Bacterial-feeding Nematodes Research Articles

Phylogenetic position of Zeldia punctata (Nematoda: Cephalobidae) using 28S rDNA from Limpopo Province, South Africa

The Cephalobidae (Free-living nematodes) family are bacterivores that inhabit soil. Bacterial-feeding nematodes are one of the main consumers of soil bacteria. Therefore, study on this group of nematodes is essential. This molecular study was conducted in 2024 at Limpopo University to identify the free-living bacterivores nematodes from South Africa's soils, using a 28S rDNA marker. The recovered nematode was extracted using the tray method, and then its DNA was extracted using the Chelex method. The nematode was identified as Zeldia punctata. Afterwards, 28S rDNA was amplified using specific primers to identify the nematode. The Nblast analysis based on the 28S rDNA showed South African Z. punctata has 98% similarity (DQ145662) with the American population. Phylogenetic analysis using maximum likelihood placed this species with those molecularly identified as Z. punctata in the same clade with highly supported (94%) bootstrap values. In conclusion, this species was properly identified using 28S rDNA. However, other rDNA markers are recommended to better understand Zeldia phylogeny.

Grazing alters the soil nematode communities in grasslands: A meta-analysis

Grazing causes great disturbances in grassland ecosystems and may change the abundance, diversity, and ecological function of soil biota. Because of their important role in nutrient cycling and as good environmental indicators, nematodes are very representative soil organisms. However, the mechanisms by which grazing intensity, livestock type, duration, and environmental factors (e.g., climate and edaphic factors) affect soil nematodes remain poorly understood. In this study, we collected 1964 paired observations all over the world from 53 studies to clarify the grazing response patterns of soil nematodes and their potential mechanisms. Overall, grazing significantly decreased the abundance of bacterial-feeding (BF) nematodes (−16.54%) and omnivorous-predatory (OP) nematodes (−36.81%), and decreased nematode community diversity indices (Shannon–Weiner index: −4.33%, evenness index: −9.22%, species richness: −5.35%), but had no effect on ecological indices under a global regional scale. The response of soil nematodes to grazing varied by grazing intensity, animals, and duration. Heavy grazing decreased OP nematode abundance, but had no effect on the abundance of other trophic groups, or on diversity or ecological indices. Grazing by small animals had stronger effects than that by large animals and mixed-size animals on BF, fungal-feeding (FF), plant-feeding (PF) and OP nematodes, the Shannon–Wiener index, and the species richness index. The abundance of FF and OP nematodes influenced significantly under short-term grazing. The evenness index decreased significantly under long-term grazing (>10 years). Climate and edaphic factors impacted the effects of grazing on nematode abundance, diversity, and ecological indices. When resources (i.e., rain, heat, and soil nutrients) were abundant, the negative effects of grazing on nematodes were reduced; under sufficiently abundant resources, grazing even had positive effects on soil nematode communities. Thus, the influence of grazing on soil nematode communities is resource-dependent. Our study provides decision makers with grazing strategies based on the resource abundance. Resource-poor areas should have less grazing, while resource-rich areas should have more grazing to conserve soil biodiversity and maintain soil health.

Biotic interactions between the human pathogen Legionella pneumophila and nematode grazers in cooling tower biofilms.

Biofilms in cooling towers represent a common habitat for the human pathogen Legionella pneumophila. Within the biofilm consortium, frequent interactions with protozoa, i.e. amoebae and ciliates, were reported, while nematodes have only recently been considered as potential environmental reservoir for the pathogenic bacteria. This study is the first approach to investigate the biotic interactions between L. pneumophila and bacterial-feeding nematodes in a semi-natural biofilm model. The species were Diploscapter coronatus, Diploscapter pachys, Plectus similis and Plectus sp., which all co-occur with L. pneumophila in the environment. Biofilms derived from cooling towers were either inoculated with mCherry-labeled L. pneumophila solely or in combination with GFP-labeled Escherichia coli. All experiments were conducted in single-species set-ups and multi-species (D. coronatus and P. similis) set-ups, to account for interspecific competition. Bacterial ingestion was assessed after 24 and 96 h as fluorescence patterns in the digestive tract of the nematodes using confocal laser scanning microscopy. L. pneumophila cells were ingested by all nematode species, with D. coronatus having the highest pathogen load. The fluorescence intensity (i.e. bacterial load) varied between compartments within the digestive tract and was independent of incubation time. Bacterial cells accumulated mostly around the cardia and in the intestine, while less cells were found within stoma and pharynx. Interspecific competition changed the pattern, i.e. with incubation of D. coronatus and P. similis in the same biofilm a significantly higher pathogen load occurred in the intestine of D. coronatus than P. similis after 24 h and 96 h. Remarkably, when given a choice between L. pneumophila and E. coli, P. similis was the only nematode species containing both bacteria after incubation for 24 h. None of the other nematode species contained E. coli after 24 h and 96 h incubation, while L. pneumophila was present. This study thus provides the first evidence, that under environmental conditions L. pneumophila is a frequent diet of bacterial-feeding nematodes, highlighting their potential as pathogen vectors or even host in cooling tower habitats.

Changes in Soil Bacterial and Nematode Communities during Long-term Continuous Cotton Cropping in an Arid Region.

larifying the effects of continuous cotton cropping (CC) on soil biological communities is essential for maintaining agricultural productivity. In this study, high-throughput sequencing was used to study the effects of different CC durations (0-yr, 5-yr, 10-yr, 15-yr, 20-yr, and 25-yr CC treatments) on soil microbial and nematode communities. The results showed that the dominant bacterial phyla were Actinobacteria and Proteobacteria, and the dominant nematode genus was Helicotylenchus in all CC treatments. The richness indexes (ACE and Chao1 index) and diversity index (Shannon index) of bacterial and nematode communities were the highest in the 15-yr and 10-yr CC treatments, respectively. Bacterial community was significantly correlated with soil pH and available potassium (AK), and nematode abundance was significantly correlated with microbial biomass carbon (MBC). Soil bacterial PICRUSt analysis results showed that carbon metabolism and amino acid metabolism were the main metabolic functions of bacteria in the CC treatments. The composition and diversity of soil nematode communities were significantly related to the structure of soil bacterial communities, and the niche breadth of soil bacteria was negatively correlated with that of nematodes. Panagrolaimus and Acrobeles were the main genera of bacterialfeeding nematodes affecting bacterial communities, and their relative abundances were significantly positively correlated with the relative abundance of bacterial communities. Overall, long-term (10-15 years) continuous cotton cropping negatively impacts soil biota and the microecological environment of cotton fields in arid regions.

Spatiotemporal distribution patterns of soil nematodes along an altitudinal gradient in the cold temperate zone of China

As important components of the cosmopolitan soil biota, soil nematodes are found at multiple trophic levels of the belowground food web and play an important role in soil function. Exploring the actual patterns of soil nematodes along the altitudinal gradients helps understand the spatial soil ecology. In this study, we used molecular analysis approaches to reveal the soil nematode spatiotemporal changes on Oakley Mountain in the northern Greater Khingan Mountain Ranges Northeast China. Our results showed that although the alpha diversity of nematode communities generally decreased with the increased altitude, it did not exhibit a monotonic decrease pattern. Bacterial feeding nematodes occupied the largest proportion among all nematode feeding types. Altitude had a more significant effect than soil depth on the structure of nematode community in all seasons. Soil bulk density, moisture, dissolved organic carbon, temperature, pH, nitrate nitrogen, and total phosphorus were the significant soil variables driving the composition of nematode community. The co-occurrence networks of soil nematode communities showed a distinct seasonal pattern. The nematode community networks in May and September had more modes and links, higher average degrees, and higher average clustering coefficients than the network in July. We demonstrated that the variance of nematode community structure in different altitudes and soil depths could be well explained by edaphic factors. This study extends our knowledge of the nematode spatial ecology in cold temperate regions and contributes to further investigation of soil ecological processes in global challenges.

Correlations Between the Soil Bacterial-Feeding Nematodes, Bacteria, and Nitrogen in the Cropland of the Upper Yangtze River, China

Correlations Between the Soil Bacterial-Feeding Nematodes, Bacteria, and Nitrogen in the Cropland of the Upper Yangtze River, China

Corrigendum to “Population energetics of bacterial-feeding nematodes: Stage-specific development and fecundity rates” [Soil Biology and Biochemistry 28 (3) 271–280, 1996

Nematodes play significant roles in carbon and nitrogen biogeochemical cycles in soils. The contributions of individual species to these processes depend, in part, on differences in their population ecology. Formatting errors were discovered that made portions of our previously published work on this subject nearly unintelligible. Herein, we correct those errors.

Food choice of bacterial-feeding nematodes: The human pathogen Salmonella enterica compared to common soil bacteria

Free-living nematodes act as reservoirs and vectors of the food-borne pathogen Salmonella enterica, one of the leading causes of gastrointestinal human infections worldwide. Although the transport of this human pathogen through soil by nematodes has major concerns for food safety, little is known about the food preference for S. enterica in nematodes. To disentangle the trophic links between nematodes and bacteria, the food choice of the nematode species Acrobeloides buetschlii, Caenorhabditis elegans and Pristionchus pacificus was examined under semi-natural conditions using a modular soil system. S. enterica serovar Typhimurium LT2 was tested against five common soil bacteria, i.e. Arthrobacter alpinus, Bacillus subtilis, Escherichia coli OP50, Granulicella arctica and Pseudomonas putida IsoF in binary food choice assays. The tested nematodes showed a general preference for bacterial strains with a low C/N ratio (E. coli), and avoidance of strains with a high C/N ratio (G. arctica and A. alpinus), indicating that food choice is rather linked to nutritional value than to bacterial pathogenicity. Moreover, the enrichment opportunists C. elegans and P. pacificus showed a stronger attraction to a suitable bacterial diet compared to the general opportunist A. buetschlii, which also thrives food-depleted soils. Interestingly, there was no evidence regarding a differentiation between common soil bacteria and the pathogen S. enterica. Overall, S. enterica was used as resource by the tested bacterial-feeding soil nematodes, highlighting their vector potential for food-borne pathogens in agricultural soils.

Impacts of plant domestication on soil microbial and nematode communities during litter decomposition

PurposePlant domestication altered leaf litter quality. Since litter traits relate to soil functions and organisms (i.e., litter decomposition and soil decomposer communities), in this study we explore if domestication-induced changes in litter quality have affected their decomposability, and bacterial, fungal, and nematode communities in the soil.MethodsWe collected leaf litter from herbaceous crops and their wild progenitors, and measured litter chemical and physical traits. Then, we performed a litter decomposition assay on a common soil. After three months of litter incubation, we measured mass loss, nematode richness and community composition in ten crops. We also measured soil bacterial and fungal richness and community composition in six crops.ResultsDomesticated litters had less carbon (C) and leaf dry matter content (LDMC), which accelerated decomposition in comparison to wild litters. Fungal richness was higher in microcosms incubated with domesticated litters, while the effects of domestication on bacterial richness differed among crops. Domestication did not affect nematode richness. The effects of domestication on bacterial and fungal community compositions differed among crops. Soils with domesticated litters tended to have nematode communities with a higher abundance of bacterial feeding nematodes, in comparison to soils fed with wild litters.ConclusionDomestication altered decomposition at different levels. Leaf litter decomposability increased with domestication, which might alter resource inputs into the soil. Feeding soils with domesticated litters had idiosyncratic effects on soil microbes, but consistent effects on soil nematodes. Overall, domestication altered the linkages between crop residues and soil communities differently for bacteria, fungi, and nematodes.

Plant clustering generates negative plant–soil feedback without changing the spatial distribution of soil fauna

Abstract. The spatial distribution of resources affects ecological processes at all levels of biological organization. However, it remains to be tested how the spatial configuration of belowground resources affects the community dynamics of soil organisms and resulting plant–soil feedbacks. We used Agrostis stolonifera plants in different spatial configurations in mesocosms to study the dispersal patterns of soil nematodes and rotifers. Plant–soil feedbacks were later assessed by re-sowing the mesocosms with Lolium perenne and Plantago lanceolata after removing all the initial A. stolonifera plants from the mesocosms. Bacterial-feeding nematodes and rotifers spread fast, whereas plant-feeding nematodes barely dispersed from the release sites. These spread patterns of nematodes and rotifers depended on the life-history traits and not on the spatial pattern of the plants. However, more clustered plants developed a higher total biomass and caused a reduced growth of the subsequent vegetation. Our results demonstrate that the mere spatial pattern of a single plant species can alter the strength of plant–soil feedbacks. This has important implications for understanding the impact of planting or replanting schemes and other changes in the spatial configuration of plants on long-term vegetation development and succession.

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.

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.

Redescription and molecular characterisation of Panagrolaimus labiatus (Kreis, 1929) Andrássy, 1960 (Rhabditida, Panagrolaimidae) from India and proposal of P. burdwanensis Chaturvedi & Khera, 1979 as a junior synonym of P. labiatus

Summary Two populations of bacterial-feeding nematodes belonging to the genus Panagrolaimus were recovered from infected slugs collected from gardens, agricultural areas and nurseries of the Baghpat district (India). Initial morphological characterisation of these populations show that they resemble Panagrolaimus labiatus from China and Bulgaria, P. burdwanensis from India, and P. cf. labiatus from Iran. To clarify taxonomical affiliations, we morphologically compared these two new populations to those recovered from China, Bulgaria, India and Iran. In addition, we sequenced several taxonomically relevant genes and used them to reconstruct phylogenetic relationships. Our results show that the two Indian populations do not significantly differ morphologically from the specimens used to describe the species P. labiatus, and also do not differ among them. We only observed small variations in the size of males and females. In addition, morphologically, the nematodes used to describe P. burdwanensis are very similar to the nematodes used to describe P. labiatus and to the two populations described in this study. Therefore, we propose P. burdwanensis as a junior synonym of P. labiatus and that the two populations recovered from India belong to the P. labiatus species. Phylogenetic analyses using the nucleotide sequences of the internal transcribed spacer (ITS), 18S and 28S rRNA gene sequences support our morphological conclusions. Our study therefore provides a detailed morphological description and molecular marker 18S and 28S gene sequences that can support future taxonomical studies of this species and highlights the importance of using both molecular and morphological data for the proper description of soil microfauna.

Morpho-anatomical traits explain the effects of bacterial-feeding nematodes on soil bacterial community composition and plant growth and nutrition

Bacterial-feeding nematodes are abundant soil animals regulating microbial communities and enhancing plant nutrition and growth. However, the biological metrics driving the variable within-trophic group effects of these organisms on soil and plant functions are not yet identified. In this study, we determined the effects of eight bacterial-feeding nematode genera (Acrobeloides butschlii, Brevibbuca sp., Cephalobus sp., Diploscapter sp., Oscheius akosreti, Panagrellus redivivus, Pristionchus pacificus, Zeldia sp.) on soil bacterial communities and Pinus pinaster growth and nutrition from organic N (glutamate) and P (phytate) supplied in a high P-adsorbing soil. Because nematode species harbored contrasting morpho-anatomical characteristics, we hypothesized that traits, in comparison to species identity or life strategy groups (cp classes), could explain the variable effects of the nematode species. After 50 days of growth, the inoculation of bacterial-feeding nematodes caused variable but never negative effect on plant growth and net plant N and P uptake depending on nematode species. We also observed significant shifts in root traits and bacterial community composition. For both soil bacterial composition and plant growth and nutrition, a selected panel of traits (e.g. body size, mouth width, procorpus width, demanian ratios b and c, relative egg size) explained soil and plant function more than did species identity or life strategy groups. For instance, traits explained 77 % of plant N and P amounts while cp classes and species-identity explained 33 % and 46 %, respectively, according to PLS models. The identity of traits varied according to the functions. Structural equation modeling with latent variables emphasized the direct effects of nematodes on plant nutrition through excretion in comparison to indirect effects through shifts in bacterial composition and improved root ramification. We discuss the relevance of bacterial-feeding nematode traits as promising biological metrics to explain the effect of these worms within the soil microbial loop framework.

The relationships of bacterial-feeding nematodes, phoD-harboring bacteria and alkaline phosphomonoesterase activity under the combined application of organic and inorganic fertilizers in an alkaline soil

Bacterial-feeding nematodes have the potential to increase soil alkaline phosphomonoesterase (AlP) activity by affecting the composition of phoD-harboring bacterial community or the abundance of phoD gene. However, the relationships between bacterial-feeding nematodes, composition of phoD-harboring bacterial community, phoD gene abundance and AlP activity with inorganic plus organic fertilization in alkaline soil where AlP is dominant is yet to be properly understood. Four fertilization regimes: non-fertilized control (CK), chemical nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK), crop straw plus chemical fertilizers (SNPK), as well as pig manure plus chemical fertilizers (MNPK), were used in determining the variation in soil bacterial-feeding nematodes, composition of phoD-harboring bacterial community, phoD gene abundance and AlP activity under different fertilization treatments as well as their relationships. Results showed that both inorganic and organic fertilizer application significantly enhanced the activity of soil AlP, which significantly decreased under NPK application compared with SNPK and MNPK treatments. Partial least squares path modeling showed that AlP activity was directly and positively affected by composition of phoD-harboring bacterial community and microbial biomass carbon (MBC), and the bacterial-feeding nematode dominant genus Eucephalobus, which was affected by MBC directly, could affect AlP activity in an indirect way by its significant direct positive effect on phoD-harboring bacterial community composition. Of those 12 top bacterial genera that harbored phoD, just the gram-positive bacteria Massilia and Saccharothrix showed significant positive correlation with AlP, while Saccharothrix showed obvious positive correlation with Eucephalobus. Overall, these results suggest that the dominant genus Eucephalobus may be the beneficial indigenous bacterial-feeding nematode that can increase the activity of soil AlP within the alkaline soil, which is affected by MBC directly and can be likely to positively affect the composition of phoD-harboring bacterial community through a passive food ingestion mechanism and then promote AlP activity indirectly, of which Saccharothrix is the intermediary bacteria for the increase in AlP activity caused by the bacterial-feeding nematode.

Concentration-Dependent Impacts of Microplastics on Soil Nematode Community in Bulk Soils of Maize: Evidence From a Pot Experiment

Agricultural land soils have become a source and sink for microplastics. Due to the low recycling rate, long durability, and small size, microplastics pose a potential risk to soil fauna, which are critical for maintaining healthy soil. However, whether and how would microplastics affect soil biodiversity and ecological functioning is not well-understood. Soil nematodes are valuable indicators of the soil food web. In the present study, the abundance, diversity, community composition, maturity indices, soil food web indices, and metabolic footprints of soil nematodes in bulk soils of maize were utilized to indicate the potential impacts of polypropylene (PP) microplastic pollution on soil fauna using a soil-incubation experiment in a climate-controlled chamber with four concentration levels of microplastic pellets (0%, 0.5%, 1%, and 2%, w/w) added to loess soil collected from the Loess Plateau in China. Soil sampling was conducted at the fully ripe stage of maize. Twenty-nine genera of nematodes, including thirteen genera of plant-feeding nematodes, seven genera of bacterial-feeding nematodes, five genera of fungal-feeding nematodes, and four genera of omnivorous nematodes were recovered from soil samples. Microplastic concentration negatively affected the abundance, diversity (including genus richness, Margalef’s richness, Shannon–Wiener index, and Simpson’s dominance index), sigma maturity index (∑MI), structural index, and metabolic footprints. The abundances of plant parasites, bacterivores, fungivores, and omnivores in 2% soils were reduced by 90.16%, 76.06%, 82.35%, and 100%, respectively, in comparison with those of control. The major drivers of soil nematode communities in bulk soils of maize at a depth range of 0–20 cm were the soil pH, soil organic carbon content, C/N, and TP content. In conclusion, the addition of 200 μm-sized PP microplastic pellets negatively affected the soil nematode community and associated ecological functioning under greenhouse conditions.

Belowground Dynamics Influence Nitrogen Cycling and Crop Productivity in Diversified Corn Systems

Ecological nutrient management is a strategy that can help create resilient cropping systems and reduce the negative impact that agricultural systems have on the environment. Ecological nutrient management enhances plant-soil-microbial interactions and optimizes crop production while providing key ecosystem services. Incorporating perennial legumes into crop rotations and implementing no-till to enhance organic nitrogen (N) soil pools could reduce the need for inorganic N fertilizer inputs and lead to improved soil health. Plant and soil N pools need to be further quantified to understand how to enhance soil health across a range of agroecosystems. This paper aims to quantify plant and soil N pools in systems contrasting in crop perenniality (corn–corn, corn–soy, and corn–forage–forage) and tillage intensity (chisel till vs. no-till). Key plant, soil, and organismal metrics of N cycling were measured including fine root production, N-Acetyl-B-Gulcosaminidase (NAG) enzyme activity, and soil protein, nematode enrichment opportunist (fungal and bacterial feeding nematodes) and the nematode Enrichment Index. Fine root production was determined using in-growth mesh cores. Findings reveal that monoculture cropping systems with reduced tillage intensity and rotations with perennial legumes had significantly greater fine root N (FRN), soil protein and NAG enzyme activity (p < 0.05) relative to corn-soy. Additionally, nematode bacterivore enrichment opportunists (b1) were significantly reduced in corn-corn systems when compared to all other crop rotation systems. Correlation analyses indicated positive and significant relationships between FRN and soil protein (p < 0.05). These results demonstrate that lengthening crop rotations with perennial legumes and incorporating no-till management can increase organic N inputs, N mineralization rates, and organic N storage. Such ecological approaches to management have the potential to reduce the need for inorganic N inputs, while increasing long-term soil health and crop productivity.

Integrating perennial bahiagrass into the conventional rotation of cotton and peanut enhances interactions between microbial and nematode communities

Integrating two years of bahiagrass (Paspalum notatum Flugge) into the peanut (Arachis hypogea L.) and cotton (Gossypium hirsutum L.) cropping system improves soil quality and crop production as compared to a conventional peanut-cotton-cotton rotation (CR). However, it is unclear if this system, known as a sod-based rotation (SBR), affects soil biological communities (e.g., soil microorganisms and nematodes) and their trophic interactions. Furthermore, how soil trophic groups respond to agricultural management (e.g., irrigation) is understudied. In April 2017, we collected pre-planting soil samples (0–30 cm) from cotton plots located in Quincy (Florida, United States) that had been under CR (cotton grown in two consecutive years) and SBR (cotton grown only once) for 17 years. We used amplicon sequencing to investigate soil microbial communities and an inverted microscope technique to quantify nematodes. Compared to CR, SBR significantly increased nematode alpha diversity (one-way ANOVA; P < 0.05) and induced different nematode communities. In contrast, there were no significant differences in the diversity and structure of bacterial communities between SBR and CR. SBR plots were significantly enriched in Nitrospira, while the second of two consecutive years of cotton growth in CR had a higher relative abundance of Alphaproteobacteria (one-way ANOVA; P < 0.05). Plant-parasitic (848 counts per 100 g dry soil) and bacterial-feeding nematodes (798 counts per 100 g dry soil) had a similar abundance in SBR, while plant-parasitic nematodes (7772 counts per 100 g dry soil) were predominant in CR (<1000 counts per 100 g dry soil for all other taxa). SBR exhibited a greater number of significant paired Pearson correlations (P < 0.05) among functional groups of bacteria and nematodes compared to CR systems. Irrigation had no effect on the diversity and structure of bacterial and nematode communities in SBR, although some soil bacterial and nematode groups responded to irrigation. Overall, these results suggest that integrating bahiagrass to diversify the conventional peanut-cotton rotation is a sustainable approach to enhance soil biodiversity, with more diverse nematode communities and complex soil trophic interactions that will affect the response to crops and irrigation. Thus, future crop rotations should increase plant functional trait diversity (e.g., by adding perennial grasses) to maximize benefits to soil communities.

Soil fauna actively change their diet to survive stress

Animals are expected to choose foods that optimize their growth, reproduction and survival, but their dietary choice changes when suffering stress. Here, we provide the first report of nematode stress resulting from exposure to earthworm-produced cyclic peptides, and confirm that this stress changes the dietary choice of the model animal Caenorhabditis elegans and other soil-dwelling bacterial-feeding nematodes. When allowed free choice in a stress-free environment, nematodes prefer feeding on high-quality bacteria to support a higher reproduction and a shorter lifespan, supporting a reproduction-dominated energy allocation pattern. However, they feed less on preferred food (high-quality bacteria) and include more unpreferred food (low-quality bacteria) in the diet when stressed by the toxic cyclic peptides. Nematodes that eat more unpreferred bacteria appear to shift towards a survival-dominated energy allocation pattern. Specifically, limited resources obtained from low-quality bacteria are preferentially allocated to repair cyclic peptide-induced damage of their DNA and complete their lifespan, although at significantly reduced reproduction level. Our results demonstrate that nematodes can actively change their dietary strategy to maintain survival at the cost of reproduction when they experience acute stress. This stress-driven adjustment of dietary choice may be the key to understand feeding ecology and food web structure.

Global patterns and controls of soil nematode responses to nitrogen enrichment: A meta-analysis

Nematodes are important components of soil food webs and have important ecosystem functions. However, the responses of soil nematode communities to nitrogen (N) deposition have not been well assessed over large spatial scales. Here, we conducted a global-scale meta-analysis of the effects of N-addition regimes (N form, N addition approach, and N addition rate) and environmental factors (ecosystem type, soil depth, climate, and soil property) on the responses of soil nematodes to N addition. The results showed that N addition significantly increased the relative abundance of bacterial-feeding nematodes (23.54%), but decreased the relative abundance of plant-feeding nematodes (−20.24%) and omnivorous-predatory nematodes (−22.28%). Nitrogen addition, however, did not significantly affect total nematode abundance or the relative abundance of fungal-feeding nematodes. Understory N addition usually had larger effects on nematode abundance than canopy N addition. The responses to N addition increased with N addition rate in the case of bacterial-feeding nematode abundance, but decreased with N addition rate in the case of plant-feeding nematode and fungal-feeding nematode abundances. Nematode abundance in grasslands were more responsive to N addition than in forests or croplands, and the responses were affected by soil depth. The response ratios of bacterial-feeding nematodes to N addition decreased with increases in mean annual temperature and mean annual precipitation, while the response ratios of plant-feeding nematodes showed the opposite trend. Soil pH and organic carbon did not affect the response ratios of nematode parameters to N addition except plant parasite index. In summary, the responses of soil nematodes to N addition on a global scale were found to be affected by both N-addition regimes and environmental factors. We suggest that our understanding of how N deposition affects soil nematodes will be increased by additional studies of canopy N addition and of tropical ecosystems.