Nematode Abundance Research Articles

Plant-parasitic nematode community and enzyme activities in soils under no-till soybean crops in Brazil

Soybean is Brazil's largest agricultural crop, grown across a variety of climates and soil conditions, and it is subjected to a large number of pests, including plant-parasitic nematodes. In general, the occurrence of plant-parasitic nematodes in soybean is influenced by various soil physicochemical properties, such as the pH, texture, and nutrient content. These soil properties may determine the nematodes community composition and affect soil quality and functioning, which can be monitored by analysing of soil enzyme activity. In this sense, the analysis of β-glucosidase and acid phosphatase enzymes can provide valuable information to assist decisions in the sustainable management of soybean cultivated soils in Brazil. In this study, we used 216 samples collected from no-till soybean fields across Brazil. The samples were used to investigate the influence of soil physical and chemical properties on the plant-parasitic nematode community and enzymatic activity. We identified seven genera of plant-parasitic nematodes including Meloidogyne, Pratylenchus, Heterodera, Rotylenchulus, Helicotylenchus, Scutellonema, and Xiphinema. Our results indicate that clay content and soil pH were the main properties modulating the plant-parasitic nematode community. We observed a higher abundance of plant-parasitic nematodes in highly acidic soils when compared to slightly acidic. In addition, soil organic matter content, available P, and pH were the main properties modulating microbial activity in the soil. No significant correlations were observed between enzymatic activity and nematode population density. This is the first study to provide insights into plant-parasitic nematode community composition and soil enzymes activity in soybean cultivated soils on a national scale in Brazil.

Soil nematode assemblages respond to interacting environmental changes.

Multi-factor experiments suggest that interactions among environmental changes commonly influence biodiversity and community composition. However, most field experiments manipulate only single factors. Soil food webs are critical to ecosystem health and may be particularly sensitive to interactions among environmental changes that include soil warming, eutrophication, and altered precipitation. Here, we asked how environmental changes interacted to alter soil nematode communities in a northern Chihuahuan Desert grassland. Factorial manipulations of nitrogen, winter rainfall, and nighttime warming matched predictions for regional environmental change. Warming reduced nematode diversity by 25% and genus-level richness by 32%, but declines dissipated with additional winter rain, suggesting that warming effects occurred via drying. Interactions between precipitation and nitrogen also altered nematode community composition, but only weakly affected total nematode abundance, indicating that most change involved reordering of species abundances. Specifically, under ambient precipitation, nitrogen fertilizer reduced bacterivores by 68% and herbivores by 73%, but did not affect fungivores. In contrast, under winter rain addition, nitrogen fertilization increased bacterivores by 95%, did not affect herbivores, and doubled fungivore abundance. Rain can reduce soil nitrogen availability and increase turnover in the microbial loop, potentially promoting the recovery of nematode populations overwhelmed by nitrogen eutrophication. Nematode communities were not tightly coupled to plant community composition and may instead track microbes, including biocrusts or decomposers. Our results highlight the importance of interactions among environmental change stressors for shaping the composition and function of soil food webs in drylands.

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.

Heavy Logging Machinery Impacts Soil Physical Properties More than Nematode Communities

Mechanized logging equipment causes considerable soil disturbance, but little information is available regarding thresholds for impacts on soil nematodes—critical members of soil foodwebs which perform important ecological functions. We examined responses of nematode communities and soil physical characteristics to the increasing number of passes (one, three, or nine) by a tracked feller buncher during thinning of a xeric mixed conifer forest in New Mexico, USA. Within and between the harvester tracks, we measured soil surface penetration resistance and shear strength, quantified bulk density at four depth increments up to a maximum depth of 27 cm, and characterized nematode assemblages in the upper 10 cm. Eight months after treatment, nematode communities were less impacted than soil physical properties by harvester passes. Total nematode abundance was unaffected by any level of feller buncher disturbance, and sensitive K-selected nematode groups were reduced only at nine passes. Conversely, soil compaction occurred with a single pass and extended deep into the soil profile to at least 23–27 cm. The first pass also decreased surface penetration resistance and shear strength, indicating disruption of soil surface structural integrity. Additional passes did not further increase bulk density or decrease surface structural integrity. Our results indicate that low levels of logging machinery traffic may have negligible effects on nematode communities, but nevertheless emphasize the importance of minimizing areas subjected to disturbance because of impacts on soil physical properties.

Abundance and diversity of terrestrial free-living nematodes in potato agroecosystem

Abstract. Mutala’liah, Manan A, Bayyinah LN. 2023. Abundance and diversity of terrestrial free-living nematodes in potato agroecosystem. Nusantara Bioscience 15: 129-136. The presence of terrestrial free-living nematodes in agroecosystems is frequently overlooked. However, these microorganisms in agroecosystems soil are beneficial for supporting plant growth. These microorganisms could recycle the nitrogen in soil, decomposition and mineralization of organic matter, and suppress the densities of plant parasitic nematodes through their life strategy. Terrestrial free-living nematodes are classified according to trophic groups such as bacterivores, fungivores, predators, and omnivores. Reports on the abundance and diversity of terrestrial free-living nematode populations in agroecosystems, especially on potato plantations, were limited. They usually focused on the plant parasitic nematode’s attack on potatoes. Therefore, this study aimed to examine the diversity and abundance of terrestrial free-living nematodes in potato agroecosystems. The current study was conducted in two potato fields in Pratin Village, Serang, Purbalingga, Central Java, Indonesia. Soil samples were collected from two potato fields planted with different varieties (Granola and Atlantik) and extracted using the Whitehead-tray method. The variables observed were the diversity of genera and the abundance of terrestrial free-living nematode populations from each field. Population density data were analyzed by T-test, and diversity (H'), evenness (E), and dominance index (D) were also calculated. The results showed that the mean population densities of terrestrial free-living nematodes in the two fields were significantly higher at 918.40 individuals/ 100 g of soil in the Atlantik field than in the Granola field 76.53 individuals/ 100 g of soil. However, the diversity, evenness, and dominance index were not significantly different in both fields. Genera of nematode found in the Granola field were Diplogaster, Dorylaimus, Trypilla, and Lotonchus, while in the Atlantik field were Rhabditis and Dorylaimus.

The Invasion of Alien Populations of Solanum elaeagnifolium in Two Mediterranean Habitats Modifies the Soil Communities in Different Ways.

We aimed to explore how the invasion of the alien plant Solanum elaeagnifolium affects soil microbial and nematode communities in Mediterranean pines (Pinus brutia) and maquis (Quercus coccifera). In each habitat, we studied soil communities from the undisturbed core of both formations and from their disturbed peripheral areas that were either invaded or not by S. elaeagnifolium. Most studied variables were affected by habitat type, while the effect of S. elaeagnifolium was different in each habitat. Compared to maquis, the soil in pines had higher silt content and lower sand content and higher water content and organic content, supporting a much larger microbial biomass (PLFA) and an abundance of microbivorous nematodes. The invasion of S. elaeagnifolium in pines had a negative effect on organic content and microbial biomass, which was reflected in most bacterivorous and fungivorous nematode genera. Herbivores were not affected. In contrast, in maquis, organic content and microbial biomass responded positively to invasion, raising the few genera of enrichment opportunists and the Enrichment Index. Most microbivores were not affected, while herbivores, mostly Paratylenchus, increased. The plants colonizing the peripheral areas in maquis probably offered a qualitative food source to microbes and root herbivores, which in pines was not sufficient to affect the much larger microbial biomass.

Top-down and bottom-up effects and relationships with local environmental factors in the water frog–helminth systems in Latvia

Semi-aquatic European water frogs (Pelophylax spp.) harbour rich helminth infra-communities, whose effects on host population size in nature are poorly known. To study top-down and bottom-up effects, we conducted calling male water frog counts and parasitological investigations of helminths in waterbodies from different regions of Latvia, supplemented by descriptions of waterbody features and surrounding land use data. We performed a series of generalized linear model and zero-inflated negative binomial regressions to determine the best predictors for frog relative population size and helminth infra-communities. The highest-ranked (by Akaike information criterion correction, AICc) model explaining the water frog population size contained only waterbody variables, followed by the model containing only land use within 500 m, while the model containing helminth predictors had the lowest rank. Regarding helminth infection responses, the relative importance of the water frog population size varied from being non-significant (abundances of larval plagiorchiids and nematodes) to having a similar weight to waterbody features (abundances of larval diplostomids). In abundances of adult plagiorchiids and nematodes the best predictor was the host specimen size. Environmental factors had both direct effects from the habitat features (e.g., waterbody characteristics on frogs and diplostomids) and indirect effects through parasite-host interactions (impacts of anthropogenic habitats on frogs and helminths). Our study suggests the presence of synergy between top-down and bottom-up effects in the water frog–helminth system that creates a mutual dependence of frog and helminth population sizes and helps to balance helminth infections at a level that does not cause over-exploitation of the host resource.

Influence of Two Cover Crops (Arachis repens L. and Desmodium adscendens Sw.) on Root Infestation of the “Great Dwarf” Dessert Banana Cultivar (Musa sp.) by Plant-parasitic Nematodes in Southeast Côte d’Ivoire

Context: In Côte d’Ivoire, industrial banana plantations are faced with the problem of weediness. However, the use of herbicides as a means of control presents significant risks for human health and the environment. The abandonment of these products for more ecological alternatives such as cover crops is imminent.
 Aims: This study aimed to compare the relative abundance and the density of the main plant-parasitic nematodes in the roots of banana and cover crops according to three weed management treatments.
 Study Design and Methodology: The experimental design was a three-repeat Fisher block of three treatments consisting of implementation of A. repens and D. adscendens as cover crops and spraying of two synthetic herbicides (glufosinate and glyphosate) for weed management. The relative abundance and density of nematodes in the roots of banana and cover crops were assessed quarterly after extraction by the rapid double centrifugation-flotation method and enumeration under an optical microscope.
 Results: Both cover crops and banana plants had their roots infested by the major parasitic nematodes evaluated (Radopholus similis, Pratylenchus spp., Helicotylenchus spp., Meloidogyne spp., Rotylenchulus reniformis and Hoplolaimus pararobustus). These infestations were not a function of weed management treatments. Compared to the use of herbicides, A. repens and D. adscendens used as ground cover did not significantly increase or decrease nematode dynamics in the plots. Individuals extracted from the roots of the cover crops, and particularly from D. adscendens, were more numerous than from the roots of the banana plants. In terms of proportions, Pratylenchus spp., R. similis, Helicotylenchus spp. and Meloidogyne spp. were most abundant. R. reniformis and H. pararobustus as well as various nematodes (plant parasites: Hirschmanniella spp., Xiphinema spp., ..., and non-plant parasites: fungivorous, carnivorous, bacterivorous, ...) were in the minority.
 Conclusion: The results, particularly those of A. repens, could be useful in the biological, ecological and sustainable management of weed in banana plantations without important risks of pest pressure.

Antioxidant enzyme activity associated to Meloidogyne and Pratylenchus infection in sugarcane

The plant-parasitic nematodes Meloidogyne and Pratylenchus are the main nematode pathogens reducing sugarcane yield worldwide. Despite, defense responses to overcome the pathogen stresses through neutralizing cytotoxicity of reactive oxygen species (ROS) have been reported for a range of important crops and pathogens, few studies have been developed for sugarcane under nematode stress. The aim of this study was to evaluate responses of the antioxidant enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APX) at different density of Meloidogyne and Pratylenchus in a sugarcane replant field and in a ratoon crop. Evaluations based on nematode densities, plant growth parameters and SOD and APX activity at six (T6) and nine (T9) months after planting (Area 1) or cutting (Area 2 - ratoon crop). Pratylenchus abundance significantly decreased in Area 1, but not in Area 2. In contrast, Meloidogyne abundance increased through time in Area 1, but decreased in Area 2. In both areas, SOD activity decreased over time, but APX activity did not present significant fluctuation over time in Area 1, in contrast to the increase over time of APX activity in Area 2. Abundance of both nematodes correlated positively with number of tillers and negatively with height of stalks, besides the negative correlation between Pratylenchus and stalk diameter. This inverse correlation between the plant-parasitic nematode and stalk number was also demonstrated by the PCA. There was not significant correlation between the antioxidant enzymes and plant growth parameters or nematode abundance, except the positive correlation between SOD activity and number of tillers.

Seasonal fluctuations attenuate stimulatory or inhibitory impacts of colonial birds on abundance, structure and diversity of soil biota.

Soil microorganisms and free-living nematodes were investigated in association with the nesting and roosting habitats of the following piscivorous and omnivorous colonial birds: black kite (Milvus migrans), great cormorant (Phalacrocorax carbo), black-crowned night heron (Nycticorax nycticorax) and little egret (Egretta garzetta), in Israel's Mediterranean region. Abiotic variables, abundance, trophic structure, sex ratio and genus diversity of soil free-living nematodes, and total abundance of bacteria and fungi, were measured during the wet season, following our previous study conducted during the dry season. The observed soil properties were important drivers of soil biota structure. Presence of the most efficient elements for soil organisms, such as phosphorus and nitrogen, was strongly dependent on the diet of the compared piscivorous and omnivorous bird colonies; levels of these nutrients were notably higher in the bird habitats than in their respective control sites during the study period. Ecological indices showed that the different species of colonial birds can have different (stimulatory or inhibitory) impacts on abundance and diversity of the soil biota, affecting the structure of the soil free-living nematode population at the generic, trophic and sexual levels during the wet season. A comparison with results from the dry season illustrated that seasonal fluctuations can change, and even attenuate the effect of bird activity on the abundance, structure and diversity of the soil communities.

Comparative Diversity, Abundance, and Community Pattern of Nematodes in Natural and Disturbed Habitats

This work evaluates the diversity, and abundance of nematodes and their use as indicators of soil health in an area strongly influenced by industrial wastes (food, metal and paper industries). The relationships between trophic groups, coloniser-persister scale and nematode community indices as well as nematode indicators of soil elements and the relationships of soil elements with different habitats were investigated. Nematodes were recovered from the soil samples of fifty sites from five different habitats. The trophic groups, colonizer-persister scale, and nematode community indices were analysed and compared. To test the significance of the dataset, bivariate linear regression; several samples repeated measure test of Analysis of Variance (ANOVA) have been performed. The Canonical Correspond Analysis (CCA); Principal Component Analysis (PCA), and clustering of habitats were performed to know the relationships between such variables among different habitats. Bacterial feeders with 15,582 individuals were found to be a highly diverse and most abundant group. The results indicated that the nematode diversity and abundance, trophic groups and coloniser-persister ratio were adversely affected by organically enriched habitats to food, metal and paper industries as compared to natural habitats. The habitats contaminated by industrial wastes were mainly dominated by bacterivores and fungivores of <i>c-p</i>2 class. Few colonizer genera were observed to be cosmopolitan and prevalent in all habitats. However, some genera showed specificity towards a particular set of conditions and were more or less endemic for specific habitats.

Changes in soil and litter properties differentially influence soil nematode communities across three successional stages in two contrasting forests

AbstractUnderstanding the linkages between aboveground and belowground ecosystems is important for explaining the variation in soil organisms with plant communities on a spatiotemporal scale. Here, soil nematode communities were investigated across three successional stages (early, mid, and late) in two contrasting forests at low and high latitudes in China. We found that forest succession affected the relative abundance of some nematode trophic groups, whereas it did not alter the total nematode abundance in the two forests. Nonmetric multidimensional scaling analysis showed that nematode community composition changed significantly from the early and mid‐stages to the late stage. The mantel analysis showed that total soil P at low latitude and litter C:N ratio at high latitude were more closely related to the variation in nematode community during forest succession, respectively. Total nematode diversity increased marginally with forest succession at low latitude, but first increased and then decreased with forest succession at high latitude. Interestingly, total nematode diversity was related to plant‐feeding nematode diversity during forest succession in both the forests. In addition, structural equation models showed that the diversity of different nematode trophic groups was directly affected by forest succession and indirectly affected by the quantity of soil resources and the quality of soil and litter. More importantly, forest succession drives total nematode diversity by directly affecting plant‐feeding nematode diversity. Collectively, forest succession alters the diversity and increases the dissimilarity of soil nematode communities. However, changes in soil and litter properties during forest succession at different latitudes differentially influence nematode communities.

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.

Integrated characterisation of Daubaylia burnupiae n. sp. (Nematoda: Daubayliidae) from a freshwater gastropod in South Africa, with comments on the biology of Daubaylia spp.

Gastropod-nematode associations are underreported worldwide. In the present study, juvenile and adult nematodes were found in the freshwater gastropod Burnupia stenochorias (Melvill & Ponsonby, 1903), from the Vaal River, South Africa. The nematodes were confirmed to belong to the genus Daubaylia chitwood & chitwood, 1934 (Daubayliidae). This is the first report of Daubaylia from a snail belonging to the family Burnupiidae, and the first report of this nematode taxon in southern Africa. Like D. pearsoni and D. malayanum from Australia and Malaysia respectively, adult females of the current species possess multiple well-developed eggs in the uteri, with larvae developing in utero. Morphological and molecular characteristics showed that the nematodes are distinct from all the described species of Daubaylia. Thus, they are considered a new species, Daubaylia burnupiae n. sp. The species differs from its congeners based on spicule shape, the short tail of the male, an anal cuticular knob-like protrusion on the female, and oesophagi with short isthmi and short glandular basal bulbs in both sexes. Three club-shaped pharyngeal lobes, extending slightly above the surface of the cephalic lips in both sexes and a pre-cloacal median papilla on the male were described using scanning electron microscopy, the first of such observations for the daubayliids. Genetic analyses showed that partial sequences of D. burnupiae n. sp. differed from species for which genetic data are available, by at least 26 and 9 base pair differences for 28S and 18S rDNA, respectively. Our results show that low prevalence and abundance of nematodes in the snails, corresponded with increased pollution in the river. We suspect that exposure to pollutants reduces the viability of the infective gravid female nematode during transmission. Therefore, the nematode is a potential bioindicator for aquatic pollution.

Urban wildflower meadow planting for biodiversity, climate and society: An evaluation at King's College, Cambridge

Abstract The biodiversity and climate crises are critical challenges of this century. Wildflower meadows in urban areas could provide important nature‐based solutions, addressing the biodiversity and climate crises jointly and benefitting society in the process. King's College Cambridge (England, UK) established a wildflower meadow over a portion of its iconic Back Lawn in 2019, replacing a fine lawn first laid in 1772. We used biodiversity surveys, Wilcoxon signed rank and ANOVA models to compare species richness, abundance and composition of plants, spiders, bugs, bats and nematodes supported by the meadow, and remaining lawn, over 3 years. We estimated the climate change impact of meadow vs lawn from maintenance emissions, soil carbon sequestration and reflectance effect. We surveyed members of the university to quantify the societal benefits of, and attitudes towards, increased meadow planting on the collegiate university estate. In spite of its small size (0.36 ha), the meadow supported approximately three times more plant species, three times more spider and bug species and individuals, and bats were recorded three times more often over the meadow than the remaining lawn. Terrestrial invertebrate biomass was 25 times higher in the meadow compared with the lawn. Fourteen species with conservation designations were recorded on the meadow (six for lawn), alongside meadow specialist species. Reduced maintenance and fertilising associated with meadow reduced emissions by an estimated 1.36 Mg CO2‐e per hectare per year compared with lawn. Relative reflectance increased by 25%–34% for meadow relative to lawn. Soil carbon stocks did not differ between meadow and lawn. Respondents thought meadows provided greater aesthetic, educational and mental wellbeing services than lawns. In open responses, lawns were associated with undesirable elitism and social exclusion (most colleges in Cambridge restrict lawn access to senior members of college), and respondents proved overwhelmingly in favour of meadow planting in place of lawn on the collegiate university estate. This study demonstrates the substantial benefits of small urban meadows for local biodiversity, cultural ecosystem services and climate change mitigation, supplied at lower cost than maintaining conventional lawn.

Prescribed fire alters nematode communities in an old-field grassland.

Fire is a common disturbance in many biomes, with both beneficial and detrimental effects on soil biology, which largely depend on fire intensity. However, little is known about the impact of fire on soil nematode communities in terrestrial ecosystem. In the present study, we investigated the effects of short-term prescribed fire on soil nematode communities and soil properties in an old-field grassland in Northern China. The results showed that burning significantly increased soil nematode abundance by 77% and genus richness by 49% compared to the control. Burning also decreased taxon dominance by 45% (Simpson's D) and increased nematode diversity by 31% (Shannon-Weaver H'). However, burning increased plant parasites (particularly genera Cephalenchus and Pratylenchus) and shifted community to more bacterial-feeding genera (i.e., decreased Channel Index). Generally, burning increased soil bio-available nitrogen (NH4 +-N and NO3 --N) content, which would be the main drivers causing nematode community to flourish via a "bottom-up" effect. These results suggest that prescribed fire increases nematode diversity and alters community composition toward more plant parasites and bacterial feeders. Our findings highlight the importance of prescribed fire management in shaping short-term nematode community structure and function, but the long-term effects and impacts of these changes on soil nutrient and carbon cycling remain unknown.

Grassland biodiversity and ecosystem functions benefit more from cattle than sheep in mixed grazing: A meta-analysis

Grasslands have been widely grazed for livestock production by cattle and sheep. However, previous studies have mainly focused on the impacts of single-species grazing on grassland biodiversity and ecosystem functions; the effects of mixed grazing of cattle and sheep remain largely unknown. We conducted a meta-analysis to examine the impacts of mixed grazing and analyzed the relative roles of cattle and sheep on grassland biodiversity and multiple ecosystem functions. Mixed grazing studies mainly originated from Europe, the USA, and China. Generally, cattle and sheep exhibited distinctive impacts on grassland biodiversity and functions in single-species and mixed grazing regimes. Cattle grazing alone increased plant diversity and soil organic carbon content (SOC), while sheep grazing alone had little impact. Compared to single-species grazing, mixed grazing generally increased plant density and richness of insect herbivores and decreased soil nematode richness, but did not alter plant biomass, soil nitrogen, or nematode abundance. Cattle in the mixed grazing regime increased plant diversity, biomasses of forbs and legumes, SOC, and liveweight gains of livestock. The mixed grazing impacts were further regulated by climate conditions, grazing intensity, and grazing duration. Our findings provide compelling evidence that mixed grazing benefits biodiversity, soil carbon sequestration, livestock production, and community structure of grasslands, and cattle are more influential than sheep in creating the benefits of mixed grazing for sustainable management of grasslands.

Effects of grazing on soil nematodes in grasslands: A global meta‐analysis

Abstract Grazing contributes substantially to grassland degradation worldwide and may alter soil biota and function. However, the effects of grassland type, grazing intensity and duration, and livestock type on soil nematodes are not fully understood. Here, we compiled 783 pair‐wise comparisons from 28 publications to better understand the pattern and underlying mechanisms of soil nematodes responses to grazing. Grazing significantly decreased the abundance of bacterial‐feeding and omnivorous‐predatory nematodes but had no effect on diversity (e.g. generic richness) and ecological indices (e.g. maturity index and plant‐parasitic index). Grazing effects on soil nematodes varied strongly by grassland type, grazing intensity and duration, and livestock type. Grazing decreased bacterial‐feeding nematodes in steppe. In meadow, grazing increased plant‐feeding nematodes and reduced nematode diversity. The abundance of bacterial‐feeding and fungal‐feeding nematodes significantly decreased in long‐term grazing (&gt;10 years). Light grazing increased fungal‐feeding nematodes and maturity index. Heavy grazing decreased total nematode abundance, the abundance of all trophic groups except plant‐feeding nematodes and the enrichment index. Sheep grazing produced a stronger negative response than cattle grazing on the abundance of bacterial‐feeding and omnivorous‐predatory nematodes, Shannon–Wiener index and enrichment index. Environment factors and soil properties influenced the grazing effects on nematode abundance. Our results showed that the grazing effects on nematode abundance were well explained by pH and soil organic carbon. Synthesis and applications. Our findings highlight that grazing effects on soil nematodes are context‐specific. As the contribution of soil nematodes to grassland management and ecosystem functions, we propose that policymakers should consider devising local‐scale grazing strategies for conserving soil biota and the functions of soil food webs.

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.

Grass harvesting eliminates the beneficial effects of legume addition on soil nematode communities in a tall grass pasture

Legume is an important type of plant functional group that can provide a myriad of ecosystem services. In general, the legume can promote the developments of soil fertility, soil biota, and other plants due to its ability to fix nitrogen. In practice, the legume-rhizobium system is one of the most ancient and successful biotic management strategies in anthropogenic ecosystems. However, little is known about how legumes interact with other agricultural management practices and affect soil biota. In this study, a full factorial design was employed to investigate the effects of a shrubby legume (Amorpha fruticosa) addition in conjunction with grass harvesting frequency on soil nematode communities in a hybrid napiergrass (Pennisetum hydridum) pasture. There were three grass harvest frequencies as two, four, and six times annually, as well as three legume densities including no legume, low legume density, and high legume density. During two-year monitoring, the results showed that the legume addition considerably enhanced abundances of total nematodes and bacterivorous nematodes as well as metabolic activities of total nematodes, bacterivores, and omnivore-predators for production and respiration, and the effects increasing with legume density. However, increased frequency of grass harvesting eliminated the effect of legume addition on soil nematode communities. The results suggest that frequent aboveground biomass export from the ecosystem may eliminate the bottom-up control of legumes on soil biota. Our findings could provide a better understanding of legume-soil interactions.