Soil Nematode Community Composition Research Articles

Increasing Levels of Physical Disturbance Affect Soil Nematode Community Composition in a Previously Undisturbed Ecosystem.

Soil is essential for the sustenance of life. Diverse soil organisms support several biological processes such as organic matter decomposition, mineralization, nutrient cycling, and controlling pests and diseases. Among multicellular soil organisms, nematodes are ubiquitous, functionally diverse, and abundant. Notably, agricultural practices have diverse impacts on plants, soils, and soil organisms. Tillage affects nematodes directly by altering pore size and disrupting the continuity of water films and indirectly by affecting the lower trophic groups such as bacteria and fungi. The primary goal of this study was to examine the effect of increasing levels of physical disturbance on nematode communities in an undisturbed forest ecosystem. The experiment included four treatments: control with no disturbance, surface litter removed with no litter and no vegetation, tilling the soil with a rototiller every 2 mon, and every 2 wk. Tillage significantly reduced the overall abundance and overall richness of nematode communities over time. Among nematode trophic groups, tillage significantly reduced the abundance and richness of bacterial feeders, predators, and omnivores over time. The abundance and richness of c-p 2, c-p 4, and c-p 5 class nematodes were significantly decreased by tillage. Unlike tillage, minimal disturbance such as removal of surface litter resulted in a significant decrease in the abundance of only three genera: Acrobeles, Aporcelaimellus, and Boleodorus. Nonmetric multidimensional scaling analysis revealed that nematodes of higher c-p classes such as Dorylaimida, Aporcelaimellus, Alaimus, Clarkus, and Tripyla were sensitive to physical disturbances. Bacterial feeders belonging to the c-p 2 class such as Tylocephalus, Acrobeles, Ceratoplectus, Plectus, and Pseudacrobeles were significantly reduced by tillage. Moreover, tillage significantly reduced the functional metabolic footprint of nematodes, which indicates decreased metabolic activity, reduced C inflow, and poorly structured soil food webs. Previous studies conducted in agricultural ecosystems determined that Clarkus, Filenchus, and Plectus were tolerant to tillage; however, they were found sensitive to tillage in our study. Overall, our study suggests that increasing levels of physical disturbance are detrimental to nematode community abundance and diversity that could affect soil ecosystem stability and sustainability.

Adaptation of soil micro-food web to elemental limitation: evidence from the forest-steppe ecotone

Stoichiometric imbalance between resources and their decomposers can alter the activity and structure of soil microbial communities and play an important role in regulating nutrient and carbon cycling in terrestrial ecosystems. However, whether and how ecological networks of soil micro-food web change to cope with the stoichiometric imbalance has never been assessed so far. In this study, we tested how the soil micro-food web responded to elemental limitations along a forest-steppe ecotone. We measured several adaptation mechanisms including soil microbial stoichiometry, enzyme activities and the composition of soil microbial and nematode communities. The microbial investment in resource acquisition shifted from nutrient-to C-acquiring enzymes with decreasing soil C:N:P ratios along the forest-steppe ecotone. The shifts in element use efficiencies could be a compensatory way besides enzyme allocation, implemented by microbial communities to cope with stoichiometric imbalance in their substrates. The community structure of soil micro-food web also changed with a decrease in saprotrophic fungi and fungivorous nematodes from the steppe plots towards the forest plots. The co-occurrence networks were less complex and stable with decreasing soil C:N:P ratios, suggesting that trophic interactions were less diverse and C-limitation plays an important role in structuring ecological interactions in soil food webs. Our findings provide insights into how stoichiometric constraints may induce shifts in ecological networks and have important implications for integrating shifts in individual physiological metabolism as well as changes in community composition of soil biota and to better understand and predict soil biogeochemical cycling in terrestrial ecosystems.

Changes in the soil nematode community among climate zones do not keep pace with changes in plant communities

Revealing the distribution patterns of soil nematode communities among climate zones helps uncover the spatial distribution patterns of belowground biodiversity. The aims of this study were to reveal the spatial distribution patterns of the taxonomic composition, diversity and trophic structure of soil nematode communities among continuous climate zones. Investigations were conducted for five altitudinal vegetation types, i.e., subtropical evergreen broad-leaved forest (SEB), subtropical evergreen and deciduous broad-leaved mixed forest (SEDB), warm temperate deciduous broad-leaved forest (WTDB), mid-temperate coniferous and broad-leaved mixed forest (MTC) and cold temperate coniferous forest (CTC), on the eastern slope of Gongga Mountain from 2014 to 2017. The taxonomic compositions of the soil nematode communities in the SEDB, WTDB, MTC and CTC were similar but differed markedly from that in the SED, with patterns varying among sampling years. Abundances and diversity showed unimodal distribution patterns, with maximum values occurring in the WTDB. The abundances of the four trophic groups varied significantly among the vegetation types. Relative abundances stabilized for bacterivores and plant parasites but declined for fungivores and increased for omnivores-predators from the SEB to the CTC. The ratio of fungivores to bacterivores in the SEB was significantly higher than those in the other vegetation types, implying that the trophic structure and material cycling channels differed among forest types. The spatial distribution of the soil nematode communities was mainly influenced by pH, total K, total P and soil temperature. These findings suggested that the taxonomic composition, abundance, diversity and trophic structure of soil nematode communities vary among climate zones, but the changes in the soil nematode communities among climate zones did not keep pace with those in aboveground plant communities.

Straw Return and Nitrogen Fertilization to Maize Regulate Soil Properties, Microbial Community, and Enzyme Activities Under a Dual Cropping System.

Soil sustainability is based on soil microbial communities’ abundance and composition. Straw returning (SR) and nitrogen (N) fertilization influence soil fertility, enzyme activities, and the soil microbial community and structure. However, it remains unclear due to heterogeneous composition and varying decomposition rates of added straw. Therefore, the current study aimed to determine the effect of SR and N fertilizer application on soil organic carbon (SOC), total nitrogen (TN), urease (S-UE) activity, sucrase (S-SC) activity, cellulose (S-CL) activity, and bacterial, fungal, and nematode community composition from March to December 2020 at Guangxi University, China. Treatments included two planting patterns, that is, SR and traditional planting (TP) and six N fertilizer with 0, 100, 150, 200, 250, and 300 kg N ha–1. Straw returning significantly increased soil fertility, enzymatic activities, community diversity, and composition of bacterial and fungal communities compared to TP. Nitrogen fertilizer application increased soil fertility and enzymes and decreased the richness of bacterial and fungal communities. In SR added plots, the dominated bacterial phyla were Proteobacteria, Acidobacterioia, Nitrospirae, Chloroflexi, and Actinobacteriota; whereas fungal phyla were Ascomycota and Mortierellomycota and nematode genera were Pratylenchus and Acrobeloides. Co-occurrence network and redundancy analysis (RDA) showed that TN, SOC, and S-SC were closely correlated with bacterial community composition. It was concluded that the continuous SR and N fertilizer improved soil fertility and improved soil bacterial, fungal, and nematode community composition.

Seasonal variation in cropland soil nematode community composition in the lower reaches of Liaohe Plain

Seasonal variation in cropland soil nematode community composition in the lower reaches of Liaohe Plain

Investigation of the soil nematode community composition in a monoculture Robusta coffee plantation in Dak Lak, Vietnam

Nematode damage to coffee poses a serious threat to coffee production all over the world, including Vietnam. Accordingly, the nematode community composition could be a reliable indicator of ecological shifts that affect coffee plants' health. Here, we analysed the nematode communities in the rhizosphere of a monoculture Robusta coffee plantation in Dak Lak of the Central Highlands, Vietnam. We found changes in the community composition of nematodes in an age gradient of replanting coffee plants and revealed distinct patterns of nematode distribution in the soils of healthy and diseased plant groups. Further analyses indicate the impact of intensive farming and inefficient nematode controls, which caused disturbances and a gradual decrease of the nematode fauna diversity in the plantation soil. These results can add to a complete prediction model for plant fitness using nematode community composition. • Rhizosphere nematode communities in a monoculture Robusta coffee plantation in Dak Lak, Vietnam, have been assessed. • Pratylenchus are the primary plant-parasitic nematodes in this area. • Remarkably, a high abundance of Chitwoodius and correlation of Aphelenchoides with plant fitness was found. • We show that colonization of coffee plants by plant-parasitic nematodes increases with plant age, and the predominance of these nematodes coincides with a lower diversity of the nematode fauna. • The nematode communities, including several important functional groups, can be utilized as a bio-indicator of plant fitness.

Analysis of soil nematode community of alpine meadow in the middle of the Tibetan Plateau

The alpine meadow of Tibet Plateau is extensively distributed, and the soil nematode community may exhibit certain regional differences. To understand whether there were differences among soil nematode communities, soil samples were collected in the Bangjietang alpine meadow which is in the middle of the Tibet Plateau, and the composition of soil nematode communities was determined by high-throughput sequencing technology. It was found that from 0-10 cm to 10-20 cm, the composition of soil nematode community changed significantly, the relative abundance of Chromadorea at the class level decreased while that of Enpolea increased, the relative abundance of Rhabdtida at the order level decreased while that of Dorylaimida increased. There were only eight genera of soil nematodes at the genus level, which was significantly different from the Northern Tibet region. The soil nematode communities were dominated by a bacterivorous trophic group. The soil chemical properties such as soil organic matter (SOM), available nitrogen (AN), total nitrogen (TN), total phosphorus (TP), Zn, Cu, Pb, and Cd affected the class and order level of soil nematodes, specifically, they both had negative effects on Chromadorea and Rhabiditida, and positive effects on Enoplea and Dorylaimida. In general, our results indicate that the composition of soil nematode communities in the alpine meadow which was in the middle of the Tibet Plateau was similar but different from that in Northern Tibet Plateau, specifically, they were mainly bacterivorous trophic group, but Bangjietang alpine meadow contained few genera, and the dominant nematode communities were different at class and order levels.

Nitrogen and phosphorus additions interactively affected composition and carbon budget of soil nematode community in a temperate steppe

Nitrogen and phosphorus additions interactively affected composition and carbon budget of soil nematode community in a temperate steppe

Large-Scale Patterns of Soil Nematodes across Grasslands on the Tibetan Plateau: Relationships with Climate, Soil and Plants

Soil nematodes are important contributors to soil biodiversity. Nonetheless, the distribution patterns and environmental drivers of soil nematode communities are poorly understood, especially at the large scale, where multiple environmental variables covary. We collected 520 soil samples from 104 sites representing alpine meadow and steppe ecosystems. First, we explored the soil nematode community characteristics and compared community patterns between the ecosystems. Then, we examined the contributions of aboveground and belowground factors on these patterns. The genus richness and abundance of nematodes on the Tibetan Plateau are lower than other alpine ecosystems, but are comparable to desert or polar ecosystems. Alpine meadows supported a higher nematode abundance and genus richness than alpine steppes; bacterial-based energy channels were pre-dominant in both the ecosystems. Soil factors explained the most variation in the soil nematode community composition in the alpine meadows, while plant factors were as essential as soil factors in the alpine steppes. Unexpectedly, the climate variables barely impacted the nematode communities. This is the first study to explore the spatial patterns of soil nematode compositions on the Tibetan Plateau, and we found that the contributions of climate, plants, and soil properties on soil nematodes community were essentially different from the previous knowledge for well-studied plant and animal communities.

Impact of land use type and organic farming on the abundance, diversity, community composition and functional properties of soil nematode communities in vegetable farming

The excessive application of chemical fertilizers in intensively managed agricultural fields worldwide has resulted in soil degradation and biodiversity loss. This has contributed to a growing interest in sustainable management, such as organic farming. Until now, studies addressing the impact of conventional and organic management on soil biodiversity and functioning have mainly focused on arable farming and only a few reports are available on vegetable production. Vegetable farming is of particular interest, since management intensity is usually very high and there is an increasing demand for vegetable products. Soil nematodes are useful indicators of management intensity on soil ecosystem functioning because they occupy several trophic levels in soil micro-food webs and play a crucial role in nutrient cycling, pest suppression, and the regulation of microbial communities. In this study, we assessed the impact of management intensity and farming system on the community structure and functional guilds of soil nematodes, comparing 20 conventional vegetable fields, 20 organic vegetable fields, and 20 extensive grasslands in Switzerland, analyzing over 30’000 nematode individuals and detecting 98 different nematode genera. We found significant differences in the community structure and functional composition across three farming systems. Extensive grasslands contained the highest nematode abundance, followed by organic vegetable fields, and conventional vegetable fields, indicating a decline due to land-use intensification. Organic farming led to a significant increase in the abundance of herbivores (+82%), bacterivores (+206%) and omnivores (+135%) in comparison with conventional farming. Organic management also enhanced composite (+195%) and herbivores (+451%) footprints, suggesting greater carbon and energy enrichment in soil food web through these functional groups. Community composition of soil nematodes varied significantly across the three farming systems, with each farming system fostering specific indicator taxa. In conclusion, our results show that farming system has a major impact on soil nematode communities with increasing nematode populations under organic vegetable farming. Although organic vegetable production may benefit from enhanced soil fertility due to increased population densities of microbe feeding and omnivorous nematodes, the threat from plant parasitic nematodes to vegetable production requires attention and control strategies should be developed further.

Soil nematode communities on five oceanic islands across a latitudinal gradient in the north of the South China Sea: Influence of biotic and abiotic factors

Factors that influence the composition and diversity of soil nematode communities on oceanic islands are poorly understood. In this study, we evaluated the soil nematode communities and associated biotic and abiotic factors on five oceanic islands in the north of the South China Sea. We detected 38 nematode genera and found that bacterivores and fungivores were the dominant trophic groups, representing 54.2–70.4% and 15.1–35.3%, respectively, of total soil nematode abundance. The abundances of total soil nematodes and of all trophic groups, maturity, structure indices and nematode diversity were positively correlated with island latitude and area, and were negatively correlated with soil total K and annual temperature. In addition, the abundances of total soil nematodes, bacterivores, herbivores and nematode dominance index were positively associated with soil available K. The abundances of total soil nematodes, fungivores, herbivores, predators and omnivores, maturity, structure, Shannon diversity indices were positively related to soil moisture. Variation partitioning analysis showed that the combination of soil properties and climatic-geographical factors explained more of the variation (26.8–61.5%). The results suggest that larger island can maintain greater nematode diversity than smaller islands due to the greater diversity of habitats on larger island. The key climatic-geographical and edaphic factors affecting soil nematode communities were latitude, annual temperature, soil moisture and total K, respectively

Soil nematode community composition, diversity, and soil properties in an age sequence of Haloxylon ammodendron plantations in an oasis-desert ecotone of northwestern China

Restoration of vegetation and soil ecosystems controls desertification, and soil nematodes have been used as bioindicators of ecosystem restoration, but the efficacy of this method is not clear in desert ecosystem. We selected different ages of Haloxylon ammodendron plantations in a desert-oasis ecotone, in Linze County, northwestern China, and sampled surface soil under and outside the canopy to examine the restoration process of plants and changes in the composition and diversity of nematode communities, and relationship between soil physicochemical properties and nematode genera. The results showed that plantation ages of H. ammodendron had significant effects on total nematodes, omnivores-predators and bacterivores. The numbers of total nematodes increased with plantation ages, and reached 228.0 per 100 g dry soil after 46 years. Bacterivores dominated in soil nematode community, accounting for 50.3–94.1% of nematode numbers. The effect of H. ammodendron on soil nematode communities and physicochemical properties was time-dependent. The significant increase of soil nematodes abundance and diversity appeared from 6 years, and soil physicochemical properties varied significantly after 11 years. Shannon–Weiner diversity index, Evenness index, Trophic diversity (TD) index, and Maturity index showed an increasing trend with plantation age, indicating that the food web became more complex, and soil environment gradually stabilized. Nematode genera in different plantation ages were separated by redundancy analysis (RDA), and soil properties significantly affected the temporal and spatial distribution of nematode communities. We concluded soil nematodes can be used as a biological indicator because they reflect the restoration process of the plant-soil ecosystem.

Considerable impacts of litter inputs on soil nematode community composition in a young Acacia crassicapa plantation

Aboveground litter inputs and root exudates provide basal resources for soil communities, however, their relative contributions to soil food web are still not well understood. Here, we conducted a field manipulative experiment to differentiate the effects of litter inputs and living root on nematode community composition of surface and subsoils in a young Acacia crassicapa plantation in southern China. Our results showed that both litter addition and root presence significantly enhanced soil nematode abundance by 17.3% and 35.3%, respectively. Litter addition altered nematode trophic group composition, decreased fungivore to bacterivore ratio, and enhanced maturity index and structure index, which led to a bacterial-based energy channel and a more complex food web structure. However, root presence had a limited impact on the nematode community composition and ecological indices. Despite nematodes surface assembly, soil depth did not affect nematode trophic group composition or ecological index. Our findings highlight the importance of litter inputs in shaping soil nematode community structure and regulating soil energy channel.

Effects of different carbon inputs on soil nematode abundance and community composition

Plants provide carbon (C) input to the soil and energy resources for soil food webs through litter and roots. However, it remains uncertain which C input pathway is more important and how different C inputs affect the community composition of the soil fauna. A long-term (9 years) field C input manipulation experiment was conducted to investigate the effects of C inputs on soil nematodes. Plant removal, litter addition, and litter removal were carried out to simulate changes in below- and aboveground C inputs. Results showed that plant removal significantly decreased soil resource availability (i.e., the soil organic C and total nitrogen). Plant removal also decreased nematode abundance (73.09%) and genus richness (17.98%). The relative abundance of bacterivores was enhanced but plant parasites and omnivores-predators were reduced by plant removal. The significantly lower soil pH and higher NO3−-N concentrations under the plant removal treatment are probably responsible for changing the community structure. Litter addition increased nematode abundance by 37.88%, but litter removal decreased the genus richness by 9.39%. There were significant interactive effects of plant removal and litter manipulation on the total nematode abundance and genus richness. Our observations suggest that belowground C input has greater impacts on soil nematodes than the above-ground C input, and that the impacts of litter on the soil nematode community could be mediated by living plants.

Long-term nitrogen addition and precipitation reduction decrease soil nematode community diversity in a temperate forest

Terrestrial ecosystems are driven by different global change factors, such as atmospheric nitrogen deposition and precipitation reduction. Nitrogen deposition and precipitation reduction have a great impact on the above- and underground processes. Most previous studies mainly focused on the effects of nitrogen deposition and/or precipitation reduction on aboveground processes, while the effects on underground processes were relatively scarce. As an important part of the underground soil food web, soil nematode community occupies different nutritional niches and is sensitive to external disturbances, and it is often used as indicator for studying underground processes. However, we know little about the response of soil nematode community to nitrogen deposition and/or precipitation reduction. Here, we used a 10-year of factorial manipulation by applying nitrogen solution and reducing the amount of precipitation to the soil, and to investigate the responses of soil nematode community to nitrogen deposition and/or precipitation reduction in a temperate forest. We expected that nitrogen addition could promote while precipitation inhibited the activity of soil nematode community. Furthermore, we expected nitrogen addition and precipitation could have interactive effect on soil nematode community. Our results found that nitrogen addition and/or precipitation reduction treatment caused significant changes in the composition of soil nematode community. Nitrogen addition and nitrogen addition combined with precipitation reduction induced negative effects and significantly decreased the abundance and diversity of soil nematode community, while precipitation reduction only decreased the abundance of soil nematode community. Nitrogen addition and precipitation reduction had synergistic effect on soil nematode community with higher trophic levels. Compared with precipitation reduction treatment, the negative effect of nitrogen addition on soil nematode community was more severe. According to the structural equation model (SEM), we found that nitrogen addition and precipitation reduction could affect the abundance of soil nematode community by affecting the plant richness and soil pH. Since the decrease of enrichment index (EI) and the increase of structure index (SI), our research results revealed that nitrogen addition could lead to soil food web in a lower nutrients available condition.

Soil nematodes in the field and fallow - density and diversity

The results presented here concern the study, which was carried out in the spring of 2009 on an arable field and a fallow. Following parameters were analysed: density, taxonomic composition, trophic and dominance structure of soil nematode communities. Shannon-Weaver diversity index, Sørensen’s index of similarity and Maturity index were also calculated. The results show that the nematode community in the soil of arable field differed from that on the fallow in respect of density and trophic structure. Nematode density was higher in the arable soil than in the fallow. The group of bacterial-feeding nematodes was the most numerous among five trophic groups recorded in the study. The higher density of that group in the arable soil than in the fallow indicates the positive response of bacterial-feeding nematodes to the higher nutrient supply after the manure applying. The results show that in three years of fallow nematode communities became more mature and diverse than in the arable soil. The study confirms the indicative value of some nematode community parameters and indices for the assessment of the varying human intervention on the functional state of the soil.

Effect of grassland degradation on soil quality and soil biotic community in a semi-arid temperate steppe

Grasslands provide a number of ecosystem services for human society. Degradation of grasslands results in the loss of biodiversity and leads to the deterioration of ecosystem functions. In order to accurately assess the influence of grassland degradation on belowground ecosystems, we conducted experiments on a temperate steppe with different levels of degradation and investigated the influence of degradation on soil quality and soil biotic communities. Our results showed that grassland degradation significantly decreased soil quality, with lower values of soil quality index (SQI) observed in the degraded grassland than the meadow steppe and the grassland from the forest-steppe ecotone. Changes in the SQI along the grassland degradation gradient were positively correlated with soil carbon stock and the aboveground biomass, and negatively correlated with the root shoot ratio. Nematode trophic diversity and the ratio of fungal to bacterial PLFA were lower in the degraded grassland than the grassland from the forest-steppe ecotone. The dissimilarities in soil microbial and nematode community composition increased with the changes in soil quality index. Our results indicate that soil quality index based on the minimum data sets could effectively assess the influence of grassland degradation on soil biodiversity and ecosystem function. In order to effectively restore degraded grasslands, the key contributors to the soil quality, such as soil carbon, should be taken on priority basis for revitalizing the soil biodiversity and ecosystem function.

Impacts of litter addition and root presence on soil nematode community structure in a young Eucalyptus plantation in southern China

Eucalyptus plantations are widely established in degraded ecosystem as a fast-growing species for restoration. However, the impact of Eucalyptus aboveground litter and living root on soil nematode community structure is poorly understood. We conducted a field manipulative experiment to investigate the impact of litter addition and root presence on soil nematode community composition in a young Eucalyptus plantation in southern China. Our results showed that both litter addition and root presence significantly increased soil nematode abundance. Litter addition altered nematode community composition by decreasing relative fungivore abundance, and increasing relative omnivore-predator abundance and the nematode channel ratio. However, no obvious effect of root presence on nematode community was detected. There were interactions between litter addition and root presence on nematode ecological indices. Litter addition increased maturity index and structure index, and reduced enrichment index in the absence of root, but did not change these indices under root presence. Our findings highlight the critical role of aboveground litter resources in shaping nematode community structure and function. Meanwhile, the influence of litter resources on soil nematode community structure and function are regulated by root input. The study provides theoretical support for plantation management in southern China.

Crop tree release increased the density of soil nematodes and improved the food web structure

As a special thinning method, crop tree release (CTR) has a beneficial effect on forest environments and structures by changing forest light, heat, and water. However, the impact of CTR on underground biodiversity remains unclear. Therefore, we analyzed the composition, diversity, and metabolic footprints of soil nematode communities under three CTR (100, 150, and 200 trees·ha–1) treatments, as well as a no CTR treatment, in Pinus massoniana Lamb. plantations. The results showed that CTR increased the density of soil nematodes (P < 0.05), the number of omnivore–predator nematodes (P < 0.05), and the diversity (H′) of nematodes (P < 0.05) and enriched the food web structure of soil nematodes. In the medium CTR density treatment (150 trees·ha–1), the nematode density and diversity (H′) were the highest (P < 0.05), the number of omnivore–predator nematodes was also the highest (P < 0.05), and the enrichment index and structure index values of the soil nematodes reached the maximum at the depth of 0–10 cm (P < 0.05). Our results indicated that the community structure of soil nematodes became more stable and mature after CTR, which may be attributed to the changes of soil condition, especially soil organic matter, and plant diversity indirectly.

A global database of soil nematode abundance and functional group composition

As the most abundant animals on earth, nematodes are a dominant component of the soil community. They play critical roles in regulating biogeochemical cycles and vegetation dynamics within and across landscapes and are an indicator of soil biological activity. Here, we present a comprehensive global dataset of soil nematode abundance and functional group composition. This dataset includes 6,825 georeferenced soil samples from all continents and biomes. For geospatial mapping purposes these samples are aggregated into 1,933 unique 1-km pixels, each of which is linked to 73 global environmental covariate data layers. Altogether, this dataset can help to gain insight into the spatial distribution patterns of soil nematode abundance and community composition, and the environmental drivers shaping these patterns.