Search

Soil nematode communities can provide valuable information about the structure and functions of soil food webs, and are sensitive to agricultural practices, including short-term straw incorporation. However, currently, such effects under long-term straw incorporation conditions at different fertility levels are largely unknown. Thus, we conducted a 13-year ongoing experiment to evaluate the effects of long-term straw incorporation on the structure and functions of the soil food web in low and high fertility soils through analyzing its effects on nematode communities, food web indices and metabolic footprints. Four treatments were included: straw removal (–S) under non-fertilized (–NPK) or fertilized (+NPK) conditions; and straw incorporation (+S) under –NPK or +NPK conditions. Soil samples from a 0–20 cm depth layer were collected when wheat and rice were harvested. Compared with straw removal, straw incorporation increased the abundances of total nematodes, bacterivores, plant-parasites and omnivores-predators, as well the relative abundances of omnivores-predators with increases of 73.06, 89.29, 95.31, 238.98, and 114.61% in –NPK soils and 16.23, 2.23, 19.01, 141.38, and 90.23% in +NPK soils, respectively. Regardless of sampling times and fertilization effects, straw incorporation increased the diversity and community stability of nematodes, as indicated by the Shannon-Weaver diversity index and maturity index. Enrichment and structure index did not show significant responses to straw incorporation, but a slight increase was observed in the structure index. The analysis of nematode metabolic footprints showed that straw incorporation increased the plant-parasite footprint and structure footprint by 97.27 and 305.39% in –NPK soils and by 11.29 and 149.56% in +NPK soils, but did not significantly influence enrichment, bacterivore and fungivore footprints. In conclusion, long-term straw incorporation, particularly under a low fertility level, favored the soil nematodes and regulated the soil food web mainly via a top-down effect.

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

It has been well documented that organic amendment affects soil nematode community structure. However, little is known about the effect of organic amendment amount on soil nematodes. To assess the effect of the amount of organic amendments on soil nematode community structure and metabolic activity, the community composition, abundance, and metabolic footprints of soil nematodes were determined in a long-term field experiment with various amounts of organic amendment in Northeast China. Fertilization treatments included an unfertilized control (CK), chemical fertilizer without manure amendment (OM0), manure applied at 7.5 Mg ha–1 plus chemical fertilizer (OM1), and manure applied at 22.5 Mg ha–1 plus chemical fertilizer (OM2). A total of 46 nematode genera were found. Treatments with the largest amount of organic amendment had the smallest number of plant parasite genera (5), but a largest number of dominant genera (7). Soil nematodes, bacterivores, and fungivores were the most abundant in OM2, followed by OM1, and the lowest in OM0 and CK. Organic amendment increased the enrichment index (EI), and the large amount of organic amendment increased the metabolic footprints of bacterivore (Baf) and fungivore (Fuf) and enrichment footprint (Ef). The relationships between Baf (or Fuf) and the increases in soil organic carbon (ΔSOC) and total nitrogen (ΔTN) were stronger than those of bacterivore (or fungivore) abundance with ΔSOC and ΔTN, except for the relationship between bacterivore abundance and ΔSOC. The EI and Ef were positively correlated with ΔSOC and ΔTN. These findings suggest that the amount of organic amendment affects soil nematode activity and function at entry levels in soil food web, and that metabolic footprints of soil nematodes may be better indicators than their abundances in assessing their relationships with soil nutrients.

Meloidogyne incognita causes significant damage to many different crops. Previous studies showed that Streptomyces rubrogriseus HDZ-9-47 is a promising biocontrol agent. Combining it with biofumigation improved its efficacy against M. incognita. In the present study, the reason for the improved efficacy of the combination was investigated by analyzing its impact on both the soil microbial and the nematode communities in the field. The results showed that the combined application reduced root galls by 41% and its control efficacy was greater than each treatment alone. Cultivation-based analyses showed that the combination treatment affected the soil microbial community. Actinomycetes and bacterial densities were negatively correlated with the root knot score. In contrast, the fungal densities were positively correlated with the root knot score. Denaturing gradient gel electrophoresis (DGGE) results showed that the combination of S. rubrogriseus HDZ-9-47 and biofumigation enriched beneficial microbes and reduced certain soil-borne fungal phytopathogens, thereby enhancing the efficacies of both S. rubrogriseus HDZ-9-47 and biofumigation against M. incognita. And HDZ-9-47 could colonize in soil. The total abundance of nematode and plant parasites, the ratio of soil fungivore nematode to fungivore plus bacterivore nematode, and the nematode diversity indices all decreased with the combination treatment. Overall, the results of this study demonstrate that combined application of HDZ-9-47 with biofumigation was a useful and effective approach to suppress M. incognita by manipulating soil microbial communities in field.

While aboveground impacts of invasive plants are well documented, their influence on soil food webs remains less understood. Previous research has revealed that bottom-up forces are widespread in soil food webs of woodlands. Thus, an invasive plant that negatively impacts the base of the food web will likely decrease primary consumers as well as their predators. We examined how a North American plant invader, garlic mustard (Alliaria petiolata), affects arthropod primary (springtails and oribatid mites) and secondary (predaceous mites) consumers of the soil food web via changes to fungal resources. We measured the abundances of plants, soil fungi, fungivores, and predators in garlic mustard-invaded and uninvaded 1-m2 plots in five Midwestern USA woodlands. We then conducted a mesocosm (0.25-m2 plots) experiment to tease apart the direct and indirect effects of garlic mustard by manipulating plant identity (garlic mustard vs. native plant), soil history (invaded vs. uninvaded), and fungicide application (fungicide vs. no fungicide). Our first study revealed that plots without garlic mustard had 2.8 and 1.4 × more fungi and fungivores, respectively. Predator densities did not differ. Fungal composition and structural equation modeling (SEM) revealed the garlic mustard effects on fungivores were correlated with fungal declines. The mesocosm experiment confirmed that the impacts were indirect, as fungicide plots harbored similar fungivore densities, whereas fungivore densities differed according to plant identity and soil history in the fungicide-free plots. Our results reveal that by altering soil fungal abundance, an invasive plant can indirectly affect primary consumers in soil food webs, but this indirect effect does not influence predators.

Beta-1,3-glucanases are enzymes that hydrolyze beta-1,3-glucans, and they are essential for the metabolism of seaweed, plants and fungi. These enzymes also participate in the digestion of herbivore and fungivore animals. Because of the importance of these enzymes in insects, beta-1,3-glucanase inhibitors may be used for the development of new control strategies against agricultural pests and disease vectors. Beta-1,3-glucanase inhibitors have been described in the brown seaweed Laminaria cichorioides, but were never recorded in Brazilian seaweed species. We evaluated the presence of beta-1,3- glucanase inhibitors in samples of Padina gymnospora, Dictyota sp., Colpomenia sinuosa, and Lobophora sp., collected in Arraial d’Ajuda (Bahia). Ethanolic or buffer extracts were used in inhibition tests against the beta-1,3-glucanase of Trichoderma sp. Extracts in buffer showed no inhibition, but ethanolic extracts from all species showed different extents of inhibition. Samples from Dictyota sp. and P. gymnospora showed inhibitions above 75% (absolute ethanol) or 50% (ethanol 50%). In summary, extraction with absolute ethanol resulted in better inhibitions, and P. gymnospora showed the higher inhibitions. Brazilian seaweed may be good sources of beta-1,3-glucanase inhibitors for biochemical and physiological studies of these enzymes. Besides that, these molecules show potential for the development of new biotechnological tools for insect control.

Soil amendments with plant materials from Medicago species are widely acknowledged for a suppressive effect on plant-parasitic nematodes but their impact on beneficial components of soil nematofauna is still unknown. A study on potted tomato was carried out to investigate the short-time effects on the overall nematofauna of dry biomasses from six different Medicago species, i.e., M. sativa, M. heyniana, M. hybrida, M. lupulina, M. murex and M. truncatula, incorporated to natural soil at 10, 20, or 40 g kg&minus, 1 soil rates. All amendments resulted in a significant decrease of the total nematofauna biomass, whereas total abundance was significantly reduced only by M. heyniana, M. hybrida, and M. lupulina biomasses. Almost all the Medicago amendments significantly reduced the relative abundance of plant-parasites and root fungal feeders. All amendments significantly increased the abundance of bacterivores, whereas fungivores significantly increased only in soil amended with M. heyniana, M. lupulina and M. sativa plant materials. Mesorhabditis and Rhabditis were the most abundant genera of bacterivores, whereas Aphelenchoides and Aphelenchus prevailed among the fungivores. Predators were poorly influenced by all the tested Medicago biomasses, whereas the abundance of omnivores was negatively affected by M. heyniana and M. lupulina. Values of the Maturity Index and Sum Maturity Index were reduced by treatments with M. heyniana, M. hybrida, M. lupulina and M. sativa plant materials, whereas most of the tested amendments decreased values of the Channel Index while increasing those of the Enrichment Index. Enrichment and bacterivore footprints raised following soil addition with Medicago biomasses, whereas composite and fungivore footprints were significantly reduced. According to their overall positive effects on soil nematofauna, amendments with Medicago plant materials or their formulated derivatives could represent an additional tool for a sustainable management of plant-parasitic nematodes.

Aspergillus nidulans produces sterigmatocystin, a secondary metabolite mycotoxin, for the protection of its reproductive structures. Previous studies on grazing behavior of fungivore arthropods, regulation of sexual development, and secondary metabolite biosynthesis have revealed the association of sterigmatocystin biosynthesis with sexual reproduction, but the spatial distribution of sterigmatocystin producing hyphae within the colony has never been investigated. In this work, we aimed to locate the site of sterigmatocystin production within the colony by employing a yCFP reporter system. We demonstrated that the stcO promoter is active only in vegetative hyphae that surround groups of hülle cells and the activity decreases and eventually ceases as the distance between the hypha and the hülle cells increases. This phenomenon indicates that the vegetative mycelium might consist of morphologically uniform, but functionally different hyphae.

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.

The Muyong forest, an indigenous secondary forest in Banaue, Ifugao, Philippines, plays a crucial role in the Muyong–Payoh system, a continuum of secondary forest and rice terrace, of the Banaue rice terraces by providing water and nutrients to the rice plants in the Payoh terraces. In recent decades, the planting of introduced tree species in the Muyong forest has threatened the sustainable provision of ecosystem services such as water balance and nutrient cycling. To further understand nutrient cycling in the Muyong–Payoh systems, this study was conducted in Poitan, Banaue, Ifugao to gather preliminary baseline data on floral diversity, leaf litterfall rate, leaf litter decomposition rate, and diversity and succession of arthropods in decomposing leaf litter in a Muyong forest. Vegetation analysis was done by identifying and describing the trees growing inside the five 10 m × 10 m quadrat sampling plots. Monthly leaf litter fall was collected in 1 m × 1 m litter traps, and the dry weight was determined after oven-drying at 65 °C for 48 h. Leaf litter decomposition experiment was established by laying out 12 nylon mesh bags containing fresh leaf litter in each of the four sites on the forest floor and one bag was retrieved every month to determine the change in dry weight of the leaf litter. Six bulk soil samples were collected from the Muyong forest floor and analyzed for organic matter, pH, available P and exchangeable K. Fresh leaf litter samples were analyzed for total N, P and K contents. Arthropods in the collected decomposing leaf litter were extracted using Berlese funnel and later identified up to families level using arthropod taxonomic key. The diversity of plants in the Muyong forest includes thirty-eight tree species belonging to 19 families dominated by indigenous tree species. Results showed that the monthly leaf litter fall was higher during the dry months of March to May and lower during the wet months. The estimated total leaf litter fall in Muyong forest was comparable to published litter fall from tropical secondary forests. The N, P and K contents of fresh leaf litter range from 1.0 to 1.2, 0.11 and 0.40%, respectively. The first month of decomposition has the fastest rate while the decomposition rate during the next 4 months ranged from 0.125 to 0.251. Complete decomposition or mass lost in the leaf litter in the Muyong forest took place within 5 months. The soil arthropods identified in the decomposing leaf litter were composed of 13 orders and 28 families. Majority of the collected arthropods were insects while other species including mites, spiders, millipedes and sowbugs were also present. Detrivore and fungivore Families were found to be dominant in the decomposing leaf litter. Moreover, the composition and succession of arthropod decomposer community varied in the three sampling methods and with the changing quality of the litter material as decomposition progressed. The wide diversity and succession of leaf litter decomposers consisting of detritivores, predators, fungivore and herbivore coupled with abundant rainfall and warm temperature are the two main factors that contribute to the fast rate of leaf litter decomposition and nutrient turn over in the Muyong forest. Thus, the Muyong forest can sustain the productivity of rice planted in the adjoining downstream Payoh terraces. Hence, the conservation and management of the Muyong forest is critical in maintaining the ecological functions of the Muyong–Payoh continuum.

A mysterious female phorid fly, known for many years to be associated with fungal sporophores ("mushrooms") is identified as Megaselia marquezi Hartop et al. 2015. Male and female flies were collected emerging from the fungus Psathyrella candolleana (Fr.) Maire, and females were observed swarming over the sporophores.

Both top-down (grazing) and bottom-up (resource availability) forces can determine the strength of priority effects, or the effects of species arrival history on the structure and function of ecological communities, but their combined influences remain unresolved. To test for such influences, we assembled experimental communities of wood-decomposing fungi using a factorial manipulation of fungivore (Folsomia candida) presence, nitrogen availability, and fungal assembly history. We found interactive effects of all three factors on fungal species composition and wood decomposition 1 year after the fungi were introduced. The strength of priority effects on community structure was affected primarily by nitrogen availability, whereas the strength of priority effects on decomposition rate was interactively regulated by nitrogen and fungivores. These results demonstrate that top-down and bottom-up forces jointly determine how strongly assembly history affects community structure and function.

Nematode community indices have been broadly used to assess and monitor soil conditions. Most studies focused on agricultural or other disturbed soils and were usually applied at local-field scale. In this study, we focused on the variation of nematode community indices across fine (among microhabitats) and landscape level scales with the aim to identify indices or combinations of indices that are efficient at distinguishing microhabitats and landscape properties. We calculated nematode community indices in five microhabitats to account for variability in basal resources/organic input (soils, mosses on soil, mosses on rocks, as well as mosses on the lower and the upper part of trees trunks). The different microhabitats were located across the landscape in sites that differed in vegetation cover type (forested and non-forested), altitude (low, high) and aspect (North, East, South). Results of our models showed that microhabitat type could be predicted by all indices except the Maturity Index (MI) and the Fungivore/Bacterivore (F/B) ratio. Soil could be distinguished from mosses by the higher Plant Parasitic Index (PPI) and Enrichment Index (EI) and the lower Channel Index (CI). The different moss microhabitats could be distinguished from each other by the Summed Maturity Index (SMI) the Structure Index (SI) as well as the Basal Index (BI). At the larger scale, among landscape properties, variation by altitude was more pronounced compared to vegetation cover type and aspect. Samples originated from low altitudes were characterized by higher EI and F/B ratio. Indices for predicting landscape properties of the site a sample was taken from were more efficient when analyzed separately within each microhabitat. The interaction of the BI and the F/B ratio was able to predict vegetation cover type in soils while the same holds for BI, SI and their interaction in mosses. We conclude that nematode community structure is strongly shaped by variation in basal resources in the different microhabitats and microhabitats can be well predicted by most nematode community indices. Landscape properties constitute gradients of exposure of basal resources to ambient conditions, which affects basal resource transformations and availability. This variation across the landscape can also be predicted by some nematode community indices.

Three experiments were conducted to find out the feeding type and age structure of nematodes in different soil habitats; to know the efficiency of different extraction techniques of nematodes and to observe the hatching behavior of Meloidogyne juvenile in a Baermann device. Bacterivore, Omnivore, Predator, Fungivore and Plant Parasitic nematodes were recorded in the soil of flower, vegetable, moss, grass, and corn and compost habitats. Bacterivore was the highest feeder (67.5%) in the soil habitats. In comparison of nematode extraction methods, Seinhorst method extracted more cysts (188), but less juvenile (34) and eggs (18) from cysts than stirring (145, 87 and 50, respectively) while AZC was found superior (936) over Cobb method (204) in extracting nematodes. The AZC method also extracted huge juvenile number from roots which was higher than Baermann funnel method. In Baermann funnel, juvenile hatched more in favorable condition than unfavorable condition which led to an increasing and decreasing pattern of hatching.

In the Midwestern United States, corn–soybean rotation is an essential agricultural practice, but relatively little is known about the impact of different corn–soybean cropping sequences on soil ecology. A long-term research site in Waseca, Minnesota was established in 1982 to study corn–soybean rotation. At the site, various corn–soybean crop sequences can be compared each year including corn and soybean in 1 to 5 years of monoculture and continuous monoculture of each crop. Additionally, granular nematicides (terbufos or aldicarb) have been applied to half of each plot since 2010 to minimize nematode populations, particularly plant-parasitic nematodes, across crop sequences. The nematode community, a sensitive indicator of changes in soil ecology, was assessed at this site to determine the impact of corn–soybean crop sequences and nematicide application on the soil ecosystem. Nematicide application was effective against target nematodes, herbivores, but also impacted non-target nematodes and thus soil ecology. Nematicide application decreased fungivore and bacterivore populations, diversity, and maturity; but significantly increased enrichment compared to no nematicide application. The nematode community and thus soil ecology was significantly different in corn compared to soybean cropping systems and changed most during initial years after switching crops. Cropping systems in corn supported significantly greater fungivore populations, fungal decomposition pathways, more diversity, and a more mature ecosystem compared to soybean systems. Soybean systems supported significantly greater bacterivore populations and a more disturbed, enriched ecosystem. These differences between corn and soybean systems demonstrate that each crop has a distinct impact on the soil ecosystem.

Variation in grazing intensity determines the way in which mycelial growth and physiology is influenced by invertebrate fungivores. Recently, low-intensity grazing by facultative mesofaunal fungivores, small dipteran larvae and collembola, was found to enhance the activity of fungal defensive secondary metabolism. Here, we ask whether higher intensity grazing by macrofaunal fungivores induces a different fungal response. To test this, we quantified changes in the expression of two anti-fungivore chemical defence marker genes, laeA and aflR, in the ascomycete Aspergillus nidulans exposed to grazing pressure exerted by individuals of the isopod Oniscus asellus. Compared to no and low-intensity grazing pressure, higher intensity grazing significantly reduced the transcript levels of these genes. This finding suggests a negative relationship between grazing pressure intensity and the capacity of a saprotrophic fungus to resist fungivory.

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

Wood-pastures are grazed systems resulting from a long-term use of natural woodlands by humans. These social-ecological systems, covering vast areas of Europe and other temperate regions, have both high biodiversity and economic values, so many are classified as High Nature Value Farmlands. However, in some regions a loss of spatial heterogeneity threatens this natural value. We investigated the potential contribution of tiny shrubby patches to increase spatial heterogeneity and functional diversity in wood-pasture landscapes. Specifically, we compared functional composition (Community Weighted Means) and functional diversity (Functional Dispersion and Functional Evenness) of assemblages of plants, beetles and lichens in those patches (252–3000 m2) and in the wood-pasture matrix. We found that shrubby patches and matrix harbour species assemblages with very distinct functional compositions in all studied taxonomic groups. Evergreen, woody, broad-leafed and fleshy-fruited are better represented in the patches. In beetles, the main differences were a greater prevalence of small-sized and fungivore species in the patches. Shrubby patches also mostly harboured lichens with fruticose- and foliose-broad growth forms, a greater humidity preference, and lower eutrophication tolerance. Moreover, the two indexes used to quantify functional diversity (Functional Dispersion and Functional Evenness) show that, overall, diversity is greater in patches than in the matrix; in patches Functional Dispersion is statistically higher for plants, and Evenness is statistically higher for beetles and lichen. These differences are all consistent with the very distinct ecological conditions in the matrix and patches. The greater overall functional diversity of shrubby patches, and the major differences in functional composition between patches and matrix, observed for all taxa, indicate that these patches greatly enhance the functional diversity of species assemblages in wood-pasture landscapes. Consequently, preserving and promoting tiny shrubby patches is a potentially valuable low-cost management tool to increase biodiversity and improve ecosystem functioning in wood-pasture landscapes., Doctoral and post-doctoral grants: (PD/BD/106044/2015), (SFRH/BPD/88056/2012), (SFRH/BPD/118635/2016), and (SFRH/BPD/101983/2014).

Meloidogyne arenaria (peanut root-knot nematode (PRKN)) is a major pest of peanut. Nematicide application is an important tool for the management of PRKN. Nematicides with minimal effects on free-living nematodes are desired. Fluopyram nematicide is recently introduced in peanut production and needs to be assessed. The objective of this research is to evaluate fluopyram and the established nematicides 1,3-Dichloropropene (1,3-D) and aldicarb for efficacy at managing PRKN and impacts on free-living nematodes. Nematicides were evaluated in field studies in 2017 and 2018 conducted in commercial peanut fields. All nematicides increased peanut yield in 2017 compared with untreated control, but did not affect soil PRKN abundances or root galling. In 2018, PRKN infestation was too low to accurately assess PRKN management by nematicides. Aldicarb and fluopyram did not affect any free-living nematode trophic group or individual genera. In contrast, 1,3-D decreased total fungivore and fungivore genera Filenchus and Aphelenchus soil abundances, but did not affect bacterivores, omnivore-predators, total herbivores, or any other nematode genera. In summary, 1,3-D, but not aldicarb or fluopyram, had non-target effects on free-living nematodes, particularly fungivores. Meloidogyne arenaria (peanut root-knot nematode (PRKN)) is a major pest of peanut. Nematicide application is an important tool for the management of PRKN. Nematicides with minimal effects on free-living nematodes are desired. Fluopyram nematicide is recently introduced in peanut production and needs to be assessed. The objective of this research is to evaluate fluopyram and the established nematicides 1,3-Dichloropropene (1,3-D) and aldicarb for efficacy at managing PRKN and impacts on free-living nematodes. Nematicides were evaluated in field studies in 2017 and 2018 conducted in commercial peanut fields. All nematicides increased peanut yield in 2017 compared with untreated control, but did not affect soil PRKN abundances or root galling. In 2018, PRKN infestation was too low to accurately assess PRKN management by nematicides. Aldicarb and fluopyram did not affect any free-living nematode trophic group or individual genera. In contrast, 1,3-D decreased total fungivore and fungivore genera Filenchus and Aphelenchus soil abundances, but did not affect bacterivores, omnivore-predators, total herbivores, or any other nematode genera. In summary, 1,3-D, but not aldicarb or fluopyram, had non-target effects on free-living nematodes, particularly fungivores.

Root litter decomposition is a major component of carbon (C) cycling in grasslands, where it provides energy and nutrients for soil microbes and fauna. This is especially important in grasslands where fire is common and removes aboveground litter accumulation. In this study, we investigated whether fire affects root decomposition and C flow through the belowground food web. In a greenhouse experiment, we applied 13C-enriched big bluestem (Andropogon gerardii) root litter to intact tallgrass prairie soil cores collected from annually burned (AB) and infrequently burned (IB) treatments at the Konza Prairie Long Term Ecological Research (LTER) site. Incorporation of 13C into microbial phospholipid fatty acids and nematode trophic groups was measured on six occasions during a 180-day decomposition study to determine how C was translocated through the soil food web. Results showed significantly different soil communities between treatments and higher microbial abundance for IB. Root decomposition occurred rapidly and was significantly greater for AB. Microbes and their nematode consumers immediately assimilated root litter C in both treatments. Root litter C was preferentially incorporated in a few groups of microbes and nematodes, but depended on burn treatment: fungi, Gram-negative bacteria, Gram-positive bacteria, and fungivore nematodes for AB and only omnivore nematodes for IB. The overall microbial pool of root-litter-derived C significantly increased over time but was not significantly different between burn treatments. The nematode pool of root-litter-derived C also significantly increased over time, and was significantly higher for the AB treatment at 35 and 90 days after litter addition. In conclusion, the C flow from root litter to microbes to nematodes is not only measurable but also significant, indicating that higher nematode trophic levels are critical components of C flow during root decomposition, which, in turn, is significantly affected by fire. Not only does fire affect the soil community and root decomposition, but the lower microbial abundance, greater root turnover, and the increased incorporation of root litter C by microbes and nematodes for AB suggests that annual burning increases root-litter-derived C flow through the soil food web of the tallgrass prairie.