plant-parasitic nematodes in coffee production.

Coffee is an important commodity for Kenya, where production is steadily declining, despite a global rise in demand. Of the various constraints affecting production, plant-parasitic nematodes are a significant, but often overlooked, threat. As a perennial crop, treating plantations once infected with nematodes becomes difficult. The current study evaluated the drenching application of two biocontrol agents, Trichoderma asperellum and Purpureocillium lilacinum, for their nematode control efficacy, as well as their impact on the soil nematode community structure on mature, established coffee trees in Kenya. Seven Arabica coffee field trials were conducted over two years on trees of various ages. All the fields were heavily infested with Meloidogyne hapla, the first report of the species on coffee in Kenya. Both fungal biocontrol agents were detected endophytically infecting roots and recovered from soil but not until six months after initial applications. The population densities of M. hapla had significantly declined in roots of treated trees 12 months after the initial application, although soil nematode density data were similar across treatments. Based upon the maturity index and the Shannon index, treatment with T. asperellum led to improved soil health conditions and enrichment of diversity in the microbial community. Application of P. lilacinum, in particular, led to an increased abundance of fungivorous nematodes, especially Aphelenchus spp., for which P. lilacinum would appear to be a preferred food source. The soils in the trials were all stressed and denuded, however, which likely delayed the impact of such treatments or detection of any differences between treatments using indices, such as the functional metabolic footprint, over the period of study. A longer period of study would therefore likely provide a better indication of treatment benefits. The current study positively demonstrates, however, the potential for using biologically based options for the environmentally and climate-smart management of nematode threats in a sustainable manner on established, mature coffee plantations.

Nitrogen-fixing tree species rather than tree species diversity shape soil nematode communities in subtropical plantations

Positive relationships between tree species diversity and soil communities are reported in many studies. However, the effects of tree species richness and nitrogen (N)-fixing tree species on soil fauna communities are not yet fully understood. Here, we conducted a field experiment to investigate changes in soil nematode communities under a gradient of tree species richness (e.g., 1, 2, 4 and 6 tree species) with N-fixing tree species (absence or presence). We found that N-fixing tree species strongly affected soil nematode trophic groups, and significantly increased the abundance of omnivore-predators and structure index via promoting more trophic links and multi-trophic interactions, leading to a more stable and complex soil food web. In the presence of N-fixing tree species, tree species richness significantly increased the abundance and relative abundance of fungivores and the channel index, with the shift in soil energy channel through increased the C/N ratio of leaf litter. In contrast, tree species richness detrimentally affected the abundance of plant parasites due to the decline of leaf litter N content under the presence of N-fixing tree species. The results revealed that the bottom-up effects of N-fixing tree species on soil nematode community structure were crucial drivers in shaping nematode communities in subtropical plantations. Our study suggests that N-fixing tree species is more important than tree species richness to regulate soil nematode community structure and soil energy channel, and therefore, should be preferentially considered in multispecies forest plantations.

Soil Macrofauna Disperse and Reconstruct Soil Nematode Communities: Takeaways from a Microcosm Study

Soil macrofauna is an important component of soil biodiversity and plays a key role in soil ecosystem function. Little work, however, has explored how macrofauna may contribute, directly or indirectly, to soil microfauna communities. In this study, we explored the impact of two classes of common soil macrofauna, earthworms (Eisenia foetida) and millipedes (Spirobolus walkeri), on soil nematode community diversity and structure. We found that earthworms and millipedes play an important role in maintaining soil nematode communities and increasing soil nutrients. Both earthworms and millipedes act as hosts for soil nematodes, and play a valuable role in dispersing and distributing these important microfauna throughout the soil landscape. We tested the efficacy of this strategy on multiple soil layers and found that layer does not have a significant influence on soil nematode community. These results suggest that soil nematode abundance, diversity, and structure are tightly linked to the existence of soil macrofauna, which may contribute to the maintenance mechanism of forest soil biodiversity.

Elevational patterns of soil nematode diversity, community structure and metabolic footprint in the Trikuta mountains of Northwestern Himalaya

Nematodes are an integral part of soil biodiversity and play a vital role in soil nutrient cycling. The Himalayan mountainous ecosystems are amongst the extreme environments in the world. Still little is known about the diversity and distribution patterns of soil nematodes along the elevation gradient in the region, thus limiting our ability in understanding and comparing the structural patterns of nematode communities across different regions. To address this knowledge gap, we aim to disentangle the elevational patterns of soil nematode community structure and trophic diversity by studying the abundance, composition, diversity and functional indices, and metabolic footprint of soil nematodes at four elevation classes (Elev1, Elev2, Elev3, and Elev4 each being 400 m) along an altitudinal gradient (1,000–2,600 m) in the Trikuta mountain range of Pir-Panjal to Shivalik Himalaya. Overall, a total of 55 genera were found in the study region. The diversity and richness of soil nematodes varied significantly among the elevation classes, and exhibit a decreasing trend with elevation. Also, the nematode community composition varied significantly among the elevation classes along the elevational gradient. The bacterivores were the dominant trophic group at each elevation class. Further, the soil properties played a key role in explaining the changes in the nematode community composition across the elevation classes. Moreover, the total nematode, bacterivore and herbivore abundances showed an increasing trend, while as that of fungivores and predators exhibit a negative trend with elevation. In addition, a declining pattern in the overall maturity and metabolic footprint with elevation was observed, thus depicting the lower sustenance of k-strategic nematodes and their relatively lower contribution to belowground carbon cycling at higher elevations. The finding of our study could enhance our understanding of the overall community structure and diversity patterns of soil nematode along the elevation gradient, and the response of soil nematodes to ongoing climate change in the rapidly warming Himalayas.

Effects of fertilization on soil nematode communities in an alpine meadow of Qinghai-Tibet plateau

Nitrogen and phosphorus are important nutrient elements for plants and underground organisms. The nematode is an important part of the soil food web. Although many studies have explored the effects of fertilization on soil nematode community structure, little is known about the response mechanism of the nematode community to fertilization. In this study, we investigated the diversity and functional diversity of soil nematode communities, as well as soil physicochemical properties, root functional traits, and plant richness. We explored the response mechanism of soil nematode communities to nitrogen and phosphorus fertilizer. Nitrogen fertilizer increased the abundance and richness of bacterivorous nematodes, while phosphorus fertilizer decreased the total abundance of bacterivorous nematodes. Meanwhile, the diversity of the nematode community was significantly affected by soil physicochemical properties and plant root functional traits. Therefore, our study revealed the effects of nitrogen and phosphorus fertilizer on soil nematode community diversity and functional diversity. Exploring the response mechanism of soil nematode communities to fertilization interference provides further evidence for the role of nematodes in maintaining the function of subsurface ecosystems.

Effects of target tree management of Pinus massoniana plantation on soil nematode community structure at different soil depths

To understand soil nematode community structure at different soil depths and its responses to target tree management, we collected soil samples (0-10, 10-20, and 20-50 cm) and litter samples from the target tree management plots and control plots of Pinus massoniana plantation and analyzed community structure, soil environmental factors, and their relationship. The results showed that target tree management increased the abundance of soil nematodes, with the most significant effect at a depth of 0-10 cm. The highest abundance of herbivores was found in the target tree management treatment, while that of bacterivores was found in the control. Compared with the control, Shannon diversity index, richness index, maturity index of nematodes at 10-20 cm soil layer and Shannon diversity index at 20-50 cm soil layer of target trees were significantly improved. According to the results of Pearson correlation and redundancy analysis, soil pH, total phosphorus, available phosphorus, total potassium, and available potassium were the main environmental factors affecting community structure and composition of soil nematodes. In general, target tree management was conducive to the survival and development of soil nematodes and promoted the sustainable development of P. massoniana plantations.

Impact of marshy area reclamation by various vegetations on soil-nematode community structure in Dachigam National Park

• Impact of marshy area reclamation by various vegetations on soil nematode community was investigated.• Nematode abundance was lowered by reclamation mostly due to bacterivores.• Reclamation effectively diminished the nematode metabolic footprint.• Robust management strategies must be adapted for conservation and protection of marshy ecosystems.Marshy areas are ecologically important and sensitive areas which are under immense pressure, such as reclamation by various terrestrial vegetations. However, how these vegetation types disrupt the stability of nematode community is scarce. The present study determined how the soil nematode community responded to shifting environmental states by using nematode abundances, nematode indices and metabolic footprints as indicators. In this context, we selected three types of reclaimed vegetation around a marshy land (MR) in Dachigam National Park, Kashmir, which includes grassland (GL), forest (FR) and cropland (CL) to investigate the soil nematode community. Acrobeloides, Plectus, Eudorylaimus, and Aphelenchus proved more sensitive to reclamation effect. Results revealed decrease in total nematode and bacterivore abundance. Reclamation reduced diversity in CL, whereas no effect was observed in the GL and FR as compared to MR. Channel index indicated shift from fungal decomposition to bacterial decomposition pathway in GL. The nematode faunal profile depicted grassland (GL) as the most structured ecosystem compared to MR, FR, and CL. Our results suggest that vegetation type regulates the structure, function, and stability of the soil food web, which has significant implications for managing the vegetation cover in a sustainable manner in the Dachigam National Park.

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.

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.

Exploring the effects of warming and nitrogen deposition on desert steppe based on soil nematodes

AbstractThe combined effects of warming and increased nitrogen (N) deposition in various ecosystems have become global issues. We used high‐throughput sequencing in an 8‐year field experiment to evaluate the impacts of the interactions between warming and nitrogen addition on soil nematode communities in a desert steppe. The soil nematode community presented with a certain degree of tolerance to warming. Warming mainly altered soil nematode diversity and community stability in deep soils whereas nitrogen addition primarily affected the nematode community in surface soils. Moreover, warming interacted with nitrogen addition exacerbated its negative effects on nematode richness and diversity. A Mantel analysis showed that soil pH was significantly negatively correlated with soil NH4+ and NO3− content. All three soil physicochemical (pH, NH4+ and NO3−) parameters were significantly correlated with desert steppe soil nematode community structure. Based on network and relative abundance analyses, we determined that Paratylenchus, Cervidellus, and Acrobeloides were the major hub soil nematode genera responding to soil warming and nitrogen addition in a desert steppe. The present study comprehensively analyzed the responses of desert steppe soil nematode communities to warming and nitrogen addition and provided an exemplar for studying the impact of environmental factors on soil nematodes communities worldwide.