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Biosolids (sewage sludge) can be beneficially applied to degraded lands to improve soil quality. Plants grown on biosolids-amended soils have distinct concentrations of macronutrients and trace elements, which can be beneficial or present a risk to humans and ecosystems. Potentially, biosolids could be blended with other biowastes, such as sawdust, to reduce the risks posed by rebuilding soils using biosolids alone. We sought to determine the effect of mixing biosolids and sawdust on the macronutrient and trace element concentration of ryegrass over a 5-mo period. was grown in a low fertility soil, typical for marginal farm areas, that was amended with biosolids (1250 kg N ha), biosolids + sawdust (0.5:1) and urea (200 kg N ha), as well as a control. Biosolids increased the growth of from 2.93 to 4.14 t ha. This increase was offset by blending the biosolids with sawdust (3.00 t ha). Urea application increased growth to 4.93 t ha. The biowaste treatments increased N, P, Cu, Mn, and Zn relative to the control, which may be beneficial for grazing animals. Although biowaste application caused elevated Cd concentrations (0.15-0.24 mg kg) five- to eightfold higher than control and urea treatments, these were below levels that are likely to result in unacceptable concentrations in animal tissues. Mixing biosolids with sawdust reduced Cd uptake while still resulting in increased micronutrient concentrations (P, S, Mn, Zn, Cu) in plants. There were significant changes in the elemental uptake during the experiment, which was attributed to the decomposition of the sawdust.

Biodegradability is a desired characteristic for synthetic soil amendments. Cross-linked polyacrylic acid (PAA) is a synthetic superabsorbent used to increase the water availability for plant growth in soils. About 4% within products of cross-linked PAA remains as linear polyacrylic acid (PAAlinear). PAAlinear has no superabsorbent function but may contribute to the apparent biodegradation of the overall product. This is the first study that shows specifically the biodegradation of PAAlinear in agricultural soil. Two (13)C-labeled PAAlinear of the average molecular weights of 530, 400, and 219,500 g mol(-1) were incubated in soil. Mineralization of PAAlinear was measured directly as the (13)CO2 efflux from incubation vessels using an automatic system, which is based on (13)C-sensitive wavelength-scanned cavity ring-down spectroscopy. After 149 days, the PAAlinear with the larger average molecular weight and chain length showed about half of the degradation (0.91% of the initial weight) of the smaller PAAlinear (1.85%). The difference in biodegradation was confirmed by the δ(13)C signature of the microbial biomass (δ(13)Cmic), which was significantly enriched in the samples with short PAAlinear (-13‰ against reference Vienna Pee Dee Belemnite,VPDB) as compared to those with long PAAlinear (-16‰ VPDB). In agreement with other polymer studies, the results suggest that the biodegradation of PAAlinear in soil is determined by the average molecular weight and occurs mainly at terminal sites. Most importantly, the study outlines that the size of PAA that escapes cross-linking can have a significant impact on the overall biodegradability of a PAA-based superabsorbent.

The knowledge about element leaching and biogeochemical cycles during initial stages of soil development is very limited. Therefore, we studied the effects of parent material characteristics and plant litter addition on element leaching from young sandy soils in a microcosm experiment. Our objective was to evaluate the function of young soils as a source and/or sink for nutrients during initial pedogenesis and to identify main processes which are involved in the initial development of biogeochemical cycles. The main research questions were: (1) How do differences in parent material characteristics affect nutrient leaching?; and (2) How is nutrient leaching of young soils influenced by litter addition of different plant functional groups (e.g., legume and grass species)? Combined treatments of two minimally weathered parent materials (pure sand and loamy sand) with plant litter of two plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were investigated in a soil column experiment. In addition, control columns with parent material or plant litter only were included. Carbonate weathering as a main source for calcium leaching was induced by the moderately acidic irrigation solution used in the experiment. It was 7.5 fold greater for the loamy sand parent material compared to the pure sand despite lower carbonate contents in the loamy sand. Leaching of K was very low for both parent materials but greater for the loamy sand parent material, likely due to transfer processes from fixed to exchangeable potassium forms in the clay minerals of the loamy sand. Plant litter addition generally increased leaching losses. Carbonate dissolution was intensified by both plant litter types, especially by L. corniculatus, very likely due to H+ released during nitrification of N released from plant litter and an increase in partial pressure of CO2 from microbial respiration. In contrast, K was largely retained in the soils, probably due to fixation by clay minerals and microbial immobilization. Only the pure sand treated with L. corniculatus litter leached K, resulting in 4–6 fold greater leaching losses compared to all other treatments. Nitrogen released from L. corniculatus litter was almost completely nitrified and was nearly doubled as compared to that from C. epigejos, resulting in greater N leaching. The results of our study allow identifying the general function and processes of vegetation patches in young ecosystems formed as a result of initial parent material characteristics and invading vegetation with respect to litter decomposition, soil solution composition, nutrient retention and leaching, and effects on the soil mineral phase. These patterns are not mere additive effects of parent materials plus plant litter, but reflect differences in biogeochemical process intensities and could result in an increasing heterogeneity of soil properties, nutrient availability, and element leaching fluxes with time.

Estimates of biochar residence times in soils range over three orders of magnitude. We present the first direct comparison between the biodegradation of a char from hydrothermal carbonization (htcBC) and pyrolysis (pyrBC) with high temporal resolution. Mineralization of the biochars and their shared Miscanthus feedstock in three soils was determined directly by the 13CO2 efflux using a novel method incorporating wavelength scanned cavity ring-down spectroscopy. Biochar half-life (t1/2) was estimated with three empirical models. (1) The htcBC was readily biodegradable, whereas pyrBC was more recalcitrant. (2) Cumulative degradation of both biochars increased with soil organic carbon and nitrogen content. (3) The corrected Akaike information criterion (AICC) showed an overall preference for the double exponential model (DEM) reflecting a labile and a recalcitrant C-pool, over the first-order degradation model (FODM) and a logarithmic model. (4) The DEM resulted in t1/2 ranging from 19.7–44.5, 0.7–2.1 and 0.8–1.3 years for pyrBC, htcBC and feedstock, respectively. The degradation was rather similar between feedstock and htcBC but one order of magnitude slower for pyrBC. The AICC preferred FODM in two cases, where the DEM parameters indicated no distinction between a labile and recalcitrant carbon pool.

Biosolids (sewage sludge) can be beneficially applied to degraded lands to improve soil quality. Plants grown on biosolids-amended soils have distinct concentrations of macronutrients and trace elements, which can be beneficial or present a risk to humans and ecosystems. Potentially, biosolids could be blended with other biowastes, such as sawdust, to reduce the risks posed by rebuilding soils using biosolids alone. We sought to determine the effect of mixing biosolids and sawdust on the macronutrient and trace element concentration of ryegrass over a 5-mo period. was grown in a low fertility soil, typical for marginal farm areas, that was amended with biosolids (1250 kg N ha), biosolids + sawdust (0.5:1) and urea (200 kg N ha), as well as a control. Biosolids increased the growth of from 2.93 to 4.14 t ha. This increase was offset by blending the biosolids with sawdust (3.00 t ha). Urea application increased growth to 4.93 t ha. The biowaste treatments increased N, P, Cu, Mn, and Zn relative to the control, which may be beneficial for grazing animals. Although biowaste application caused elevated Cd concentrations (0.15-0.24 mg kg) five- to eightfold higher than control and urea treatments, these were below levels that are likely to result in unacceptable concentrations in animal tissues. Mixing biosolids with sawdust reduced Cd uptake while still resulting in increased micronutrient concentrations (P, S, Mn, Zn, Cu) in plants. There were significant changes in the elemental uptake during the experiment, which was attributed to the decomposition of the sawdust.

CO(2) fixation is one of the most important processes on the Earth's surface, but our current understanding of the occurrence and importance of chemolithoautotrophy in the terrestrial subsurface is poor. Groundwater ecosystems, especially at organically polluted sites, have all the requirements for autotrophic growth processes, and CO(2) fixation is thus suggested to contribute significantly to carbon flux in these environments. We explored the potential for autotrophic CO(2) fixation in microbial communities of a petroleum hydrocarbon-contaminated aquifer by detection of functional marker genes (cbbL, cbbM), encoding different forms of the key enzyme RubisCO of the Calvin-Benson-Bassham cycle. Quantification of (red-like) cbbL genes revealed highest numbers at the upper fringe of the contaminant plume and the capillary fringe where reduced sulphur and iron species are regularly oxidized in the course of groundwater table changes. Functional gene sequences retrieved from this area were most closely related to sequences of different thiobacilli. Moreover, several cultures could be enriched from fresh aquifer material, all of which are able to grow under chemolithoautotrophic conditions. A novel, nitrate-reducing, thiosulfate-oxidizing bacterial strain, recently described as Thiobacillus thiophilus D24TN(T) sp. nov., was shown to carry and transcribe RubisCO large-subunit genes of form I and II. Enzyme tests proved the actual activity of RubisCO in this strain.

Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web dynamics in soils at different developmental stages. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland). 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L.) Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL). Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PLFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria, especially actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain., Biogeosciences, 8 (11), ISSN:1726-4170

Initial ecosystems are characterized by a low availability of nutrients and a low soil organic matter content. Interactions of plants and microorganisms in such environments, particularly in relation to litter decomposition, are very important for further ecosystem development. In a litter decomposition study using an initial substrate from a former mining area, we applied the litter of two contrasting pioneer plant species (legume vs. pasture plants), Lotus corniculatus and Calamagrostis epigejos , which are commonly observed in the study area. Litter decomposition was investigated and carbon (C) translocation from litter into soil microorganisms was described by following 13C from labelled plant litter materials into the fraction of phospholipid fatty acids. Labile C compounds of both plant litter types were easily degraded during the first 4 weeks of litter decomposition. In contrast to climax ecosystems, where the importance of fungi for litter degradation has been shown in many studies, in our experiment, data clearly indicate an outcompetition of fungi by Gram-positive bacteria as soon as available nitrogen is limited in the detritusphere.

A high percentage of photosynthetically assimilated carbon is released into soil via root exudates, which are acknowledged as the most important factor for the development of microbial rhizosphere communities. As quality and quantity of root exudates are dependent on plant genotype, the genetic engineering of plants might also influence carbon partitioning within the plant and thus microbial rhizosphere community structure. In this study, the carbon allocation patterns within the plant-rhizosphere system of a genetically modified amylopectin-accumulating potato line (Solanum tuberosum L.) were linked to microbial degraders of root exudates under greenhouse conditions, using 13C-CO2 pulse-chase labelling in combination with phospholipid fatty acid (PLFA) analysis. In addition, GM plants were compared with the parental cultivar as well as a second potato cultivar obtained by classical breeding. Rhizosphere samples were obtained during young leaf developmental and flowering stages. 13C allocation in aboveground plant biomass, water-extractable organic carbon, microbial biomass carbon and PLFA as well as the microbial community structure in the rhizosphere varied significantly between the natural potato cultivars. However, no differences between the GM line and its parental cultivar were observed. Besides the considerable impact of plant cultivar, the plant developmental stage affected carbon partitioning via the plant into the rhizosphere and, subsequently, microbial communities involved in the transformation of root exudates.

The influence of long-term chronic ozone exposure on carbon fluxes from young beech trees (Fagus sylvatica L.) into the phospholipid fraction of microbial communities (PLFA) in the rhizosphere and into the dissolved organic carbon (DOC) fraction was studied in a lysimeter experiment using 13C depleted CO2 over one vegetation period to identify possible changes in below ground carbon translocation processes due to the plant stress. It could be shown that microbial biomass as well as individual microbial communities and their activity pattern in the rhizosphere of young beech trees are mainly driven by the vegetation period. An increase in total microbial biomass as well as individual microbial communities was detected during the vegetation period from June to September. However, also a clear ozone effect was visible mainly at the end of the vegetation period. Enzyme activities and PLFA data indicated earlier induced plant senescence as a response to the elevated ozone treatment. Furthermore higher microbial biomass and abundance of plant C utilizing microbes was observed in elevated ozone treatments over the whole vegetation period.

In this study the influence of different farming systems on microbial community structure was analyzed using soil samples from the DOK long-term field experiment in Switzerland, which comprises organic (BIODYN and BIOORG) and conventional (CONFYM and CONMIN) farming systems as well as an unfertilized control (NOFERT). We examined microbial communities in winter wheat plots at two different points in the crop rotation (after potatoes and after maize). Employing extended polar lipid analysis up to 244 different phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL) were detected. Higher concentrations of PLFA and PLEL in BIODYN and BIOORG indicated a significant influence of organic agriculture on microbial biomass. Farmyard manure (FYM) application consistently revealed the strongest, and the preceding crop the weakest, influence on domain-specific biomass, diversity indices and microbial community structures. Esterlinked PLFA from slowly growing bacteria (k-strategists) showed the strongest responses to long-term organic fertilization. Although the highest fungal biomass was found in the two organic systems of the DOK field trial, their contribution to the differentiation of community structures according to the management regime was relatively low. Prokaryotic communities responded most strongly to either conventional or organic farming management.

In the present study, biogenic volatile organic compound (BVOC) emissions and photosynthetic gas exchange of salt-sensitive (Populus x canescens (Aiton) Sm.) and salt-tolerant (Populus euphratica Oliv.) isoprene-emitting and non-isoprene-emitting poplars were examined under controlled high-salinity and high-temperature and -light episode ('sunfleck') treatments. Combined treatment with salt and sunflecks led to an increased isoprene emission capacity in both poplar species, although the photosynthetic performance of P. × canescens was reduced. Indeed, different allocations of isoprene precursors between the cytosol and the chloroplast in the two species were uncovered by means of (13)CO2 labeling. Populus × canescens leaves, moreover, increased their use of 'alternative' carbon (C) sources in comparison with recently fixed C for isoprene biosynthesis under salinity. Our studies show, however, that isoprene itself does not have a function in poplar survival under salt stress: the non-isoprene-emitting leaves showed only a slightly decreased photosynthetic performance compared with wild type under salt treatment. Lipid composition analysis revealed differences in the double bond index between the isoprene-emitting and non-isoprene-emitting poplars. Four clear metabolomics patterns were recognized, reflecting systemic changes in flavonoids, sterols and C fixation metabolites due to the lack/presence of isoprene and the absence/presence of salt stress. The studies were complemented by long-term temperature stress experiments, which revealed the thermotolerance role of isoprene as the non-isoprene-emitting leaves collapsed under high temperature, releasing a burst of BVOCs. Engineered plants with a low isoprene emission potential might therefore not be capable of resisting high-temperature episodes.

In initial ecosystems concentrations of all macro- and micronutrients can be considered as extremely low. Plant litter therefore strongly influences the development of a degraders' food web and is an important source for C and N input into soil in such ecosystems. In the present study, a 13C litter decomposition field experiment was performed for 30 weeks in initial soils from a post-mining area near the city of Cottbus (Germany). Two of this regions' dominant but contrasting pioneering plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were chosen to investigate the effects of litter quality on the litter decomposing microbial food web in initially nutrient-poor substrates. The results clearly indicate the importance of litter quality, mainly the amount of N stored in the litter material and its bioavailability for the degradation process and the development of microbial communities in the detritusphere and bulk soil. Whereas the degradation process of the L. corniculatus litter which had a low C/N ratio was fast and most pronounced changes in the microbial community structure were observed 1–4 weeks after litter addition, the degradation of the C. epigejos litter material was slow and microbial community changes mainly occurred at between 4 and 30 weeks after litter addition to the soil. However for both litter materials a clear indication for the importance of fungi for the degradation process was observed both on the abundance level as well as on the level of 13C incorporation (activity).

While the importance of anaerobic methane oxidation has been reported for marine ecosystems, the role of this process in soils is still questionable. Grasslands used as pastures for cattle overwintering show an increase in anaerobic soil micro-sites caused by animal treading and excrement deposition. Therefore, anaerobic potential methane oxidation activity of severely impacted soil from a cattle winter pasture was investigated in an incubation experiment under anaerobic conditions using 13C-labelled methane. We were able to detect a high microbial activity utilizing CH4 as nutrient source shown by the respiration of 13CO2. Measurements of possible terminal electron acceptors for anaerobic oxidation of methane were carried out. Soil sulfate concentrations were too low to explain the oxidation of the amount of methane added, but enough nitrate and iron(III) were detected. However, only nitrate was consumed during the experiment. 13C-PLFA analyses clearly showed the utilization of CH4 as nutrient source mainly by organisms harbouring 16:1ω7 PLFAs. These lipids were also found as most 13C-enriched fatty acids by Raghoebarsing et al. (2006) after addition of 13CH4 to an enrichment culture coupling denitrification of nitrate to anaerobic oxidation of methane. This might be an indication for anaerobic oxidation of methane by relatives of "Candidatus Methylomirabilis oxyfera" in the investigated grassland soil under the conditions of the incubation experiment.

Initial ecosystems are characterized by a low availability of nutrients and a low soil organic matter content. Interactions of plants and microorganisms in such environments, particularly in relation to litter decomposition, are very important for further ecosystem development. In a litter decomposition study using an initial substrate from a former mining area, we applied the litter of two contrasting pioneer plant species (legume vs. pasture plants), Lotus corniculatus and Calamagrostis epigejos, which are commonly observed in the study area. Litter decomposition was investigated and carbon (C) translocation from litter into soil microorganisms was described by following (13) C from labelled plant litter materials into the fraction of phospholipid fatty acids. Labile C compounds of both plant litter types were easily degraded during the first 4 weeks of litter decomposition. In contrast to climax ecosystems, where the importance of fungi for litter degradation has been shown in many studies, in our experiment, data clearly indicate an outcompetition of fungi by Gram-positive bacteria as soon as available nitrogen is limited in the detritusphere.

The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO2 and the soil matrix, such as CO2 diffusion and dissolution processes within the soil profile. Finally, we highlight state-of-the-art stable isotope methodologies and their latest developments. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or currently impede the interpretation of isotopic signals in CO2 or organic compounds at the plant and ecosystem level. This review tries to identify present knowledge gaps in correctly interpreting carbon stable isotope signals in the plant-soil-atmosphere system and how future research approaches could contribute to closing these gaps.

Strain N35T was isolated from surface-sterilized wheat roots and is a Gram-negative, aerobic, motile straight rod. Strain N35T tested oxidase-positive and catalase-negative and grew optimally at pH 7.0, 30 °C and in the absence of NaCl. 16S rRNA gene sequence analysis showed over 97 % sequence similarity to strains of the environmental species Acidovorax delafieldii, A. facilis, A. defluvii, A. temperans, A. caeni and A. soli, as well as Acidovorax valerianellae, A. anthurii and Simplicispira metamorpha. DNA–DNA hybridization between strain N35T and phylogenetically closely related type strains was 25.3–55.7 %, which clearly separates the strain from these closely related species. Additionally, phenotypic properties, such as substrate metabolism profiles as determined by a Biolog GN2 assay and cell-wall fatty acid profiles, particularly contents of the fatty acids C16 : 0, C16 : 1ω7c/t, C17 : 0, C17 : 0 cyclo, C18 : 0 cyclo and C19 : 0 cyclo, facilitated the differentiation of the newly isolated strain N35T from its closest relatives. The isolate underwent phenotypic variation at high frequency in laboratory media. The DNA G+C content was 64.9 mol%. We propose that strain N35T is classified as a representative of a novel species within the genus Acidovorax, and suggest the name Acidovorax radicis sp. nov. The type strain is strain N35T ( = DSM 23535T = LMG 25767T).

Ethyl tert butyl ether (ETBE) and tert amyl methyl ether (TAME) are oxygenates used in gasoline in order to reduce emissions from vehicles. The present study investigated their impact on a soil microflora that never was exposed to any contamination before. Therefore, soil was artificially contaminated and incubated over 6 weeks. Substrate induced respiration (SIR) measurements and phospholipid fatty acid (PLFA) analysis indicated shifts in both, microbial function and structure during incubation. The results showed an activation of microbial respiration in the presence of ETBE and TAME, suggesting biodegradation by the microflora. Furthermore, PLFA concentrations decreased in the presence of ETBE and TAME and Gram-positive bacteria became more dominant in the microbial community.

Soil respiration measurements are an established method to test the abundance, activity and vitality of the soil microorganisms. However, abnormal progressions of soil respiration curves impede a clear interpretation of the data. The aim of this study was to investigate the changes in the microbial structure during the formation of phenomena like double peaks and terraces by analysis of the PLFA composition (phospholipid fatty acid composition). Moreover, 13C labeled glucose was used as substrate; therefore it was possible to measure delta13C values both within the PLFA fraction as well as within the carbon dioxide evolved during respiration. As contaminants trinitrotoluene, cycloheximide, and hexadecane were used. The results showed that the appearance of double peaks was mainly related to the growth of fungi with the marker 18:2delta9,12 due to a toxic effect of trinitrotoluene and cycloheximide. In contrast, the phenomenon of terrace formation was related to the utilization of hexadecane as a carbon source mainly by bacteria.

In this study the influence of different farming systems on microbial community structure was analyzed using soil samples from the DOK long-term field experiment in Switzerland, which comprises organic (BIODYN and BIOORG) and conventional (CONFYM and CONMIN) farming systems as well as an unfertilized control (NOFERT). We examined microbial communities in winter wheat plots at two different points in the crop rotation (after potatoes and after maize). Employing extended polar lipid analysis up to 244 different phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL) were detected. Higher concentrations of PLFA and PLEL in BIODYN and BIOORG indicated a significant influence of organic agriculture on microbial biomass. Farmyard manure (FYM) application consistently revealed the strongest, and the preceding crop the weakest, influence on domain-specific biomass, diversity indices and microbial community structures. Esterlinked PLFA from slowly growing bacteria (k-strategists) showed the strongest responses to long-term organic fertilization. Although the highest fungal biomass was found in the two organic systems of the DOK field trial, their contribution to the differentiation of community structures according to the management regime was relatively low. Prokaryotic communities responded most strongly to either conventional or organic farming management.