Diversity Of Nematode Communities Research Articles

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.

Glyphosate-based restoration of a degraded grassland threatens soil health and the diversity of nematode communities

Invasive species have become a dominant component of native grasslands, leading to a reduction in biodiversity and ecosystem functioning. Grasslands hold the potential to sequester more carbon than forests, yet few large-scale intact grasslands remain on Earth. Consequently, the restoration of degraded grasslands is critical to resurrect the ecological and economic services they once provided. Although glyphosate-based herbicide restoration projects are among the most effective strategies to remove invasive plants and allow native species to reestablish, their off-target effects on belowground diversity are unclear. Nematodes are the most abundant and diverse animals on Earth and have been recognized as indicators of soil health due to their positioning at all trophic levels and ability to respond to environmental change such as pollution, disturbance, and climate change. The goal of this study was to examine the response of nematode communities to a glyphosate-based grassland restoration project. We applied different frequencies of Roundup ProMax® to field plots in the first year of the project and characterized the impact on nematode communities over the following four years using morphological counts and 18S rRNA metabarcoding. To test the effects of the herbicide on nematode community diversity, composition, and structure, we utilized a modelling approach with general linear models, PERMANOVAs, distance-based redundancy and co-occurrence network analyses. We show persistent negative effects on nematode diversity across all four years. In addition, compositional shifts and changes in nematode-specific functional indices indicated less healthy soils in herbicide-treated plots. Co-occurrence networks further confirmed less structured and more disturbed communities. No recovery of nematode communities in glyphosate treated plots was observed after four years, demonstrating the longevity of effects. In conclusion, this study reports negative off-target effects of glyphosate herbicide restoration projects on belowground diversity and the need to consider these factors in evaluating the long-term success of herbicide-based grassland restoration.

Use of PCR-DGGE-Based Molecular Methods to Analyze Nematode Community Diversity.

DGGE (denaturing gradient gel electrophoresis) is a nucleic acid separation technique applied to the evaluation of microbial biodiversity. This technique is quite rapid and cheap compared to other types of analysis. Here we describe the comparison of nematode communities inhabiting different ecosystems. After an ecologically representative sampling collection and the nematode extraction from soil, nematodes are centrifuged in Eppendorf tubes to facilitate DNA extraction. DNA from the whole community of each type of soil is extracted, amplified with primers for 18 S rDNA and used in DGGE analysis. The profiles of DGGE can be analyzed with appropriate software, and biodiversity indices can be estimated.

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.

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.

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.

Shrub and precipitation interactions shape functional diversity of nematode communities on the Qinghai-Tibet Plateau.

Land use and climate change alter biodiversity patterns and ecosystem functioning worldwide. Land abandonment with consequent shrub encroachment and changes in precipitation gradients are known factors in global change. Yet, the consequences of interactions between these factors on the functional diversity of belowground communities remain insufficiently explored. Here, we investigated the dominant shrub effects on the functional diversity of soil nematode communities along a precipitation gradient on the Qinghai-Tibet Plateau. We collected three functional traits (life-history C-P value, body mass, and diet) and calculated the functional alpha and beta diversity of nematode communities using kernel density n-dimensional hypervolumes. We found that shrubs did not significantly alter the functional richness and dispersion, but significantly decreased the functional beta diversity of nematode communities in a pattern of functional homogenization. Shrubs benefited nematodes with longer life-history, larger body mass, and higher trophic levels. Moreover, the shrub effects on the functional diversity of nematodes depended strongly on precipitation. Increasing precipitation reversed the effects shrubs have on the functional richness and dispersion from negative to positive but amplified the negative effects shrubs have on functional beta diversity of nematodes. Benefactor shrubs had stronger effects on the functional alpha and beta diversity of nematodes than allelopathic shrubs along a precipitation gradient. A piecewise structural equation model showed that shrubs and its interactions with precipitation indirectly increased the functional richness and dispersion through plant biomass and soil total nitrogen, whereas it directly decreased the functional beta diversity. Our study reveals the expected changes in soil nematode functional diversity following shrub encroachment and precipitation, advancing our understanding of global climate change on nematode communities on the Qinghai-Tibet Plateau.

Structure and composition of the nematode community in a restoration area affected by iron tailings

In 2015, the Fundão Dam collapse released over 40 million m3 of iron mine tailings, causing several environmental damages. Certain affected areas were revegetated with a mix of fast-growing species that can allowed the return of some organisms of soil fauna. Nematodes are the most abundant multicellular organisms in soil and are commonly used as bioindicators. Therefore, this study aimed to use the nematode community as bioindicators of the restoration process of an area affected by iron tailings at the margins of the Gualaxo do Norte River. Soil samples were collected from affected and native forest areas to perform physical, chemical, biochemical, and biological analyses. Nematodes were identified and classified according to feeding habits and on a colonizer-persisters (cp) scale. A non-metrical multidimensional scaling and PERMANOVA were conducted to assess differences between communities. Shannon’s diversity index and the maturity index were significantly higher in the restoration area. There was a difference in the composition and the structure of nematode communities of the restoration and reference area, nematode genus occurrence and abundance were different between the areas resulting in differences in feeding habits and life strategies according to the cp scale. The cp-5 nematodes are more abundant in the restoration area and cp-1 in the forest reference area. Bacterivore nematodes were more abundant in the reference forest area. In addition, the soil attributes in the restoration area were altered following the tailings deposition. Such alterations include high pH, low organic matter content, and low microbial biomass, which consequently influenced the structure and the composition of the nematode community. This is likely the first report of soil nematode community diversity in the areas of the Rio Doce Basin impacted by the Fundão tailings, and nematodes proved to be good bioindicators to show the differences between the restoration and forest reference area.

Database and primer selections affect nematode community composition under different vegetations of Changbai Mountain

High-throughput sequencing technology is increasingly used in the study of nematode biodiversity. However, the annotation difference of commonly used primers and reference databases on nematode community is still unclear. We compared two pairs of primers (3NDf/C_1132rmod, NF1F/18Sr2bR) and three databases (NT_v20200604, SILVA138/18s Eukaryota and PR2_v4.5 databases) on the determination of nematode community from four different vegetation types in Changbai Mountain, including mixed broadleaf-conifer forest, dark coniferous forest, betula ermanii Cham and alpine tundra. Our results showed that the selection of different primers and databases influenced the annotation of nematode taxa, but the diversity of nematode community showed consistent pattern among different vegetation types. Our findings emphasize that it is necessary to select appropriate primer and database according to the target taxonomic level. The difference in primers will affect the result of nematode taxa at different classification levels, so sequencing analysis cannot be used for comparison with studies using different primers. In terms of annotation effect in this study, 3NDf/C_1132rmod primers with NT_v20200604 database could provide more information than other combinations at the genus or species levels.

Carbon nanomaterial addition changes soil nematode community in a tall fescue mesocosm

Carbon nanomaterials have been widely used in industry and inevitably enter the environment. However, there is little information about their influence on the abundance and diversity of soil nematode community. We evaluated the impact of three kinds of carbon nanomaterials (graphene, graphene oxide, and carbon nanotubes) on the abundance and diversity of soil nematodes after growing tall fescue for 130 d using a laboratory pot experiment. A total of 29 genera of nematodes were identified in all the treatments. Carbon nanomaterials significantly increased the abundance of total nematodes and plant parasites. The presence of graphene and graphene oxide increased the numbers of bacterivores, and graphene benefited fungivores. The total nematode abundance was 1.9–2.9 times greater in the carbon nanomaterial treatments than in the control with no carbon nanomaterial addition. However, graphene oxide and carbon nanotubes decreased the values of nematode community parameters, e.g ., diversity, species richness, and structure index. Compared with the control, the addition of graphene resulted in a community with a higher plant-parasitic index ( i.e. , the maturity index of the plant-parasitic nematodes). Overall, our findings highlight that the addition of carbon nanomaterials has a negative influence on the composition and diversity of the nematode community, simplifying the community structure.

Biodiversity of Nematode Communities Associated with Wheat (Triticum aestivum L.) in Southern Morocco and Their Contribution as Soil Health Bioindicators

Soil nematodes are major soil organisms known to reduce wheat production worldwide. However, they are a crucial part of soil biodiversity. Due to the limited data available regarding nematode biodiversity associated with cereal crops in Morocco, a survey was conducted in 2019 across 80 wheat fields. Thirty-three nematode taxa were obtained with different trophic groups: 11 bacterivores (i.e., Rhabditis and Cephalobus spp.), 11 herbivores (i.e., Pratylenchus and Heterodera spp.), 6 fungivores (i.e., Ditylenchus and Aphelenchoides spp.), 4 omnivores (i.e., Dorylaimus and Aporcelaimus spp.) and one predator (Mononchus spp.). For each locality, the diversity of nematode communities was assessed through multiple diversity indices. Three areas (Ait Melloul, Oulad Dahou, and Sidi Boushab) were more diversified and had pronounced nematode occurrence. Moreover, few localities (e.g., Ait Amira and Lqliaa) were shown to be disturbed. Our study underlined that several nematode taxa were significantly correlated with edaphic and climatic/geographic properties. On the other hand, the spatial and parsimony analyses revealed that plant feeders were most associated with bacterial feeders in disturbed soils. This work revealed that the soil nematodes associated with wheat crops are diverse and can serve as an important tool for soil biomonitoring at a large scale.

Increase in rainfall intensity promotes soil nematode diversity but offset by nitrogen addition in a temperate grassland

Precipitation regime in arid and semi-arid regions is exhibiting a trend of increase in rainfall intensity but reduction in frequency under global climate change. In addition, nitrogen (N) deposition occurs simultaneously in the same regions. Nematodes are the dominant soil biota in terrestrial ecosystems and are involved in various underground processes. How the diversity of nematode communities responds to changing precipitation regime and how N deposition regulates the responses remain unclear. Here, we performed a field experiment initiated in 2012 to examine the effect of changes in the precipitation regime (2 mm precipitation intensity, 5 mm precipitation intensity, 10 mm precipitation intensity, 20 mm precipitation intensity, and 40 mm precipitation intensity) and N addition (10 g N m−2 yr−1) on soil nematode community in a semi-arid grassland in Inner Mongolia of China. We found that the abundance and diversity of nematodes increased under the treatments with fewer but stronger precipitation events (the largest abundance of total nematodes was 1458.37 individuals/100 g dry soil occurred under 40 mm intensity treatment). However, N addition reduced nematode diversity under these treatments, which largely offset the positive effects of increased rainfall intensity alone. Soil pH and plant belowground biomass were the main factors affecting nematode diversity. Our results imply that, as a consequence of global climate change, an increase in the intensity of rainfall events in the coming decades may favor the nematode communities within arid and semi-arid ecosystems. However, this positive effect may be largely offset by soil acidification in the regions experiencing heavy N deposition.

青藏高原不同牧草人工草地对土壤线虫群落的影响

为缓解草蓄矛盾，青藏高原人工草地得到快速发展。土壤线虫对环境变化敏感，是草地生态系统的重要组成部分。然而，不同牧草人工草地对土壤线虫群落的影响尚不明确。2016年7月，对多年生禾本科（垂穗披碱草Elymus nutans Griseb.、老芒麦Elymus sibiricus L.、早熟禾Poa annua L.和羊茅Festuca ovina L.）、一年生禾本科燕麦Avena sativa L.和多年生豆科紫花苜蓿Medicago sativa L.等6种单播牧草人工草地（建植期4年）和天然草地（对照）的土壤线虫群落进行了调查。结果表明：（1）土壤线虫隶属于2纲8目32科58属，平均密度为1754个/100 g干土；紫花苜蓿样地的线虫密度最低，为949个/100 g干土；燕麦样地最高，为3267个/100 g干土；（2）与天然草地相比，燕麦样地的线虫群落总密度、多样性以及植食性和杂食-捕食性线虫密度显著增加，而其他人工草地的线虫群落密度、多样性以及植食性、食真菌和食细菌线虫密度均无显著变化；（3）土壤线虫总密度以及各营养类群密度在不同人工草地间差异显著，且均在燕麦样地最高；（4）建植人工草地改变了土壤线虫的群落组成，冗余分析（RDA）表明土壤全钾、碳氮比、全磷和有效钾是影响线虫群落组成的重要因子。研究表明青藏高原建植人工草地通过改变植物群落和土壤理化性质对土壤线虫群落产生影响，其中种植燕麦短期内可显著提高土壤线虫群落的密度和多样性。青藏高原生态环境脆弱，在大面积建植人工草地前应对地下生态过程进一步深入研究。;Artificial grassland with higher productivity has developed rapidly in recent years in order to balance available pasture and stocking rates on the Qinghai-Tibetan Plateau. Soil nematodes are sensitive to environmental changes, which are important components of grassland ecosystems. However, little is known about the effects of the artificial grasslands with the different forage species on the diversity of soil nematode communities. Soil nematode communities in the natural grasslands (control) and artificial grasslands were investigated in July 2016. Four perennial grass (Elymus nutans Griseb., Elymus sibiricus L., Poa annua L., and Festuca ovina L.), one annual grass (Avena sativa L.), and one perennial legume (Medicago sativa L.) were selected. Forages were grown for four years in monoculture in this study. Soil nematodes were extracted from 50 g of fresh soil using Baermann funnels for each composite soil sample. The composite samples were comprised of three soil cores taken from the upper 0-15 cm soil. Soil nematodes were identified into 2 classes,8 orders,32 families,and 58 genera. The results showed that:(1) the average nematodes abundance was 1754 ind./100 g dry soil, ranging from 949 ind./100 g dry soil in the M. sativa to 3267 ind./100 g dry soil in the A. sativa. (2) The total abundances, taxonomic richness, Shannon diversity index of the soil nematodes communities, and the abundances of herbivores and omnivores-predators were significantly higher in the A. sativa grasslands compared to the natural grasslands. However, no significant difference was observed in the total abundances and diversity of the nematode communities and the abundances of fungivores, bacterivores and omnivores-predators between the rest artificial grasslands and natural grasslands. (3) The abundances of the soil nematode communities and each trophic group differed significantly among the different artificial grasslands, with the maximum values occurring in the A. sativa grasslands. (4) Redundancy analysis results showed that soil total K, C/N, total P and available K were the important factors affecting the composition of the soil nematode communities. The results suggested that establishing artificial grasslands with changes in plant communities and soil physico-chemical properties led to the change of soil nematode communities on the Qinghai-Tibetan Plateau, and the abundances and diversity of soil nematode communities were significantly increased by planting A. sativa. Given the vulnerability of ecological environment on the Qinghai-Tibetan Plateau, the changes in soil nematode communities depicted here indicate that underground process should be further studied before the area of artificial grasslands has been greatly increased.

The functional role and diversity of soil nematodes are stronger at high elevation in the lesser Himalayan Mountain ranges.

Soil nematodes are a foremost component of terrestrial biodiversity; they display a whole gamut of trophic guilds and life strategies, and by their activity, affect major ecosystem process, such as organic matter degradation and carbon cycling. Based on nematodes' functional types, nematode community indices have been developed, and can be used to link variation in nematodes community composition and ecosystem processes. Yet, the use of these indices has been mainly restricted to anthropogenic stresses. In this study, we propose to expand the use of nematodes' derived ecological indices to link soil and climate properties with soil food webs, and ecosystem processes that all vary along steep elevation gradients. For this purpose, we explored how elevation affects the trophic and functional diversity of nematode communities sampled every 300 m, from about 1,000 m to 3,700 m above sea level, across four transects in the lesser Himalayan range of Jammu and Kashmir. We found that (a) the trophic and functional diversity of nematodes increases with elevation; (b) differences in nematodes communities generate habitat‐specific functional diversity; (c) the maturity index (ΣMI) increases with elevation, while the enrichment index decreases, indicating less mature and less productive ecosystems, enhanced fungal‐based energy flow, and a predominant role of nematodes in generating carbon influxes at high‐elevation sites. We thus confirm that the functional contribution of soil nematodes to belowground ecosystem processes, including carbon and energy flow, is stronger at high elevation. Overall, this study highlights the central importance of nematodes in sustaining soil ecosystems and brings insights into their functional role, particularly in alpine and arctic soils.

Nematode community diversity and function across an alpine landscape undergoing plant colonization of previously unvegetated soils

Climate warming is a key factor driving species range shifts. While previous work has focused on shifts of aboveground plant communities, changes in climate and vegetation should affect soil communities and hence ecosystem-level nutrient cycling and ecosystem functioning. High alpine ecosystems are particularly sensitive to climate warming because snow is among the main drivers of ecosystem structure and function. Climate-warming snow cover changes at Niwot Ridge in the Colorado Rocky Mountains have resulted in a consistent plant colonization of previously unvegetated soils generating a natural gradient of soil habitats ranging from unvegetated to increasingly vegetated. We used this gradient of plant communities at different successional stages to determine if nematodes respond to climate-driven changes in this high-alpine landscape and if they play a role in changes in soil C and N. We hypothesized that: 1) there would be clear shifts in nematode communities along the gradient as a function of snow cover, plant richness and density, and water holding capacity but that these shifts would be dependent on nematode feeding habits and their positioning in the soil foodweb and 2) the shifts would be associated with accumulating soil C and N. To test these hypotheses, we measured nematodes, plants, and soil microbes, snow cover, pH, soil water holding capacity, and different forms of soil C and N in 98 plots across the plant successional gradient. As predicted, nematode communities exhibited extensive shifts from a few individuals of a single species in unvegetated soils to hundreds of individuals and tens of species within every feeding group under complex plant communities. Representatives of omnivorous and bacterivorous K-strategists preceded plants and plant parasites and root associates depended on plants most. Linear regression models indicated that plants, microbial communities and soil water holding capacity, but not snow cover, were the most predictive factors of nematode diversity and density across all trophic levels and that all nematode groups were positively related to all measures of soil C and N. Structural equation models confirmed these results, but also indicated that effects of climate warming on nematodes were indirect primarily through shifts in plant and microbial communities and changes of soil water holding capacity. Moreover, nematode trophic group densities, but not their diversity, played a potential role in the accumulation of soil N, and to a lesser degree of soil C. Because nematode communities at Niwot Ridge are largely at their early phases of assembly, with continuing climate warming, we predict their increasing abundance and diversity will likely continue, as will their impact on soil C and N processes.

Response of the soil food web to warming and litter removal in the Tibetan Plateau, China

Both climate warming and litter removal alter soil nematode communities and the structure, stability, and function of soil food webs. The soil nematode metabolic carbon footprint, based on nematode biomass and respiration, can be used to indicate ecosystem function and the response of nematodes to nutrient enrichment in the ecosystem. However, it is unclear whether or how climate warming and litter removal affect the metabolic carbon footprint of soil nematodes and soil food webs. In this study, we investigated four warming and litter removal treatments in the Qinghai-Tibet Plateau, China, to determine the effects of climate warming and litter removal on soil microbial food webs. The treatments included: (1) control (CK), (2) warming, (3) litter removal, (4) warming + litter removal. We found that warming and litter removal had significant negative effects on the diversity and richness of soil nematodes. In addition, our results showed warming indirectly and directly affected vegetation diversity, thereby altering soil nematode diversity. Vegetation played an important role in the maintenance of soil nematode community diversity. The enrichment and structural footprints reflected nematodes that could respond most rapidly to resource enrichment and those with higher trophic levels in soil food webs, respectively. Overall, warming and litter removal significantly negatively affect the enrichment metabolic footprint, indicating they could significantly reduce the external resource inputs into the food web. Both warming and litter removal reduced the structural metabolic footprint of the soil food web, although the changes were not significant, indicating that the metabolic activity of nematodes of high nutrient levels decreased and the ability to regulate the food web from top-bottom effects was weakened under warming and litter removal. The nematode functional metabolic footprints indicated that litter removal could aggravate the effect of warming on the soil food web and result in more severe degradation. The combination of warming and litter removal significantly inhibited the connectance of the bacterial channel, but had no significant effect on the fungal channel. These results suggest that the soil food web enhanced resistance to the environment by increasing the proportion of the fungal channel. It is critical to understand the responses of soil food webs to climate warming and litter removal to better predict how ecosystem functions will change in the future.

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.

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.

Organic or conventional production system and nutrient rate affect the nematode community in carrot production.

Organic and conventional production are common in horticulture crops and each system may exert a different influence on the soil ecosystem, particularly the nematode community. Crop nutrient rate is an important choice in both production systems. The objectives of this study were to assess the impacts of (i) organic and conventional production systems and (ii) nutrient rate in both systems on the nematode community in carrot production. To investigate these objectives, field studies in organic and conventional production – which included fumigation with 1,3-dichloropropene – were conducted in North-Central Florida. In both production systems, nutrient rate treatments were 168, 224, 280, 336, and 392 kg N/ha. Poultry litter was the nitrogen source in organic production whereas synthetic, inorganic fertilizer was used in conventional production. All nematode trophic groups were consistently more abundant in organic than conventional production. The nematode community was more diverse and had greater trophic structure in organic production. Greater rates of organic nutrients increased enrichment opportunists (bacterivores and fungivores), but inconsistently across years. Conventional production had similar results except that only moderate nutrient rates increased fungivore abundances. Extreme enrichment opportunists (Rhabditis spp.) drove bacterivore trends in organic production whereas moderate enrichment opportunists (Cephalobus spp.) drove trends in conventional production. Nutrient rates did not affect omnivore-predators, herbivores, nematode community diversity, or structure in either system. In summary, type of production system, organic or conventional, exerts a strong influence on the nematode community, but nutrient rate has less consistent effects in horticulture production.

Effect of Soil Treatments and Amendments on the Nematode Community under Miscanthus Growing in a Lead Contaminated Military Site

Applying phytotechnologies with energy crops on lands contaminated with trace elements provides cellulosic biomass and improves soil health. The process can be reflected in changes in the soil nematode community structure. This study assessed the nematode community composition of soil with Miscanthus grown with different agronomic practices. The research was conducted at Fort Riley, Kansas, USA, in soil with aged contamination by Pb at 1000 to 1500 mg/kg. The experimental design was a randomized complete block composed of four replications of five treatments: Control-undisturbed mixed plant cover and four conditions of Miscanthus growth, which consisted of No-till, Till (immediately before planting), Till + P, and Till + biosolids. Analysis of abundance, diversity, and community functional status indicators showed differential sensitivity of nematode taxa to agronomic treatments. Significant transformations in the nematode trophic group structure occurred under Miscanthus cultivation compared with the undisturbed mixed plant cover. Shannon and Pielou index response to agronomic treatments illustrated decreasing nematode community diversity with all Miscanthus agronomic conditions. However, agronomic practices led to increasing nematode community maturity, but those effects varied between spring and fall seasons. Increasing herbivores and omnivore-predators were the primary drivers of the observed changes in the nematode community due to planting Miscanthus. The nematode ecological structure indicators suggested that growth in Pb-contaminated land using different agronomical practices likely affects essential soil processes. More study is needed to define the effects of pre-plant tillage and amendments to soil nematode communities and Miscanthus yield over multiple growing seasons of this perennial crop.