Nematode Food Web Research Articles

Continuous cropping obstacles: Insights from the community composition and the imbalance carbon fluxes within soil nematode food web

Long-term continuouscroppingcan lead to the deterioration of soil environment and the decrease of soil productivity. However, the biological mechanism on the negative effects of long-term continuous cropping has not been extensively explored. Soil nematode food web with multiple trophic levels play critical roles in nutrient cycling and energy flowing in the agroecosystem. Quantifying the carbon flux through different trophic channels within the nematode food web can indicate how continuous cropping influences carbon cycling in the agroecosystem by altering soil biota communities. Therefore, the effects of continuous peanut cropping with different years (1, 5, 20, and 30 years) on soil properties, soil nematode community composition, carbon flux within nematode food web and crop yields were investigated. Results showed that soil pH significantly decreased with increasing continuous cropping years. Differently, soil organic carbon and total nitrogen were the highest in 20-year, and decreased in 30-year of continuous cropping. As continuous cropping years increased, the relative abundance of microbivorous nematodes decreased and that of plant parasites reached as high as 76.11 % and 68.22 % in 20- and 30-year, respectively. Pearson correlation analysis revealed the nematode diversity, the carbon flux uniformity and peanut yield had a significant negative correlation with continuous cropping years. The random forest model indicated that the soil pH and the relative abundance of plant parasites were the key influence factor of the carbon flux uniformity within soil nematode food web. Outbreaks of plant parasites lead to the disruption of carbon flux uniformity within soil nematode food web, which can increase the risk of peanut yield decline after long-term continuous cropping. In conclusion, continuous peanut cropping changed soil properties, reduced soil nematode diversity, and disturbed the multitrophic carbon flux complementarity and uniformity in soil nematode food web, ultimately limiting the crop productivity. This study enhances our understanding of the importance of the resource transfers among soil food web in maintaining sustainable agroecosystem productivity.

Linking soil health and carbon dynamics to conservation measures: Evidence from nematode communities in Souss-Massa National Park, Morocco

Global environmental policies have effectively designated 17 % of the Earth's surface as protected areas and implemented robust measures to address climate change. However, the importance of soils as critical reservoirs of biodiversity and carbon is often overlooked in global policy making. In the present study, we used nematodes as indicators to assess the impact of conservation strategies on soil food web connectance. We explored nematode metabolic footprints and their carbon budget, and evaluated soil health by identifying factors that influence nematode functional diversity. We collected 180 soil samples from three zones in the Souss Massa National Park in Morocco: transitional zone (organic cropping and grazing activities), buffer zone (grazing activity), core zone (strictly protected area), and a nearby intensively farmed non-protected area. We noted a consistent decline in diversity within all trophic groups from the core zone (56 taxa) to the non-protected zone (18 taxa). A notable increase in total nematode abundance and herbivore diversity was observed in the organic soils of the transitional zone. In contrast, nematode abundance and diversity were lower in non-protected zones. Meloidogyne, a sedentary endoparasite, was prevalent in conventional crops outside the park but was not reported within the park. Nitrogen, phosphorus, and potassium were the major soil parameters affecting nematode food webs. The functional metabolic footprints of nematodes were enhanced by nature conservation, highlighting the crucial role of nematodes in generating carbon influxes in protected areas. Our results show that 3.11× 1012 nematodes (with a total biomass of 330.47 tonnes) inhabit surface soils across the park, which is 14.38 times greater than the same area in the non-protected zone. Daily production and storage of biomass and carbon budget were 43.85 and 48.93 % higher in the park top soils than in the non-protected zone, respectively. This knowledge is significant for decision makers when formulating nature conservation programs, planning sustainable land use strategies, and addressing the challenges of rising CO2 emissions.

Nitrogen addition and precipitation reduction alter ecosystem multifunctionality and decrease soil nematode abundance and trophic energy fluxes in a temperate forest

Soil biota and energy flow within their food webs have a profound impact on various ecosystem functions. However, there are still significant gaps in our understanding of how climate change factors, such as nitrogen deposition and reduced precipitation, impact ecosystem functioning, particularly in temperate forest ecosystems. In this study, we evaluated the response of ecosystems to long-term nitrogen deposition and/or reduced precipitation due to climate change. We assessed these responses by examining nematode community energy fluxes and their associated ecosystem multifunctionality. Field experiments were conducted in a temperate forest to simulate nitrogen deposition (5.0 kg N·ha−1·yr−1) using NH4NO3 application and to reduce precipitation (to 70 % of a normal year) using rain shelters. Our findings showed that nitrogen addition and/or precipitation reduction treatments altered soil nematode composition. Nitrogen addition alone reduced the abundance and energy fluxes of high trophic groups such as omnivore-predators, which served as proxies for total abundance and energy fluxes. In contrast, precipitation reduction did not exhibit significant effects on overall abundance and energy fluxes. Environmental factors influencing changes in soil nematode abundance and energy fluxes included soil pH, NH4+-N, and total nitrogen in the soil. Nitrogen addition increased ecosystem multifunctionality by promoting nutrient cycling, while precipitation reduction promoted plant productivity and inhibited carbon cycling, without changing ecosystem multifunctionality. Regression analysis showed that soil nematode energy fluxes were negatively correlated with ecosystem multifunctionality. The effects of these two factors on soil nematode food webs showed temporal variation, as well as indicators related to multiple functions of the ecosystem. Our study suggests that soil nematode energy fluxes are more sensitive than nematode abundance for quantifying the relationship between biodiversity and ecosystem multifunctionality.

Energy flows through nematode food webs depending on the soil carbon and nitrogen contents after forest conversion

The swift proliferation of forests converted into monoculture plantations has profound impacts on soil nutrients, microbial communities, and many ecological processes and functions. Nematodes are soil microfauna that play a pivotal role in biogeochemical cycling and in soil food web, whereas the response of soil nematode communities and energy flows to forest conversion remains unknown. Here, we assessed the community composition and the energy flows of the nematode food webs as a function of soil chemistry after conversion from natural forests (Forest) to four plantations (8-year-old): Amygdalus persica (Peach), Myrica rubra (Berry), Camellia oleifera (Oil), and Cunninghamia lanceolata (Fir). After forest conversion, soil organic carbon (SOC) and total nitrogen (TN) contents decreased by 65 % and 55 %, respectively. Forest conversion strongly reduced the abundance (particularly large-bodied omnivorous-predatory nematodes), diversity, maturity, and stability of the soil nematode community. The shifts in composition and structure of nematode communities after forest conversion are reflected in changes in the abundance of predominant genera and trophic taxa, especially bacterivorous, fungivorous, and omnivorous-predatory nematodes. Acrobeloides notably increased, whereas Plectus, Prismatolaimus, Tylencholaimus, and Tripyla decreased. Accordingly, the abundances of r-strategy nematodes (cp value = 1–2) increased, but that of the K-strategists (cp value = 3–5) declined. Additionally, the energy flow across the soil nematode food web was reduced by 36 % and flow uniformity declined by 24 % after forest conversion. These changes in nematode diversity and abundance were triggered by diminishing soil C and N contents, thereby affecting the energy flows via the nematode food webs. Thus, forest conversion affects soil biotas and multi-functions from the perspective of nematode food web structure and energy flows, and underlines the interconnections between ecosystem and energy dynamics across multi-trophic levels, which is crucial for sustainable forest management.

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.

Leguminous crop restores the carbon flow attenuation from nitrogen loading within soil nematode food web in a Camellia oleifera plantation

Excessive nitrogen (N) loading poses a substantial risk to soil biodiversity and disrupts carbon (C) flows within the soil food web. Intercropping with legumes is often considered a sustainable way to maintain soil N availability and mitigate the associated detrimental effects. However, it remains unclear whether and how legume crops restore energetic attenuation caused by N loading within the soil food web. Here, we conducted a two-year field experiment using randomized block design in a subtropic Camellia oleifera plantation with high wet N deposition. We examined the effects of applying N fertilizers at normal or half levels (168 or 84 kg N ha−1yr−1) and intercropping legumes (Arachis hypogaea or Cassia tora) on the soil nematode food web. We observed that N fertilization suppressed the majority of nematode trophic groups, weakened the stability of food web structure, and diminished the C flows across the bacterial and fungal energy channels. Conversely, intercropping with legumes (particularly with C. tora) bolstered the densities of bacterivore and fungivore nematodes. This enhancement facilitated interactions within the soil micro-food web, and subsequently augmented the C flows within their respective channels. Model predictions suggested that the detrimental effects of N fertilizers on the nematode food web are primarily linked to decreased soil pH resulting from soil N accumulation. Notably, higher soil organic C was found to mitigate these effects. Furthermore, N-enriched legume substrates played a beneficial role in stimulating soil microbial activities and facilitating C flows through bottom-up control. Our findings emphasize the positive impacts of legume crops on mitigating soil biodiversity loss and restoring energetic attenuation within soil food web under N-saturated soil conditions. These findings provide valuable insights for agroforestry management practices aimed at sustaining soil health and ecosystem resilience.

Energy flow across soil food webs of different ecosystems: Food webs with complex structures support higher energy flux

Energy flux in food webs is a fundamental feature of ecosystems and an important link between biodiversity and ecosystem function. Studies of energy flow through the soil nematode food web have emerged in recent year; however, it is not clear whether and how the nematode food web structure affects the energy flow. In this study, the structures and carbon flux of soil nematode food webs in four different ecosystems, namely, forageland, cropland, secondary forest, and grass-shrubland, were assessed. The food web structure was represented by nematode community indices such as maturity index, structure index, genus and trophic group diversity, and slope of size spectra. The results showed that carbon flux through the nematode food webs was the highest and lowest in the secondary forest and forageland, respectively. The total carbon flux of nematode food web was higher in the cropland than that in the grass-shrubland. The magnitudes of bacterial and fungal energy channels were basicallyequal in the forageland and secondary forest. The energy flow through the bacterial channel was greater than that through the fungal channel in the grass-shrubland, whereas the pattern was reversed in the cropland. The total carbon flux through the nematode food web, the carbon fluxes through the bacterial or fungal channel, and the energy flow uniformity were positively correlated with the nematode structure index, maturity index, and genus diversity index. The trophic group diversity and size spectra slope of nematode communities were not significantly correlated with the carbon flux. The results indicate that mature and complex soil communities support high energy flux across soil food webs.

The functional composition of dune nematode communities is structured by both biogeographic region and the local marram grass environment

Nematodes are involved in many important ecosystem functions such as nutrient cycling and plant growth. Nematode communities are thought to be structured at regional scales mainly by abiotic soil characteristics and climatic drivers and at local scales by habitat heterogeneity and biotic interactions. Blond dunes are dominated by marram grass (Calamagrostis arenaria), the key dune-forming plant species in Western Europe. Consequently, nematode food webs are mainly associated with marram grass in these coastal areas.We investigated the relative importance of regional biogeographic factors and local biotic drivers, such as the vegetation's spatial structure and the occurrence of an invasive plant species, in determining the functional diversity of belowground nematode communities inhabiting the roots of marram grass and surrounding soil in coastal dune areas.We found that nematode functional group abundances mainly differed among biogeographic regions, but that abundances could not be linked to plant-associated parameters, such as plant vitality or abundance. Additionally, the abundances of different functional groups seemed to be positively associated within both rhizosphere and bulk soil, an effect that could be the result of ecological filtering or facilitative interactions.Nematode pressure has been assumed to be an important driver of marram grass degeneration under ceasing sand dynamics. We here show that variation in nematode functional group composition is only weakly related to these local changes in plant vigour, but that large-scale patterns in nematode communities may explain regional variation in marram dynamics in coastal dunes.

Biochar enhances multifunctionality by increasing the uniformity of energy flow through a soil nematode food web

Soil multifunctionality is the consequence of biotic interactions that drive decomposition, nutrient cycling and net primary production. Energy flux describes the energy consumed and transferred among multitrophic groups in the soil food web, which are logically linked to multifunctionality. In a subtropical agroecosystem with an annual sweet potato-oilseed rape rotation, we explored how biochar and synthetic fertilizer jointly affected agroecosystem multifunctionality (e.g., crop production, soil carbon storage and nutrient cycling) and the energetic structure of the nematode food web during two consecutive years. Results showed that biochar increased soil multifunctionality by 37–110% mainly by promoting a uniform energy flow through the soil nematode food web, which was largely due to increased energy fluxes of fungivores and omnivores-carnivores at the expense of decreased energy flux through herbivores. Applying a lower rate of synthetic fertilizer led to non-uniform energy flow in the soil nematode food web, suggesting that nitrogen limitation could offset the stimulatory effect of biochar on soil multifunctionality. This was because biochar induced oligotrophic conditions (a stoichiometry-induced nitrogen limitation), effectively warranting that continuous biochar application would aggravate nutrient limitations to crops, especially when low rates of synthetic fertilizer are applied. Notably, soil nutrient impoverishment could lead to resource reallocation from aboveground shoot to belowground root production, thereby fueling the energy flow through the herbivore channel. Our findings highlight the importance of balancing biochar and synthetic fertilizer applications to sustain a stable energetic structure in soil nematode food webs, which are associated with greater crop production and soil health in subtropical region.

Afterlife effect of cover crops on soil nematode food web: Implications from the plant ecological strategy

Afterlife effect of cover crops on soil nematode food web: Implications from the plant ecological strategy

Arthropod Community Responses Reveal Potential Predators and Prey of Entomopathogenic Nematodes in a Citrus Orchard

The contributions of soil arthropods to entomopathogenic nematode (EPN) food webs are mainly studied in artificial conditions. We investigated changes in arthropod communities in a citrus orchard following soil inundation with Steinernema feltiae or Heterorhabditis bacteriophora. We hypothesized that arthropod taxa, which decline or increase in response to EPN augmentation, represent potential prey or predators of EPN, respectively. Soil was sampled periodically after nematodes were applied, DNA was extracted from organisms recovered by sucrose centrifugation, libraries were prepared, and the ITS2 and CO1 genes were sequenced using Illumina protocol. Species from 107 microarthropod (mites and collembola) families and 121 insect families were identified. Amplicon sequence variant (ASV) reads for H. bacteriophora were less than 10% of those for S. feltiae three days after inundation, whereas microarthropod ASVs were double in plots with H. bacteriophora compared to those with S. feltiae. Significantly fewer microarthropod and insect reads in S. feltiae compared to untreated plots suggest the possibility that S. feltiae preyed on mites and Collembola in addition to insects. The responses over time of the individual microarthropod species (MOTU) suggest that regulation (up or down) of these EPN resulted from a cumulative response by many species, rather than by a few key species.

The Short-Term Effects of Amendments on Nematode Communities and Diversity Patterns under the Cultivation of Miscanthus × giganteus on Marginal Land

The short-term effects of soil amendments on the structure, diversity and function of a nematode community of Miscanthus × giganteus was investigated. Crop was cultivated on marginal, nutrient-poor land amended with biochar in single and double doses (BD1 and BD2), biogas digestate (D), sewage sludge (SS), and hemicellulose waste (HW). Sampling was done after planting, in the middle and end of vegetation; morphology-based approach was used. 28 nematode taxa were identified, including 5 bacterivores genera, 4 fungivores genera, 5 herbivores genera (11 species), 2 omnivores genera, 5 predators genera. The general linear models, correspondence analysis and clustering were applied for evaluation. The total abundance of nematode taxa Filenchus, Dorylaimus, Cephalobus, Panagrolaimus, Aphelenchus, and Ditylenchus was depended on the sampling time and amendments. The incorporation of amendments affected nematode food web and resulted in suppression of plant-parasitic nematodes (PPNs). It was revealed that community structure was more mature for SS, less stable for D and had inconclusive effects for BD1, BD2, and HW. Using amendments ensured pest control benefits which is important given concern that PPNs can inflict crop damage during increased cultivation of M × g. Further research is needed to examine amendments which can minimise PPNs without reducing populations of nitrogen-fixing bacterivores and fungivores.

Organic amendments increase the flow uniformity of energy across nematode food webs

Energy dynamics within ecological communities are important in delivering ecosystem services. However, it remains elusive how the energy fluxes within soil food webs respond to agricultural fertilization regimes. Here, we studied the effects of long-term organic amendments and mineral fertilizers on the energetic structure of soil nematodes from a food-web perspective. We replicated our experiment in a rice paddy and in an upland maize cropping system. Results showed that the abundance of most trophic groups was higher in organically amended soils compared with mineral fertilizer treatments in both systems. Organic amendments, but not mineral fertilizers, increased the energy flux of total nematodes and most trophic groups compared with the no-fertilizer treatment. Furthermore, organic amendments increased the relative allocation of energy flux to microbivores but decreased the relative allocation to herbivores, supporting a higher flow uniformity than mineral fertilizers. We further found that organic amendments favored a higher total energy flux by supporting a greater nematode diversity, while sustained a higher flow uniformity by altering nematode community composition. Taken together, the result provides the evidence that a complex and species-rich community could transfer more energy to support ecosystem services. A broader perspective on linkages of biodiversity and energy dynamics spanning multitrophic groups is crucial for sustainable management, particularly in the light of non-random species loss under future environmental change.

Energy flux across multitrophic levels drives ecosystem multifunctionality: Evidence from nematode food webs

Energy flux in food webs, i.e., energy consumption by different trophic groups and describing their energetic structure, has been proposed as a powerful tool to understand the relationships between biodiversity and multiple ecosystem functions (ecosystem multifunctionality). Here we examined how different fertilization regimes affected the energy flux across multitrophic levels of soil nematodes in the paddy rice and upland maize fields. We considered 13 ecosystem functions of four ecological processes related to plant productivity, nutrient cycling processes and drivers, and functional stability, which are central to energy and nutrient flow across trophic levels. To confirm whether multitrophic flux would underpin the relationships between biodiversity and multifunctionality, we compared energy flux with other approaches including taxonomic diversity, functional diversity and community composition. Results showed that organic fertilizer supported 33–340% greater multitrophic energy flux of soil nematode community and enhanced 41–264% of ecosystem multifunctionality in both fields compared with mineral fertilizer treatments. Organic fertilization enhanced ecosystem multifunctionality by favoring energy flux in multitrophic levels of soil nematodes, while fertilization-mediated changes in other facets of biodiversity were less related to multifunctionality. Our study provides empirical evidence that energy flux within food webs can be used to understand the impacts of environmental change drivers on ecosystem multifunctionality.

Effect of reclamation of abandoned salinized farmland on nematode community in arid northwest China

Soil salinization is a serious problem worldwide and has resulted in large areas of abandoned land in Northwest China. In order to ensure the stability of cultivated land and food security, abandoned salinized farmland was reclaimed. However, the response of the nematode community to the reclamation remains unclear. In order to assess the response of the nematode community to reclamation and examine the relationships between soil properties and nematodes, we identified nematodes to the genus levels and determined their trophic groups from four reclamation treatments: natural succession (CK), cropland (CL), grassland (GL), and woodland (WL). The results showed that the artificial reclamation treatments significantly increased soil organic carbon (SOC) and total nitrogen (TN), while significantly decreased electrical conductivity (EC) in compared with that of CK. Compared with CK, CL and GL significantly increased significantly in the total nematode abundance. However, CL had the lowest Shannon-Weiner diversity index (H’), generic richness (GR) and trophic diversity (TD) among four treatments. Compared with CK, nematode food webs of GL and WL were more mature. SOC and DOC were the main factors driving nematode community variation. The analysis of nematode community structure provided important indicators of changes in soil food webs during the reclamation of salinized farmland.

Long-term vegetation restoration promotes the stability of the soil micro-food web in the Loess Plateau in North-west China

Soil nematode communities play a significant role in soil ecosystems. Indeed, soil nematode metabolic carbon footprint, based on nematode biomass, is used to evaluate ecosystem functioning and assess nematode response to ecosystem nutrient enrichment. However, it is unclear whether vegetation restoration affects the metabolic carbon footprint of soil nematodes and soil food webs. We selected five periods for this study including: (1) farmland (0 years), (2) grassland (30 years), (3) shrubland (60 years), (4) pioneer forest (100 years), and (5) climax forest (160 years). Community composition, diversity, and metabolic footprint of soil nematodes, and carbon flow changes through the food web were investigated. The Shannon diversity (H′) index of the soil nematode community increased in the process of restoration, and the Pielou index (J′) appeared to be lower at 30 years after vegetation restoration than at 60, 100, and 160 years. The connectance of the soil nematode food web values increased continuously, from 30 years to 160 years, reaching the highest value at 100 and 160 years, which indicated that the food web had the strongest carbon flow at 100 years after vegetation restoration on the Loess Plateau, indirectly reflecting the stability of the soil food web. Bacteria were more important than fungi in the carbon flow in the food web during vegetation restoration. The study demonstrated that vegetation restoration promoted the input of the availability of external resources, enhanced the metabolic activity of omnivorous carnivores and the soil carbon flow, and stabilized the soil food web. However, the increase in vegetation restoration time not only changed the species composition but also changed the carbon input, due to the lack of interference by agriculture. Therefore, the intrinsic mechanism needs to be studied further.

Soil management induced shifts in nematode food webs within a Mediterranean vineyard in the Central Coast of California (USA)

The soil food web regulates several key processes that support soil health and agricultural production. Here we investigated how soil management within a commercial Pinot noir Mediterranean vineyard affects nematode abundance and community structure, as a proxy to evaluate the status of the soil food web. We compared the soil under the vine to the soil in the tractor row which receive different water and nutrient inputs and different strategies to manage herbaceous vegetation cover. Furthermore, we compared the effects of different fertilizers (organic, synthetic and no fertilizer) applied under the vine. Our results showed that the soil in the tractor row hosted a more complex food web, with a higher abundance of microbial feeding nematodes and processing of the soil C and organic matter through omnivore and bacterivore nematodes leading to higher amounts of plant available N, likely due to increased mineralization rates. Thus, the tractor row has a great value as a reservoir of biodiversity within vineyards and support soil ecosystem services such as C sequestration and N cycling. The soil under the vine was characterized by a higher abundance of herbivore nematodes and high plant parasitic index that were alleviated by the addition of organic fertilizers increasing the abundance of bacterivore and fungivore nematodes, contributing to a more balanced food web. Changes in nematode community composition and food web status were strongly associated to soil physicochemical properties such as the active C, nitrate and soil pH. Thus, a change in fertilizer management could significantly boost soil health in these intensively managed soils.

Exploring N fertilizer reduction and organic material addition practices: An examination of their alleviating effect on the nematode food web in cropland

AbstractExcessive nitrogen (N) fertilization in croplands results in environmental problems, such as soil quality deterioration, water contamination, and biodiversity losses, which threaten the sustainable development of soil ecosystems. The soil nematode food web plays key roles in soil organic matter decomposition and nutrient cycling, and thus the sustainable development of cropland ecosystems. However, how the negative impact from the excessive N fertilization on the nematode food web is effectively alleviated remains uncertain. This study aimed to explore the effects of different N fertilization management practices (N fertilizer reduction or organic material addition) on alleviating the negative effects on the nematode food web in croplands. Four treatments/ management practices were examined: conventional fertilization (N control), N fertilizer reduction of 100% (N0), N fertilizer reduction of 50% (N1), and conventional fertilization with organic material addition (N+S). The results showed that the abundance of nematodes and microbial phospholipid fatty acids (PLFAs) both increased in the treatments of N0, N1, and N+S compared with N. Besides, N+S also increased the nematodes' biomass, diversity, and metabolic footprint, which correspondingly strengthened the nutrient turnover through the nematode food web. Overall, two management practices 1)N fertilizer reduction and 2) organic material addition, differ in the abiotic or biotic process in alleviating the negative effects of N fertilization on the nematode food web. The reducing N fertilization can directly alleviate the negative effect of fertilizer on soil acidification and then benefit for the growth of microorganisms and nematodes. The exogenous carbon input from organic material addition might promote carbon flowing and immobilization into nematode food web, and ultimately enhance the stability of soil food web.

Community Structure of Soil Nematodes Associated with the Rhizosphere of Solanum Lycopersicum in a Major Production Area in Argentina: a Case Study Among Agroecosystem Types

The objective of this work was to describe the status of the assemblages of soil nematodes associated with tomato crops, in a major tomato production area in Argentina, by studying ecological indices of nematode food web and determining which indices describe alterations in horticultural soils. Three agroecosystem types were compared: agroecological, conventional with organic amendments, and conventional with methyl bromide (MeBr) application. A pristine site without anthropogenic intervention was also studied. Abundance, frequency, diversity indices, maturity indices, trophic groups, colonizer-persister values (cp), and guilds of nematodes were analyzed and compared statistically between the sampling sites. The most abundant genera in the agroecosystems were Rhabditis, Helicotylenchus, and Filenchus belonging to the guilds bacterivorous (Ba1), plant feeders (Pl3), and fungivorous (Fu2). Within agroecosystems, the agroecological site showed the highest values of diversity and maturity, while the lowest values were found in the site treated with MeBr. Trophic groups, cp, guilds, and the indices provided useful information on the state of maturity and enrichment that effectively contrasted and differentiated the practices of horticultural management. This updated report of the nematode fauna constitutes one of the most important for the horticultural region of La Plata considering the scarcity of studies on this subject.

Long-term nitrogen addition shifts the soil nematode community to bacterivore-dominated and reduces its ecological maturity in a subalpine forest

Nitrogen deposition from anthropogenic sources is a global problem that reaches even the most remote ecosystems. Responses belowground vary by ecosystem, and have feedbacks to geochemical processes, including carbon storage. A long-term nitrogen addition study in a subalpine forest has shown carbon loss over time, atypical for a forest ecosystem. Loss of microbial biomass is likely linked to lower soil carbon, but the mechanism behind this is still unknown. One possible explanation is through increased turnover due to grazing by soil fauna. Because nematodes occupy many trophic levels and are sensitive to trophic and environmental changes, assessing their communities helps reveal belowground responses. In this study, we tested the hypothesis that long-term nitrogen fertilization affects nematode community structure and maturity beneath coniferous forests in the Rocky Mountains, indicating a faster cycling, bacterial-driven system. We identified and enumerated nematodes by trophic group and family from experimental plots. Total nematode abundance was 40–96% greater in fertilized plots compared to the control, but richness, diversity, and ecological maturity were lower. The differences in abundance were driven by opportunistic bacterivores (e.g., Rhabditidae) and plant parasites (e.g., Tylenchidae), which made up 23 and 13% of the community in fertilized compared to 7 and 5% in control plots, respectively. Nematode maturity indices showed that the nematode food web was enriched (indicating high nutrient/resource status) and structured (all trophic levels present, including long-lived predators) in both treatments, but significantly more enriched in the fertilized treatment. Nonmetric multidimensional scaling of the relative abundance of nematode families demonstrated that nematode community composition differed between treatments, driven largely by opportunistic bacterivores (e.g., Rhabditidae) in the fertilized plots. The mechanism of the aboveground–belowground link between nitrogen deposition and nematode community composition is likely through increased microbial turnover, and sustained high-quality food for microbial grazing nematodes.