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Growing evidence suggests that conservation agricultural practices, like no-till and cover crops, help protect annual crops from insect pests by supporting populations of resident arthropod predators. While adoption of conservation practices is growing, most field crop producers are also using more insecticides, including neonicotinoid seed coatings, as insurance against early-season insect pests. This tactic may disrupt benefits associated with conservation practices by reducing arthropods that contribute to biological control. We investigated the interaction between preventive pest management (PPM) and the conservation practice of cover cropping. We also investigated an alternative pest management approach, integrated pest management (IPM), which responds to insect pest risk, rather than using insecticides prophylactically. In a 3-year corn (Zea mays mays L.)-soy (Glycine max L.) rotation, we measured the response of invertebrate pests and predators to PPM and IPM with and without a cover crop. Using any insecticide provided some small reduction to plant damage in soy, but no yield benefit. In corn, vegetative cover early in the season was key to reducing pest density and damage, likely by increasing the abundance of arthropod predators. Further, PPM in year 1 decreased predation compared to a no-pest-management control. Contrary to our expectation, the IPM strategy, which required just one insecticide application, was more disruptive to the predator community than PPM, likely because the applied pyrethroid was more acutely toxic to a wider range of arthropods than neonicotinoids. Promoting early-season cover was more effective at reducing pest density and damage than either intervention-based strategy. Our results suggest that the best pest management outcomes may occur when biological control is encouraged by planting cover crops and avoiding broad-spectrum insecticides as much as possible. As part of a conservation-based approach to farming, cover crops can promote natural-enemy populations that can help provide biological effective control of insect pest populations.

This white paper presents a series of perspectives on current and future phytobiome management, discussed at the Wild and Tamed Phytobiomes Symposium in University Park, PA, U.S.A., in June 2018. To enhance plant productivity and health, and to translate lab- and greenhouse-based phytobiome research to field applications, the academic community and end-users need to address a variety of scientific, practical, and social challenges. Prior discussion of phytobiomes has focused heavily on plant-associated bacterial and fungal assemblages, but the phytobiomes concept covers all factors that influence plant function. Here we discuss various management considerations, including abiotic conditions (e.g., soil and nutrient applications), microorganisms (e.g., bacterial and fungal assemblages, bacterial and fungal inoculants, and viruses), macroorganisms (e.g., arthropods and plant genetics), and societal factors (e.g., communication approaches and technology diffusion). An important near-term goal for this field should be to estimate the potential relative contribution of different components of the phytobiome to plant health, as well as the potential and risk of modifying each in the near future.

Entomopathogenic nematodes (EPNs) have potential as an alternate means of controlling soil-dwelling pests in settings such as school athletic fields, where use of chemical pesticides is often restricted or prohibited. Athletic fields are also unique among turfgrass systems, as their distinct pattern of foot traffic can result in compaction and other soil properties varying across different areas of the field, potentially causing variability in EPN performance even within a single field, as many abiotic and biotic soil properties are known to influence EPN efficacy. We tested the efficacy of the EPNs Steinernema feltiae and Heterorhabditis bacteriophora against third-instar grubs of the Japanese beetle Popillia japonica in high-traffic and low-traffic areas of two soccer fields in New York State, one grown atop loam soil and the other atop loamy sand. Efficacy was low in the loam soil but modest for both species in the loamy sand, though the only significant increase over controls occurred in S. feltiae-inoculated plots within low traffic areas in 2016. Non-metric multidimensional scaling revealed positive associations between efficacy of both EPN species and soil sand content, suggesting that sandy soils are most optimal for curative applications against turfgrass pests. Soil biotic factors, such as microarthropod abundance, were not found to have an effect on EPNs. These results will aid turfgrass managers by improving knowledge of the conditions required for effective use of EPNs.

Neonicotinoids from insecticidal seed coatings can contaminate soil in treated fields and adjacent areas, posing a potential risk to nontarget organisms and ecological function. To determine if cover crops can mitigate neonicotinoid contamination in treated and adjacent areas, we measured neonicotinoid concentrations for three years in no-till corn-soybean rotations, planted with or without neonicotinoid seed coatings, and with or without small grain cover crops. Although neonicotinoids were detected in cover crops, high early season dissipation provided little opportunity for winter-planted cover crops to absorb significant neonicotinoid residues; small grain cover crops failed to mitigated neonicotinoid contamination in either treated or untreated plots. As the majority of neonicotinoids from seed coatings dissipated shortly after planting, residues did not accumulate in soil, but persisted at concentrations below 5 ppb. Persistent residues could be attributed to historic neonicotinoid use and recent, nearby neonicotinoid use. Tracking neonicotinoid concentrations over time revealed a large amount of local interplot movement of neonicotinoids; in untreated plots, contamination was higher when plots were less isolated from treated plots.

Onion maggot, Delia antiqua (Meigen), is a serious pest of onion Allium cepa L. in northern temperate regions. Over the last decade, D. antiqua has been managed principally using a pesticide seed treatment package containing the reduced-risk insecticide spinosad. While spinosad protects onion seedlings from D. antiqua, very little is known regarding how protection occurs. The main objectives of this study were to assess susceptibility of 1- and 2-wk-old larvae to spinosad through two different modes of exposure: ingestion and contact, and to evaluate larval feeding behavior in choice and no-choice tests with onion seedlings grown from treated and untreated seeds. Results showed that spinosad was more than twice as lethal to 1-wk than 2-wk-old larvae when it was ingested, but was equally toxic to both larval ages via contact exposure. In choice assays, larvae preferred feeding on untreated plants; however, without a choice, larvae fed and survived equally well on untreated and treated plants, suggesting that spinosad may have a deterrent effect. In a field study, levels of spinosad within young onion plants and in the soil around roots were monitored in addition to the cumulative number of onion seedlings killed by D. antiqua. Spinosad was detected in the soil and in both aboveground and belowground plant tissue, indicating that spinosad translocates into foliage, but declines in plant tissue and soil as plant mortality from D. antiqua feeding increases. Together, these results provide valuable insight into how spinosad protects onion seedlings and reveal key areas in need of further investigation.

Slow and consistent nutrient release by organic fertilizers can improve plant nutrient balance and defenses, leading to herbivore avoidance of organically managed crops in favor of conventional crops with weaker defenses. We propose that this relative attraction to conventional plants, coupled with the use of genetically modified, insecticidal crops (Bt), has created an unintentional attract-and-kill system. We sought to determine whether Bt and non-Bt corn Zea mays L. plants grown in soil collected from five paired organic and conventional fields differed in attractiveness to European corn borer [Ostrinia nubilalis (Hübner)] moths, by conducting ovipositional choice and flight tunnel assays. We then examined the mechanisms driving the observed differences in attraction by comparing soil nutrient profiles, soil microbial activity, plant nutrition, and plant volatile profiles. Finally, we assessed whether European corn borer abundance near corn fields differed based on soil management. European corn borer preferred plants grown in conventional soil but did not discriminate between Bt and non-Bt corn. Organic management and more alkaline soil were associated with an increased soil magnesium:potassium ratio, which increased plant magnesium, and were linked to reduced European corn borer oviposition. There was an inconsistent trend for higher European corn borer moth activity near conventional fields. Our results extend the mineral balance hypothesis describing conventional plant preference by showing that it can also improve attraction to plants with genetically inserted toxins. Unintentional attract (to conventional) and (Bt) kill is a plausible scenario for pest declines in response to Bt corn adoption, but this effect may be obscured by variation in other management practices and landscape characteristics.

Plant response to water stress can be modified by the rhizosphere microbial community, but the range of responses across plant genotypes is unclear. We imposed drought conditions on 116 Festuca arundinacea (tall fescue) accessions using a rainout shelter for 46 days, followed by irrigation, to stimulate drought recovery in 24 days. We hypothesized that prolonged water deficit results in a range of phenotypic diversity (i.e., green color index) across tall fescue genotypes that are associated with distinct microbial taxonomic and functional traits impacting plant drought tolerance. Microbial extracellular enzyme activities of chitinase and phenol oxidase (targeting chitin and lignin) increased in rhizospheres of the 20 most drought tolerant genotypes. Lower rates of fungal (dark septate) endophyte root infection were found in roots of the most drought tolerant genotypes. Bacterial 16S rRNA gene and fungal ITS sequencing showed shifts in microbial communities across water deficit conditions prior to drought, during drought, and at drought recovery, but was not patterned by drought tolerance levels of the plant host. The results suggest that taxonomic information from bacterial 16S rRNA gene and fungal ITS sequences provided little indication of microbial composition impacting drought tolerance of the host plant, but instead, microbial extracellular enzyme activities and root fungal infection results revealed patterned responses from drought.

Phenolic compounds perform various functions in soil ranging from microbial substrate to toxin and form the basis of several plant-mediated processes. The aim of this study was to investigate how phenolics commonly exuded by tree roots influence soil organic matter (SOM) decomposition and interact with other labile forms of carbon (C) abundant in root exudates. Therefore, we performed a 38-day incubation experiment and assessed whether phenolic compounds (benzoic acid, caffeic acid and catechin) facilitated or inhibited SOM decomposition in a glucose-amended forest soil. Changes in decomposition, substrate use, fungal and bacterial community composition, and microbial abundance and activity were measured over time using 13C-stable-isotope tracing, DNA-based molecular methods and enzyme assays. Our findings showed that phenolics inhibited microbial activity and abundance to varying degrees. Yet, benzoic acid was the only compound producing a substantial priming effect leading to a 21% increase in SOM decomposition, which was amplified in glucose-amended soils. This stimulation in microbial activity was associated with an increase in β-1,4-glucosidase activity and the bacterial genera Paraburkholderia and Caballeronia of the Burkholderiaceae family. Phenolics drove microbial community shifts in glucose-amended soils with negligible interactive effects. In conclusion, phenolic priming of SOM decomposition is associated with microbial community shifts and amplified in the presence of glucose. This evidence emphasizes the need for considering phenolics and interactions among root exudates as priming mechanisms in the rhizosphere and other soil environments where aromatics and phenolic compounds are abundant.

Belowground arthropod communities are diverse and our ability to characterize them remains logistically difficult and time consuming. Molecular metabarcoding techniques are routinely used to assess the diversity of both microbial and some ‘macrobial’ taxa across a range of environments, but the use of such techniques for characterizing soil arthropod diversity remains limited. Here we used three approaches to profile soil arthropod communities at the family level of resolution across 10 distinct sites via morphological identification, metabarcoding of DNA from the extracted arthropods, and metabarcoding directly from bulk soils. Although the three methods differed to some degree in their ability to detect some individual taxa, we found that all three methods yielded well-correlated site-level estimates of diversity (Spearman's ρ ≥ 0.63 with P

Root herbivory is a pervasive rhizosphere process but its role in regulating root inputs to soil and subsequent impact on soil organic matter has been largely overlooked. We present the first manipulative field study investigating the effects of root-feeding Japanese beetle larvae on soil organic matter cycling under tall fescue. Our results show that root-feeding larvae cause an increase of plant photosynthetic products in soil over a 7-month study period. However, soils exposed to root herbivores also exhibited a ~ 8% decrease in total soil carbon, along with a 13% increase in microbial biomass carbon, and a 16% increase in microbial biomass nitrogen. In addition, there was a marginally significant increase in microbial extracellular glucosidase and cellobiohydrolase activities and a decrease in oxidase activities. These findings highlight the potential of root herbivores to accelerate root inputs to soil and stimulate the decomposition of existing soil organic matter.

In this study, the utility of inoculative releases of local strains of Heterorhabditis bacteriophora and Steinernema feltiae isolated from northern New York (NY) State for managing soil-dwelling pests in sod (turfgrass production systems) was evaluated. The objectives of the project were to (a) quantify changes in biocontrol potential during the sod production process and (b) evaluate the potential for the nematodes to suppress populations of soil-dwelling turf pests following harvest and installation at a new site. A field study was conducted on four sod fields in central NY State on soils with varying texture and organic matter content, and a post-harvest sod installation study was performed in the greenhouse on a sandy loam soil. Nematode-induced mortality of Galleria mellonella was increased significantly one month following inoculation but differed between fields with different soil types, likely due to variation in soil organic matter content. In the following year, nematode persistence in s...

Entomopathogenic nematodes (EPNs) have potential to control many soil-dwelling insect pests but have been limited in their usage, partly by their unpredictable field performance. Numerous abiotic and biotic factors are thought to contribute to this poor predictability, but the exact impacts and relative importance of these factors in affecting EPN performance in the field are not well understood. Previous studies have highlighted diverse interactions between EPNs and other members of the soil community, from plants and fungi to arthropods and annelids. These interactions may help or hinder EPNs in a variety of ways. However, current research has yet to determine how many of these interactions influence EPN performance under field conditions, specifically, if they contribute to the variability limiting EPN efficacy and wide-scale adoption. Here we outline current knowledge of these interactions as well as challenges and avenues for future research, such as greater integration of EPN research with soil animal and rhizosphere ecology, that will better elucidate the potential, limitations, and proper use of EPNs in pest management.

Field crop growers in the United States have adopted prophylactic pest management strategies to control sporadic crop pests that are spatially and temporally difficult to predict. While evidence shows these preventative management practices, specifically pesticidal seed treatments, can be important in regions with predictable pest pressures, employing them ubiquitously in field crops across the northeastern U.S. can have variable returns on productivity. Further, prophylactics may also limit the potential of integrated pest management (IPM). A three-year field experiment (2017–2019) was conducted in a maize-soybean cropping system to compare the influence of a preventative pest management practice and a scouting-based IPM practice on biological control organisms. Aboveground predator densities were measured via pitfall trapping and predation temporal dynamics were assessed using a standard sentinel-bait assay at two time points per year. Belowground biological control potential was determined using a sentinel-bait bioassay to quantify the abundance of soil-borne entomopathogenic fungi (EPF). The variable responses of beneficial communities to pesticide inputs were strongly influenced by season and time of application, underscoring the importance of applying pesticides only when necessary. Compared with no pesticide use, pesticidal seed treatments and foliar sprays together in a maize-soybean production system suppressed total predator activity-density, spider activity-density, predation, and infection potential of soil-borne entomopathogenic fungi in one out of three years of the field study. In the third year, the activity-density of spiders increased across all fields in preventative plots that included seed treatments only. Overall, the use of pesticides did not improve crop yield in either maize or soybean. These findings highlight that the use of a prophylactic pesticide program may not always be necessary for maximum crop productivity and that this management approach can occasionally have unintended negative consequences on above- and belowground soil biota and the ecosystem services they provide.

Many factors directly and indirectly influence pest dynamics in cultivated crops and identifying the suite of factors associated with a pest’s population dynamics is an important component of pest management. Onion maggot, Delia antiqua (Meigen) (Diptera: Anthomyiidae), is a significant pest of onion in temperature regions worldwide. In the Great Lakes region of North America, D. antiqua is the most important early-season pest of onion and causes considerable damage by killing plants. Despite growers employing the same management and cultivation practices, plant damage by D. antiqua across the region is highly variable. The commonality of production and management suggests that other factors may be important in explaining the disparities in damage across the region, and previous studies have indicated that temperature and precipitation, soil organic matter, surrounding landscape composition, planting date, and plant size at peak fly activity are all important factors affecting D. antiqua. In a two-year study (2018–19), the aforementioned factors were monitored in commercial onion fields (2018: n = 15; 2019: n = 13) in central and western New York, USA. Fly activity was positively associated with plant damage in both years of the study. Onion fields surrounded primarily by forest rather than agricultural crops and those planted late rather than early in the season had higher levels of damage by D. antiqua. Plant damage also was negatively associated with soil temperature and positively associated with soil organic matter content, but these effects were context dependent and were only observed in the first year of the study. These results will be used to inform management decisions by growers and have important implications for the development of predictive models for D. antiqua infestations.

While the unintended effects of pesticide applications in agroecosystems have received much attention, the consequence of different pest management strategies for beneficial soil biota in managed grass ecosystems remains poorly documented. In this study, we investigated the responses of major soil biological traits to both the short- and long-term effects of pesticide inputs in golf turfgrass. Overall, golf course fairways receiving regular, high-rate pesticide inputs exhibited suppression in soil biological traits involved in litter decomposition/nutrient mineralization (decomposer arthropod abundance and acid phosphatase activity), and plant nutrient uptake/plant protection (mycorrhizal fungi). In contrast, most beneficial soil biota appeared to tolerate a low level of pesticide input. In a short-term manipulative experiment we observed that monthly applications of chlorothalonil and a single application of imidacloprid, both at a medium label rate, consistently suppressed decomposer microarthropods over a 4-month period. The imidacloprid application also reduced the total infection of mycorrhizae and dark septate endophytes in roots. These results suggest that the use of pesticides as a whole does not always result in negative impacts on soil biota, but rather that the pesticide effects vary among functional groups of soil biota and are contingent upon long-term patterns of pesticide input intensity, and short-term differences in active ingredient and application program (application rate and frequency). These findings highlight opportunities for optimizing management practices to achieve pest management goals without compromising soil ecosystem services.

Crop residues are potential biofuel feedstocks, but residue removal may reduce soil carbon (C). The inclusion of a cover crop in a corn bioenergy system could provide additional biomass, mitigating the negative effects of residue removal by adding to stable soil C pools. In a no-till continuous corn bioenergy system in the northern US Corn Belt, we used 13CO2 pulse labeling to trace plant C from a winter rye (Secale cereale) cover crop into different soil C pools for 2 years following rye cover crop termination. Corn stover left as residue (30% of total stover) contributed 66, corn roots 57, rye shoots 61, rye roots 50, and rye rhizodeposits 25 g C m−2 to soil. Five months following cover crop termination, belowground cover crop inputs were three times more likely to remain in soil C pools than were aboveground inputs, and much of the root-derived C was in mineral-associated soil fractions. After 2 years, both above- and belowground inputs had declined substantially, indicating that the majority of both root and shoot inputs are eventually mineralized. Our results underscore the importance of cover crop roots vs. shoots and the importance of cover crop rhizodeposition (33% of total belowground cover crop C inputs) as a source of soil C. However, the eventual loss of most cover crop C from these soils indicates that cover crops will likely need to be included every year in rotations to accumulate soil C.

Rising atmospheric CO2 concentration and global mean temperatures have stimulated interest in managing terrestrial systems to sequester more carbon and mitigate climate change. In a restored prairie experiment, we compared high diversity (HD, 25 species) with low diversity (LD, 6 species) prairies to investigate the effect of plant diversity on soil microbial communities and their residues with soil depth. We assayed lipid and amino sugar biomarkers for soil samples, taken after 9 years following the establishment of the prairie treatment, at 5 depth increment layers: 0–2 cm, 12–15 cm, 25–27 cm, 50–52 cm, and 98–100 cm. We found that the microbial biomass and residues decreased considerably with depth in both diversity treatments. Ordination analysis of lipid profiles indicated soil microbial communities were consistently distinct between the deeper and the upper layers, regardless of treatment, and also differed between the LD and HD treatments. Plant diversity effects on soil microbial communities strongly correlated with arbuscular mycorrhizal fungi (AMF), as indicated by the lipid marker 16:1ω5c. Soil microbial residues in deeper horizons were relatively more enriched in HD than LD treatments, suggesting that greater plant diversity might sustain higher soil carbon storage through relatively recalcitrant necromass inputs in the long term. Decreasing glucosamine/muramic acid (GluN/MurA) ratio in LD and increasing in HD with depth suggested that the new microbially-accumulated carbon was positively contributed by fungal-derived residues. Our results indicate that plant diversity drives soil microbial carbon sequestration through changes in AMF abundance in restored native tallgrass ecosystems. These findings have implications for understanding how the management of plant diversity can improve soil quality and sustainability in grasslands, and how efforts to conserve and restore diverse grasslands could mitigate greenhouse gas emissions.

The explicit representation of microbial communities in soil biogeochemical models is improving their projections, promoting new interdisciplinary research, and stimulating novel theoretical developments. However, microbes are the foundation of complicated soil food webs, with highly intricate and non-linear interactions among trophic groups regulating soil biogeochemical cycles. This food web includes fauna, which influence litter decomposition and the structure and activity of the microbial community. Given the early success of microbial-explicit models, should we also consider explicitly representing faunal activity and physiology in soil biogeochemistry models? Here we explore this question, arguing that the direct effects of fauna on litter decomposition are stronger than on soil organic matter dynamics, and that fauna can have strong indirect effects on soil biogeochemical cycles by influencing microbial population dynamics, but the direction and magnitude of these effects remains too unpredictable for models used to predict global biogeochemical patterns. Given glaring gaps in our understanding of fauna-microbe interactions and how these might play out along climatic and land use gradients, we believe it remains early to explicitly represent fauna in these global-scale models. However, their incorporation into models used for conceptual exploration of food-web interactions or into ecosystem-scale models using site-specific data could provide rich theoretical breakthroughs and provide a starting point for improving model projections across scales.

Soil neutral sugars are a significant component of labile soil organic carbon (SOC) and are derived from both plant and microbial biomass. While plants synthesize both pentose and hexose neutral sugars, microbes almost exclusively produce hexoses. Hexose to pentose ratios in soil thus potentially indicate the extent to which microbes process labile SOC. In this study, we used the ratio of galactose + mannose (G + M) to arabinose + xylose (A + X) to estimate the contribution of sugars derived from microbes and plants to SOC in forest ecosystems. We explored how forest type and climatic zone influence soil neutral sugar profiles by studying coniferous and broadleaf forests located in temperate and subtropical regions in China. At each site, neutral sugars from organic (O) and top-layer mineral (A) soil horizons, as well as from freshly-fallen leaf litter, were measured. Total SOC and soil neutral sugar contents were lower in the subtropical region than in the temperate region, with lower levels in the A horizon than in the O horizon. In both climatic zones, litter (G + M)/(A + X) ratios were higher in coniferous forests (1.2 ± 0.3) than in broadleaf forests (0.4 ± 0.1). Differences in the (G + M)/(A + X) ratios between forest types (coniferous and broadleaf) persisted in the O horizon (1.4 ± 0.2 > 0.9 ± 0.0) and in the A horizon (1.8 ± 0.1 > 1.3 ± 0.0). Across climate zones and forest types, ratios increased from litter over the O horizon to the A horizon. Contrary to our expectations, climate zone did not affect soil (G + M)/(A + X) ratios. Our findings emphasize the important contribution of microbial biomass to labile SOC pools while revealing that soil neutral sugar profiles do not respond to climatic zone drivers as expected.

Despite decades of research, our understanding of the importance of invertebrates for soil biogeochemical processes remains incomplete. This is especially true when considering soil invertebrate effects mediated through their interactions with soil microbes. The aim of this study was to elucidate how soil macroinvertebrates affect soil microbial community composition and function within the root zone of a managed grass system. We conducted a 2-year field mesocosm study in which soil macroinvertebrate communities were manipulated through size-based exclusion and tracked changes in microbial community composition, diversity, biomass and activity to quantify macroinvertebrate-driven effects on microbial communities and their functions within the rhizosphere. The presence of soil macroinvertebrates created distinct microbial communities and altered both microbial biomass and function. Soil macroinvertebrates increased bacterial diversity and fungal biomass, as well as increased phenol oxidase and glucosidase activities, which are important in the degradation of organic matter. Macroinvertebrates also caused distinct shifts in the relative abundance of different bacterial phyla. Our findings indicate that within the rhizosphere, macroinvertebrates have a stimulatory effect on microbial communities and processes, possibly due to low-intensity microbial grazing or through the dispersal of microbial cells and spores by mobile invertebrates. Our results suggest that macroinvertebrate activity can be an important control on microbially-mediated processes in the rhizosphere such as nitrogen mineralization and soil organic matter formation.

Roots play an important role in the formation and turnover of soil organic matter (SOM). Biological processes in the rhizosphere have the capacity to regulate the input of root materials to soil and the fate of root-derived carbon (C) in soil. While some aspects of rhizosphere ecology have received considerable research attention, one potentially important biotic driver, root herbivory, has been largely overlooked. In this study, we first review the literature on root herbivory, revealing that belowground herbivores can have substantial effects on the quality, quantity, and timing of belowground plant inputs to soil. Next, we introduce a conceptual framework in which root herbivory presents a distinct conduit that transfers C from living plants (the “green” world) to soil (the “brown” world). We also argue that direct and indirect interactions between root herbivores and the rhizosphere microbiome and other soil fauna can have significant impacts on soil microbial activities and soil C cycling. Finally, we outline key questions and topics for future research that incorporate belowground plant-herbivore interactions into soil biogeochemistry in an effort to improve our understanding of C flow in the rhizosphere and sharpen future predictions of soil C storage under changing environments.

The ecological processes that influence biogeographical patterns of microorganisms are actively debated. To investigate how such patterns emerge during ecosystem succession, we examined the biogeochemical drivers of bacterial community assembly in soils over two environmentally distinct, recently deglaciated chronosequences separated by a distance of more than 1300 km. Our results show that despite different geographic, climatic, and soil chemical and physical characteristics at the two sites, soil bacterial community structure and decomposer function converged during plant succession. In a comparative analysis, we found that microbial communities in early succession soils were compositionally distinct from a diverse group of mature forest soils, but that the differences between successional soils and mature soils decreased from early to late stages of succession. Overall differences in bacterial community composition between sites were explained by soil pH. However, within-site successional patterns – leading to community convergence across sites at the latest stage of succession – were explained by alternate factors such as soil organic carbon and soil organic matter chemistry, which were correlated to bacterial community structure across both glacial and mature forest soils.

Red imported fire ants, Solenopsis invicta, are generalist predators that can have major impacts on foliar arthropod communities in agricultural systems; however, their effects as predators at the soil surface have not been adequately characterized. We examined the contribution of fire ants to predation at the soil surface and in cotton foliage at two sites and over the course of two field seasons in Georgia, using egg masses of the beet armyworm, Spodoptera exigua. To assess interactions between fire ants and other arthropod species, we also measured the densities of edaphic predators and honeydew-producing hemipterans at both sites. The sites occurred in different growing regions (Piedmont and Coastal Plain), and allowed us to characterize the importance of fire ants as predators under different climatic and soil conditions. Fire ant suppression decreased egg predation at both field sites, and predation by fire ants at the soil surface was equal to if not greater than that in cotton foliage. However, the impact of fire ants on predation varied between sites, likely due to differences in climate and the composition and activity of the extant arthropod communities. Our study also indicates that fire ant suppression is associated with decreases in the density of honeydew-producing insects, and increasing abundance of whiteflies on the plants coincided with a decrease in egg predation at the soil surface. This finding suggests the mutualism between ants and whiteflies may lead to a shift in predation intensity from edaphic towards plant-based food webs.

While there has been long-term interest in identifying agricultural practices which promote soil ecological services, there remains little consensus on how practices such as low-input and organic impact soil microbial communities and their functions. In order to improve understanding of the response of soil microbial communities to shifts in agricultural management programs, a two year field study was conducted on large-scale conventional, low-input and organic fields associate with the Kellogg Biological Station, Long Term Ecological Research site near Kalamazoo, MI. Because large commercial agricultural fields typically exhibit diverse topography, plots were established in all fields at unique landscape positions to explore interactions between management and topographical position. Over the course of two growing seasons, differences in microbial biomass, extracellular enzyme production and carbon and nitrogen mineralization were quantified at different topographical positions (summits, slopes, and depressions) in each of the three agricultural management systems. Alone, management practices had little to no impact on soil microbial traits, however, significant management by landscape position and management by time interactions were observed for extracellular enzymes. Acid phosphatase activity on hill slopes was 35–52% greater in low input systems than in conventional and organic management systems. Similarly, spring amino peptidase activity was roughly 100% higher in low input than in organic systems. Landscape position also had substantial effects on both microbial biomass and enzyme activities. Topographical depressions exhibited significantly higher activities of β-N-acetylglucosaminadase, β-glucosidase, phenol oxidase and greater microbial biomass than summits and slopes (26%, 30%, 36%, and 55%, respectively). Similarly, peroxidase activity was approximately 38% greater in depressions and on summits than on hill slopes. Differences in microbial traits among positions were also negatively correlated with soil bulk density and sand content and positively correlated with clay, silt, carbon, nitrogen and moisture content. Our study stresses the importance of accounting for topographical heterogeneity when assessing the impact of management practices on belowground ecological function. Further, while management practices alone had little effect on soil microbial biomass and function, our study demonstrates that low input management programs may be beneficial for retaining microbial resources and thus promoting microbial activity on erosion-prone hill slopes.

Soil invertebrates, especially larger macroinvertebrates, move soil, fragment organic matter and change resource accessibility for soil microorganisms. Macroinvertebrates also affect the formation and turnover of aggregates, which are important controls of soil organic matter dynamics because they physically protect organic matter from degradation and influence many belowground processes ranging from microbial activity to nutrient sorption and water flow. We still lack a complete understanding of how different soil invertebrate functional groups affect the incorporation of root derived carbon and nitrogen into belowground pools. We assessed the effects of macroinvertebrates on soil aggregate abundance and composition and quantified the fate of organic matter derived from roots using a two-year macroinvertebrate exclusion-based field mesocosm study coupled with stable isotope labeling in a turfgrass lawn ecosystem. We hypothesized that macroinvertebrates change soil aggregates dynamics by increasing macroaggregates and decreasing microaggregates and enhancing the incorporation of root-derived organic matter into macroaggregates. We found that within the turfgrass root zone, macroinvertebrates increased the proportion of macroaggregates and decreased free microaggregates. In addition, macroinvertebrates increased carbon and nitrogen incorporation into macroaggregates, microaggregates and coarse particulate organic matter, detected via isotopic enrichment of those soil fractions. We found that macroinvertebrates affect the fate of recently fixed root- and rhizodeposit-derived organic matter in a turfgrass lawn ecosystem, and particularly its incorporation into soil aggregates, similar to findings in forest and agricultural systems.

Elucidating relationships between the soil food web, soil processes, and agroecosystem function is a critical step toward a more sustainable agriculture. Soil and crop management practices can alter these relationships, and their effects can persist even after imposing new management practices. In 2005, the Cornell Organic Grain Cropping Systems Experiment was established in central New York. Four cropping systems that varied in fertilizer inputs, tillage practices, and weed control were compared: High Fertility, Low Fertility, Enhanced Weed Management, Reduced Tillage. Two crop rotation entry points were included in the experiment. In June 2017, the entire experimental site (plots and alleyways) was plowed and seeded with sorghum sudangrass [Sorghum bicolor (L.) Moench x S. sudanense (Piper) Stapf] as part of a uniformity trial to assess legacy effects of past management practices. Prior to initiating the uniformity trial, soil samples were collected and analyzed for soil health indicators. Soil samples were also collected to assess soil invertebrate abundance and community structure 34 and 70 days after planting. Sorghum sudangrass and weed biomass were sampled at the end of the uniformity trial in September 2017. Legacy effects of past management that were observed during the uniformity trial were associated with differences in nutrient inputs and soil disturbance, as well as the preceding crop. The High Fertility system had greater soil phosphorus than the Low Fertility system, and in one of the two crop rotation entry points, soil aggregate stability and soil respiration were greater in the Reduced Tillage system compared to the Enhanced Weed Management system. The Enhanced Weed Management cropping system also had a soil invertebrate community characterized by more disturbance tolerant taxa. Weed biomass varied by crop rotation entry point, but not cropping system. Sorghum sudangrass biomass was greater in the Reduced Tillage system than the Low Fertility system, and the entry point that had greater weed biomass also had greater sorghum sudangrass biomass. Piecewise structural equation modelling (SEM) was used to test relationships between response variables and showed that soil phosphorus, soil aggregate stability, and soil respiration explained variation in abundance of some invertebrates, and that aggregate stability, soil respiration, soil moisture, weed biomass, and a select group of invertebrates affected sorghum sudangrass biomass production. Overall our findings show that soil invertebrates can mediate the relationship between soil health indicators and crop productivity, and provide support for including direct measurements of soil invertebrates in soil health assessments.

As vertebrate carrion decomposes, there is a release of nutrient-rich fluids into the underlying soil, which can impact associated biological community structure and function. How these changes alter soil biogeochemical cycles is relatively unknown and may prove useful in the identification of carrion decomposition islands that have long lasting, focal ecological effects. This study investigated the spatial (0, 1, and 5 m) and temporal (3–732 days) dynamics of human cadaver decomposition on soil bacterial and arthropod community structure and microbial function. We observed strong evidence of a predictable response to cadaver decomposition that varies over space for soil bacterial and arthropod community structure, carbon (C) mineralization and microbial substrate utilization patterns. In the presence of a cadaver (i.e., 0 m samples), the relative abundance of Bacteroidetes and Firmicutes was greater, while the relative abundance of Acidobacteria, Chloroflexi, Gemmatimonadetes, and Verrucomicrobia was lower when compared to samples at 1 and 5 m. Micro-arthropods were more abundant (15 to 17-fold) in soils collected at 0 m compared to either 1 or 5 m, but overall, micro-arthropod community composition was unrelated to either bacterial community composition or function. Bacterial community structure and microbial function also exhibited temporal relationships, whereas arthropod community structure did not. Cumulative precipitation was more effective in predicting temporal variations in bacterial abundance and microbial activity than accumulated degree days. In the presence of the cadaver (i.e., 0 m samples), the relative abundance of Actinobacteria increased significantly with cumulative precipitation. Furthermore, soil bacterial communities and C mineralization were sensitive to the introduction of human cadavers as they diverged from baseline levels and did not recover completely in approximately 2 years. These data are valuable for understanding ecosystem function surrounding carrion decomposition islands and can be applicable to environmental bio-monitoring and forensic sciences.

Applying manure to row-crop systems can reduce inorganic fertilizer dependence and enhance soil biology and crop yields. However, it remains unclear whether low manure application rates or semi-annual application rates can provide these benefits. Our objective was to evaluate the effects of variable rates and timing of manure application on soil microbial processes and crop performance in a potato-corn cropping system. We tested the effects of five manure application rates of 0.0 (Ctrl), 1.54 (T1), 3.08 (T2), 6.16 (T3), and 12.32 (T4) Mg C ha−1 on potato productivity, severity of common scab, and soil biological processes. The highest rates of manure application consistently increased crop yields but even the lowest rate (1.54 Mg C ha−1) increased potato and corn yields. The severity of common scab incidence on daughter tubers was reduced by treatments T2, T3, and T4 in year one but was unaffected by any treatment in year two. Yield increases and reduced common scab severity were related to increased activities of C- and N-acquiring enzymes and microbial biomass C and N. Manure application rates of

The terrestrial biosphere sequesters up to a third of annual anthropogenic carbon dioxide emis- sions, offsetting a substantial portion of greenhouse gas forcing of the climate system. Although a number of factors are responsible for this terrestrial carbon sink, atmospheric nitrogen deposition contributes by enhancing tree productivity and promoting carbon storage in tree biomass. Forest soils also represent an important, but understudied carbon sink. Here, we examine the contribution of trees versus soil to total ecosystem carbon storage in a temperate forest and investigate the mechanisms by which soils accumulate carbon in response to two decades of elevated nitrogen inputs. We find that nitrogen-induced soil carbon accumulation is of equal or greater magnitude to carbon stored in trees, with the degree of response being dependent on stand type (hardwood versus pine) and level of N addition. Nitrogen enrichment resulted in a shift in organic matter chemistry and the microbial community such that unfertilized soils had a higher relative abundance of fungi and lipid, phenolic, and N-bearing compounds; whereas, N-amended plots were associated with reduced fungal biomass and activity and higher rates of lignin accumulation. We conclude that soil carbon accumulation in response to N enrichment was largely due to a suppression of organic matter decomposition rather than enhanced carbon inputs to soil via litter fall and root production.

Solid and aqueous phase Al species are recognized to affect organic matter (OM) stabilization in forest soils. However, little is known about the dynamics of formation, composition and dissolution of organo-Al hydroxide complexes in microbiallyactive soil systems, where plant litter is subject to microbial decomposition in close proximity to mineral weathering reactions. We incubated gibbsite–quartz mineral mixtures in the presence of forest floor material inoculated with a native microbial consortium for periods of 5, 60 and 154 days. At each time step, samples were density separated into light ( 2.0 g cm 3 ) fractions. The light fraction was mainly comprised of particulate organic matter, while the intermediate and heavy density fractions contained moderate and large amounts of Al-minerals, respectively. Multi-method interrogation of the fractions indicated the intermediate and heavy fractions differed both in mineral structure and organic compound composition. X-ray diffraction analysis and SEM/EDS of the mineral component of the intermediate fractions indicated some alteration of the original gibbsite structure into less crystalline Al hydroxide and possibly proto-imogolite species, whereas alteration of the gibbsite structure was not evident in the heavy fraction. DRIFT, Py–GC/MS and STXM/NEXAFS results all showed that intermediate fractions were composed mostly of lignin-derived compounds, phenolics, and polysaccharides. Heavy fraction organics were dominated by polysaccharides, and were enriched in proteins, N-bearing compounds, and lipids. The source of organics appeared to differ between the intermediate and heavy fractions. Heavy fractions were enriched in 13 C with lower C/N ratios relative to intermediate fractions, suggesting a microbial origin. The observed differential fractionation of organics among hydroxy-Al mineral types suggests that microbial activity superimposed with abiotic mineral-surface-mediated fractionation leads to strong density differentiation of organo-mineral complex composition even over the short time scales probed in these incubation experiments. The data highlight the strong interdependency of mineral transformation, microbial community activity, and organic matter stabilization during biodegradation. Published by Elsevier Ltd.

a b s t r a c t Litter decomposition dynamics are influenced by soil nutrient status, yet the specific effects of soil nitro- gen (N) on litter decomposition in agricultural systems are not well understood. We explored litter decomposition and related soil organic matter dynamics in no-till, corn-based Midwestern U.S. cropping systems receiving 0, 134, and 291 kg N ha "1 y "1 . We found that total soil carbon (C) and N, light fraction organic matter, and permanganate oxidizable C were similar among treatments, but N fertilization at rates of 134 and 291 kg N ha "1 y "1 reduced potentially mineralizable C by as much as 37% and 58%, respectively, compared to the unfertilized treatment. Litter mass remaining after one year of field decomposition was greater with wheat litter (37%) than with corn litter (23%), but was not influenced by N fertilizer rate. In litter, N fertilization led to increases in the activities of two hydrolase enzymes involved in simple carbohydrate metabolism (!-d-cellobiohydrolase and !-1,4-glucosidase) and periodic increases in one related to N metabolism (!-1,4-N-acetylglucosaminidase), but had no effects on enzymes regulating the breakdown of aromatic compounds (phenol oxidase), or on enzymes measured in the soil. N fertilization also decreased arthropod densities in decomposing litter. We found contrasting effects of N fertilizer on processes regulating decomposition, but altogether our results were consistent with a limited or nil role for N fertilization in accelerating litter and soil C turnover, and thus do not support N fertilization as a contributor to depletion of C stocks in agricultural soils.

a b s t r a c t Shifts in the density and composition of arthropod communities can alter soil carbon and nitrogen cycling dynamics. However, it is uncertain how factors such as land use intensity, litter chemical composition, and climate structure arthropod communities during decomposition. During a 730-day study, we characterized temporal changes in litter-colonizing arthropod communities in two litter types (corn, Zea mays, and grass, predominantly Bromus inermis) decomposing in three ecosystems representing an agricultural management intensity gradient (conventionally tilled, no-till, and old field). Further, to assess the relationships between litter chemistry and arthropod communities, we also correlated changes in arthropod densities and community composition with shifts in litter molecular chemical characteristics. Arthropod densities were greater in decomposing grass litter than in corn litter for seven out of thirteen taxa collected and all but two taxa increased in litter with management intensity (spiders – negative, Entomobryidae – no response). In contrast, total arthropod densities in soil decreased with management intensity. Temporal variation in arthropod density and community composition in litter corresponded with precipitation events and changes in litter chemistry during decomposition. For example, collembolan, oribatid, and mesostigmatid mite densities were negatively correlated with the relative abundance of lignin and positively correlated with nitrogen containing compounds. Our study demonstrates that the influence of agricultural management intensity on arthropods in litter is strikingly different from that in bulk soil, and suggests that management intensity interacts with litter chemistry and climate over the course of decomposition to determine both the density and composition of arthropod communities inhabiting litter at the soil surface.

International audience; Increases in nitrogen (N) availability reduce decay rates of highly lignified plant litter. Although microbial responses to N addition are well documented, the chemical mechanisms that may give rise to this inhibitory effect remain unclear. Here, we ask: Why does increased N availability inhibit lignin decomposition? We hypothesized that either (1) decomposers degrade lignin to obtain N and stop producing lignin-degrading enzymes if mineral N is available, or (2) chemical reactions between lignin and mineral N decrease the quality of lignin and limit the ability of decomposers to break it down. In order to test these hypotheses, we tracked changes in carbon (C) mineralization, microbial biomass and enzyme activities, litter chemistry, and lignin monomer concentrations over a 478-day laboratory incubation of three maize genotypes differing in lignin quality and quantity (F(292)bm(3) (high lignin) < F-2 (medium lignin) < F(2)bm(1) (low lignin)). Maize stem internodes of each genotype were mixed with either an acidic or neutral pH sandy soil, both with and without added N. Nitrogen addition reduced C mineralization, microbial biomass, and lignin-degrading enzyme activities across most treatments. These dynamics may be due to suppressed fungal growth and reduced microbial acquisition of lignin-shielded proteins in soils receiving N. However, N addition alone did not significantly alter the quantity or quality of lignin monomers in any treatment. Our results suggest that abiotic interactions between N and phenolic compounds did not influence lignin chemistry, but mineral N does alter microbial enzyme and biomass dynamics, with potential longer-term effects on soil C dynamics.

Increasing evidence suggests that much of belowground, heterotrophic activity in terrestrial ecosystems is fueled by inputs of low molecular weight carbon compounds (LMWCCs). Root exudation (rhizodeposition) is a primary source of these inputs and will likely increase with rising atmospheric CO2. Yet the fates of these compounds belowground, as well as the environmental factors that influence them, are relatively unexplored. Using stable isotopes we track the fate of one dominant LMWCC, glucose, in three pasture and three forest sites located in South Carolina, USA. We resolve glucose-derived C in CO2, dissolved and soil organic C (DOC, SOC), microbial biomass, and microarthropods (Collembola, oribatid and mesostigmatid mites). After 72 h, the greatest proportions of glucose-C are in microbial biomass and SOC, followed by CO2, DOC, and microarthropods. Within this short time frame, glucose-C propagates through the foodweb to the highest trophic level, predatory mesostigmatid mites. The biomass of these predators is the only variable that explains the relative partitioning across sites of glucose-C, with higher biomass associated with reduced partitioning of glucose-C to respiration and hence greater retention belowground. Our results suggest that LMWCCs entering belowground systems may propagate through soil foodwebs rapidly, and that their partitioning belowground may potentially be determined by higher trophic levels.

Soil microorganisms are key drivers of terrestrial biogeochemical cycles, yet it is still unclear how variations in soil microbial community composition influence many ecosystem processes. We investigated how shifts in bacterial community composition and diversity resulting from differences in carbon (C) availability affect organic matter decomposition by conducting an in situ litter manipulation experiment in a tropical rain forest in Costa Rica. We used bar-coded pyrosequencing to characterize soil bacterial community composition in litter manipulation plots and performed a series of laboratory incubations to test the potential functional significance of community shifts on organic matter decomposition. Despite clear effects of the litter manipulation on soil bacterial community composition, the treatments had mixed effects on microbial community function. Distinct communities varied in their ability to decompose a wide range of C compounds, and functional differences were related to both the relative abundance of the two most abundant bacterial sub-phyla (Acidobacteria and Alphaproteobacteria) and to variations in bacterial alphadiversity. However, distinct communities did not differ in their ability to decompose native dissolved organic matter (DOM) substrates that varied in quality and quantity. Our results show that although resource-driven shifts in soil bacterial community composition have the potential to influence decomposition of specific C substrates, those differences may not translate to differences in DOM decomposition rates in situ. Taken together, our results suggest that soil bacterial communities may be either functionally dissimilar or equivalent during decomposition depending on the nature of the organic matter being decomposed.

It is widely accepted that microarthropods influence decomposition dynamics but we know relatively little about their effects on litter chemistry, extracellular enzyme activities, and other finer-scale decomposition processes. Further, few studies have investigated the role of individual microarthropod species in litter decomposition. The oribatid mite Scheloribates moestus Banks (Acari: Oribatida) is abundant in many U.S. ecosystems. We examined the potential effects of S. moestus on litter decomposition dynamics and chemical transformations, and whether these effects are influenced by variation in initial litter quality. We collected corn and oak litter from habitats with large populations of S. moestus and in microcosms with and without mites measured respiration rates, nitrogen availability, enzyme activities, and molecular-scale changes in litter chemistry. Mites stimulated extracellular enzyme activities, enhanced microbial respiration rates by 19% in corn litter and 17% in oak litter over 62 days, and increased water-extractable organic C and N. Mites decreased the relative abundance of polysaccharides in decomposing corn litter but had no effect on oak litter chemistry, suggesting that the effects of S. moestus on litter chemistry are constrained by initial litter quality. We also compared the chemistry of mite feces to unprocessed corn litter and found that feces had a higher relative abundance of polysaccharides and phenols and a lower relative abundance of lignin. Our study establishes that S. moestus substantially changes litter chemistry during decomposition, but specific effects vary with initial litter quality. These chemical transformations, coupled with other observed changes in decomposition rates and nutrient cycling, indicate that S. moestus could play a key role in soil C cycling dynamics.

Current conceptual models predict that changes in plant litter chemistry during decomposition are primarily regulated by both initial litter chemistry and the stage—or extent—of mass loss. Far less is known about how variations in decomposer community structure (e.g., resulting from different ecosystem management types) could influence litter chemistry during decomposition. Given the recent agricultural intensification occurring globally and the importance of litter chemistry in regulating soil organic matter storage, our objectives were to determine the potential effects of agricultural management on plant litter chemistry and decomposition rates, and to investigate possible links between ecosystem management, litter chemistry and decomposition, and decomposer community composition and activity. We measured decomposition rates, changes in litter chemistry, extracellular enzyme activity, microarthropod communities, and bacterial versus fungal relative abundance in replicated conventional-till, no-till, and old field agricultural sites for both corn and grass litter. After one growing season, litter decomposition under conventional-till was 20% greater than in old field communities. However, decomposition rates in no-till were not significantly different from those in old field or conventional-till sites. After decomposition, grass residue in both conventional- and no-till systems was enriched in total polysaccharides relative to initial litter, while grass litter decomposed in old fields was enriched in nitrogen-bearing compounds and lipids. These differences corresponded with differences in decomposer communities, which also exhibited strong responses to both litter and management type. Overall, our results indicate that agricultural intensification can increase litter decomposition rates, alter decomposer communities, and influence litter chemistry in ways that could have important and long-term effects on soil organic matter dynamics. We suggest that future efforts to more accurately predict soil carbon dynamics under different management regimes may need to explicitly consider how changes in litter chemistry during decomposition are influenced by the specific metabolic capabilities of the extant decomposer communities.

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