Nematode Trophic Groups Research Articles

Changes in Arenosol Nematode Abundance and Trophic Composition as Influenced by Different Faidherbia albida (Delile) A. Chev. Tree Stand Ages in Northern Ethiopia

ABSTRACTFaidherbia albida (Delile) A. Chev., hereafter F. albida is an important agroforestry tree species in the semi‐arid highlands of Tigray, northern Ethiopia. The paper analyses how different stand ages of the tree could influence nematodes' abundance, trophic composition and selected community index values. A total of 40 composite soil samples were collected from out‐canopies and under‐canopies of different tree stand age classes designated as young (15–20 years), medium age (35–40 years) and older (> 60 years). Nematodes were extracted following the Baermann funnel technique, identified and counted under an inverted Olympus microscope according to their trophic groups. The highest total count of nematodes and relative abundance of fungivores, omnivores and predatory nematode trophic groups were counted from soil samples influenced by older F. albida trees. The relative abundance of bacterivores and plant parasitic nematodes was low. The nematode channel ratio became lower in soils as influenced by older trees while the Wasilewska index was significantly high. The age difference of the trees influenced the abundance of the soil nematode feeding groups and their ecological index values. Moreover, the results have shown the enhancement of nematode trophic diversity. Redundancy analysis showed that tree age significantly influenced the relationships of nematode trophic groups with the studied soil bio‐physicochemical properties. Generally, the findings indicate that the soil food web becomes more complex and functional under the older trees.

Urban greenspaces shape soil nematode community across soil depth gradients: Belowground life at The Ohio State University

Urban greenspaces face significant anthropogenic transformation, impacting soil ecosystems, multifunctionality, and global biodiversity. With increasing population and urbanization, understanding the drivers influencing soil nematode communities in urban greenspaces is crucial for sustainable urban ecosystem management. We chose the campus of The Ohio State University (OSU) due to its unique urban settings with minimally disturbed both turf and non-turf ecosystems. This study focuses on nematodes, the often-overlooked ecological engineers which play diverse roles in ecosystem functions. Nematodes were collected from 99 sampling locations across three soil depths to represent two ecosystem types (i.e., turf and non-turf) of the OSU campus. Among plant parasitic nematodes (PPN), Helicotylenchus and Pratylenchus populations were above damage threshold limits. No specific pattern of community composition was observed in the spatial variation map. The presence of rare PPN genera in the lower soil layers had a significant impact on beta diversity. Trophic group abundances displayed distinct patterns, with turf ecosystems exhibiting higher PPN as well as total nematode abundance decreasing with soil depths. In the subsurface layer (10–30 cm), both bacterivores and fungivores were higher in the non-turf than turf ecosystem. Fungal-dominated decomposition of organic matter was observed in both ecosystem types. Soil physiochemical properties, specifically, total organic carbon and soil texture, had a significant impact on PPN community composition. However, nematode trophic group composition was more altered by ecosystem type than edaphic factors followed by soil depths. Together these three explanatory variables explained 27.5 % of the total variance in trophic group composition. Overall, this study provides insights into the complex interactions between PPN, trophic groups, soil properties, and urban ecosystem characteristics, contributing valuable knowledge for sustainable urban greenspace management.

Temporal monitoring of free-living nematode communities for evaluation of soil health in an arable crop rotation

There is a growing interest in finding reliable methods for monitoring soil health using bioindicators. Free-living nematodes are an ideal indicator group because of their rapid response to changes in soil conditions. This UK study aims to assess their efficacy as bioindicators using two field experiments. In Experiment-1, the treatments included Farmyard Manure, Green Manure consisting of a mix of Raphanus sativus and Vicia sp., and Standard Practice serving as the control receiving N-fertiliser only. The same treatments, except Farmyard Manure, were compared in Experiment-2, which was on a sloping site with a different textured soil. Soil samples were collected twice during each crop season, in Spring and Autumn, for Experiment-1, and only in Autumn for Experiment-2. Ecological indices that categorise nematodes by feeding preference using morphological differences and life strategies (i.e. functional guilds) were calculated. Indices were compared with the abundance of nematode trophic groups to evaluate their use as soil indicators for understanding crop management practices and their legacy effects. Results showed that identification to trophic groups alone was not a sufficiently sensitive approach for assessing changes in the selected management practices. The variations among trophic groups and treatments within the same sampling period were significantly different for bacterivores, fungivores, predators, omnivores, and herbivores. These differences did not always cooccur within the same sampling period, with bacterivores and plant-parasites of economic importance showing greater responses. The food web analyses, calculated by applying the Enrichment Index and Structure Index, and Plant Parasite Index, provided a more sensitive indicator and allowed more effective diachronic monitoring. While using the composition of trophic groups appears to be an attractive solution, their application is best linked to quantifying short-term changes in soil condition and were not as well suited to longer-term soil health monitoring.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

Grazing weakens the linkages between plants and soil biotic communities in the alpine grassland

Livestock grazing alters the diversity and composition of plants and soil biota in grassland ecosystems. However, whether and how grazing affects plant-soil biota interactions are limited. Here, we performed a field investigation on the Tibetan grasslands to determine the relationships between plant community properties (biomass, diversity and richness) and soil biota (abundance, diversity and composition of bacteria, fungi and nematodes) in the long-term yak grazing and ungrazed plots, and responses of plant-soil biota linkages to grazing in alpine meadows and alpine swampy meadows were compared. The results found that grazing did not cause significant changes in plant community properties but increased the soil water content. Further, grazing weakened plant-soil microbes/nematode relationships in alpine meadows. The bacterial and fungal abundances were correlated with plant belowground biomass and Simpson index in the ungrazed plots of alpine meadows, while the correlation was not significant under grazing. Bacterial composition was correlated with plant richness only in the ungrazed meadows. Plant-soil nematode linkages were more sensitive to grazing than plant-microbes linkages. Grazing decoupled the relationships between the abundances of nematode trophic groups and plant aboveground biomass, richness and Simpson index in alpine meadows, while the decoupling phenomenon is less evident in alpine swampy meadows. The SEM results indicate that grazing altered the plant above- and belowground biomass to affect the soil nematode community, while influenced soil microbes only through alterations of plant belowground biomass. The findings highlight the importance of grazing in influencing the interactions between aboveground plant communities and soil biological communities in Tibetan grasslands.

Nematodes as bioindicators of soil health in different land uses in the São Francisco River Valley, Brazil

Summary Brazilian Caatinga is one of the most diverse, seasonally dry, tropical forests of the world and is threatened by strong land use pressure and poor protection. One way of understanding changes in the soil conditions caused by anthropogenic activities is using the nematode assemblages as potential bioindicators. This study analysed changes in nematode communities in three different types of land use (natural forest-CA, natural area with accumulation of salts-SS, and agricultural growing areas, such as cover crops-CC for cattle and fruit trees-IC) in the Caatinga, in the sub-median region of the São Francisco River Valley (SFRV), Pernambuco, northeastern Brazil. We recorded a total of 63 262 nematode individuals, representing 42 genera, belonging to 23 families. Nematode abundance, diversity and maturity indices were highest in the CC and lowest in the SS. Among the nematode trophic groups, bacterivores, omnivores + predators and plant parasites were significantly affected by type of land use. Different soil properties were related to the differences in taxonomic composition among the natural and agricultural areas, accounting for 26.6% of the total variation. In general, our results indicate that soil salinisation and desertification in the natural areas, as well as soils subjected to cover crops and fruit tree production, significantly influenced the composition of nematode communities in the São Francisco River Valley.

Effects of Silver, Gold, and Platinum Nanoparticles on Selected Nematode Trophic Groups

Abstract As trophic organisms, nematodes play an essential role in the soil environment: they mineralize nutrients into plant-available forms, are a food source for other soil organisms, and feed on pathogenic organisms and plant pests, therefore regulating populations of soil microorganisms. The plant-parasitic nematodes are important pests of crops. Nanoparticles (NP) are increasingly used in agriculture and other production sectors. They are present in the soil, not necessarily in trace amounts, and can affect various soil organisms, including nematodes. In this article, the effects of silver (Ag), gold (Au), and platinum (Pt) nanoparticles on the mortality and reproduction activity of selected nematode species from two trophic groups: entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and Steinernema feltiae) and plant parasitic nematodes (PPN) (Xiphinema diversicaudatum, Ditylenchus dipsaci, Heterodera schachtii) were studied under laboratory conditions. All nanoparticles decreased the nematode population to an extent depending on the nematode species, nanoparticle type, and exposure time. AgNP had the greatest nematicidal effect, except for AuNP, which reduced the population of H. schachtii the most. The greatest sensitivity to AgNP was observed in X. diversicaudatum (100% mortality), D. dipsaci (90% mortality), and 37 to 13% mortality in other species. Effect of AuNP and PtNP on entomopathogenic nematodes was comparable to the control, not treated with nanoparticles. AuNP and PtNP similarly influenced nematode mortality. However, the effect of nanoparticles on new generations of entomopathogenic nematodes developing in host larvae Galleria mellonella was inconclusive. All nanoparticles decreased the number of larvae of S. feltiae and increased the number of H. bacteriophora migrating outside the cadavers compared to the control.

Leguminous crop restores the carbon flow attenuation from nitrogen loading within soil nematode food web in a Camellia oleifera plantation

Excessive nitrogen (N) loading poses a substantial risk to soil biodiversity and disrupts carbon (C) flows within the soil food web. Intercropping with legumes is often considered a sustainable way to maintain soil N availability and mitigate the associated detrimental effects. However, it remains unclear whether and how legume crops restore energetic attenuation caused by N loading within the soil food web. Here, we conducted a two-year field experiment using randomized block design in a subtropic Camellia oleifera plantation with high wet N deposition. We examined the effects of applying N fertilizers at normal or half levels (168 or 84 kg N ha−1yr−1) and intercropping legumes (Arachis hypogaea or Cassia tora) on the soil nematode food web. We observed that N fertilization suppressed the majority of nematode trophic groups, weakened the stability of food web structure, and diminished the C flows across the bacterial and fungal energy channels. Conversely, intercropping with legumes (particularly with C. tora) bolstered the densities of bacterivore and fungivore nematodes. This enhancement facilitated interactions within the soil micro-food web, and subsequently augmented the C flows within their respective channels. Model predictions suggested that the detrimental effects of N fertilizers on the nematode food web are primarily linked to decreased soil pH resulting from soil N accumulation. Notably, higher soil organic C was found to mitigate these effects. Furthermore, N-enriched legume substrates played a beneficial role in stimulating soil microbial activities and facilitating C flows through bottom-up control. Our findings emphasize the positive impacts of legume crops on mitigating soil biodiversity loss and restoring energetic attenuation within soil food web under N-saturated soil conditions. These findings provide valuable insights for agroforestry management practices aimed at sustaining soil health and ecosystem resilience.

The bioindicator role of phytonematode groups in the assessment of the state of transformation of secondary forest ecosystems

The methodology for assessing the state of terrestrial ecosystems using diagnostic properties of soil microfauna remains underestimated in contemporary Ukrainian science. We have analyzed a significant amount of foreign and domestic literature to demonstrate the importance of this aspect in the overview article concerning the monitoring of natural ecosystems. Based on our own research results, we have shown the outcomes that can be achieved by utilizing the bioindicative properties of a specific group of organisms, such as phytonematodes. The fundamental principles and methodologies that should be applied, including using the functional characteristics of phytonematode complexes, have also been described. For evaluating the state of ecosystems, the most valuable information pertains to organisms that are widely distributed over a significant territory, have high population density, play a significant role in ecosystem functioning, and can rapidly respond to environmental changes. Organisms fitting these criteria can be considered bioindicators. This group of organisms is sensitive to natural or anthropogenic environmental transformations and can respond to them by altering their population density, distribution, or specific characteristics. Therefore, the use of soil animals from specific taxonomic groups as bioindicators has a long-standing tradition. Groups of soil invertebrates are integral structural components of natural ecosystems, together providing them with stable development and resilience. Assessment of the functional role of soil fauna in the ecosystem involves establishing the structural-functional organization of different groups of soil invertebrates, which differ both morphologically and functionally in the ecosystem and their impact on soil-forming processes. The use of soil nematodes as bioindicators is promising for evaluating the sanitary condition of forest ecosystems based on the indicator of energy utilization by trophic groups of nematodes, as well as for bioindication of soil quality based on the relative ratio of persisters and colonizers. The zoological method of soil diagnostics was established as a separate scientific direction thanks to the works of M.S. Gilyarov. This method is based on the presence of certain species of invertebrates in the soil and the analysis of the structure of their communities. Later, it found practical application in the research of forest ecosystems. Therefore, nematodes are an effective model group for the indirect assessment of the zoocenosis’ state.

Effects of protected areas on soil nematode communities in forests of the North of Portugal

AbstractNature conservation policy is mainly concerned with aboveground terrestrial species and soil biodiversity has been largely ignored, resulting in a lack of information about the conservation status of most soil organisms and about the effects that nature conservation policies have on soil systems. Forests in Northern Portugal are characterized by a remarkable diversity of ecosystems and provide habitat for an enormous diversity of living organisms. This study aims to investigate whether and to what extent protected areas and forest typology (native vs. exotic) affect soil nematode biodiversity and functions in forest ecosystems. We studied soil nematode communities, which have been widely used for their bioindicator value, to: (i) assess differences in soil biodiversity and functions between protected and non-protected areas, and between native and exotic forest types; and (ii) infer how protected areas deal with pressures and drivers of soil biodiversity and functions. We showed that current work done by nature conservation in Northern Portugal is producing some significant effects on the soil system, showing a larger Structure and Omnivore footprints and greater abundance of fungivorous and omnivorous nematodes in protected areas. Furthermore, native forest areas are better suited to ensure soil biodiversity and ecological functioning and should have a greater importance in nature conservation measures. Soil organic carbon, apparent density, soil moisture, and deciduous forest cover mainly influenced soil functional biodiversity with higher nematode trophic groups being positively associated with soil organic carbon and moisture and negatively associated with apparent density. Finally, conservation efforts targeted at the protection of native forests need to better consider effects on soil biodiversity and function, to provide an integrated protection of both aboveground and belowground components.

Network analysis of nematodes with soil microbes on cool-season golf courses

Nematodes are an active part of complex soil food webs on golf courses, with some members promoting plant growth, while others are pathogenic or neutralists. The artificial, sand-based rootzone mixtures of putting greens, the most intensely managed areas of a golf course, are especially prone to nematode damage. A better understanding of the interactions of nematodes with soil microbes is key to developing improved turf management strategies. The coupling of amplicon sequencing with network analysis provides a way of better understanding which taxa may be closely associated, allowing hypothesis generation to learn more about how nematodes interact with soil microbes. We performed weighted gene correlation network analyses on bacteria, fungi, and bacteria with nematodes and fungi with nematodes collected from the soil of roughs, fairways, and putting greens of three cool-season turfgrass golf courses on Martha's Vineyard, Massachusetts. Rhodoplanes spp. were found in many bacterial modules, suggesting they may be a common species. Many nematodes formed positive correlations with known nematode antagonizing microbes. Among five nematode trophic groups, the carnivorous nematodes were most connected to both bacteria and fungi, suggesting these nematodes may have previously overlooked interactions with soil microbes. Consensus eigengene networks were highly preserved among management areas on each golf course for both the bacteria and fungi, showing conserved meta-modules despite management differences. The results of this work provide deeper insight into a unique, complex perennial ecosystem on golf courses that could be leveraged for future investigations on these relationships and eventually to improved turf health and disease management in the future. To our knowledge this study is the first use of network analysis to explore the relationship of the turf-associated bacterial and fungal phytobiomes with nematodes.

Soil conditions under great cormorant and grey heron colonies in a wetland: Effect on soil nematode abundance and trophic structure

This study aimed to investigate how great cormorants and grey herons affect the density and trophic diversity of soil nematodes under breeding colonies located in Stawy Raszyńskie Nature Reserve (central Poland). Soil samples from the colonies were compared to control samples from adjacent areas unaffected by birds. Samples were taken at each site (two colonies and two relevant control sites) to a depth of 20 cm, and the soil cores were split into topsoil (0–10 cm) and subsoil (10–20 cm). A modified Baermann method was used to extract nematodes from the soil. The soil under nests supported more abundant nematode communities, but with a lower trophic diversity compared to the control sites. The cormorants had a greater impact on nematodes than the herons. We found that the external nitrogen input, the higher organic matter content and abundance of ammonifying bacteria, as well as the lower soil pH under the colonies than in the control sites, affected the nematode trophic groups in different ways. Compared to the control sites, there were significantly more bacterivorous nematodes but fewer herbivorous nematodes under the colonies. No predatory nematodes were found under the bird colonies and, in the case of the cormorant colony, no omnivorous nematodes. No significant differences in the abundance of fungivorous nematodes between the impact and the control plots were noticed. The results indicate that allochthonous input under bird colonies promotes microbial activity and the most opportunistic trophic group of nematodes, which may at least temporarily enhance decomposition and mineralisation processes and consequently affect nutrient cycling in the wetland soil.

Nitrogen-fixing tree species rather than tree species diversity shape soil nematode communities in subtropical plantations

Positive relationships between tree species diversity and soil communities are reported in many studies. However, the effects of tree species richness and nitrogen (N)-fixing tree species on soil fauna communities are not yet fully understood. Here, we conducted a field experiment to investigate changes in soil nematode communities under a gradient of tree species richness (e.g., 1, 2, 4 and 6 tree species) with N-fixing tree species (absence or presence). We found that N-fixing tree species strongly affected soil nematode trophic groups, and significantly increased the abundance of omnivore-predators and structure index via promoting more trophic links and multi-trophic interactions, leading to a more stable and complex soil food web. In the presence of N-fixing tree species, tree species richness significantly increased the abundance and relative abundance of fungivores and the channel index, with the shift in soil energy channel through increased the C/N ratio of leaf litter. In contrast, tree species richness detrimentally affected the abundance of plant parasites due to the decline of leaf litter N content under the presence of N-fixing tree species. The results revealed that the bottom-up effects of N-fixing tree species on soil nematode community structure were crucial drivers in shaping nematode communities in subtropical plantations. Our study suggests that N-fixing tree species is more important than tree species richness to regulate soil nematode community structure and soil energy channel, and therefore, should be preferentially considered in multispecies forest plantations.

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

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

Effects of long-term fertilization with contemporary Danish human urine, composted household waste and sewage sludge on soil nematode abundance and community structure

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health.Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure.At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding.Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2–5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments.We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

Contrasting Responses of Soil Nematode Trophic Groups to Long-Term Nitrogen Addition

Contrasting Responses of Soil Nematode Trophic Groups to Long-Term Nitrogen Addition

Soil Nematode Trophic Group Composition and Influence on Growth of Amaranthus palmeri and Parthenium hysterophorus

Weeds have a significant impact on agricultural systems. They not only cause a loss in crop yield by competing with them for resources, but they can also serve hosts for several pests and parasties such as plant parasitic nematodes casusing additional crop loss. The aim of this study was to analyze plant-nematode feedback in two major weeds, Amaranthus palmeri S Watson and Parthenium hysterophorus L. First, a field survey was conducted to determine the rhizosphere nematode trophic groups associated with these two plants in the summer of 2020 and 2021. Then a 6-week greenhouse study was conducted where the two weed species were treated with nematode communities extracted from their respective rhizospheres. Results from this study show that both weeds harbored a high number of herbivore nematodes, followed by fungivore and bacterivore nematodes. Total number of these nematodes were highly influenced by total sol carbon, pH and salinity. Under greenhouse conditions, the nematode treatment did not have any impact on the growth of P. hysterophorus but A. palmeri plants treated with nematodes had significantly higher above ground biomass. In conclusion, plant-nematode relationships are complex. Given the extent of direct damage caused by these weeds and plant parasitic nematodes in global crop production, the weeds-nematode feedback warrants further detailed studies.

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.

The impacts of rock pulverization on soil quality and functional soil nematode and respiration properties of boreal lands converted from forest to agricultural use

Rock pulverization is recommended when converting boreal forests to agricultural land use to facilitate tillage operations. Resulting rock dust incorporation might alter physical, chemical, and biological properties of soils. We assessed soil nematode trophic group abundances and indices, basal and burst respiration, and phosphorus extractability after land use conversion (LUC) and recent pulverization (<1 year) on three soil types in eastern Newfoundland, Canada. Nine treatments representing varied pulverization statuses (managed pulverized, managed unpulverized, natural) were nested in soil type (Podzol, Luvisol, and Organic). Conversion to agriculture impacted soil quality more than the recent rock pulverization. Nonetheless, nematode indices (fungivore/bacterivore, fungivore/fungivore+bacterivore, fungivore + bacterivore/herbivore) suggested no significant functional differences with either LUC or pulverization. Soil organic matter (SOM) and pH were substantial direct and indirect drivers of nematode community composition and soil respiration, mainly by altering availability of aluminium and iron. The functional parameters diverged between Organic and mineral soils. For all soils, most respiration parameters were significantly related to SOM, pH, available iron and aluminium. For nematodes, significant relationships were identified in the Organic soil: bacterivores and fungivores abundances were inversely related to SOM, and bacterivore abundance was positively related to pH. While for the mineral soils, citric acid extracted more phosphorus than the Mehlich-3 or water methods, Mehlich-3 was most effective for the Organic soil. Pulverization did not affect phosphorus extractability. The distinct relationships between soil quality properties and functional parameters between mineral and Organic soils are of interest for further investigations into the concepts of soil quality and soil health.

Forest dieback switches the relationships between microfaunal bacterivore guilds and soil nutrients

The current increase of severe droughts associated with climate change is one of the main causes of the observed dieback in Mediterranean holm-oak (Quercus Ilex subs ballota) forests. Effects of forest dieback in soils are greatly variable and depend on a number of local factors, but generally include increased soil organic C due to increased litter inputs, alterations in soil nutrient contents, changes in the nitrogen cycle, and detrimental effects on soil microbial communities and their functioning. There is little evidence, however, of the effects of forest dieback on soil faunal diversity. In this study, we assessed the effects of holm-oak dieback and induced nutrient shifts on soil microfaunal communities and their relationships with soil properties and functioning. We studied 13 Holm oak forest sites affected by tree dieback in the Iberian Peninsula and assessed the relationship between soil properties, microbial functions, and nematode diversity under healthy, defoliated, and dead trees at each site. We found that nematode abundances were variable and significantly patchy across sites. Bacterivore and herbivore nematodes were the most abundant nematode trophic groups. Nematode abundance increased with increasing levels of soil C only if soil P was available, indicating that nematode abundances might be P-limited in these semi-arid systems. Bacterivore nematodes were especially affected by tree death, since tree dieback switched the relationship between bacterivore abundance and soil nutrient contents. Opportunistic bacterivores, able to exploit ephemeral bacterial resources blooming after soil organic enrichment, seemed more resilient to tree death than generalist ones, while fungivores did not clearly respond to forest dieback. We found complex and unexpected effects of tree dieback on soil microfaunal communities, which should receive further attention.