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The herbicide Roundup (and glyphosate, its active ingredient) is extensively used for weed control on a worldwide scale. It is absorbed after foliar application and quickly translocated inside the plant. In this study, we investigated the effects of Roundup speed, a commercial glyphosate formulation, on the structural composition (dominance of microbial groups, phospholipid fatty acid analysis - PLFA) and functional diversity (use of carbon sources, Multiple Substrate Induced Respiration - MSIR) of soil microorganisms. We specifically aimed at understanding the potential impact of biotic interactions on herbicide effects and included plants, earthworms, and endomycorrhizal fungi in the experimental setup. For this, we grew clover (Trifolium repens) in the greenhouse and added mycorrhizal inoculum (Glomus mosseae) and earthworms (Lumbricus terrestris) to the pots. Two weeks after foliar Roundup application and subsequent plant death, the pots were destructively sampled. The application resulted in a significant increase of microbial respiration (SIR) by approximately 30%. A multivariate analysis of the MSIR data exhibited small but significant differences between the microbial communities of treated and untreated pots, while no significant difference was apparent for the PLFA data. Bacterial PLFAs generally decreased following herbicide application, while mycorrhizal and fungal PLFAs were not affected. We did not find a consistent difference between the fatty acid markers of gram negative and gram positive bacteria. For all investigated parameters, there were highly significant differences between the upper (0-5 cm depth) and lower (5-10 cm) soil layers. The fact that rooting density differed by a factor of 3.5 between the two layers indicated that herbicide effects were especially pronounced in the clover rhizosphere and were likely due to changes in root exudate composition. We found significant, though very small, interactions between Roundup and other experimental factors (especially mycorrhizal inoculum)., (Copyright © 2019. Published by Elsevier Inc.)

Soil fungi play an essential role in the decomposition of plant-derived organic material entering soils. The quality and quantity of organic compounds vary seasonally as well as with soil depth. To elucidate how these resources affect fungal communities in an arable soil, a field experiment was set up with two plant species, maize and wheat. Resource availability was experimentally manipulated by maize litter input on one half of these maize and wheat plots after harvest in autumn. Fungal biomass was determined by ergosterol quantification, and community structure was investigated by fungal automated ribosomal intergenic spacer analysis (F-ARISA). An annual cycle was assessed across a depth gradient, distinguishing three soil habitats: the plough layer, rooted soil below the plough layer, and deeper root-free soil. Fungal communities appeared highly dynamic and varied according to soil depth and plant resources. In the plough layer, the availability of litter played a dominant role in shaping fungal communities, whereas in the rooted layer below, community structure and biomass mainly differed between plant species. This plant effect was also extended into the root-free soil at a depth of 70 cm. In winter, the availability of litter also affected fungal communities in deeper soil layers, suggesting vertical transport processes under fallow conditions. These distinct resource effects indicate diverse ecological niches along the soil profile, comprising specific fungal metacommunities. The recorded responses to both living plants and litter point to a central role of fungi in connecting primary production and decomposition within the plant-soil system.

Plant residues provide a major source of nitrogen (N) for plant growth. Litter N mineralization varies with litter carbon-to-nitrogen (C-to-N) ratio and presence of bacterial-feeding fauna. We assessed the effect of amoebae, major bacterial feeders in soil, on mineralization of litter of low (high quality) and high C-to-N ratio (low quality) and evaluated consequences for plant growth. We used stable isotopes to determine plant N uptake from litter and plant C partitioning. Stable isotope probing of phospholipid fatty acids was used to follow incorporation of plant C into microorganisms. Amoebae increased plant N uptake independent of litter quality and thereby the biomass of shoots and roots by 33% and 66%, respectively. Plant allocation of total (13)C to roots in low (42%) exceeded that of high-quality litter treatments (26%). Amoebae increased plant allocation of (13)C to roots by 37%. Microbial community structure and incorporation of (13)C into PLFAs varied significantly with litter quality and in the low-quality litter treatment also with the presence of amoebae. Overall, the results suggest that in particular at low nutrient conditions, root-derived C fosters the mobilization of bacterial N by protozoa, thereby increasing plant growth when microorganisms and plants compete for nutrients., (© 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.)

Subsurface microorganisms are essential constituents of the soil purification processes associated with groundwater quality. In particular, soil enzyme activity determines the biodegradation of organic compounds passing through the soil profile. Transects from surface soil to a depth of 3.5 m were investigated for microbial and chemical soil characteristics at two groundwater recharge sites and one control site. The functional diversity of the microbial community was analyzed via the activity of eight enzymes. Acid phosphomonoesterase was dominant across sites and depths, followed by L-leucine aminopeptidase and beta-glucosidase. Structural [e.g. phospholipid fatty acid (PLFA) pattern] and functional microbial diversities were linked to each other at the nonwatered site, whereas amendment with nutrients (DOC, NO(3)(-)) by flooding uncoupled this relationship. Microbial biomass did not differ between sites, whereas microbial respiration was the highest at the watered sites. Hence, excess nutrients available due to artificial groundwater recharge could not compensate for the limitation by others (e.g. phosphorus as assigned by acid phosphomonoesterase activity). Instead, at a similar microbial biomass, waste respiration via overflow metabolism occurred. In summary, ample supply of carbon by flooding led to a separation of decomposition and microbial growth, which may play an important role in regulating purification processes during groundwater recharge.

Subsurface microorganisms are crucial for contaminant degradation and maintenance of groundwater quality. This study investigates the microbial biomass and community composition [by phospholipid fatty acids (PLFAs)], as well as physical and chemical soil characteristics at woodland flooding sites of an artificial groundwater recharge system used for drinking water production. Vertical soil profiles to c. 4 m at two watered and one nonwatered site were analyzed. The microbial biomass was equal in watered and nonwatered sites, and considerable fractions (25-42%) were located in 40-340 cm depth. The microbial community structure differed significantly between watered and nonwatered sites, predominantly below 100 cm depth. Proportions of the bacterial PLFAs 16:1omega5, 16:1omega7, cy17:0 and 18:1omega9t, and the long-chained PLFAs 22:1omega9 and 24:1omega9 were more prominent at the watered sites, whereas branched, saturated PLFAs (iso/anteiso) dominated at the nonwatered site. PLFA community indices indicated stress response (trans/cis ratio), higher nutrient availability (unsaturation index) and changes in membrane fluidity (iso/anteiso ratio) due to flooding. In conclusion, water recharge processes led to nutrient input and altered environmental conditions, which resulted in a highly active and adapted microbial community residing in the vadose zone that effectively degraded organic compounds.

Increased carbon translocation to the rhizosphere via 'leakage' induced by low amounts of plant parasitic nematodes can foster microorganisms. The effects of the root-knot nematode Meloidogyne incognita on microbial biomass (C(mic)) and community structure (phospholipid fatty acids) in the rhizosphere of barley were studied. Inoculation densities of 2000, 4000, and 8000 nematodes were well below the threshold level for plant damage. A (13)CO(2) pulse-labelling was performed to assess the distribution of assimilated (13)C in the rhizosphere. Infection with M. incognita increased the carbon concentration in shoots, and enhanced root biomass slightly. The presence of nematodes did not affect microbial biomass, but significantly changed the allocation of the recent photosynthate. Less plant carbon was sequestered by microorganisms with increasing nematode abundance. Microbial community structure was distinctly altered in the early stages of the plant-nematode interactions. Both, bacteria and fungi, showed a positive response with 2000, and a negative one with 4000 and 8000 M. incognita added. The results suggest that low-level root herbivory still imposes a considerable carbon demand, and that proliferation of microorganisms due to increased rhizodeposition may be short-termed. The carbon flow to rhizosphere microbial communities is likely dependent on the specific nematode-plant association and the developmental stage of the nematode in the host.

This study analyses trophic interactions between soil fungi, micro- and mesofauna in microcosm experiments. The trophic shift of 15N and fatty acids (FAs) was investigated in different food chains, which comprised either two (fungi and grazers) or three (fungi, nematodes and Collembola) levels. Contrary to the widely accepted assumption of 15N enrichment in trophic cascades the experiments revealed enrichment, depletion or no change in 15N of consumers compared to their diet. Factors responsible for this pattern were suggested to be: (1) the main metabolic pathway used for N excretion in ammonotelic nematodes to be similar or depleted in the heavier isotope, and uricotelic Collembola mostly enriched in the heavier isotope; (2) a higher shift in 15N with a high-protein diet (e.g. for predators); (3) compensation due to low-quality food altering the fractionation of 15N. Analysis of the lipid composition showed phospholipids to be generally unaffected and neutral lipids closely related to the FA pattern of the food source. Dietary routing of FAs into neutral lipids occurred, as evidenced by corresponding frequencies of FAs in host and consumer profiles. Additionally, several FAs were only detected in the grazer when present in the food source. Oleic acid showed a shift over three trophic levels, from fungi to nematodes to Collembola. The assimilation of dietary FAs resulted in a more diverse neutral lipid profile, i.e. animals higher in the food chain contained more individual FAs compared to animals lower in the food chain. The results indicate that monoenoic C18 and monoenoic C20 FAs have the potential to act as tools for the bioindication of feeding strategies in belowground systems. We suggest that primary consumers will have no or only trace amounts of monoenoic C20 acids in their neutral lipid profile, whereas consumers feeding on a eukaryote diet will show a considerably higher frequency.

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1600-0706.2009.18169.x Byline: Valentyna Krashevska, Mark Maraun, Liliane Ruess, Stefan Scheu Abstract: We investigated the role of carbon, nitrogen and phosphorus as limiting factors of microorganisms and microbial grazers (testate amoebae) in a montane tropical rain forest in southern Ecuador. Carbon (as glucose), nitrogen (as N[H.sub.4]NO.sub.3) and phosphorus (as Na[H.sub.2]PO.sub.4) were added separately and in combination bimonthly to experimental plots for 20 months. By adding glucose and nutrients we expected to increase the growth of microorganisms as the major food resource of testate amoebae. The response of microorganisms to experimental treatments was determined by analysing microbial biomass (SIR), fungal biomass and microbial community composition as measured by phospholipid fatty acids (PLFAs). We hypothesized that the response of testate amoebae is closely linked to that of microorganisms. Carbon addition strongly increased ergosterol concentration and, less pronounced, the amount of linoleic acid as fungal biomarker, suggesting that saprotrophic fungi are limited by carbon. Microbial biomass and ergosterol concentrations reached a maximum in the combined treatment with C, N and P indicating that both N and P also were in short supply. In contrast to saprotrophic fungi and microorganisms in total, testate amoebae suffered from the addition of C and reached maximum density by the addition of N. The results indicate that saprotrophic fungi in tropical montane rain forests are mainly limited by carbon whereas gram positive and negative bacteria benefit from increased availability of P. Testate amoebae suffered from increased dominance of saprotrophic fungi in glucose treatments but benefited from increased supply of N. The results show that testate amoebae of tropical montane rain forests are controlled by bottom-up forces relying on specific food resources rather than the amount of bacterial biomass with saprotrophic fungi functioning as major antagonists. Compared to temperate systems microbial food webs in tropical forests therefore may be much more complex than previously assumed with trophic links being rather specific and antagonistic interactions overriding trophic interactions. Author Affiliation: (1)J. F. Blumenbach Inst. of Zoology and Anthropology, Animal Ecology, Georg-August-Univ. of Goettingen, Berliner Str. 28, DE-37073 Goettingen, Germany (2)Dept of Ecology, Inst. of Biology, Humboldt-Univ. Berlin, Invalidenstra[sz]e 42, DE-10115 Berlin, Germany Article History: Paper manuscript accepted 5 October 2009 Article note: V. Krashevska, J. F. Blumenbach Inst. of Zoology and Anthropology, Animal Ecology, Georg-August-Univ. of Goettingen, Berliner Str. 28, DE-37073 Goettingen, Germany. E-mail: vkrashe@gwdg.de

Microorganisms in forest soils provide essential ecosystem services, such as decomposition of organic matter and nutrient mineralization. However, microbial community structure and function can be affected by environmental conditions, such as regional climate and soil properties and, moreover, by human activity through forest management. We examined the biomass and composition of microbial assemblages in 150 forest stands in the organic layer (Oi, Oe, Oa) and upper mineral soil (0–10 cm) in three regions across Germany (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin) by phospholipid fatty acid (PLFA) analysis. Different explanatory environmental variables (total C, N, S, P, organic C, inorganic C, pH, water content) were identified. The intensity of land use was characterized with the Forest Management Intensity Index (ForMI). The total amount of PLFAs, as measure for microbial biomass, was different among the three regions both in the organic layer and mineral soil. In the organic layer, total PLFAs decreased from Schwäbische Alb over Hainich-Dün to Schorfheide-Chorin, with the latter comprising a fourfold and twofold lower amount in fungal and bacterial PLFAs, respectively. In contrast, in the mineral soil the forests in the Hainich-Dün showed the highest microbial biomass. Discriminant function analysis of PLFA pattern indicated that Gram-positive bacteria and fungi accounted mainly for the regional differences in the organic layer, whereas in the mineral soil additionally Gram-negative and actinobacteria were important. Redundancy analysis showed that PLFA profiles were predominantly affected by sampling site and environmental variables, with the water content in the organic layer and the soil texture in the mineral soil explaining most of the variability in microbial communities between the three regions. Additionally, forest stands were classified into four management groups (conifer; deciduous with low, medium, and high intensity) based on the ForMI. In the mineral soil, forest management accounted for a small proportion of the observed regional differences. Within regions, fungal biomass in the organic layer decreased with management intensity at the Schwäbische Alb and increased in the mineral soils of Hainich-Dün region. Microbial community structure discriminated coniferous and deciduous forests in all three regions, and moreover showed a separation based on forest management intensity in the Schorfheide-Chorin. In conclusion, microbial biomass and community composition in forest organic layer and mineral soil were more influenced by regional conditions, including environmental properties such as moisture, soil texture, C/N ratio and pH, than by forest management intensity. However, within given environments, microbial assemblages can be influenced by forest management, in particular through changes in the tree species composition. [ABSTRACT FROM AUTHOR]

Using bulk tissue and fatty acid 13C analysis we investigated major trophic pathways from soil microorganisms to microbial consumers to predators in conventional versus organic farming systems planted for the first time with maize. Organic farming led to an increase in microbial biomass in particular that of fungi as indicated by phospholipid fatty acids (PLFAs). Microbial PLFAs reflected the conversion from C3 to C4 plants by a shift in δ13C of 2‰, whereas the isotopic signal in fatty acids (FAs) of Collembola was much more pronounced. In the euedaphic Protaphorura fimata the δ13C values in maize fields exceeded that in C3 (soybean) fields by up to 10‰, indicating a close relationship between diet and vegetation cover. In the epedaphic Orchesella villosaδ13C values shifted by 4‰, suggesting a wider food spectrum including carbon of former C3 crop residues. Differences in δ13C of corresponding FAs in consumers and resources were assessed to assign food web links. P. fimata was suggested as root and fungal feeder in soybean fields, fungal feeder in conventional and leaf consumer in organically managed maize fields. O. villosa likely fed on root and bacteria under soybean, and bacteria and fungi under maize. Comparison of δ13C values in FAs of the cursorial spider Pardosa agrestis and O. villosa implied the latter as important prey species in soybean fields. In contrast, the web-building spider Mangora acalypha showed no predator–prey relationship with Collembola. The determination of δ13C values in trophic biomarker FAs allowed detailed insight into the structure of the decomposer food web and identified diet-shifts in both consumers at the base of the food web and in top predators in organic versus conventional agricultural systems. The results indicate changes in major trophic links and therefore carbon flux through the food web by conversion of conventional into organic farming systems. [ABSTRACT FROM AUTHOR]

The effect of food resources, varying in C/N ratio, lipid and ω3 polyunsaturated fatty acid (ω3-PUFA) content, on the fitness of three Collembola species (the euedaphic Protaphorura fimata , hemiedpahic Folsomia candida and epedaphic Lepidocyrtus violaceus) was investigated. Dietary routing of fatty acids served as an indicator for resource consumption and assimilation. Laboratory feeding experiments were performed with single and mixed diets made from algae, cyanobacteria, fungi, soil bacteria or plant roots and leaves. Collembola exhibited species-specific responses in biomass and survival rate to the diets differing in quality, reflecting adaptations to their soil environment. Generally, wide dietary C/N ratios had a negative impact, with roots especially unfavorable, while the dependence on ω3-PUFAs varied. Mixing diets did mostly result in intermediate results where high-quality resources compensate for low-quality resources, with only mixes of resources favoured by Collembola in the wild showing synergistic positive effects. The results suggest that most resources of soil detritivores, irrespective of green or brown food chain, represent a non-optimal diet, with clear adaptations depending on habitat and the potential to truly exploit any resource mostly exhibited in euedaphic species. • Trophic shift of marker fatty acid can assess assimilation into consumer tissue. • Dietary ω3-fatty acid content and C/N ratio influence Collembola biomass/survival. • Effects of low-quality diet aren't compensated by mixing with high-quality diets. [ABSTRACT FROM AUTHOR]

Free-living nematodes act as reservoirs and vectors of the food-borne pathogen Salmonella enterica , one of the leading causes of gastrointestinal human infections worldwide. Although the transport of this human pathogen through soil by nematodes has major concerns for food safety, little is known about the food preference for S. enterica in nematodes. To disentangle the trophic links between nematodes and bacteria, the food choice of the nematode species Acrobeloides buetschlii , Caenorhabditis elegans and Pristionchus pacificus was examined under semi-natural conditions using a modular soil system. S. enterica serovar Typhimurium LT2 was tested against five common soil bacteria, i.e. Arthrobacter alpinus, Bacillus subtilis, Escherichia coli OP50 , Granulicella arctica and Pseudomonas putida IsoF in binary food choice assays. The tested nematodes showed a general preference for bacterial strains with a low C/N ratio (E. coli), and avoidance of strains with a high C/N ratio (G. arctica and A. alpinus), indicating that food choice is rather linked to nutritional value than to bacterial pathogenicity. Moreover, the enrichment opportunists C. elegans and P. pacificus showed a stronger attraction to a suitable bacterial diet compared to the general opportunist A. buetschlii, which also thrives food-depleted soils. Interestingly, there was no evidence regarding a differentiation between common soil bacteria and the pathogen S. enterica. Overall, S. enterica was used as resource by the tested bacterial-feeding soil nematodes, highlighting their vector potential for food-borne pathogens in agricultural soils. • Tested nematodes fed on Salmonella enterica , suggesting a general vector potential. • Food selection is mainly due to bacterial nutritional value and not pathogen status. • Nematode life-history traits may additionally affect choice behavior. [ABSTRACT FROM AUTHOR]

Examines effects of environmental manipulations simulating climate change on soil microorganisms and nematode population in Arctic terrestrial ecosystems. Influence of high temperature and global warming on the nematode community at high altitudes; Impact of increasing heath temperature on microbial populations.

Abstract: The origin and quantity of plant inputs to soil are primary factors controlling the size and structure of the soil microbial community. The present study aimed to elucidate and quantify the carbon (C) flow from both root and shoot litter residues into soil organic, extractable, microbial and fungal C pools. Using the shift in C stable isotope values associated with replacing C3 by C4 plants we followed root- vs. shoot litter-derived C resources into different soil C pools. We established the following treatments: Corn Maize (CM), Fodder Maize (FM), Wheat+maize Litter (WL) and Wheat (W) as reference. The Corn Maize treatment provided root- as well as shoot litter-derived C (without corn cobs) whereas Fodder Maize (FM) provided only root-derived C (aboveground shoot material was removed). Maize shoot litter was applied on the Wheat+maize Litter (WL) plots to trace the incorporation of C4 litter C into soil microorganisms. Soil samples were taken three times per year (summer, autumn, winter) over two growing seasons. Maize-derived C signal was detectable after three to six months in the following pools: soil organic C (Corg), extractable organic C (EOC), microbial biomass (Cmic) and fungal biomass (ergosterol). In spite of the lower amounts of root- than of shoot litter-derived C inputs, similar amounts were incorporated into each of the C pools in the FM and WL treatments, indicating greater importance of the root- than shoot litter-derived resources for the soil microorganisms as a basis for the belowground food web. In the CM plots twice as much maize-derived C was incorporated into the pools. After two years, maize-derived C in the CM treatment contributed 14.1, 24.7, 46.6 and 76.2% to Corg, EOC, Cmic and ergosterol pools, respectively. Fungi incorporated maize-derived C to a greater extent than did total soil microbial biomass. [Copyright &y& Elsevier]

Abstract: Recent stable isotope analyses indicate that a number of putative detritivorous soil microarthropods is not typical detritivores but rather live as predators or scavengers. Using molecular gut content analyses the present study investigates if nematodes indeed form part of the diet of oribatid mites. First, in a no-choice laboratory feeding experiment two nematode species (Phasmarhabditis hermaphrodita and Steinernema feltiae) were offered to eight species of oribatid mites and one gamasid mite. Second, after feeding for 4 and 48h on each nematode species the detection time of prey DNA in the oribatid mite species Steganacarus magnus was investigated. Third, in a field experiment nematode prey (P. hermaphrodita and S. feltiae) in the diet of microarthropods was investigated distinguishing between scavenging and predation. In the no-choice laboratory experiment not only the gamasid mite but also several of the studied oribatid mite species consumed nematodes. After feeding on nematodes for 4h prey DNA was detectable in S. magnus for only 4h, but after feeding for 48h prey DNA was detectable for 128h, indicating that the duration of feeding on prey is an important determinant for prey DNA detection. The field experiment confirmed that oribatid mite species including Liacarus subterraneus, Platynothrus peltifer and S. magnus intensively prey on nematodes. Interestingly, DNA of dead P. hermaphrodita was detectable to a similar degree as that of living individuals indicating that scavenging is of significant importance in decomposer food webs. Results of our study indicate that predation and scavenging on nematodes by “detritivorous” microarthropods in soil food webs need to be reconsidered. [Copyright &y& Elsevier]

This study assessed the carbon (C) budget and the C stocks in major compartments of the soil food web (bacteria, fungi, protists, nematodes, meso- and macrofauna) in an arable field with/without litter addition. The C stocks in the food web were more than three times higher in topsoil (0–10 cm) compared to subsoil (>40 cm). Microorganisms contained over 95% of food web C, with similar contributions of bacteria and fungi in topsoil. Litter addition did not alter C pools of soil biota after one growing season, except for the increase of fungi and fungal feeding nematodes in the topsoil. However, the C budget for functional groups changed with depth, particularly in the microfauna. This suggests food web resilience to litter amendment in terms of C pool sizes after one growing season. In contrast, the distinct depth dependent pattern indicates specific metacommunities, likely shaped by dominant abiotic and biotic habitat properties. [ABSTRACT FROM AUTHOR]

• SIP (13CO2 and 18O water) revealed impacts of soil fauna on microbial functioning. • Nematode grazing increased net assimilation of plant derived C in microbial biomass. • Bacterivore nematodes impacted directly bacteria and indirectly saprophytic fungi. • Grazing activated bacterial taxa typical for the rhizosphere microbiome. • Grazing enhances allocation of plant C and thus energy to the soil food web. Microbially driven soil processes are crucial for ecosystem functions such as soil carbon storage and nutrient cycling. The functioning of the microbial community, in turn, largely depends on plant-derived carbon inputs. However, besides the energy supply by plants, the microbial community also underlies a top-down control by higher trophic levels, which has often not been considered when investigating soil microbial processes. Here we investigated the impact of bacterivore and fungivore-grazing nematodes on the net assimilation of carbon into the bacterial and fungal biomass in a microcosm experiment. We manipulated bacterivorous or fungivorous nematodes to obtain different grazing densities. In combination with a 13CO 2 pulse labelling we traced the carbon flow from plants into the soil microbial community using PLFA biomarkers. Furthermore, we investigated if nematode grazing, independent of the carbon flow, shifted the active bacterial community using H 2 18O DNA stable isotope probing. We found that the microbial biomass was unaffected by nematode grazers. However, bacterivore nematodes stimulated the incorporation of the 13C label directly into biomarkers of bacteria groups and indirectly into biomarkers of saprophytic fungi. The nematode grazing furthermore enhanced the activity of bacterial taxa typically for the rhizosphere microbiome that utilize mainly root deposits, while bacterial groups that degrade already stored soil organic matter were inhibited. We conclude that grazing of higher trophic levels impacts soil processes and likely the entire soil biota via two mechanisms: firstly, through the constant grazing on soil microorganisms and their constant regrowth, the allocation of plant-derived carbon that enters the soil food web increases; and secondly, it preferentially activates bacteria of the rhizosphere microbiome that putatively contribute to soil organic matter storage. [ABSTRACT FROM AUTHOR]

Abstract: Many studies of the microbial ecology of agricultural ecosystems focus on surface soils, whereas the impacts of management practice and season on soil microbial community composition and function below the plough zone are largely neglected. Deep soils have a high potential to store carbon; therefore any management driven stimulation or repression of microorganisms in subsoil could impact biogeochemical cycling in agricultural sites. The aim of this study was to understand whether soil management affects microbial communities in the topsoil (0–10 cm), rooted zone beneath the plough layer (40–50 cm), and the unrooted zone (60–70 cm). In a field experiment with different crops [wheat (Triticum aestivum L.) and maize (Zea mays L.)] and agricultural management strategies (litter amendment) we analysed microbial biomass as phospholipid fatty acids (PLFAs) and enzyme activities involved in the C-cycle (β-glucosidase, N-acetyl-β-d-glucosaminidase, β-xylosidase, phenol- and peroxidase) across a depth transect over a period of two years. Wheat cultivation resulted in higher bacterial and fungal biomass as well as higher enzyme activities at most sampling dates in comparison to maize cultivated plots, and this effect was visible to 50 cm depth. Litter application increased bacterial and fungal biomass as well as hydrolytic enzyme activities but effects were apparent only in the topsoil. In winter high microbial biomass and enzyme activities were measured in all soil layers, possibly due to increased mobilization and translocation of organic matter into deeper soil. Hydrolytic enzyme activities decreased with depth, whereas oxidative enzyme activities showed no decrease or even an increase with depth. This could have been due to differing sorption mechanisms of hydrolytic and oxidative enzymes. Specific enzyme activities (enzyme activity per microbial biomass) were higher in the deeper layers and possible reasons are discussed. [Copyright &y& Elsevier]

Abstract: This study investigates an arable field soil with long-term (27 and 28 years) mineral (NPK) and organic (cattle manure, cattle manure with biodynamic preparations) fertilizer amendments at low, medium and high amounts. Arbuscular mycorrhizal (AM) fungi host plant wheat was cultivated in the first vegetation period and non-host amaranth in the second. Phospholipid fatty acids (PLFA) were used to assess soil microbial biomass and community structure. AM fungi were quantified using the marker fatty acid 16:1ω5, with its occurrence in soil PLFAs representing hyphae and in neutral lipid fatty acid (NLFA) spores. Soil microbial biomass was enhanced by the addition of manure and at higher amounts for both fertilizers. AM fungal hyphae and spore biomass responded positively to manure application. The soil microbial community under both crops was dominated by bacteria. The ratio of fungal to bacterial (f/b) PLFAs increased with higher fertilizer amounts but decreased in amaranth plots with the application of manure. Meanwhile the ratio of Gram+/Gram− bacteria indicating environmental conditions (e.g. pH, temperature) was higher in amaranth plots with the addition of manure as compared to wheat plots. Soil PLFA revealed distinct effect of crop type displayed by changes in the occurrence of saturated fatty acids and biomarkers for Gram-negative bacteria and saprotrophic fungi. The latter additionally accounted for the dissimilarity between fertilizer treatments. In sum, the soil PLFA pattern distinctively separated wheat from amaranth plots at 0–5cm soil depth, indicating a stronger effect of crop rotation and crop identity on soil microorganisms than long-term fertilizer practice. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web. [Copyright &y& Elsevier]