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Previous work has shown that endogeic earthworms cause different, i.e. apparent as well as true positive priming effects, presumably due to unknown interactions of substrate-colonising fungi and labile SOM, e.g. rhizodeposits. To explore these interactions, a soil that had previously been enriched with 13 C- and 15 N-labelled rhizodeposits of pea ( Pisum sativum L.) plants was used in an incubation experiment. The objective was to determine whether Aporrectodea caliginosa causes a priming effect on the decomposition of young rhizodeposits and old soil organic matter (SOM) following wheat straw addition. After 56 days of incubation at 12 °C, earthworm effects on autochthonous SOM-derived CO 2 (+88%) were higher than on rhizodeposit-derived CO 2 (+16%), indicating a stronger true positive priming effect on old SOM than on young rhizodeposits. Feeding of A. caliginosa significantly reduced microbial biomass C (−12%) and N (−30%) derived from rhizodeposits. In contrast, SOM-derived microbial biomass C and N remained unaffected, indicating a higher palatability of rhizodeposits. However, they were not catabolized to CO 2 , but preferentially anabolized, i.e. transferred to the biomass of microorganisms and earthworms. Not only straw but also A. caliginosa generally caused a shift in the microbial community towards saprotrophic fungi, as indicated by increased ergosterol contents and ergosterol to microbial biomass C ratios. A. caliginosa decreased δ 15 N, total N, and N derived from rhizodeposits in the non-decomposed straw recovered as particulate organic matter, indicating the importance of rhizodeposits as an N source. [ABSTRACT FROM AUTHOR]

Abstract: C mineralization and aggregate stability directly depend upon organic matter and clay content, and both processes are influenced by the activity of microorganisms and soil fauna. However, quantitative data are scarce. To achieve a gradient in C and clay content, a topsoil was mixed with a subsoil. Single soils and the soil mixture were amended with 1.0mg maize litter C g soil−1 with and without endogeic earthworms (Aporrectodea caliginosa). The differently treated soils were incubated for 49 days at 15°C and 40% water holding capacity. Cumulative C mineralization, microbial biomass, ergosterol content and aggregate fractions were investigated and litter derived C in bulk soil and aggregates were determined using isotope analyses. Results from the soil mixture were compared with the calculated mean values of the two single soils. Mixing of soil horizons differing in carbon and clay content stimulated C mineralization of added maize residues as well as of soil organic matter. Mixing also increased contents of macro-aggregate C and decreased contents of micro-aggregate C. Although A. caliginosa had a stimulating effect on C mineralization in all soils, decomposition of added litter by A. caliginosa was higher in the subsoil, whereas A. caliginosa decreased litter decomposition in the soil mixture and the topsoil. Litter derived C in macro-aggregates was higher with A. caliginosa than with litter only. In the C poor subsoil amended with litter, A. caliginosa stimulated the microbial community as indicated by the increase in microbial biomass. Furthermore, the decrease of ergosterol in the earthworm treated soils showed the influence of A. caliginosa on the microbial community, by reducing saprotrophic fungi. Overall, our data suggest both a decrease of saprotrophic fungi by selective grazing, burrowing and casting activity as well as a stimulation of the microbial community by A. caliginosa. [Copyright &y& Elsevier]

A 56-day incubation experiment was carried out to investigate decomposition and microbial use of 15N-labelled maize (Zea mays L.) residues incubated under four winter temperature scenarios. The residues were mixed to mesocosms equivalent to 1.2 mg C and 42.5 μg N g−1 dry soil, after which the samples were incubated at a constant temperature of +4 °C, a constant −3 °C, and under multiple and single freeze–thaw conditions. A constant +4 °C was most favourable for microbial substrate use, with 4- and 6-fold higher total and maize-C mineralization, respectively, in comparison with constant frost. The cumulative maize mineralization was not determined by the frequency of freeze–thaw events, but regulated by the overall time of frost and thaw conditions. The decomposition of maize straw significantly increased soil organic C mineralization (in all scenarios) and incorporation into microbial biomass (in the freeze–thaw scenarios only). The positive priming effects observed were equivalent to an additional loss of total soil organic C of between about 0.2 (continuous frost) and 0.8% (single freeze–thaw). Microbial biomass was significantly increased after maize straw amendment, with constant frost and freeze–thaw scenarios not having any negative effect on microbial biomass C compared with constant +4 °C. Highest fungal biomass was found after constant frost without fresh substrates and also after extended frost followed by a warm period when fresh plant residues were present. On average, 50% of the added maize N were recovered in the soil total N after 56 days of constant 4 °C and in the freeze–thaw scenarios, with the strongest effect after single freezing and thawing. [ABSTRACT FROM AUTHOR]

Abstract: Goals of ecosystem restoration in California grasslands include the reestablishment of plant communities with a high proportion of native species, and simultaneously improve soil nutrient cycling. Addition of annual lupines and a litter mulch layer were hypothesized to be factors that would promote the growth of the native perennial bunchgrass, Nassella pulchra, in a restored California grassland. To test this hypothesis, field mesocosms were installed, each encircling a Nassella plant, at a perennial grassland restoration site in Carmel Valley, California. Two sets of treatments were imposed: (1) seeding of the annual N-fixing legume, Lupinus bicolor; and (2) exchanging the grassland litter for a thicker mulch layer of C4 grass litter (C/N=99). Stable isotope analysis allowed the tracking of fates of N fixed by the legume and the C4-litter derived C. Treatments continued for 28 months, from December 2002 to April 2005, when most of the destructive measurements were taken. In 2005, neither treatment had significantly increased the biomass of the annuals or the perennial bunchgrass, and there was little effect on total soil C and N. Lupinus decreased the δ15N content, but did not affect the biomass, N and P content of the litter, which was largely composed of annual plants from the previous year. Lupinus resulted in higher soil microbial biomass carbon (SMB-C), and distinct effects on soil microbial communities, especially soil fungi, as measured by phospholipid fatty acid analysis (PLFA) and ergosterol. The high C/N litter mulch tended to increase biomass of Nassella, despite its lower P concentration, and it reduced SMB-C, presumably due to lower decomposition rates compared to the ambient litter. Using a high C/N litter mulch thus is ambiguous for grassland restoration. Repeated increases of legumes over a longer time frame may potentially increase soil fertility and soil C pools in California grasslands, but this study suggests that native perennial grasses may be slow to benefit. [Copyright &y& Elsevier]

Abstract: To monitor the effects of liming on forest ecosystems, experimental plots were installed in forests in mid-western Germany. In addition to soil chemical indices, earthworm communities were investigated on these plots about 15years after first lime applications took place. As a “natural reference”, communities were compared to earthworm records that derived from a beech forest on limestone. In the non-acidified plots that had never been limed only epigeic earthworms were detected in small numbers and low species richness. Forest liming caused higher pH and a higher base saturation in the mineral topsoils. To a large extent, epigeic earthworm species seemed to benefit from this and had increased in number and biomass at all three different locations selected for the investigations. The epigeic dominated communities were completed by anecic Lumbricus terrestris that was rarely found in some of the samples from one location and a number of endogeic species that showed a very patchy distribution in limed plots. In contrast to this, the soil of the beech forest on limestone showed a different community composition. It was dominated by endogeic species in abundance and by anecic species in biomass. On limestone the total biomass of earthworms clearly exceeded the biomass values from all other plots. In conclusion, a long-term support of forest earthworm fauna due to liming was detected. This support was mainly effective for epigeic species, but in some cases for endogeic and anecic species, too. [Copyright &y& Elsevier]

Abstract: Agricultural practices have strong impacts on soil microbes including both the indices related to biomass and activity as well as those related to community composition. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Three treatments were compared: annual grassland, bare soil fallow, and restored perennial grassland. Soil profiles down to 80cm in depth were investigated in four separate layers (0–15, 15–30, 30–60, and 60–80cm) using both phospholipid ester-linked fatty acid (PLFAs) and ergosterol as biomarkers in addition to microbial biomass C by fumigation extraction. PLFA fingerprinting showed much stronger differences between the tilled bare fallow treatment vs. grasslands, compared to fewer differences between restored perennial grassland and annual grassland. The presence or absence of plants over several years clearly distinguished microbial communities. Microbial communities in lower soil layers were little affected by management practices. Regardless of treatment, soil depth caused a strong gradient of changing habitat conditions, which was reflected in Canonical Correspondence Analysis of PLFAs. Fungal organisms were associated with the presence of plants and/or litter since the total amount and the relative proportion of fungal markers were reduced in the tilled bare fallow and in lower layers of the grassland treatments. Total PLFA and soil microbial biomass were highly correlated, and fungal PLFA biomarkers showed strong correlations to ergosterol content. In conclusion, microbial communities are resilient to the grassland restoration process, but do not reflect the change in plant species composition that occurred after planting native bunchgrasses. [Copyright &y& Elsevier]

Abstract: Long-term continuous mixing at 40% water holding capacity (WHC) or as slurry at 400% WHC should result in increased soil organic matter decomposition rates in comparison to a control treatment at 40% WHC, but may have strong impacts on soil microbial indices for activity, biomass, and community structure. The amount of extractable inorganic N (NO3–N+NH4–N) accumulated in the soil solution after 40 weeks of incubation at 25°C was 3% of total N in the control treatment and 4% in the two continuous mixing treatments. However, in the treatment mixing at 40% WHC, this 33% increase compared to the control treatment might be explained solely by the decrease in microbial biomass N. In the control treatment, microbial indices decreased in the order microbial biomass C (−10%), microbial biomass N (−40%), ergosterol (−45%) and ATP (−60%). In the treatment mixing at 40% WHC, all four microbial biomass indices were significantly lower than the respective index in the control treatment. This was especially true for microbial biomass N. In the treatment mixing as slurry, only the contents of microbial biomass C and ATP were significantly lower in comparison to the control treatment. The correspondence analysis ordination biplot of the phospholipid fatty acid (PLFA) profiles showed distinct clusters for the three treatments at the end of the incubation. The strongest relative decline of 64% was observed for the fungi-specific PLFA 18:3ω6 in the treatment mixing as slurry in comparison to the control treatment. The content of total bacterial PLFA decreased only by 23%. The differences between the control treatment and the treatment mixing at 40% WHC were less apparent. Fungi represent on average 21% of total microbial biomass C at the end of the incubation if the ergosterol content is recalculated into fungal biomass C. In accordance with this percentage, 22% of the group-specific PLFA could be attributed to fungi. [Copyright &y& Elsevier]

Abstract: An incubation experiment was carried out with maize (Zea mays L.) leaf straw to analyze the effects of mixing the residues with soil and N amendment on the decomposition process. In order to distinguish between soil effects and nitrogen effects for both the phyllospheric microorganisms already present on the surface of maize straw and soil microorganisms the N amendment was applied in two different placements: directly to the straw or to the soil. The experiment was performed in dynamic, automated microcosms for 22 days at 15°C with 7 treatments: (1) untreated soil, (2) non-amended maize leaf straw without soil, (3) N amended maize leaf straw without soil, (4) soil mixed with maize leaf straw, (5) N amended soil, (6) N amended soil mixed with maize leaf straw, and (7) soil mixed with N amended maize leaf straw. 15NH4 15NO3 (5at%) was added. Gas emissions (CO2, 13CO2 and N2O) were continuously recorded throughout the experiment. Microbial biomass C, biomass N, ergosterol, δ13C of soil organic C and of microbial biomass C as well as 15N in soil total N, mineral N and microbial biomass N were determined in soil samples at the end of the incubation. The CO2 evolution rate showed a lag-phase of two days in the non-amended maize leaf straw treatment without soil, which was completely eliminated when mineral N was added. The addition of N generally increased the CO2 evolution rate during the initial stages of maize leaf straw decomposition, but not the cumulative CO2 production. The presence of soil caused roughly a 50% increase in cumulative CO2 production within 22 days in the maize straw treatments due to a slower decrease of CO2 evolution after the initial activity peak. Since there are no limitations of water or N, we suggest that soil provides a microbial community ensuring an effective succession of straw decomposing microorganisms. In the treatments where maize and soil was mixed, 75% of microbial biomass C was derived from maize. We concluded that this high contribution of maize using microbiota indicates a strong influence of organisms of phyllospheric origin to the microbial community in the soil after plant residues enter the soil. [Copyright &y& Elsevier]

The determination of the isotopic composition of the microbial biomass C in soil is an important tool to study soil microbial ecology and the decomposition and microbial immobilization of soil organic C. We discuss advantages and disadvantages of different methods to determine 13C/12C in soil microbial biomass and propose a new procedure that is based on the UV-catalyzed liquid oxidation of fumigated and non-fumigated soil extracts combined with trapping of the released CO2 in liquid nitrogen and subsequent determination of δ13O2-C by a gas chromatograph connected with an isotope ratio mass spectrometer (IRMS). This method was evaluated using test solutions with known isotopic composition and soil extracts. Additionally, the method was compared with an off-line sample preparation technique combined with isotope analysis by a dual-inlet IRMS and an on-line analysis using an elemental analyser connected with an IRMS. All methods applied obtained comparable results and there were no significant differences between the δ13Cvalues measured. The off-line preparation procedure had the highest precision but it was also the most labour-intensive. The choice of the most suitable method depends mainly on the number of samples that have to be analysed, the salt concentration of the extracts and the differences of δ13Cthat have to be detected. The application of this method with liquid oxidation and subsequent GC-IRMS analysis showed that microbial biomass C of a grassland soil was 13C-enriched by 2‰δ13CPDBcompared with the total soil organic C. The addition of maize straw resulted in a rapid immobilization of maize C in the microbial biomass. [Copyright &y& Elsevier]

Effects of soil type and microclimate on winter decomposition of maize (Z ea mays L) leaf litter and microbial carbon use efficiency (CUE) were investigated, using a reciprocal soil transplantation experiment. The clay site DEP is located at an elevated plateau on limestone, the silt site NEB at a broad valley on loess. At DEP, the mean soil temperature was 0.4 °C higher than at NEB. Mean CO 2 efflux was 62.8 g C m−2 130 d−1 at NEB, more than 4 times higher than that of 15.1 g C m−2 130 d−1 at DEP. At both sites, no differences in CO 2 efflux were observed between soil type and maize leaf litter treatments. The alkaline clay and the calcareous bedrock at DEP apparently trapped all CO 2 evolved below 4 cm depth. Microbial biomass C (MBC) content was about 50% lower in the silt than in the clay at 0–4 cm depth. The ergosterol to MBC ratio was 13% higher in the clay than in the silt. Maize leaf litter application increased MBC as well as the MB-C/N ratio from 7.9 to 9.7 but decreased the ergosterol to MBC ratio by 9%. Total recovery of maize leaf litter C was 65%, i.e. the sum of MBC (10%), microbial residue C (32%) and particulate organic matter C (23%), while the remaining 35% must have been lost as CO 2. From these data, a CUE of 0.55 was calculated for maize leaf litter in the field, which was not affected by soil type and site conditions. • The silt contained about 50% less microbial biomass than the clay. • Soil type and maize leaf litter amendment did not affect CO 2 efflux. • A C use efficiency of 0.55 was calculated for maize leaf litter in the field. [ABSTRACT FROM AUTHOR]

Mechanical soil disturbance is one among the key factors influencing soil biodiversity in agriculture. Although many soil organisms are sensitive to soil disturbance, fungi could be highly impacted due to their sessile lifestyle, relatively slow growth and filamentous body structure. Arbuscular mycorrhizal (AM) fungi are of particular interest in arable lands, providing crop plants with numerous vital services such as nutrient acquisition and protection against abiotic and biotic stressors. Considering this, tillage practices that aim to reduce soil disturbance are often seen as a fungal‐friendly alternative to conventional inversion tillage. Although local studies exist on the impacts of minimal tillage practices on AM fungi, the universality of this approach has been debated. Our objective was to assess the effects of reduced tillage intensity on AM fungi in comparison with conventional tillage. Using high‐throughput sequencing techniques in long‐term field experiments in five European countries, we show that the effects of reduced tillage intensity may not necessarily be positive on soil AM fungal diversity. Plots which were tilled using reduced tillage techniques had lower AM fungal richness in three countries, whereas in one of them, no significant differences were found. We also observed a shift in AM fungal communities where prevalence of taxa preferring root colonisation rather than soil exploration increased under reduced tillage regimes. Here, we argue that more detailed and long‐term studies are needed to understand the factors that could make the reduction of soil disturbance more beneficial to AM fungi if agricultural sustainability goals are to be met. [ABSTRACT FROM AUTHOR]

Abstract: Chisel plough or no-till practises are clearly attributed to sustainable farming for the support of soil organisms and soil biological functioning. However, in organic farming these techniques are only applied to a very small extent since there is a need for cultivation to control weeds. In organic farming it is important to develop and establish less destructive soil tillage practises to benefit from the support of soil organisms, especially from ecosystem engineers like earthworms. In this study three tillage systems were compared on a silty, loess'' derived soil in a 6 crop rotation. The tillage systems established were: (1) “ecomat” shallow (10cm) inversive ploughing; (2) a ridge culture system; and (3) conventional tillage (inversion tillage) down to 30cm. In fall 2005, three years after establishment of the field plots earthworm communities were investigated using formalin extraction. In total 6 species were detected. The earthworm abundance was low, ranging from 0 to 84 individuals m−2. Shallow ploughing using the “ecomat” technique was not different than conventional ploughing in its effects on earthworm populations, while the ridge culture system was significantly reduced in earthworm numbers and biomass compared to conventional ploughing. We conclude that both “ecomat” and “ridge culture” do not support earthworms and significantly reduce earthworm densities. The reductions in tillage depth alone are not effective for improving the habitat quality for earthworms in soil. [Copyright &y& Elsevier]

A reduction in tillage intensity, organic farming, and introduction of ley-grass periods into the crop rotation are means to improve the sustainable use of arable soils. The current study uses an on-farm approach to investigate soils from different practical farms in Northern France, Central Sweden, and Romania in comparison with previously published results from randomized field-experiments nearby. No-tillage generally increased the mean SOC and total N contents of arable fields in comparison with ploughing. However, this increase was only significant for the 70 % increase at 0–10 cm depth in France. No-tillage had no general effects on MBC or MBN and increased the ergosterol content at 0–10 cm depth in France and Sweden but not in Romania. Averaging depths and tillage systems, median MBC significantly increased in the order France (220 μg g−1 soil), Romania (324 μg g−1 soil), and Sweden (384 μg g−1 soil), whereas the median MB-C/N ratios followed the order France (5.6), Sweden (8.3), and Romania (10.4). The study region-specific changes in soil pH significantly affected covariate MBC and MBN in the regression equations for equal slopes ANCOVA models. In Northern France, organic farming and ley-grass implementation into the crop rotation increased SOC and total N contents to the level of the no-tillage fields. On-farm research gives similar results to long-term field experiments in France, Romania, and Sweden. For this reason, on-farm research on practical fields is an important, less expensive alternative to randomized field experiments, with a high potential for investigating actual and relevant research objectives. This will intensify exchange in knowledge between scientists and farmers. • No-tillage had stronger effects on soil organic matter than on microbial biomass. • No-tillage increased particularly the presence of saprotrophic fungi. • In France, organic farming and ley-grass management had similar effects than no-tillage. • On-farm results are like those of long-term experiments in France, Romania, and Sweden. [ABSTRACT FROM AUTHOR]

Background: The role of soil mesofauna in decomposition processes still is debated and this applies in particular to arable systems. Aim: This study investigates the role of Collembola in decomposition processes of crop residues in two different tillage systems. Methods: We conducted a litterbag experiment in a long‐term field site in Germany managed by conventional tillage (CT; mouldboard ploughing) and minimum tillage (MT). Litterbags filled with maize leaf litter of two mesh sizes (2 mm and 48 μm) were used. Litterbags were buried at 23 cm (CT) and 5–8 cm (MT), and retrieved after 2, 5 and 7 months. Litter mass, concentrations of carbon and nitrogen, litter C/N ratio as well as the abundance and community structure of Collembola and the incorporation of maize‐derived carbon into Collembola were investigated. Results: Mesofauna enhanced the loss of litter carbon, while litter mass loss was reduced. Litter C/N ratio in MT was generally lower than that in CT and decreased faster in litterbags with coarse mesh size. Abundance of Collembola in litterbags in CT exceeded that in MT, but species composition remained unaffected by tillage. Overall, Collembola effectively colonised the litter irrespective of tillage system, but benefited in particular from translocation deeper into the soil by conventional tillage. Conclusions: Mesofauna accelerates litter carbon loss and increases litter nitrogen accumulation irrespective of tillage system. This may reduce nitrogen losses due to leaching in winter and facilitate nitrogen capture from decomposing litter material by crops in the following season, thereby contributing to the sustainable management of arable systems. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effect of plant residue decomposability and fungal biomass on the dynamics of macroaggregate (250–2000μm) formation in a three months'' incubation experiment and determined the distribution of residue-derived C and N in the microbial biomass and in aggregate size fractions (250–2000μm, 53–250μm and <53μm) using 13C and 15N data. A silty loam soil (sieved <250μm) was incubated with and without addition of 15N labelled maize leaves (C/N=27.4) and roots (C/N=86.4). Each treatment was carried out with and without fungicide application. The addition of maize residues enhanced soil respiration and microbial biomass C and N and resulted in increased macroaggregate formation with a higher and more rapid maximum macroaggregation in the soil amended with maize leaves than in that with addition of roots. Fungicide application led to a significant decline of microbial biomass C and mineralization of the added residues compared to untreated soils, which demonstrates a successful suppression of part of the active microbial biomass by the fungicide. However, this was not confirmed by a generally lower ergosterol concentration. Consequently, ergosterol was no reliable fungal biomarker in periods of rapid decline of the fungal biomass. A single addition of fungicide was insufficient for continued inhibition of the fungal biomass. Yet, a significant delay (28–42 days) in macroaggregation in fungicide treated compared to untreated samples highlighted the importance of the fungal biomass in macroaggregate formation. Macroaggregates were enriched in maize-derived 13C and 15N compared to microaggregates or the fraction<53μm. They turned over rapidly with decreasing substrate availability, which entailed a transfer of maize-derived C and N stored within macroaggregates during the first weeks of incubation to microaggregates with proceeding incubation time. Our results indicate that this transfer happened within macroaggregates, because no considerable amount of free particulate organic matter (POM) was released upon macroaggregate breakdown. We conclude that substrate decomposability and fungal activity are key factors determining extent and dynamics of macroaggregation during decomposition processes. Macroaggregate formation implied rapid incorporation and thereby short-term protection of maize-derived C and N. Moreover, macroaggregates allowed a transfer of maize-derived organic matter into microaggregates within macroaggregates, which prevented the release of significant amounts of free POM upon macroaggregate breakdown. Consequently, macroaggregates constitute to the transfer of recently added C into more stable soil organic matter fractions. [Copyright &y& Elsevier]

Agriculture benefits from soil functions, whereof many depend on soil biota, but some management practices can threaten soil organisms. We inventoried values that European farmers associate to soils and soil biota into their soil management decisions. We used Dewey's pragmatic epistemology, stating that values can be observed through active behaviours, attitudes and communication acts. We applied a plural values framework on a dataset composed of 35 scientific articles and five focus groups. Farmers saw the soil as a single object. They hardly distinguished soil biota from other elements in their soils. Soil biota remained poorly known and little valued. Besides instrumental values, many other values, such as soil ecosystem resilience, influence farmers' management choices. We conclude that soils and soil biota values are plural and that they can evolve along with changes in farmers' practices. Further studies investigating values dynamics in time and space could be beneficial for designing an effective European soil conservation policy. [ABSTRACT FROM AUTHOR]

Abstract Soil biodiversity is deteriorating in Europe due to an on-going intensification of agriculture, climate change and food production supporting measures of the European Common Agricultural Policy (CAP). Nevertheless, the CAP tries to take biodiversity into account via proposing a range of agri-environmental measures. These ES contribute to food security, climate change mitigation, water retention and plant biomass growth. Healthy soils also help to prevent erosion, desertification, and landslides and to stabilise crop yields. The provision of ES by soil biota is a result of their impact on soil processes in interaction with soil conditions as well as soil management practices of the farmers such as tillage or crop rotations. Some taxa amongst soil biota play key roles in regulating soil processes. With respect to biocontrol of soil-borne pests, the earthworm species Lumbricus terrestris is known to play an important role in suppressing toxigenic plant pathogens, such as Fusarium culmorum and its mycotoxin deoxynivalenol (DON). We highlight the importance of earthworms for pest control to conceptualise and show how farmers' management practices influence soil ecosystem services and outline how this can be examined in a socio-ecological context by providing a concrete example of an economical evaluation of ES provided by earthworms. [ABSTRACT FROM AUTHOR]

Climate change will affect the survival of plant pathogens and the decomposition of crop residues on temperate arable soils. Information on the survival of fungal plant pathogens is important for assessing the subsequent infection risk of susceptible agricultural crops. Therefore, a soil warming experiment was performed to examine the effects of rising winter soil temperatures on the inoculum load of fungal plant pathogens ( Fusarium culmorum , F. graminearum , Rhizoctonia solani ) and the decomposition of infested maize leaves under field conditions. Using heating cables, an arable soil was subjected to temperature treatments simulating medium (+1.3 °C up to the year 2050) and long-term (+2.7 °C up to the year 2100) climate warming scenarios. Litterbags filled with pathogen-inoculated and non-inoculated maize leaves were placed on top of the soil. Soil microbial biomass below the litterbags, maize leaf decomposition as well as microbial colonisation of leaves were measured after 152 days. Pathogen load was estimated by DNA, total saprotrophic biomass by fungal glucosamine and bacterial muramic acid. Rising soil temperatures increased decomposition of pathogen-infested, but not that of non-inoculated maize leaves, without correlation to fungal and bacterial biomass. F. culmorum DNA produced the largest increase in DNA on maize leaves, but did not significantly respond to soil temperatures. In contrast, the increase in F. graminearum DNA was considerably lower, but revealed a significant positive response to rising soil temperatures. DNA from mycelia and sclerotia of R. solani strongly decreased. Rising winter soil temperatures will most likely cause shifts within the plant residue colonizing fungal community, especially between different Fusarium species. [ABSTRACT FROM AUTHOR]

Climate scenarios predict increasing temperatures and higher precipitation rates in late autumn to early spring, both of which holding the potential to change the dynamics of plant residue decomposition and overall microbial activity in soil. In company with consequences for nutrient release patterns influences on the survival of fungal plant pathogens and their phytopathogenicity can be expected. Both, litter decomposition and pathogen survival, was analyzed in a 70-day litterbag incubation experiment. Continuous +4 °C was compared to permanent frost (−3 °C) and different freeze-thaw cycles for the decomposition of maize residues and disease potential of soil-borne plant pathogens Fusarium culmorum, Fusarium graminearum, and Rhizoctonia solani. Frost generally reduced maize residue decomposition. On the lower levels of CO2 production in the permanent or occasionally frost treatments pathogen inoculation had large effects on microbial maize use, indicating high saprotrophic activity of pathogens even in cold winter scenarios. Pathogen inoculation led to higher amino sugar contents of maize residue dwelling microbial organisms. At constant 4 °C remarkable high amounts of glucosamine were detected, indicating higher substrate use efficiency without frost. Both, temperature treatments as well as intra- and interspecific competition directed the development of pathogens after inoculation. F. culmorum took large advantage from the non-frost scenario, while no significant increase was found under continuous frost. F. graminearum was also able to increase its abundance at +4 °C. But this was strongly reduced when F. graminearum was in competition to the other two pathogens. In summary, F. culmorum was found to be highly frost tolerant and competitive against F. graminearum, particularly under conditions of freeze-thaw cycles since F. culmorum was able to take a large share of saprotrophic litter residue use under the cold conditions. Biomass of R. solani was strongly decomposed in all treatments. We conclude that constant mild conditions during winter can increase biomass of F. culmorum and F. graminearum in crop residues, causing increased infection pressure in the next season. In contrast to that, frost and freeze-thaw events can lower the build-up of Fusarium biomass and thus diminish the risk of crop infection. [ABSTRACT FROM AUTHOR]

Abstract: The common earthworm Lumbricus terrestris L. is an invasive species that was introduced to North America by European settlers. Subsequently, earthworms have been distributed by human activity, invaded a wide geographic range and changed previously earthworm-free ecosystems. In the present study we analyzed seven European and four North American populations from a wide geographic range at three formerly described nuclear microsatellite markers. All three markers produced multi-banding patterns and marker presence versus absence was scored in 88 narrow size intervals. Similar levels of genetic variation were observed for North American (Nei''s gene diversity = 0.058, Shannon''s I = 0.100) and European populations (Nei''s gene diversity = 0.064, Shannon''s I = 0.104). North American populations showed a higher similarity among each other than European populations in accordance with their recent introduction to North America. The relatively high level of genetic variation in North American populations and the high similarity among each other suggest their establishment from genetically diverse founder populations and rapid human-mediated population expansion. The source regions in Europe are still unclear from this analysis. [Copyright &y& Elsevier]

Abstract: Earthworms are used in an increasing number of microcosm experiments that investigate their behaviour and biology or that consider earthworms an environmental factor that influences soil properties and biological interactions. However, there exists no standardized protocol for performing comparable studies. After giving a short overview of the different experimental approaches using earthworms as model organisms, the present paper provides recommendations for the planning and execution of earthworm experiments that help in achieving comparable results. The recommendations, summarized in a workflow diagram, pertain to the acquisition, treatment and description of earthworms for experimentation, the description and preparation of test soils and the criteria that should be met for valid experimental results. [Copyright &y& Elsevier]

Abstract: A microcosm experiment was carried out for 56 days at 12 °C to evaluate the feeding effects of the endogeic geophagous earthworm species Aporrectodea caliginosa on the microbial use of 15N-labelled maize leaves (Zea mays) added as 5 mm particles equivalent to 1 mg C and 57 μg N g−1 soil. The dry weight of A. caliginosa biomass decreased in the no-maize treatment by 10% during the incubation and increased in the maize leaf treatments by 18%. Roughly 5% and 10% of the added maize leaf-C and leaf-N, respectively, were incorporated into the biomass of A. caliginosa. About 29% and 33% of the added maize leaf-C were mineralised to CO2 in the no-earthworm and earthworm treatments, respectively. The presence of A. caliginosa significantly increased soil-derived CO2 production by 90 μg g−1 soil in the no-maize and maize leaf treatments, but increased the maize-derived CO2 production only by 40 μg g−1 soil. About 10.5% of maize leaf-C and leaf-N was incorporated into the soil microbial biomass in the absence of earthworms, but only 6% of the maize leaf-C and 3% of the maize leaf-N in the presence of earthworms. A. caliginosa preferentially fed on N rich, maize leaf-colonizing microorganisms to meet its N demand. This led to a significantly increased C/N ratio of the unconsumed microbial biomass in soil. The ergosterol-to-microbial biomass C ratio was not significantly decreased by the presence of earthworms. A. caliginosa did not directly contribute to comminution of plant residues, as indicated by the absence of any effects on the contents of the different particulate organic matter fractions, but mainly to grazing of residue-colonizing microorganisms, increasing their turnover considerably. [Copyright &y& Elsevier]

In the context of sustainable agriculture, a deeper knowledge of the effects of soil management on soil annelids is needed, as they play an important role in many soil processes. In a laboratory mesocosm experiment, we compared the simulated effect of ploughing by inverting the top soil (crop residues at 15 cm depth) to a non-inversion treatment (crop residues on the soil surface) using the soil type Haplic Luvisol. We investigated the response of earthworms and enchytraeids and the consequences for microbial and chemical soil parameters. Four treatments with soil fauna were established by adding: (i) endogeic earthworms (Octolasion cyaneum), (ii) anecic earthworms (Lumbricus terrestris), (iii) a combination of two enchytraeid species (Enchytraeus crypticus and Enchytraeus christenseni) and (iv) having control columns (without annelids). Feeding behaviour of annelids was investigated using isotopic analysis (δ13C, δ15N), and chemical and microbial soil properties were measured. Carbon and nitrogen losses in the form of gas emissions (CO 2 , N 2 O) and leachate were recorded during the time of incubation. We found no interactions of soil inversion and annelid addition on chemical and microbial soil properties; these properties were closely related to crop residue placement, indicated by the effect of soil inversion between 0 and 20 cm. Below 20 cm, this effect disappeared. Here, the presence of enchytraeids enhanced soil microbial properties, regardless of soil inversion. Stimulating microbial activity and increasing soil aeration seem to be the most important factors that increase CO 2 -C emissions in the presence of anecic earthworms. N 2 O-N emissions were consistently higher (+188%) in the inverted columns. Our results show that regardless of the placement of crop residues, anecic earthworms and enchytraeids fed more on crop residue derived carbon than endogeic earthworms, while endogeic earthworms appeared to avoid feeding at the soil surface. Moreover, it was found that the inversion and the annelid effects did not interact in an experimental setting where soil inversion is carried out in a form without detracting or impairing the annelids directly. • L. terrestris were not impaired by crop residue placement at 15 cm depth. • O. cyaneum benefitted from buried crop residues due to soil inversion. • The presence of L. terrestris significantly increased CO 2 emissions. • Soil inversion greatly increased N 2 O emissions when compared with non-inversion. [ABSTRACT FROM AUTHOR]

It is widely known that annelids have strong soil functional impacts like the decomposition of crop residues, which affects carbon dynamics and nutrient cycling. In this study the objective was to investigate the combined effect of the vertical placement of organic material and soil annelids on carbon pathway and plant available nutrients. We hypothesize that endogeic earthworms, such as anecic earthworms and thus enchytraeids react differently because of their various lifestyles. A microcosm experiment with undisturbed soil columns (30 cm high, 15 cm Ø) was carried out from October 2017 to February 2018 in a dark climate chamber at 10 °C. The soil columns were taken from a long-term experimental field-site at plots with reduced tillage after winter wheat harvest. The soil type is a Haplic Luvisol with a silt loam texture. Soil columns were defaunated by freezing for one week at -20°C before the experiment started. During the experiment they were hermetically sealed, continuously supplied with fresh air and automatically irrigated (3 times day-1 10 ml). Gas fluxes were obtained and analyzed every 4.5 hours utilizing a gas chromatograph. For the organism treatment we used: (i) the endogeic earthworm species Octolasion cyaneum (four individuals each column), (ii) the anecic earthworm species Lumbricus terrestris (two individuals each column) or (iii) a combination of the two enchytraeid species Enchytraeus crypticus and E. christenseni (350 individuals each column). Half of the columns were inverted manually to simulate inverse tillage. For these columns we placed 5 g of maize leaves, which was used as a crop residue, in a depth of 15 cm. For the columns with simulation of no-till systems, the organic material was put on the surface. All annelid treatments were combined with both organic matter location treatments.At the end of the experiment, soil columns were harvested destructively. Carbon-dioxide was measured as an indicator of biological activity [mg CO2-C kg-1 dry soil]. For biotic soil properties mircrobial biomass carbon was measured by Chloroform-Fumigation-Extraction (CFE) and ergosterol concentration was quantified as a proxy for fungal biomass. The path of carbon through the system is investigated by isotope ratio mass spectometry 13C/12C. First results show that earthworms reached a higher biomass in all treatments and numbers of enchytraeid individuals increased ten times. Contrary to the expectation that anecic earthworms only pick up organic matter, which is on the surface, the uptake of maize leaves could be shown by isotopic analysis in both treatments. On the other hand, it could be confirmed that the position of organic material in a depth of 15 cm seems to be of advantage for endogeic earthworms. Analysis of the biological activity shows that soil annelids respond in a different way the location of the organic material, depending on size scales (enchytraids vs. earthworms) and on ecological performance (endogeic vs. anecic earthworms). [ABSTRACT FROM AUTHOR]

It is well known that annelids such as earthworms and enchytraeids provide ecosystem services concerning soil fertility and sustainability, e.g. by structuring the soil and building stable aggregates, which reduces soil erosion. The objective of this study was to quantify the combined effect of soil annelids and organic matter location on water-stable aggregate size class distribution. In a microcosm experiment, undisturbed soil columns (30 cm height, 15 cm diameter) were used, which were taken at the long-term field trial "Garte Süd" near Göttingen, Germany, in reduced tillage plots. The soil type of the field trial is a Haplic Luvisol with a silt loam texture. The soil columns were defaunated by freezing before the start of the experiment. As annelids we used (i) the endogeic earthworm species Octolasion cyaneum (four individuals), (ii) the anecic earthworm species Lumbricus terrestris (two individuals) or (iii) a combination of the two enchytraeid species Enchytraeus crypticus and E. christenseni (350 individuals). As organic material we used maize leaves (5 g per column) and either put them on the soil surface (simulation of organic matter location of no-till systems) or in 15 cm soil depth (simulation of organic matter location of conventional tillage systems). All three annelids were combined with both organic matter location treatments. We also included control columns with and without maize leaves, in both cases without annelids. The columns were incubated for three months at a temperature of 10 °C. First results show that the macroaggregate concentration in the top 10 cm was lowest in the columns without annelids and highest for the soil columns with O. cyaneum. The location of the organic material influenced the aggregate distribution in the soil columns with L. terrestris (more large and less small macroaggregates in the columns with maize leaves at the soil surface in the top soil) and with Enchytraeus (less microaggregates in the columns with maize leaves at the soil surface in the top soil), while having no effect on the columns with O. cyaneum.Further planned analyses include the measurement of the isotopic signature of the carbon contents in the different aggregate size classes to quantify the maize carbon included in each aggregate size class dependent on the soil annelid species and the organic matter location. [ABSTRACT FROM AUTHOR]