Nematode Biomass Research Articles

Impact of Solidago gigantea invasion on nematode communities in grasslands

Summary Solidago gigantea is one of the most problematic species of invasive plants in Europe, where its rapid spread threatens the stability of ecosystems. The effect of invasion by S. gigantea on soil ecosystems and food webs can be evaluated using nematode communities as suitable and useful soil bioindicators. We compared the effect of S. gigantea on nematode communities in plots invaded with S. gigantea and non-invaded grasslands across three sites with varying soil and climatic conditions. Our findings indicated that invasion by S. gigantea did not strongly affect nematode taxonomic diversity but negatively affected functional diversity. This effect was evident in the increased abundance of bacterivore and fungivore nematodes and decrease in values of ecological and functional indices. The evaluation of the soil food web using nematode communities confirmed that soil in plots with S. gigantea were less mature and more disturbed with a degraded or depleted food web indicated by lower values of maturity, enrichment and structure indices, compared with non-invaded grasslands. On the other hand, taxonomic diversity, abundance, biomass and the functional indices differed between three study sites, but site had little or no effect on the values of the maturity indices. The interaction between site and invasion status confirmed the effect of invasion on nematode biomass, with the abundance of bacterivore and fungivore nematodes and the functional indices more prominent at sites characterised by cold and humid climates. These findings underscore the importance of considering both taxonomic and functional diversity and the characteristics of the plants and sites when evaluating the impact of plant invasion on soil biota.

Are microplastics efficient remediation tools for removing the statin Lipitor? A laboratory experiment with meiobenthic nematodes

IntroductionThe current experiment investigated the multifaceted effects induced by microplastics and the statin Lipitor on marine benthic nematodes.MethodsThe nematodes were exposed to a single polystyrene and polyvinyl chlorides (both at 1 mg.kg-1 Dry Weight) and two Lipitor concentrations (0.1 and 1 mg.l-1), as well as to a mixture of both types of pollutants, for 30 days.ResultsThe results highlighted a significant decrease in the abundance, individual biomass, and diversity of nematodes directly with the addition of polyvinyl chlorides and/or Lipitor. These treatments induced a greater mortality rate among microvores and diatom feeders compared to other feeding types of nematodes.DiscussionThe nematofauna underwent a strong restructuring phase following exposure to microplastics and Lipitor when added alone, leading to the disappearance of sensitive species and their replacement by more tolerant taxa. The toxicity of Lipitor is attenuated by the physical bonding with polystyrene when added to a mixture and has no negative effect on marine nematode species.

Close-to-nature forest management effects on soil nematodes and microbial activity in pine plantations on aeolian sands

AbstractClose-to-nature forest management combines the economic use of forests with nature conservation in forest, aiming promote stability, productivity, diversity and continuity within forest ecosystems. While close-to-nature management is expected to positively impact the tree growth, its effect on the belowground micro-biota has been poorly investigated. Nematodes and microbes are species-rich and abundant soil microorganisms that have long been used as ecological indicators of soil health. In this study, was assessed the impact of close-to-nature forest management on soil nematode communities and microbial activity in the pine plantations on aeolian sands in Southern Slovakia, 10 years after the introduction of this management approach. Fifteen stands in close-to-nature forest managed and fifteen stands with applying standard forest management were chosen. Our findings revealed that close-to-nature forest management significantly increased the abundance of soil nematodes and nematode biomass in each of the plots. Moreover, close-to-nature forest management significantly increased the mean abundance of omnivores and predators as stress sensitive nematodes (c–p4, c–p5). Additionally, close-to-nature forest management reduces the proportion of stress tolerant nematodes (c–p1) and enrichment opportunists (c–p2), increased all maturity and structure indices as well as composite, structure, predator and omnivore footprints. Furthermore, close-to-nature forest management significantly increased soil moisture, soil carbon content, microbial biomass carbon, basal respiration and N-mineralization, and understory vegetation diversity. These findings suggest that close-to-nature management practice, resulting in forest of different ages, positively influenced nematode communities and microbial activity by changing the quantity and quality of resources associated with increased understory cover and diversity.

Multiple nutrient limitation of the soil micro-food web in a tropical grassland revealed by nutrient-omission fertilization

Although involved in key functions of the terrestrial ecosystems, the activity and the diversity of soil microorganisms can be severely limited by energy and nutrients in weathered tropical soils. To optimize nutrient cycling for crop nutrition, assessing which nutrients limit the activity of the microbial food web is thus essential. This was our aim in this study carried out on a tropical ferrallitic soil from a natural grassland in Madagascar. For this purpose, we employed an innovative nutrient-omission approach in microcosms to test the distinct effects of omitting C, six nutrients (N, P, K, S, Ca, Mg) and a cocktail of micronutrients (B, Mn, Cu, Na and Mo) on the composition, biomass and activities of the microbial community and on the abundance and biomass of their nematode grazers. C and P were identified as primary limitations, but other nutrients (N, Mg and S) played significant roles as co-limiting factors. Some bacterial and fungal taxa were significantly associated to specific nutrient deficiencies and can act as biological indicators. Additionally, the abundance and biomass of microbial-feeding nematodes provided valuable insights into the responses of the soil microbial community to nutrient deficiencies. These findings contribute to our understanding of nutrient dynamics and microbial community growth in tropical grassland ecosystems and have implications for sustainable crop fertility management and ecosystem ecology in similar environments.

Nematode production in artificial ponds: a long-term perspective

Summary Nematodes are the most abundant multicellular animals on Earth and play an important role as intermediaries in energy fluxes. However, estimations of nematode biomass turnover and secondary production have been poorly defined for decades and it is difficult to reach a consensus about the importance of nematodes for ecosystem functioning. Here we monitored monthly the nematode species composition, abundance and biomass over 3-10 years in a set of artificial urban ponds, and we used different allometric models to estimate biomass turnover and secondary production. During the first 3 years of colonisation of the pond bottom, the nematode community was rather species-poor and mostly composed of small bacterivorous species (Monhysterids); however, the community quickly reached impressive numbers (up to 21 million individuals m−2) achieving a maximum annual production of 3.8-11.6 gC m−2 year−1 depending on the allometric model used for estimation. However, over the long-term (3-10 years), abundance and community structure eventually became dramatically altered by anoxic events occurring in one pond, dampening nematode production to low levels (0.3-0.6 gC m−2 year−1) without clear resilience. The comparison of models helped us to formulate general recommendations in order to popularise the use of nematode secondary production as a useful ecosystem diagnostic tool. Overall, results indicated that under good conditions of oxygenation nematodes are a highly productive component of the zoobenthos of ponds. We also discussed the consequences of this finding for sustainable pond aquaculture, as nematodes constitute an important local and nutritive resource for juveniles of economically important fish, such as carp and tilapia.

Nematodes as biological indicators of urban heat island effects in the Chongqing area urban green spaces

The urban heat island effect (UHIE) is defined as the tendency of urban regions to have higher temperatures than suburbs in their immediate vicinity. A better understanding of UHIE and its biological indicators facilitates the prediction of ecological changes, which is particularly important due to ongoing global warming. To determine whether soil nematodes may serve as biological indicators of UHIE, we compared soil nematode communities under three urban green spaces, namely, urban cold islands (CI), urban heat island transition regions (HIT), and urban heat islands (HI). Distinct soil nematodes characteristics were found in the 3 urban green spaces. In addition, seasonal variations in community composition were identified. Among the 30 nematode genera identified, Eucephalobus was the most dominant in CI and HIT, while Monhystera was the most dominant in HI. The mean nematode abundance significantly differed (p ≤ 0.01) between CI (322 ± 24 individuals/100 g dry soil), HIT (112 ± 9 individuals/100 g dry soil), and HI (107 ± 10 individuals/100 g dry soil). We found that UHIE had detrimental effects on the nematode community structure (i.e., abundance and Margalef, Shannon-Wiener, and Simpson diversity indices) and ecological function [Free-living Nematode Maturity Index (MI), Nematode Channel Ratio (NCR), Enrichment Index (EI), and Structure Index (SI)]. These detrimental effects were reflected in nematode community structure indices, which were all highest in CI and lowest in HI, as well as in MI and SI, which were lower in HI than in CI. Furthermore, nematodes found in HI were shorter (L = 502.15 μm), thinner (W = 38.42 μm), and exhibiting higher length-to-width ratios (L:W) (15.83) compared to nematodes found in CI (L = 986.13 μm, W = 83.58 μm, L:W: 12.24) and HIT (L = 786.80 μm, W = 58.88 μm, L:W: 14.82). Nematode biomass spectra (NBS) shifted towards smaller biomass classes in HI compared to CI, while nematodes of the HIT showed intermediary spectra, further confirming the detrimental effects of UHIE on the soil nematode community. Regarding the physicochemical properties of the 3 green spaces, CI was found to have the highest soil pH, moisture, organic carbon content, total nitrogen content, and available potassium content, while HI had the lowest. Soil physicochemical characteristics were inversely correlated with soil temperature, except for available soil phosphorus, which was positively corrected with temperature. We also found that soil characteristics were significantly correlated with nematode community structure and ecological function, suggesting that the effects of UHIE on soil nematodes could have been indirectly affected by changes in soil physicochemical characteristics.

Evaluation of nematophagous and biocontrol efficacy of Dactylellina phymatopaga against Meloidogyne graminicola on rice (Oryza sativa L.)

Dactylellina phymatopaga is a nematode-trapping fungus which traps, kills and parasitizes nematodes. The rice root-knot nematode, Meloidogyne graminicola, is an important plant-parasitic nematode that threatens rice production worldwide. Therefore, it is most important to find new substitute for chemical control of M. graminicola. The present study aimed to investigate the in vitro trapping, germination and nematophagous ability in soil and fungus efficacy to reduce the number and biomass of developing stages of M. graminicola in rice roots. Isolates of D. phymatopaga were found to produced sessile adhesive knobs on growing hypahe to trap and paralyze M. graminicola J2 up to 98.8 % within 120 h of inoculation, in in-vitro conditions. Test for germination and nematophagous activities in various soils showed that spores of D. phymatopaga frequently germinate in soil with formation of adhesive sessile knobs on their germ lings, capturing and parasitizing nearby free living nematodes. Application of D. phymatopaga in M. graminicola-infested soil at the time and prior to rice sowing showed significant reduction in the number of root galls, number and biomass of developing stages of M. graminicola in rice roots (62.65–80.73 %) increasing plant health as compared to plants grown in nematode infested soil. Application of D. phymatopaga 7 days before sowing showed the highest biocontrol ability by decreasing in the nematode biomass in the associated rice roots per plant and the expended nematode-to-root biomass ratio (NB:RB). The results showed that the nematode-trapping behavior of D. phymatopaga yields a bio-management potential in reducing the number of developing stages of M. graminicola and their biomass in rice roots.

Livestock grazing modifies soil nematode body size structure in mosaic grassland habitats

Body size is closely related to the trophic level and abundance of soil fauna, particularly nematodes. Therefore, size-based analyses are increasingly prominent in unveiling soil food web structure and its responses to anthropogenic disturbances, such as livestock grazing. Yet, little is known about the effects of different livestock on the body size structure of soil nematodes, especially in grasslands characterized by local habitat heterogeneity. A four-year field grazing experiment from 2017 to 2020 was conducted in a meadow steppe characterized by typical mosaics of degraded hypersaline patches and undegraded hyposaline patches to assess the impacts of cattle and sheep grazing on the body size structure of soil nematodes within and across trophic groups. Without grazing, the hypersaline patches harbored higher abundance of large-bodied nematodes in the community compared to the hyposaline patches. Livestock grazing decreased large-bodied nematodes within and across trophic groups mainly by reducing soil microbial biomass in the hypersaline patches, with sheep grazing resulting in more substantial reductions compared to cattle grazing. The reduction in large-bodied nematode individuals correspondingly resulted in decreases in nematode community-weighted mean (CWM) body size, nematode biomass, and size spectra slopes. However, both cattle and sheep grazing had minimal impacts on the CWM body size and size spectra of total nematodes in the hyposaline patches. Our findings suggest that livestock grazing, especially sheep grazing, has the potential to simplify soil food webs by reducing large-bodied nematodes in degraded habitats, which may aggravate soil degradation by weakening the bioturbation activities of soil fauna. In light of the widespread land use of grasslands by herbivores of various species and the ongoing global grassland degradation of mosaic patches, the recognition of the trends revealed by our findings is critical for developing appropriate strategies for grassland grazing management.

Effect of land use on soil nematode community composition and co-occurrence network relationship

Land use influences soil biota community composition and diversity, and then belowground ecosystem processes and functions. To characterize the effect of land use on soil biota, soil nematode communities in crop land, forest land and fallow land were investigated in six regions of northern China. Generic richness, diversity, abundance and biomass of soil nematodes was the lowest in crop land. The richness and diversity of soil nematodes were 28.8 and 15.1% higher in fallow land than in crop land, respectively. No significant differences in soil nematode indices were found between forest land and fallow land, but their network keystone genera composition was different. Among the keystone genera, 50% of forest land genera were omnivores-predators and 36% of fallow land genera were bacterivores. The proportion of fungivores in forest land was 20.8% lower than in fallow land. The network complexity and the stability were lower in crop land than forest land and fallow land. Soil pH, NH4+-N and NO3−-N were the major factors influencing the soil nematode community in crop land while soil organic carbon and moisture were the major factors in forest land. Soil nematode communities in crop land influenced by artificial management practices were more dependent on the soil environment than communities in forest land and fallow land. Land use induced soil environment variation and altered network relationships by influencing trophic group proportions among keystone nematode genera.

Cover crops in pear (Pyrus communis) orchards: effects on soil nematode assemblage

Long-term vegetation cover can affect soil organic carbon content and carbon flow within the soil food web. Nematode trophic structure and soil properties were evaluated in pear rows (intra) maintained without weeds applying herbicide and in the inter-rows (between rows) covered with: Medicago+grasses (MG), fescue or spontaneous vegetation. Soil samples were taken at 0-20 and 20-40 cm depths from 2012 to 2014. Nematode assemblage was different in each inter-row and row, mainly in the topsoil. The inter-rows were reservoirs of omnivores-predators. The MG inter-row promoted the highest accumulation of organic carbon, total N and exchangeable K in the soil. The enrichment index was related to the quantity of dry matter produced by cover crops with the highest index observed in MG. Nematode biomass showed a positive correlation with intra and inter-rows soil organic carbon. Carbon flow through bacterivores prevailed in intra-rows, while bacterivores or herbivores canalized the inter-rows. Highlights: Each cover crop (Medicago+grasses, spontaneous vegetation and fescue) was associated with a different nematode assemblage, mainly in the topsoil. Omnivores-predators were higher in the inter-row than its associated row. Nematode Biomass showed a positive correlation with the content of SOC in the row and in the inter-row. Soil energy channels revealed higher carbon flow within the soil food web under Medicago+grasses and spontaneous vegetation than under fescue.

Contrasting responses of nematode composition, richness and biomass to long-term warming

It is well established that climate warming has become a growing issue globally, posing a threat to native ecosystems. Alpine ecosystems, such as meadows of the Qinghai-Tibet Plateau, are expected to be particularly sensitive to warming given current temperature constraints. While many studies have explored the effects of warming on aboveground ecosystems and edaphic properties, few studies have assessed the effects on soil biota. We assessed edaphic, plant, microbial and nematode responses to warming in a long-term (8 year) multilevel warming experiment and applied piecewise structural equation modelling to reveal how warming affected nematode communities directly and indirectly via biotic and abiotic factors. We found that (1) warming had a significant effect on nematode community composition, which was mainly due to direct warming effects on herbivores and omnivore-predatory nematode composition; (2) warming affected nematode richness mainly through effects on bacterial richness, with a strong negative relationship between bacterial richness and bacterivore richness as well as bacterivore richness and omnivore-predatory richness; and, (3) the predominantly direct effect of warming on nematode biomass was mainly due to significant responses of omnivore-predatory biomass. Our study provides insight into the effects of long-term warming on nematode communities and highlights the contrasting responses of composition, diversity and biomass to warming. It contributes to forecasting warming effects on the structure of soil food webs and ecosystem functioning on the Qinghai-Tibet plateau in the future.

Nematode biomass changes along an elevational gradient are trophic group dependent but independent of body size.

Aboveground, large and higher trophic-level organisms often respond more strongly to environmental changes than small and lower trophic-level organisms. However, whether this trophic or size-dependent sensitivity also applies to the most abundant animals, microscopic soil-borne nematodes, remains largely unknown. Here, we sampled an altitudinal transect across the Tibetan Plateau and applied a community-weighted mean (CWM) approach to test how differences in climatic and edaphic properties affect nematode CWM biomass at the level ofcommunity, trophic group and taxon mean biomass within trophic groups. We found that climatic and edaphic properties, particularly soil water-related properties, positively affected nematode CWM biomass, with no overall impact of altitude on nematode CWM biomass. Higher trophic-level omnivorous and predatory nematodes responded more strongly to climatic and edaphic properties, particularly to temperature, soil pH, and soil water content than lower trophic-level bacterivorous and fungivorous nematodes. However, these differences were likely not (only) driven by size, as we did not observe significant interactions between climatic and edaphic properties and mean biomasses within trophic groups. Together, our research implies a stronger, size-independent trophic sensitivity of higher trophic-level nematodes compared with lower trophic-level ones. Therefore, our findings provide new insights into the mechanisms underlying nematode body size structure in alpine grasslands and highlight that traits independent of size need to be found to explain increased sensitivity of higher trophic-level nematodes to climatic and edaphic properties, which might affect soil functioning.

Parasite load effects on sex ratio, size, survival and mating fitness of Heleidomermis magnapapula in Culicoides sonorensis.

Heleidomermis magnapapula parasitizes the blood-feeding midge Culicoides sonorensis. Most (84%) single mermithid infective second stage juveniles (J2) developed into adult females, while parasitism by multiple J2 yielded 97% male adults. Nematodes emerged from the midge larval host as adults and mated immediately; females were ovoviviparous. Host larvae were exposed to nematode J2 and examined intact microscopically to score initial parasite load. Midge hosts were reared individually. Premature midge death, nematode survival within the host, and emerging adult nematode sex ratio and size as a function of load and host size were all tracked. Higher nematode loads produced smaller adult nematode males. The higher loads also increased and accelerated premature host death. Emergence of > 7-9 adult nematode males was rare, but up to 19 tiny males emerged from a single host. Larger midges supported higher parasite loads and a larger total volume of emerged nematode biomass. Virgin adult nematode males then were paired with females of variable, known sizes (volume) and held to determine size effects on fertility (egg hatch), and male survival (longevity). Tested adult males ranged in size from 0.0025 - 0.0334 mm3 and females from 0.0121 - 0.1110 mm3. Logistic regression indicated female nematode fertility was positively influenced by male nematode size, while nematode load and female nematode size had no significant effect. While fertility was reduced statistically in smaller males, even some of the smallest male and female individuals could be fertile. Findings are related to field studies in this system.

Alfalfa and maize intercropping enhances soil nematode structure and food web complexity in low-nitrogen soils

Soil nematodes play key roles in soil ecosystem processes and functions. Although agricultural practices such as intercropping and nitrogen (N) fertilization are known to have a strong influence on soil nematodes, less is known about the responses of the soil nematode community to the combined effects of intercropping and N fertilization. This study was conducted to test whether the intercropping of maize and alfalfa can enhance the nematode community and quantified the effects of intercropping and N fertilization on nematode abundance, diversity, and metabolic footprints compared with soils under monoculture systems. An experiment involving maize and alfalfa was conducted in a 2 × 3 factorial completely randomized block design with four replications. The factors consisted of two N levels, namely, no N fertilization and N fertilization (225 kg N ha−1 yr−1), and three cropping modes: monoculture maize, monoculture alfalfa and maize intercropped with alfalfa. The results showed that, compared with the monoculture systems, intercropping increased total nematode and omnivore–predator abundances but reduced herbivore abundance. The total nematode biomass and metabolic footprint of omnivores and predators significantly increased in the intercropping treatments, regardless of N fertilization. The soil food web in the intercropping system without N fertilization was mature, structured, and enriched, as indicated by high maturity, structure and enrichment index values. However, all these effects decreased in the monoculture treatments, particularly after N fertilization. These results indicated that, compared with the monoculture systems, maize/alfalfa intercropping in low-N soil can improve the structural complexity of the soil food web. The observed complexity was attributed to the high soil moisture content, soil organic carbon and total N under the intercropping and low-N conditions. Therefore, this study provides a promising way to improve soil health and ecosystem stability, revealing that alfalfa intercropping in low-N soils can improve resource flow in the soil food web through the increase in total nematode biomass and the metabolic footprints of nematodes.

Infaunal community structure, diversity, and function in Pacific-Arctic shelf sediments: a comparison of meiofaunal- and macrofaunal-sized nematodes

Meiofauna, and nematodes in particular, perform essential roles in benthic ecosystems and serve as bioindicators of disturbance and environmental change. In the Pacific Arctic, a region experiencing rapid environmental change, this component of the fauna has received little attention, and the role of meiofauna in ecosystem processes is poorly understood. We collected multi-core samples at 10 stations in the northern Bering and southern Chukchi Seas in June 2018 and characterized the sedimentary environment. We also assessed meiofauna community structure and abundance at higher taxonomic levels and evaluated genus-level nematode composition in meiofaunal (63-500 µm) and macrofaunal (>500 µm) size fractions. Nematodes were classified by feeding type and life-history strategies. Total meiofauna abundance and biomass varied greatly, with 1449-12875 ind. 10 cm-2 and 373-2325 µg dry weight 10 cm-2 for the upper 5 cm of sediment. Estimated production of meiofaunal-sized nematodes was 5-28 g C m-2 yr-1. Four distinct communities of meiofaunal-sized nematodes were identified in different sub-regions reflecting food availability and substrate type. The meiofaunal- and macrofaunal-sized nematodes represented 2 distinct communities. The unique taxonomic composition and large standing stock of the macrofaunal-sized nematodes (22 ± 15% of total nematode biomass) suggest they are critical components of the infauna and merit further research to assess their role in critical ecosystem functions. This study provides the first genus-level characterization of nematodes and some of the first measurements of meiofauna standing stock in the region, contributing important data for assessing ecosystem function in a rapidly changing Arctic.

Life in a Contaminated Environment: How Soil Nematodes Can Indicate Long-Term Heavy-Metal Pollution.

We investigated the genera, trophic groups, and functional guilds of soil nematodes at five alluvial meadows along the Litavka River in the Czech Republic to assess their usefulness as indicators of heavy metal pollution in soils. The Litavka River flows around the waste-sedimentation pond of a smelter in the city of Příbram in the Central Bohemian Region. Lead, zinc, and arsenic are the main pollutants in the soils in the vicinity of the smelter. The alluvial meadows closest to the pond and mine waste were the most heavily polluted sites, and contamination decreased downstream along the river with increasing distance from the sources of pollution. The nematode communities were sensitive to pollution, with the most contaminated sites having considerably fewer nematode individuals, fewer genera, and a less diverse and more degraded food web with less nematode biomass. Arsenic, lead, and zinc contents were significantly negatively correlated with the numbers of bacterivores, predators, omnivores, plant parasites, and fungivores, which were significantly less abundant at highly polluted sites. This correlation suggests that nematode groups with higher c-p values, and those with c-p 1 and 2 designations, can be useful indicators of high heavy-metal contamination in areas polluted for a long time. In contrast, the abundance of c-p 3 plant parasitic nematodes was positively correlated with copper, nickel, and zinc contents and with soil-moisture content in the alluvial meadows. Maturity index (MI) and MI2-5 were the most sensitive indices of the degree of disturbance of the soil ecosystem, with enrichment index, structure index, and basal index indicating the altered decomposition channels and diminished structure of the food web.

Relationships between Soil Nematode Communities and Soil Quality as Affected by Land-Use Type

Researchers have used both soil nematode data and soil quality index (SQI) data as indicators of soil quality. However, the relationship between soil nematodes and soil quality index is poorly understood. This study explored the relationship between soil nematode properties and soil quality in different land-use types in a subtropical karst region of Southwest China. We selected the following five typical land-use types that differ in the degree of soil disturbance: cropland (maize and soybean), sugarcane, mulberry, forage grass, and forest. SQI was calculated on the basis of bulk density (BD), soil pH, the ratio of soil organic carbon to total nitrogen (C:N), the contents of soil water (SWC), soil total nitrogen (TN), soil organic carbon content (SOC), calcium (Ca), magnesium (Mg), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), ammonium nitrogen (AN), nitrate nitrogen (NN), bacteria, fungi, actinomycetes (ACT), and arbuscular mycorrhizal fungi (AMF). We found that the abundance, Simpson dominance index, and metabolic footprint of soil nematodes were highest in the forest, followed by sugarcane, cropland (maize and soybean), forage grass, and mulberry. The SQI was highest in the forest and lowest in the cropland. There was no significant difference observed among the other three regions. In addition, the SQI was positively correlated with the total nematode biomass and abundances of total nematodes, fungivores, and herbivores, the abundances of total nematodes biomass and total nematode abundance, fungivores, and herbivores. A random forest model revealed that the dominant nematode genera (i.e., Coomansus and Acrobeloides) and the rare genera (i.e., Heterocephalobus) were closely associated with soil quality. Our results suggest that the soil nematodes (especially keystone genera) may mediate the effects of ecosystem disturbance on soil quality. These findings increase our understanding of the relationships between soil organisms and soil quality.

Temporal dynamics of range expander and congeneric native plant responses during and after extreme drought events.

Climate change is causing range shifts of many species to higher latitudes and altitudes and increasing their exposure to extreme weather events. It has been shown that range-shifting plant species may perform differently in new soil than related natives; however, little is known about how extreme weather events affect range-expanding plants compared to related natives. In this study we used outdoor mesocosms to study how range-expanding plant species responded to extreme drought in live soil from a habitat in a new range with and without live soil from a habitat in the original range (Hungary). During summer drought, the shoot biomass of the range-expanding plant community declined. In spite of this, in the mixed community, range expanders produced more shoot biomass than congeneric natives. In mesocosms with a history of range expanders in the previous year, native plants produced less biomass. Plant legacy or soil origin effects did not change the response of natives or range expanders to summer drought. During rewetting, range expanders had less biomass than congeneric natives but higher drought resilience (survival) in soils from the new range where in the previous year native plant species had grown. The biomass patterns of the mixed plant communities were dominated by Centaurea spp.; however, not all plant species within the groups of natives and of range expanders showed the general pattern. Drought reduced the litter decomposition, microbial biomass, and abundances of bacterivorous, fungivorous, and carnivorous nematodes. Their abundances recovered during rewetting. There was less microbial and fungal biomass, and there were fewer fungivorous nematodes in soils from the original range where range expanders had grown in the previous year. We concluded that in mixed plant communities of range expanders and congeneric natives, range expanders performed better, under both ambient and drought conditions, than congeneric natives. However, when considering the responses of individual species, we observed variations among pairs of congenerics, so that under the present mixed-community conditions there was no uniformity in responses to drought of range expanders versus congeneric natives. Range-expanding plant species reduced soil fungal biomass and the numbers of soil fungivorous nematodes, suggesting that the effects of range-expanding plant species can trickle up in the soil food web.

First insights into the meiofauna community of a maerl bed in the Bay of Brest (Brittany)

Maerl beds, particularly those of Brittany, are important, structurally complex biogenic coastal habitats that form a unique ecosystem with high benthic biodiversity. Although they are relatively well studied throughout Europe, several faunal groups of maerl beds, such as those belonging to the meiofauna, have received little attention. We investigated the meiofaunal abundance, distribution and community structure, with a focus on nematode biomass and diversity, in a maerl area in the Bay of Brest, Brittany, compared with that on a sandy beach (Anse de Dinan, Brittany). Meiofauna was five times more abundant on the maerl bed than on the sandy beach, and 1.5 times more diversified (12 vs. 8 taxa, respectively). Nematode diversity was more than three times higher on the maerl bed than on the sandy beach and showed a distinctive nematode community that was absent from the sandy beach. Maerl beds create more heterogeneous microhabitats and promote a higher diversification of meiofauna and nematode communities than sandy beaches.

Partial organic substitution weakens the negative effect of chemical fertilizer on soil micro-food webs

Soil biotic communities play vital roles in enhancing soil nutrient cycling and soil fertility. Long-term excessive nitrogen (N) application is disadvantageous to the stability of soil food webs and affects arable soil health and sustainable utilization. Proper organic substitution is essential to improve soil health and alleviate the disadvantages of excessive chemical fertilization. However, the biological effects of various organic amendments on soil micro-food webs are poorly understood. In order to explore the effects of various organic amendments including stover, biochar and manure on soil micro-food webs (microbial and nematode communities), a field plot experiment with maize having five treatments viz., 100% urea (100% N), 70% urea (70% N), 70% urea plus stover (Stover), 70% urea plus cattle manure (Manure) and 70% urea plus biochar (Biochar) was conducted. Manure treatment increased the carbon (C) to N use efficiency of soil microbes, which contributed to the retention of soil C, while Biochar treatment elevated soil organic C (SOC) and soil pH. Additionally, Biochar treatment mitigated the negative effects of soil acidification on the soil micro-food web and reduced the abundance of plant parasites. Overall, the biological effect of organic amendments was distinguished from chemical fertilization (100% N and 70% N) through principal co-ordinates analysis. Negative relationships among soil properties, microbial and nematode biomass in the 100% N treatment were diminished in treatments where chemical fertilizer was reduced. The bottom-up effects on soil food webs were observed in organic substitution treatments. In conclusion, organic amendments improved soil fertility by regulating soil microbial and nematode communities in the cropland ecosystem, alleviated the negative effects of chemical fertilizer on the micro-food webs and controlled the trophic cascades among soil biota.