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Summary: Plant–soil feedbacks (PSFs) underlying grassland plant richness and productivity are typically coupled with nutrient availability; however, we lack understanding of how restoration measures to increase plant diversity might affect PSFs. We examined the roles of sward disturbance, seed addition and land‐use intensity (LUI) on PSFs.We conducted a disturbance and seed addition experiment in 10 grasslands along a LUI gradient and characterized plant biomass and richness, soil microbial biomass, community composition and enzyme activities.Greater plant biomass at high LUI was related to a decrease in the fungal to bacterial ratios, indicating highly productive grasslands to be dominated by bacteria. Lower enzyme activity per microbial biomass at high plant species richness indicated a slower carbon (C) cycling. The relative abundance of fungal saprotrophs decreased, while pathogens increased with LUI and disturbance. Both fungal guilds were negatively associated with plant richness, indicating the mechanisms underlying PSFs depended on LUI.We show that LUI and disturbance affect fungal functional composition, which may feedback on plant species richness by impeding the establishment of pathogen‐sensitive species. Therefore, we highlight the need to integrate LUI including its effects on PSFs when planning for practices that aim to optimize plant diversity and productivity. [ABSTRACT FROM AUTHOR]

To improve our understanding of early microbial colonization of pristine minerals and their group-specific C utilization, we exposed minerals (illite/goethite/quartz) amended with artificial root exudates (ARE, glucose, and citric acid) in grassland soils for a period of 24 weeks. FTIR spectra indicated that mineral-associated ARE were used within the first 2 weeks of exposure and were replaced by other carbohydrates derived from living or dead cells as well as soil-borne C sources transported into the mineralosphere after heavy rain events. Fungi and Gram-positive bacteria incorporated ARE-derived C more rapidly than Gram-negative bacteria. Gram-negative bacteria presumably profited indirectly from the ARE by cross-feeding on mineral-associated necromass of fungi and Gram-positive bacteria. The Gram-negative bacterial phyla Verrucomicrobia, Planctomycetes, Gemmatimonadetes, Armatimonadetes, and Chloroflexi showed a positive correlation with Gram-negative PLFA abundances. After 24 weeks of exposure in the grassland soils, abundances of soil microorganisms in the mineralosphere reached only 3.1% of the population density in soil. In conclusion, both bacteria and fungi slowly colonize new surfaces such as pristine minerals, but quickly assimilate artificial root exudates, creating an active microbial community in the mineralosphere. [ABSTRACT FROM AUTHOR]

Land‐use intensification drives changes in microbial communities and the soil functions they regulate, but the mechanisms underlying these changes are poorly understood as land use can affect soil communities both directly (e.g. via changes in soil fertility) and indirectly (e.g. via changes in plant inputs).The speed of microbial responses is also poorly understood. For instance, whether it is long‐term legacies or short‐term changes in land‐use intensity that drive changes in microbial communities.To address these topics, we measured multiple microbial functions, bacterial and fungal biomass and abiotic soil properties at two time intervals 3 years apart. This was performed in 150 grassland sites differing greatly in management intensity across three German regions.Observed changes in microbial soil properties were related to both long‐term means and short‐term changes in: abiotic soil properties, land‐use intensity, community abundance‐weighted means of plant functional traits and plant biomass properties in regression and structural equation models. Plant traits, particularly leaf phosphorus, and soil pH were the best predictors of change in soil microbial function, as well as fungal and bacterial biomass, while land‐use intensity showed weaker effects.Indirect legacy effects, in which microbial change was explained by the effects of long‐term land‐use intensity on plant traits, were important, thus indicating a time lag between plant community and microbial change. Whenever the effects of short‐term changes in land‐use intensity were present, they acted directly on soil microorganisms.Synthesis. The results provide new evidence that soil communities and their functioning respond to short‐term changes in land‐use intensity, but that both rapid and longer time‐scale responses to changes in plant functional traits are at least of equal importance. This suggests that management which shapes plant communities may be an effective means of managing soil communities and the functions and services they provide. [ABSTRACT FROM AUTHOR]

• Earthworms affect the distribution of Si among fractions in soil. • More Si extracted from earthworm casts than from undigested materials. • Silicon bound to SOM is the major contributor to additionally extractable Si in soil. • Aggregates occlude plant-available Si in the casts. It is known that earthworms can increase the content of water-extractable silicon (Si) in soil, thus contributing to the availability of Si for plants. However, effects of earthworms on other Si fractions in soil, such as adsorbed Si, Si bound to SOM, Si occluded in pedogenic oxides and amorphous silica have not yet been studied. Therefore, we investigated the effects of the endogeic earthworm Octolasion cyaneum Savigny on the fractionation of Si in soils and that of the epigeic earthworm Eisenia andrei Bouché on the release of Si from model substances (quartz, wheat straw, bioopal). We quantified the amounts of Si in different soil fractions and those released from model substances before and after passage through the earthworm gut by sequential Si extraction. The amounts of Si extracted from the earthworms' casts were generally larger than in the undigested samples. This was especially pronounced for Si bound to soil organic matter (SOM; up to 41%), and for Si in wheat straw (up to 71%) and quartz (up to 1730%). With the soils, the increase in extracted Si was pronounced for the more mobile fractions (Si bound to SOM and occluded in pedogenic oxides) at the expense of amorphous silica. The amounts of mobile and adsorbed Si (plant-available Si) in soil tended to decrease after the passage through the earthworm gut, possibly by occlusion of adsorbents in aggregates formed in the gut. Our results indicate that both mechanical weathering of ingested Si-containing particles and microbial processes, promoting aggregate formation, SOM transformation and mineral solubilization, contribute to the increased release of Si, which induced the redistribution of Si among fractions. [ABSTRACT FROM AUTHOR]

Resource quality and availability modify the microbial contribution to soil organic matter turnover and formation. We created a microbial hotspot at the soil-litter interface in a microcosm experiment to better understand and integrate specific microbial habitats into C turnover models. Reciprocal transplantation of 13 C and 12 C litter on top of soil cores allowed us to follow C flow into specific members of the microbial food web (bacteria and fungi) and to calculate the turnover times of litter-derived C in these microorganisms at three different stages of maize litter decomposition; early stage (0–4 days), intermediate stage (5–12 days) and later stage (29–36 days). Litter age influenced the incorporation rate of C into bacteria and fungi and subsequent turnover in phospholipid fatty acid (PLFA) biomarkers. When fresh litter was applied, both fungi and bacteria were able to assimilate labile litter C in the early stage of decomposition, while lower substrate quality in the intermediate stage of decomposition promoted fungal utilization. Utilization of complex litter C sources was minor in both fungi and bacteria in the later stage of decomposition. Different bacterial substrate utilization strategies were reflected by either a decline of the isotopic signal after exchange of 13 C by 12 C litter or by storage and/or reuse of previously released microbial 13 C. The mean residence time of C in the fungal PLFA 18:2ω6,9 was estimated from 46 to 32 days, which is the same or shorter time than that of bacterial PLFAs. This highlights the role of fungi in rapid turnover processes of plant residues, with implications for implementation of bacterial and fungal processes into C turnover models. [ABSTRACT FROM AUTHOR]

In fertilized paddy soils, the role of resource availability on ammonium (NH 4 + ) assimilation and immobilization by archaea requires advanced understanding as this may have considerable implications on subsequent catalytic steps in the soil N cycle including archaeal nitrous oxide (N 2 O) reduction. To gain a deeper understanding about these process links, we incubated a temperate paddy soil under submerged conditions with or without straw and fertilized with either 15 N-enriched (99 atom% 15 N) or non-enriched (NH 4 ) 2 SO 4 . Notably, a change in community structure and a higher abundance of archaeal N 2 O reductase ( arc-nosZ ) genes in the no straw treatment was observed. This was attributed to NH 4 + assimilation by N 2 O reducing archaea as was further corroborated by a considerable 15 N-enrichment of archaeal glutamate dehydrogenase ( gdhA ) genes. Moreover, indications were found that denitrifying archaea controlled their chemotrophic and heterotrophic metabolisms in response to different availabilities of inorganic and organic N and C resources. However, in the presence of straw, bacterial nosZ genes may have also contributed to the completion of denitrification. Our results suggest that N assimilation contributes to the last step of archaeal denitrification. Likewise, archaea may play a key role in regulating major N fluxes in fertilized paddy soils, especially in the absence of rice straw. [ABSTRACT FROM AUTHOR]

While habitat conditions influencing the abundance of microorganisms in topsoil are well known, these dynamics have been largely unexplored in deeper soil horizons. We investigated the effects of different substrate availabilities and environmental conditions on microbial community composition and carbon flow into specific groups of microorganisms in subsoils using a reciprocal soil transfer experiment within an acid and sandy Dystric Cambisol from a ∼100-year old European beech ( Fagus sylvatica L.) forest in Lower Saxony, Germany. Containers filled with subsoil from 10 to 20 cm (SUB20) and 110 to 120 cm (SUB120) soil depths and with additions of different amounts of 13 C labelled cellulose (1% and 5% of the respective organic carbon content of both soil layers) were exposed either in their home field environment or transferred reciprocally between SUB20 and SUB120 horizons for periods of one, four and twelve months. During the exposure of twelve months, 13 C accumulated up to 15 percent in total microbial biomass and up to 25 percent in fungal PLFAs. Similar microbial 13 C incorporation rates in SUB20 samples located at either 20 or 120 cm depth indicated comparable microclimatic conditions in both soil environments with no depth-dependent effects on the decomposer communities. While low nitrogen availability (when primary C-limitation was alleviated) and water content limited bacterial growth and activity at both depths, fungal abundance and activity were less affected due to their ability to efficiently exploit resources in surrounding soil by hyphal growth and higher drought resistance. Consequently, bacterial PLFAs (phospholipid fatty acids) incorporated less 13 C than fungi. The relatively high, from 1% to 5% cellulose addition linearly increased, 13 C incorporation rates in SUB120 samples at 120 cm depth clearly showed the potential of efficient carbon turnover in deeper soil layers. Spatial separation between subsoil microorganisms and their substrates may therefore be an important factor influencing carbon accumulation in subsoil. [ABSTRACT FROM AUTHOR]

Climate change is affecting agricultural crop production, but there is little information to date from climate change experiments on agricultural ecosystems over the long-term. Data from a ten-year experimental arable field using several climate change factors and their interactions were analyzed with respect to their impacts on crop biomass and harvestable yield production. From a crop rotation of wheat, barley, and oilseed rape was exposed to increased soil temperature (+2.5 °C), reduced summer precipitation amount (−25%), and frequency (−50%) in a multifactorial design. Depending on the growing period, aboveground biomass and crop yield of spring wheat, winter wheat, and spring barley were either increased or unaffected under soil warming. In moist years with high cumulative ambient precipitation, cereal productivity was enhanced due to soil warming, whereas no effect was visible in dry years. Experimental reductions in summer precipitation amount had only minor effects on aboveground biomass and yield of wheat, barley, or oilseed rape, possibly due to an increase in those crops' water use efficiency under water scarcity. However, a reduction in summer precipitation frequency had no effects on aboveground biomass and yield of the selected crops. The results illustrate that effects of climate change on plant development and yield also depend on the immediate weather conditions during the growing period. This underscores the need for long-term climate change experiments under field conditions where, in addition to manipulated experimental treatments, annual variations in precipitation and temperature can be studied. • Year-to-year weather variations studied in ten-year climate change field experiment. • Inter-annual variations in precipitation explained soil warming effects on cereals. • Soil warming enhanced cereal (wheat, barley) biomass and yield in moist years. • Whereas in dry years soil warming showed no effects on biomass and yield of cereals. [ABSTRACT FROM AUTHOR]

The future nicrease of soil temperatures will affect the activity of decomposer organisms, potentially enhancing element cycling and greenhouse gas (i.e. CO 2 and N 2 O) emissions. In a three-factorial microcosm experiment, we investigated the effects of the incorporation of N-rich green manure litter ( Phacelia tanacetifolia Benth.) into an arable soil, of the presence of endogeic earthworms and of elevated soil temperatures (+3.5 °C) on C and N cycling over a period of 42 days. Effects of litter addition were most pronounced. Litter strongly increased amounts of mineral and organic N in the leachate, soil extractable mineral and organic N and organic C, denitrification activity, CO 2 and N 2 O emissions as well as earthworm biomass. Elevated soil temperatures also increased CO 2 emissions, but this effect was more pronounced in treatments without litter. Furthermore, elevated soil temperature reduced the amounts of extractable organic C and NH 4 + , but increased amounts of NO 3 − , indicating enhanced nitrification activity in warmed soils. Earthworm presence increased NO 3 − leaching and this was more pronounced under elevated soil temperatures. N 2 O emissions were strongly increased by 70–90% by earthworm activity, with the highest emissions in the treatment with litter incorporation under elevated temperatures. This treatment also had the largest amount of NO 3 − leaching and the highest denitrification activities. Our results indicate an increasing risk for N losses in the form of nitrate leaching and/or N 2 O emissions from earthworm populated arable soils with a warmer climate in the future. [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: The objective of this study was to underpin the capability of diffuse reflectance Fourier transform mid-infrared spectroscopy (midDRIFTS)-based partial least squares regression (PLSR) analyses to accurately predict soil microbiological properties across six temperate grassland ecosystems differing in their land-use intensity; three sites of low land-use intensity (low LUI) and three fertilized mown meadows (high LUI). In addition, the potential of midDRIFTS-PLSR analyses for spatial studies between soils of contrasting grassland ecosystems was evaluated. 304 samples were subjected to midDRIFTS-PLSR-based predictions of soil microbial biomass, activities of beta-d-glucosidase, xylosidase and urease, as well as bacterial abundance based on 16S rRNA gene quantification. Accuracies of midDRIFTS-PLSR-based predictions across both LUI were, on basis of the residual prediction deviation (RPD), ‘acceptable’ for all soil microbiological properties, in particular soil microbial biomass (coefficient of determination (R 2) = 0.92; RPD = 3.55), urease (0.91; 3.42) and beta-d-glucosidase (0.89; 3.01). Predictions of ‘moderately successful’ accuracy were developed for 16S rRNA gene copies (0.88; 2.93) and xylosidase (0.84; 2.55). Spatial midDRIFTS-PLSR-based predictions between grassland ecosystems were only ‘acceptable’ for soil microbial biomass, while the other studied soil microbiological properties revealed only ‘moderately successful’ predictions. The potential of midDRIFTS-PLSR to predict a range of soil microbiological properties including molecular data with ‘acceptable’ accuracies across the two investigated grassland ecosystems with contrasting land-use intensities was substantiated. However, the prevailing ‘moderately successful’ prediction accuracies between grassland ecosystems were probably due to the dependence on land use-specific data sets for calibration and validation. For prospective application of cost- and time-efficient midDRIFTS-PLSR-based approaches, predictions of soil microbiological properties considering particularly, but not yet ‘acceptable’ molecular data will greatly advance the understanding on the abundance and functional dynamics of soil microbial communities across spatial and temporal scales of contrasting ecosystems. [Copyright &y& Elsevier]

Abstract: Modifications in temperature and precipitation due to climate change will likely affect carbon cycling and soil respiration in terrestrial ecosystems. Despite the important feedback mechanism of ecosystems to climate change, there is still a lack of experimental observation in agricultural ecosystems. In July 2008, we established the Hohenheim Climate Change (HoCC) experiment to investigate effects of elevated temperature and altered precipitation on soil respiration in an arable soil (mean annual temperature and precipitation 8.7°C and 679mm, respectively). We elevated soil temperature to 4cm depth by 2.5°C, reduced the amount of summer precipitation by 25%, and extended dry intervals between precipitation events. For two years, CO2 fluxes were measured weekly and aboveground plant biomass and soil microbial biomass was determined. The results of the two-year study underline the importance of soil moisture as a driving factor in ecosystem response to climate change. Soil warming did not increase soil respiration in the first year; in the second year, a 27% increase was measured. The differential response of soil respiration to warming was most likely driven by soil moisture. In summer 2009, water limitation reduced microbial biomass in the heated plots thereby suppressing the stimulatory effect of elevated temperature on soil microorganisms. In summer 2010, the reduction in soil moisture was less pronounced and microbial biomass and respiration were not affected by water limitation. Temperature elevation significantly reduced Q 10 values of soil respiration by 0.7–0.8. Altered precipitation showed only minor effects during the first two years of the experiment. We conclude from our study that the moisture regime of soils under elevation of temperature will largely determine whether different soils will serve either as carbon sources or as carbon sinks. [Copyright &y& Elsevier]

Abstract: The rhizosphere and the detritusphere are hot spots of microbial activity, but little is known about the interface between rhizosphere and detritusphere. We used a three-compartment pot design to study microbial community structure and enzyme activity in this interface. All three compartments were filled with soil from a long-term field trial. The two outer compartments were planted with maize (root compartment) or amended with mature wheat shoot residues from a free air CO2 enrichment experiment (residue compartment) and were separated by a 50 μm mesh from the inner compartment. Soil, residues and maize differed in 13C signature (δ13C soil −26.5‰, maize roots −14.1‰ and wheat residues −44.1‰) which allowed tracking of root- and residue-derived C into microbial phospholipid fatty acids (PLFA). The abundance of bacterial and fungal PLFAs showed clear gradients with highest abundance in the first 1–2 mm of the root and residue compartment, and generally higher values in the vicinity of the residue compartment. The δ13C of the PLFAs indicated that soil microorganisms incorporated more carbon from the residues than from the rhizodeposits and that the microbial use of wheat residue carbon was restricted to 1 mm from the residue compartment. Carbon incorporation into soil microorganisms in the interface was accompanied by strong microbial N immobilisation evident from the depletion of inorganic N in the rhizosphere and detritusphere. Extracellular enzyme activities involved in the degradation of organic C, N and P compounds (β-glucosidase, xylosidase, acid phosphatase and leucin peptidase) did not show distinct gradients in rhizosphere or detritusphere. Our microscale study showed that rhizosphere and detritusphere differentially influenced microbial C cycling and that the zone of influence depended on the parameter assessed. These results are highly relevant for defining the size of different microbial hot spots and understanding microbial ecology in soils. [Copyright &y& Elsevier]

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: The aim of the present study was to investigate whether land-use intensity (LUI) contributes to spatial variation in microbial abundance and function in grassland ecosystems. At one time point, three sites at low (unfertilized pastures), at intermediate (fertilized mown pastures) and at high (fertilized mown meadows) LUIs were selected in southern Germany. Within each of these nine grassland sites, 54 soil samples (0–10cm) were taken in a 10m×10m area in spring. Plot-scale spatial dependence and autocorrelation of soil biogeochemical properties, microbial biomass and enzymes involved in C-, N- and P-cycling were analyzed. Applying geostatistics (exponential or spherical model) revealed that most chemical and microbiological properties showed at least a moderate spatial autocorrelation. Chemical soil properties (e.g. Corg, Nt, pH) were characterized by practical ranges (pRange) of between 1 and 14m, whereas soil microbiological properties showed a greater variation of pRanges, providing evidence of spatial heterogeneity at multiple scales. The expected decrease in small-scale spatial heterogeneity in high LUI could not be confirmed for microbiological soil properties, because sampling in early spring might have reduced the influence of growing plants and fertilization. However, microbial biomass carbon was significantly greater in high LUIs, indicating that the benefit to soil microbial populations from the long-term increase in substrate and nutrient availability in fertilized grasslands is independent from factors affecting spatial structures in the short-term. [Copyright &y& Elsevier]

Elevated atmospheric carbon dioxide concentrations ([CO]) might change the abundance and the function of soil microorganisms in the depth profile of agricultural soils by plant-mediated reactions. The seasonal pattern of abundance and activity of nitrate-reducing bacteria was studied in a Mini-FACE experiment planted with oilseed rape ( Brassica napus). Three depths (0-10, 10-20 and 20-30 cm) were sampled. Analyses of the abundances of total (16S rRNA gene) and nitrate-reducing bacteria ( narG, napA) revealed strong influences of sampling date and depth, but no [CO] effects. Abundance and activity of nitrate reducers were higher in the top soil layer and decreased with depth but were not related to extractable amounts of nitrogen and carbon in soil. Dry periods reduced abundances of total and nitrate-reducing bacteria, whereas the potential activity of the nitrate reductase enzyme was not affected. Enzyme activity was only weakly correlated to the abundance of nitrate-reducing bacteria but was related to NH and NO concentrations. Our results suggest that in contrast to the observed pronounced seasonal changes, the elevation of atmospheric [CO] has only a marginal impact on nitrate reducers in the investigated arable ecosystem. [ABSTRACT FROM AUTHOR]

Increased plant productivity under elevated atmospheric CO2 concentrations might increase soil carbon (C) inputs and storage, which would constitute an important negative feedback on the ongoing atmospheric CO2 rise. However, elevated CO2 often also leads to increased soil moisture, which could accelerate the decomposition of soil organic matter, thus counteracting the positive effects via C cycling. We investigated soil C sequestration responses to 5 years of elevated CO2 treatment in a temperate spring wheat agroecosystem. The application of 13C-depleted CO2 to the elevated CO2 plots enabled us to partition soil C into recently fixed C (Cnew) and pre-experimental C (Cold) by 13C/12C mass balance. Gross C inputs to soils associated with Cnew accumulation and the decomposition of Cold were then simulated using the Rothamsted C model ‘RothC.’ We also ran simulations with a modified RothC version that was driven directly by measured soil moisture and temperature data instead of the original water balance equation that required potential evaporation and precipitation as input. The model accurately reproduced the measured Cnew in bulk soil and microbial biomass C. Assuming equal soil moisture in both ambient and elevated CO2, simulation results indicated that elevated CO2 soils accumulated an extra ∼40–50 g C m−2 relative to ambient CO2 soils over the 5 year treatment period. However, when accounting for the increased soil moisture under elevated CO2 that we observed, a faster decomposition of Cold resulted; this extra C loss under elevated CO2 resulted in a negative net effect on total soil C of ∼30 g C m−2 relative to ambient conditions. The present study therefore demonstrates that positive effects of elevated CO2 on soil C due to extra soil C inputs can be more than compensated by negative effects of elevated CO2 via the hydrological cycle. [ABSTRACT FROM AUTHOR]

Abstract: Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of −0.0063 and −0.0316MPa) and with or without addition of 13C labelled rye residues (δ13C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at −0.0063MPa, whereas 41.7% remained on soils at −0.0316MPa. Most of the lost litter C was mineralised to CO2, with 47.9% and 43.4% at −0.0063 and −0.0316MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils. [Copyright &y& Elsevier]

Abstract: It has been hypothesized that defoliation and herbivory alter the availability of soluble carbon in the rhizosphere and thereby the biomass and activity of soil microorganisms, and presumably higher trophic levels as well. To test this hypothesis, we established a laboratory experiment investigating effects of shoot cutting of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) on soil microorganisms and juvenile endogeic earthworms of the species Octolasion tyrtaeum (Savigny), and Aporrectodea caliginosa (Savigny). Plants were grown in microcosms for 4 weeks, cut 5cm above the soil surface and left to regrow until microcosms were destructively sampled after another 4 weeks. Defoliation decreased total shoot biomass of T. repens but had no significant effect on shoot biomass of L. perenne. Root biomass of L. perenne significantly exceeded that of T. repens, but defoliation reduced root biomass of L. perenne and T. repens by 48.6 and 67.3%, respectively. Microbial biomass per gram of soil in treatments with L. perenne exceeded that in treatments with T. repens, but when calculated per gram of roots, microbial biomass in treatments with T. repens exceeded that in treatments with L. perenne. Defoliation of both plant species significantly increased microbial biomass. Microbial activity differed between treatments and was higher in the grass than in the clover treatment in the beginning, but the reverse was the case later. The biomass of both earthworm species decreased and was only slightly affected by the treatments. In addition, neither earthworm species affected plant growth, microbial biomass or the production of CO2. Our results suggest that defoliation of perennial ryegrass and white clover increased the availability of carbon in the rhizosphere as indicated by the increase in microbial biomass, but that quality and quantity of rhizodeposits differed over time and between plant species. Furthermore, endogeic earthworms were unable to exploit the microbial biomass pool in soil, rather, rhizosphere microorganisms appeared to have effectively competed with endogeic earthworms and exploited root exudates. [Copyright &y& Elsevier]

The influence of elevated atmospheric CO2 concentrations ([CO2]) on the decomposition of spring wheat (Triticum aestivum L. cv. Triso) residues remaining in the soil after harvest was simulated in a microcosm incubation experiment in the lab. Undisturbed soil cores with and without visible wheat residues were taken in the third year after establishment from a Mini-free-air carbon dioxide enrichment (FACE) system, in which we used 13C-depleted CO2 to determine the contribution of plant-derived carbon to overall carbon mineralization. The Mini-FACE system is located on a Gleyic Cambisol near Hohenheim (Baden-Württemberg, Germany). Carbon dioxide production and leaching of nitrogen and inorganic and organic carbon were measured during 191 days of incubation. Rates of CO2 production were generally highest in all treatments during the first two weeks of the incubation and this was followed by a steady decrease until day 58. After this day mineralization rates declined only weakly until the end of the incubation. Cumulative carbon mineralization was similar in the two treatments without visible wheat residues, but significantly lower in the elevated (−19.0%) versus ambient [CO2] treatment with visible plant residues (significant [CO2]×residue interaction; F 1,13 =7.17; P =0.019). This result demonstrated reduced decomposition of wheat residues grown under elevated [CO2]. The contribution of plant-derived carbon to soil respiration was highest in the beginning, followed by a steady decrease until the end of the incubation. Irrespective of incubation time, the amount of mineralized, plant-derived carbon was higher in the treatment with visible wheat residues. Leaching of inorganic carbon (DIC) tended to be affected by [CO2] (F 6,8 =4.50; P =0.057), with more DIC leached in the elevated [CO2] treatment without (+47.2%) and with visible plant residues (+29.5%) than in the respective ambient CO2 treatments. The amount of carbon potentially sequestered as DIC in the wheat cropping system was small compared to the effects of elevated [CO2] on the amounts and decomposition of plant residues. Increased input of plant residues and reduced decomposition of plant-derived carbon are discussed as possible mechanisms for enhanced carbon sequestration under elevated atmospheric CO2 concentration. [Copyright &y& Elsevier]

Abstract: Anecic earthworm species function as ecosystem engineers by structuring the soil environment, incorporating large amounts of litter and seeds into soil and, thereby influence the composition of plant communities. The aim of the present greenhouse experiment was to investigate the effects of three apparently anecic earthworm species on wheat seed burial, seedling establishment, wheat growth and litter incorporation. The three species differed substantially in their behavior and effect on plant establishment. Aporrectodea longa did not incorporate litter into the soil while Lumbricus terrestris (−69%) and Lumbricus rubellus friendoides (−75%) reduced the litter layer considerably during 9 weeks of incubation. Moreover, L. terrestris and L. rubellus friendoides buried more wheat seeds than A. longa. Fewer seeds germinated when buried by A. longa compared to L. terrestris. The behavior of L. terrestris and L. rubellus friendoides was characteristic for anecic earthworm species whereas that of A. longa rather resembled that of endogeic species. The present study is the first experimental evidence for anecic behavior in L. rubellus friendoides. [Copyright &y& Elsevier]

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 (Cmic) 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 13CO2 pulse-labelling was performed to assess the distribution of assimilated 13C 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. [ABSTRACT FROM AUTHOR]

Abstract: Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic matter and soil microorganisms in the different particle-size fractions. We investigated soil organic matter content, xylanase- and microbial activity and community structure in bulk soil and particle size fractions of Lumbricus terrestris L. casts and in soil with and without the addition of beech litter. Earthworm gut passage did not affect the particle-size distribution but the content of soil organic matter was decreased in the fine sand fraction in treatments without litter (−6.80%) and increased in treatments with litter (+33.23%). The soil organic matter content of the clay fraction tended to be higher in earthworm casts. Xylanase activity was at a maximum in the fine sand fraction, lower in the coarse sand fraction and at a similar minimum in the silt- and clay-sized fraction. In the coarse sand fraction of the cast and litter treatments xylanase activity was increased by 39.1% and 124.8%, respectively. In the silt-sized fraction of casts the addition of litter increased xylanase activity (+58.6%) whereas, in casts without litter it was decreased (−36.25%). In the particle size fractions of casts, the content of bacterial PLFAs was decreased in the fine sand fraction and tended to be decreased in the clay fraction compared to the respective fractions in soil. In the silt fraction the fungal-to-bacterial PLFA ratio was higher in casts than in soil. We conclude that earthworms stabilize soil organic matter in cast aggregates predominantly by increasing the soil organic matter content in the clay fraction where it becomes protected against microbial attack. Organic matter in the coarse and fine sand fractions is decomposed primarily by fungi; xylanase is very active in these sand fractions and incorporation of litter into these fractions by the earthworms increased fungal biomass. Comminution of litter during passage through the earthworm gut increased the biomass and activity of fungi also in the silt fraction. The use of PLFA profiles in combination with other quantitative microbial methods improves the understanding of stabilizing and mobilizing processes in earthworm casts. [Copyright &y& Elsevier]

Abstract: The anecic earthworm Lumbricus terrestris L. is known to strongly affect organic matter transformation and soil development in temperate ecosystems. Processes in the gut of the earthworm play an important role where sand grains contribute to the grinding of leaf litter in the muscular gizzard. To investigate effects of sand and litter availability and earthworm gut passage on carbon and nitrogen mineralisation two experiments were set up, one with beech forest soil and beech litter, the other with arable soil and rye litter, thereby exploring the effects of agricultural management and litter type on mobilisation and stabilisation of organic matter. Three different sand concentrations were tested in the forest soil: without, with 25% and with 50% sand (dry weight). In the arable soil only treatments without and with 25% sand were established. The soil was taken from a beech forest on limestone and from a long-term agricultural experiment. Earthworms were fed fragmentised beech or rye litter (<4 mm), or were kept without litter. Earthworm casts produced during 65 days were placed in microcosms and incubated at 20 °C for 280 days. CO2 production and mineral nitrogen in leaching water were measured at regular intervals. Earthworms lost more mass in arable than in forest soil; even though in arable soil the earthworms produced two times more casts. Litter availability reduced burrow construction. Casts were more enriched in carbon and nitrogen if litter was available. Leaching of Nmin from casts of L. terrestris strongly exceeded that of the corresponding soil treatments in the arable soil but not in the forest soil. In earthworm casts decomposition of rye litter was strongly increased, in particular early in the experiment. In contrast, the decomposition of beech litter was reduced initially and stimulated later. The addition of sand stimulated carbon mineralisation in both organic matter in soil and enclosed in earthworm casts. In soils with high clay content (forest soil) the stimulating effect of sand was less pronounced than in soils with low clay content (arable soil). Overall, except in earthworm casts of the forest soil without litter, cumulative CO2 production exceeded that in the corresponding soil suggesting that in earthworm casts mobilisation rather than stabilisation processes prevail. [Copyright &y& Elsevier]

Summary: Endogeic earthworms play an important role in mobilisation and stabilisation of carbon and nitrogen in forest and arable soils. Soil organic matter is the major food resource for endogeic earthworms, but little is known about the size and origin of the organic matter pool on which the earthworms actually live. We measured changes in body mass of juvenile endogeic earthworms, Octolasion tyrtaeum (Savigny), in soils with different C and N contents resulting from different fertiliser treatments. The soil was taken from a long-term experiment (Statischer Düngungsversuch, Bad Lauchstädt, Germany). The treatments included (1) non-fertilised soil, (2) NPK fertilised soil, (3) farmyard manure fertilised soil and (4) NPK + farmyard manure fertilised soil. The soil was incubated in microcosms with and without one juvenile O. tyrtaeum for 80 days. Earthworm biomass decreased in non-fertilised soil by 48.6%, in NPK soil by 9.4%, but increased in farmyard manure soil by 19.7% and 42.8% (soil with additional NPK application). In farmyard manure treatments the biomass of bigger individuals decreased, but in smaller individuals it increased. In NPK fertilised soil without farmyard manure only small O. tyrtaeum increased in body mass, whereas in the non-fertilised soil all individuals decreased in body mass. Generally, soil respiration correlated positively with soil carbon content. Earthworms significantly increased soil respiration and nitrogen leaching and this was most pronounced in farmyard manure treatments. Microbial activity was generally higher in farmyard manure soil indicating that farmyard manure increases labile organic matter pools in soil. Also, biomass of earthworms and microorganisms was increased in farmyard manure soil. The presence of earthworms reduced microbial biomass, suggesting that earthworms feed on microorganisms or/and that earthworms and soil microorganisms competed for similar organic matter pools in soil. The results demonstrate that NPK fertilisation only is insufficient to sustain O. tyrtaeum, whereas long-term fertilisation with farmyard manure enables survival of endogeic species due to an increased pool of utilisable soil organic matter in arable soil. [Copyright &y& Elsevier]

Earthworms are important members of the soil macrofauna. They modify soil physical properties, soil organic matter decomposition, and thus regulate carbon and nitrogen cycling in soil. However, their interactions with soil microorganisms are still poorly understood, in particular the effect of gut passage on the community structure of ingested microorganisms. Moreover, it is still unsolved, if earthworms, like many other soil-feeding invertebrates, possess an indigenous gut microbial community. Therefore, we investigated the bacterial and archaeal community structure in soil (with and without additional beech litter), gut, and fresh casts of Lumbricus terrestris, an anecic litter-feeding earthworm, by means of terminal-restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA gene fragments. Ecological indices of community diversity and similarity, calculated from the T-RFLP profiles, revealed only small differences between the bacterial and archaeal communities in soil, gut, and fresh casts under both feeding conditions, especially in comparison to other soil-feeding invertebrates. However, multivariate statistical analysis combining multidimensional scaling and discriminant function analysis proved that these differences were highly significant, in particular when the earthworms were fed beech litter in addition. Because there were no dominant gut-specific OTUs detectable, the existence of an abundant indigenous earthworm microbial community appears unlikely, at least in the midgut region of L. terrestris. [Copyright &y& Elsevier]

Microplastics (MP, plastic particles between 0.1 and 5000 μm) contaminate agricultural soils through the application of organic fertilizers, sewage sludge, and plastic mulch. MP surfaces and the MP-soil interface provide specific habitats for soil microorganisms—the plastisphere. Microorganisms in the plastisphere may benefit from utilizing MP as a carbon (C) source. Hydrolyzable MP with ester bonds are susceptible to enzymatic depolymerization by hydrolysis. In a microcosm experiment, we investigated MP biodegradation of small and large (< 0.5 mm and 0.5–2 mm respectively), hydrolyzable (a poly(lactic acid)/poly(butylene co-adipate terephthalate) blend, PLA/PBAT) and non-hydrolyzable (low-density polyethylene, LDPE) polymers, and the effects of these MP on microorganisms in dry and wet MP-amended soil. MP affected neither abundance and composition of the main soil microbial groups (fungi, Gram-negative, and Gram-positive bacteria), specific activities of ß-glucosidase, ß-xylosidase, lipase, and phenoloxidase, nor respiration in MP-amended soil. Only large PLA/PBAT particles in dry soil were significantly mineralized (15.4% of initial PLA/PBAT-C after 230 days). PLA/PBAT mineralization coincided with enhanced lipase and ß-glucosidase activities on the surfaces of individual PLA/PBAT particles extracted from the soil after incubation (compared to LDPE and non-incubated PLA/PBAT particles). We detected cracks on the surfaces of PLA/PBAT particles using scanning electron microscopy, indicating initiation of MP biodegradation, presumably due to depolymerization by lipases. Results suggest that the PLA/PBAT plastisphere is a polymer-specific habitat for lipase-producing soil microorganisms. Our study demonstrates that analyzing biogeochemical interactions within polymer-specific plastispheres is essential to assess MP fate and their impacts on microbially driven soil processes. [ABSTRACT FROM AUTHOR]

It is known that earthworms can increase the content of water-extractable silicon (Si) in soil, thus contributing to the availability of Si for plants. However, effects of earthworms on other Si fractions in soil, such as adsorbed Si, Si bound to SOM, Si occluded in pedogenic oxides and amorphous silica have not yet been studied. Therefore, we investigated the effects of the endogeic earthworm Octolasion cyaneum Savigny on the fractionation of Si in soils and that of the epigeic earthworm Eisenia andrei Bouché on the solubility of Si-containing model substances. We quantified the amounts of Si before and after passage through the earthworm gut by using a sequential Si extraction procedure. The amounts of Si extracted from the earthworms' casts were generally larger than in the undigested samples. This increase was especially pronounced for Si bound to soil organic matter (up to 41%), and for Si in wheat straw (up to 71%) and quartz (up to 1730%). With the soils, the increase in extracted Si was pronounced for the more mobile fractions (Si bound to organic matter and occluded in pedogenic oxides) at the expense of the fraction of amorphous silica. The amounts of mobile and adsorbed Si (plant-available Si) in soil tended to decrease after the passage through the earthworm gut, possibly by occlusion in aggregates formed in the gut. Our results indicate that both mechanical weathering of ingested Si-containing particles and microbial processes, promoting aggregate formation, SOM degradation and mineral solubility, contribute to the increased solubility of Si, which induced the redistribution of Si among fractions. [ABSTRACT FROM AUTHOR]

Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled 'real world' ecosystems remains challenging due to environmental variation among sites, confounding biodiversity ecosystem functioning relations in observational studies. To bridge the gap between classical biodiversity‐ecosystem functioning experiments and observational studies of naturally assembled and managed ecosystems, we created regionally replicated, within‐site gradients of species richness by seeding across agricultural grasslands differing in land‐use intensity (LUI) and abiotic site conditions.Within each of 73 grassland sites, we established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance and measured 12 ecosystem functions related to productivity, and carbon and nutrient cycling after 4 years. We then analysed the effects of plant diversity (seeded richness as well as realized richness), functional community composition, land use and abiotic conditions on the ecosystem functions within (local scale) as well as among grassland sites (landscape scale).Despite the successful creation of a within‐site gradient in plant diversity (average increase in species richness in seeding treatments by 10%–35%), we found that only one to two of the 12 ecosystem functions responded to realized species richness, resulting in more closed nitrogen cycles in more diverse plant communities. Similar results were found when analysing the effect of the seeding treatment instead of realized species richness. Among sites, ecosystem functioning was mostly driven by environmental conditions and LUI. Also here, the only functions related to plant species richness were those associated with a more closed nitrogen cycle under increased diversity.The minor effects of species enrichment we found suggest that the functionally‐relevant niche space is largely saturated in naturally assembled grasslands, and that competitive, high‐functioning species are already present.Synthesis: While nature conservation and cultural ecosystem services can certainly benefit from plant species enrichment, our study indicates that restoration of plant diversity in naturally assembled communities may deliver only relatively weak increases in ecosystem functioning, such as a more closed nitrogen cycle, within the extensively to moderate intensively managed agricultural grasslands of our study. [ABSTRACT FROM AUTHOR]

Lacking comparability among rainfall manipulation studies is still a major limiting factor for generalizations in ecological climate change impact research. A common framework for studying ecological drought effects is urgently needed to foster advances in ecological understanding the effects of drought. In this study, we argue, that the soil–plant–atmosphere‐continuum (SPAC), describing the flow of water from the soil through the plant to the atmosphere, can serve as a holistic concept of drought in rainfall manipulation experiments which allows for the reconciliation experimental drought ecology. Using experimental data, we show that investigations of leaf water potential in combination with edaphic and atmospheric drought – as the three main components of the SPAC – are key to understand the effect of drought on plants. Based on a systematic literature survey, we show that especially plant and atmospheric based drought quantifications are strongly underrepresented and integrative assessments of all three components are almost absent in current experimental literature. Based on our observations we argue, that studying dynamics of plant water status in the framework of the SPAC can foster comparability of different studies conducted in different ecosystems and with different plant species and can facilitate extrapolation to other systems, species or future climates. [ABSTRACT FROM AUTHOR]

Even small changes in microbial decomposition rates of soil organic carbon (SOC) at the regional scale have the potential to modify land-atmospheric feedbacks at the global scale. Limited understanding of the regulation of microbial driven processes has led to major uncertainty in global SOC estimates. Therefore, to better understand the large scale processes controlling SOC dynamics, we examined the influence of SOC quantity, quality, and soil physical and biochemical properties on soil basal respiration and of the temperature sensitivities (Q 10 ) of soil respiration and enzymes (β-glucosidase and xylanase) at two scales: landscape (two individual areas, each approximately 27 km 2 ) and regional (pooled data of both areas). Soil samples (0–30 cm soil depth) originated from 41 agricultural sites distributed over two areas in southwest Germany differing in climatic and geological conditions. We used a two-step data analysis procedure; variable selection through random Forest regression, followed by shortlisting of significant explanatory variables using linear mixed-effect models. Microbial biomass regulated soil basal respiration at both scales, whereas soil C:N ratio played an important role only at the regional scale based on mixed-effect models. Soil texture significantly explained temperature sensitivity (Q 10 ) of soil respiration at both scales. Different SOC quality fractions characterized by midDRIFTS played a minor role, whereas extractable organic C related negatively to the respiration Q 10 . Soil properties controlling soil enzymes (Q 10 ) were scale-specific. We found pH to be the main factor affecting β-glucosidase Q 10 at the landscape scale. We argue that scale-specificity of variables may depend on homogeneity of study areas and should be considered when exploring SOC dynamics. Our study identified direct and indirect controlling factors affecting soil basal respiration and its temperature sensitivity, providing vital information for SOC dynamics at large scales. [ABSTRACT FROM AUTHOR]

Global warming will likely enhance greenhouse gas ( GHG) emissions from soils. Due to its slow decomposability, biochar is widely recognized as effective in long-term soil carbon (C) sequestration and in mitigation of soil GHG emissions. In a long-term soil warming experiment (+2.5 °C, since July 2008) we studied the effect of applying high-temperature Miscanthus biochar (0, 30 t/ha, since August 2013) on GHG emissions and their global warming potential ( GWP) during 2 years in a temperate agroecosystem. Crop growth, physical and chemical soil properties, temperature sensitivity of soil respiration ( R s), and metabolic quotient ( qCO2) were investigated to yield further information about single effects of soil warming and biochar as well as on their interactions. Soil warming increased total CO2 emissions by 28% over 2 years. The effect of warming on soil respiration did not level off as has often been observed in less intensively managed ecosystems. However, the temperature sensitivity of soil respiration was not affected by warming. Overall, biochar had no effect on most of the measured parameters, suggesting its high degradation stability and its low influence on microbial C cycling even under elevated soil temperatures. In contrast, biochar × warming interactions led to higher total N2O emissions, possibly due to accelerated N-cycling at elevated soil temperature and to biochar-induced changes in soil properties and environmental conditions. Methane uptake was not affected by soil warming or biochar. The incorporation of biochar-C into soil was estimated to offset warming-induced elevated GHG emissions for 25 years. Our results highlight the suitability of biochar for C sequestration in cultivated temperate agricultural soil under a future elevated temperature. However, the increased N2O emissions under warming limit the GHG mitigation potential of biochar. [ABSTRACT FROM AUTHOR]

Background: Microplastics (MP, plastic particles <5 mm) are ubiquitous in arable soils due to significant inputs via organic fertilizers, sewage sludges, and plastic mulches. However, knowledge of typical MP loadings, their fate, and ecological impacts on arable soils is limited. Aims: We studied (1) MP background concentrations, (2) the fate of added conventional and biodegradable MP, and (3) effects of MP in combination with organic fertilizers on microbial abundance and activity associated with carbon (C) cycling, and crop yields in an arable soil. Methods: On a conventionally managed soil (Luvisol, silt loam), we arranged plots in a randomized complete block design with the following MP treatments (none, low‐density polyethylene [LDPE], a blend of poly(lactic acid) and poly(butylene adipate‐co‐terephthalate) [PLA/PBAT]) and organic fertilizers (none, compost, digestate). We added 20 kg MP ha–1 and 10 t organic fertilizers ha–1. We measured concentrations of MP in the soil, microbiological indicators of C cycling (microbial biomass and enzyme activities), and crop yields over 1.5 years. Results: Background concentration of MP in the top 10 cm was 296 ± 110 (mean ± standard error) particles <0.5 mm per kg soil, with polypropylene, polystyrene, and polyethylene as the main polymers. Added LDPE and PLA/PBAT particles showed no changes in number and particle size over time. MP did not affect the soil microbiological indicators of C cycling or crop yields. Conclusions: Numerous MP occur in arable soils, suggesting diffuse MP entry into soils. In addition to conventional MP, biodegradable MP may persist under field conditions. However, MP at current concentrations are not expected to affect C turnover and crop yield. [ABSTRACT FROM AUTHOR]

Abstract: Endogeic earthworms ingest large amounts of organic matter enclosed in mineral soil. Part of the soil organic matter is mobilised during the gut passage, but the overall effect of earthworms on the dynamics of soil organic carbon (SOC) is poorly understood because the origin and age of the mobilised SOC pool are unknown. To determine whether endogeic earthworms mobilise old SOC pools, we studied the effect of Octolasion tyrtaeum (Savigny) on 13C signatures of CO2 evolved from soil of a maize field incubated in microcosms with and without earthworms for 150days. Cultivation on this field had changed from wheat (C3 plant) to maize (C4 plant) 23years ago. Earthworms generally decreased in body mass during the experiment but increased CO2 production. Compared to the initial signature (−22.8±0.1‰PDB), δ13C signatures of O. tyrtaeum were more depleted in the wheat (−23.6±0.3‰PDB) and more enriched in the maize soil (−21.0±0.4‰PDB) at the end of the experiment. The δ13CO2-C signatures in the wheat soil were not affected by earthworms, but earthworms decreased δ13CO2-C values in the maize soil during the second half of the incubation period. This indicates enhanced mineralization of old wheat-derived carbon. The results suggest that lumbricid endogeic earthworms contribute to the mobilisation of old carbon pools in soils. [Copyright &y& Elsevier]

Climate change factors alter soil microbial biomass and respiration, which represent two key parameters of carbon (C) cycling in soils. While these interrelations are increasingly well described for soils in natural ecosystems, long-term studies conducted in temperate agricultural ecosystems do rarely exist. Here we used the 'Hohenheim Climate Change Experiment (HoCC)' to describe the response of microbial biomass and respiration to interacting effects of climate change factors. We were interested in whether effects would be season specific, and if ultimately, climate change factors would affect the total soil organic carbon (SOC) content in the arable soil. The HoCC experiment is an agroecosystem where soils were permanently warmed for one decade, and summer precipitation amount and frequency were reduced. We found that soil respiration was not affected by reduced summer precipitation, but strongly increased by warming. This increase was not season specific and persisted over the years. Further, warming continuously enhanced labile C availability, while microbial biomass did not differ between warmed and ambient temperature soils. Therefore, soil respiration stimulated by warming was independent of microbial biomass, and accordingly, we found an increase of the metabolic quotient. Despite the warming induced increase in soil respiration, no indications for a loss in SOC content of the arable soil was detected. These results suggest that in an arable soil with overall low SOC content, the persisting stimulation of respiration due to warming is driven by an agroecosystem specific labile C pool dynamic. • Warming persistently stimulated soil respiration over ten years across seasons. • Reduced summer precipitation only played a minor role within respiration dynamics. • Microbial biomass was largely unaffected by climate change factors across seasons. • Warming increased labile C availability which explains increase in respiration. • No SOC loss from warmed arable soil despite persistent increase in respiration. [ABSTRACT FROM AUTHOR]

Climate is changing and predicted future scenarios include both changes in longterm mean climatic conditions and intensification of extreme events such as drought. Drought can have a major impact on soil functional processes; soil microorganisms, key to these processes, depend on water and temperature dynamics. Consequently, feedback mechanisms regarding microbially mediated carbon and nitrogen cycling in soils may be affected. There are indications that microbial exposure to increasingly unfavorable environmental conditions influences their stress responses. Here, the long-term field experiment Hohenheim Climate Change (HoCC) provided a research platform to explore how microbial exposure to long-term reduced water availability and soil warming modifies microbially driven soil processes, especially gas fluxes from soil, both during drought and after rewetting. The HoCC experiment is an agroecosystem in which the soil microbiome has been exposed to reduced annual mean precipitation and elevated temperature since 2008. Treatment levels were chosen based on a realistic future climate scenario. In June 2019, we exposed this system to a drought period of four weeks. We found that even after 11 years, warming remained a driver of CO2 and N2O fluxes across the different soil moisture conditions in our drought experiment. Importantly, however, microbial exposure to long-term reduced water availability limited the stimulatory effect of warming on gas fluxes during drought and after rewetting. Our results were neither related to a legacy effect within overall microbial biomass carbon levels nor a shift towards enhanced fungal abundance. We found no indications that extracellular enzyme activities or microbial substrate availability explained the gas flux dynamics observed in our drought experiment. Our study indicates that soil warming promotes gaseous C and N loss even under extreme drought conditions. We suspect, however, that a shift in microbial function following long-term water limitation can hamper the enhancing effect of warming on soil gas fluxes. [ABSTRACT FROM AUTHOR]

One of the challenges in soil ecology is to determine which organisms utilise stable forms of carbon in soil. Recent studies have indicated that endogeic earthworms are able to mobilise such stable carbon compounds. However, it remains unclear which particular compounds of stabilised carbon in soil are utilised by earthworms. Furthermore, current knowledge on ecological groups and food resources of earthworms is mainly based on direct observations, hence only reflecting what was ingested but not what was actually assimilated. We analysed seven earthworm species in beech and spruce forests and the associated litter, earthworm middens and soils, and employed compound-specific 13C stable isotope analysis of fatty acids (FAs) to identify the origins of carbon resources of the earthworms. To relate food resources to carbon compounds of different stability, we analysed 13C signatures of FAs of different particle size fractions. FA δ13C profiles of epigeic and endogeic earthworm species indicated assimilation of recently-fixed and recalcitrant carbon resources, respectively, whereas anecic earthworms assimilated a mixture of resources of different stability. Utilisation of carbon resources did not differ between beech and spruce forests. Endogeic species were associated with neutral lipids of soil particle size fractions with δ13C signatures of the bacterial marker a15:0 in earthworms resembling those of the clay fraction. This suggests that they assimilated carbon associated with small particle size fractions attached to clay-humus complexes. The results showed that earthworms of different ecological groups utilise carbon pools of different origin and stability. As indicated by neutral lipids of bacterial origin, physically-stabilised organic matter appears to contribute to the nutrition of endogeic earthworms in forest systems. [ABSTRACT FROM AUTHOR]

Sustainable forest management requires understanding of ecosystem phosphorus (P) cycling. Lang et al. (2017) [Biogeochemistry,https://doi.org/10.1007/s10533-017-0375-0] introduced the concept of P-acquiring vs. P-recycling nutrition strategies for European beech (Fagus sylvatica L.) forests on silicate parent material, and demonstrated a change from P-acquiring to P-recycling nutrition from P-rich to P-poor sites. The present study extends this silicate rock-based assessment to forest sites with soils formed from carbonate bedrock. For all sites, it presents a large set of general soil and bedrock chemistry data. It thoroughly describes the soil P status and generates a comprehensive concept on forest ecosystem P nutrition covering the majority of Central European forest soils. For this purpose, an Ecosystem P Nutrition Index (ENIP) was developed, which enabled the comparison of forest P nutrition strategies at the carbonate sites in our study among each other and also with those of the silicate sites investigated by Lang et al. (2017). The P status of forest soils on carbonate substrates was characterized by low soil P stocks and a large fraction of organic Ca-bound P (probably largely Ca phytate) during early stages of pedogenesis. Soil P stocks, particularly those in the mineral soil and of inorganic P forms, including Al- and Fe-bound P, became more abundant with progressing pedogenesis and accumulation of carbonate rock dissolution residue. Phosphorus-rich impure, silicate-enriched carbonate bedrock promoted the accumulation of dissolution residue and supported larger soil P stocks, mainly bound to Fe and Al minerals. In carbonate-derived soils, only low P amounts were bioavailable during early stages of pedogenesis, and, similar to P-poor silicate sites, P nutrition of beech forests depended on tight (re)cycling of P bound in forest floor soil organic matter (SOM). In contrast to P-poor silicate sites, where the ecosystem P nutrition strategy is direct biotic recycling of SOM-bound organic P, recycling during early stages of pedogenesis on carbonate substrates also involves the dissolution of stable Ca-Porg precipitates formed from phosphate released during SOM decomposition. In contrast to silicate sites, progressing pedogenesis and accumulation of P-enriched carbonate bedrock dissolution residue at the carbonate sites promote again P-acquiring mechanisms for ecosystem P nutrition. [ABSTRACT FROM AUTHOR]

Changes in frequency and intensity of drought events are anticipated in many areas of the world. In pasture, drought effects on soil nitrogen (N) cycling are spatially and temporally heterogeneous due to N redistribution by grazers. We studied soil N cycling responses to simulated summer drought and N deposition by grazers in a 3-year field experiment replicated in two grasslands differing in climate and management. Cattle urine and NHNO application increased soil NH and NO concentrations, and more so under drought due to reduced plant uptake and reduced nitrification and denitrification. Drought effects were, however, reflected to a minor extent only in potential nitrification, denitrifying enzyme activity (DEA), and the abundance of functional genes characteristic of nitrifying (bacterial and archaeal amoA) and denitrifying ( narG, nirS, nirK, nosZ) micro-organisms. NO emissions, however, were much reduced under drought, suggesting that this effect was driven by environmental limitations rather than by changes in the activity potential or the size of the respective microbial communities. Cattle urine stimulated nitrification and, to a lesser extent, also DEA, but more so in the absence of drought. In contrast, NHNO reduced the activity of nitrifiers and denitrifiers due to top-soil acidification. In summary, our data demonstrate that complex interactions between drought, mineral N availability, soil acidification, and plant nutrient uptake control soil N cycling and associated NO emissions. These interactive effects differed between processes of the soil N cycle, suggesting that the spatial heterogeneity in pastures needs to be taken into account when predicting changes in N cycling and associated NO emissions in a changing climate. [ABSTRACT FROM AUTHOR]

Abstract: Spring barley was grown in a field experiment under moderately elevated soil temperature and changed summer precipitation (amount and frequency). Elevated temperature affected the performance and grain quality characteristics more significant than changes in rainfall. Except for the decrease in thousand grain weight, warming had no impacts on aboveground biomass and grain yield traits. In grains, several proteinogenic amino acids concentrations were increased, whereas their composition was only slightly altered. Concentration and yield of total protein remained unaffected under warming. The concentrations of total non-structural carbohydrates, starch, fructose and raffinose were lower in plants grown at high temperatures, whereas maltose was higher. Crude fibre remained unaffected by warming, whereas concentrations of lipids and aluminium were reduced. Manipulation of precipitation only marginally affected barley grains: amount reduction increased the concentrations of several minerals (sodium, copper) and amino acids (leucine). The projected climate changes may most likely affect grain quality traits of interest for different markets and utilisation requirements. [Copyright &y& Elsevier]

Aims: An essential task of agricultural systems is to improve internal phosphorus (P) recycling. Cover crops and tillage reduction can increase sustainability, but it is not known whether stimulation of the soil microbial community can increase the availability of soil organic P pools. Methods: In a field experiment in southwest Germany, the effects of a winter cover crop mixture (vs. bare fallow) and no-till (vs. non-inversion tillage) on microbial P-cycling were assessed with soybean as the main crop. Microbial biomass, phospholipid fatty acids (PLFAs), P cycling enzymes, and carbon-substrate use capacity were linked for the first time with the lability of organic P pools measured by enzyme addition assays (using phosphodiesterase, non-phytase-phosphomonoesterase and fungal phytase). Results: Microbial phosphorus, phosphatase, and fatty acids increased under cover crops, indicating an enhanced potential for organic P cycling. Enzyme-stable organic P shifted towards enzyme-labile organic P pools. Effects of no-till were weaker, and a synergy with cover crops was not evident. Conclusions: In this experiment, cover crops were able to increase the microbially mediated internal P cycling in a non-P-limited, temperate agroecosystems. [ABSTRACT FROM AUTHOR]

Summary: Nutrient imbalances cause the deterioration of tree health in European forests, but the underlying physiological mechanisms are unknown. Here, we investigated the consequences of decreasing root carbohydrate reserves for phosphorus (P) mobilisation and uptake by forest trees.In P‐rich and P‐poor beech (Fagus sylvatica) forests, naturally grown, young trees were girdled and used to determine root, ectomycorrhizal and microbial activities related to P mobilisation in the organic layer and mineral topsoil in comparison with those in nongirdled trees.After girdling, root carbohydrate reserves decreased. Root phosphoenolpyruvate carboxylase activities linking carbon and P metabolism increased. Root and ectomycorrhizal phosphatase activities and the abundances of bacterial genes catalysing major steps in P turnover increased, but soil enzymes involved in P mobilisation were unaffected. The physiological responses to girdling were stronger in P‐poor than in P‐rich forests. P uptake was decreased after girdling. The soluble and total P concentrations in roots were stable, but fine root biomass declined after girdling.Our results support that carbohydrate depletion results in reduced P uptake, enhanced internal P remobilisation and root biomass trade‐off to compensate for the P shortage. As reductions in root biomass render trees more susceptible to drought, our results link tree deterioration with disturbances in the P supply as a consequence of decreased belowground carbohydrate allocation. [ABSTRACT FROM AUTHOR]

Aerated topsoils are important sinks for atmospheric methane (CH4) via oxidation by CH4‐oxidizing bacteria (MOB). However, intensified management of grasslands and forests may reduce the CH4 sink capacity of soils. We investigated the influence of grassland land‐use intensity (150 sites) and forest management type (149 sites) on potential atmospheric CH4 oxidation rates (PMORs) and the abundance and diversity of MOB (with qPCR) in topsoils of three temperate regions in Germany. PMORs measurements in microcosms under defined conditions yielded approximately twice as much CH4 oxidation in forest than in grassland soils. High land‐use intensity of grasslands had a negative effect on PMORs (−40%) in almost all regions and fertilization was the predominant factor of grassland land‐use intensity leading to PMOR reduction by 20%. In contrast, forest management did not affect PMORs in forest soils. Upland soil cluster (USC)‐α was the dominant group of MOBs in the forests. In contrast, USC‐γ was absent in more than half of the forest soils but present in almost all grassland soils. USC‐α abundance had a direct positive effect on PMOR in forest, while in grasslands USC‐α and USC‐γ abundance affected PMOR positively with a more pronounced contribution of USC‐γ than USC‐α. Soil bulk density negatively influenced PMOR in both forests and grasslands. We further found that the response of the PMORs to pH, soil texture, soil water holding capacity and organic carbon and nitrogen content differ between temperate forest and grassland soils. pH had no direct effects on PMOR, but indirect ones via the MOB abundances, showing a negative effect on USC‐α, and a positive on USC‐γ abundance. We conclude that reduction in grassland land‐use intensity and afforestation has the potential to increase the CH4 sink function of soils and that different parameters determine the microbial methane sink in forest and grassland soils. [ABSTRACT FROM AUTHOR]

Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four German temperate forest sites representing a gradient in total P stocks. We analyzed the oxygen isotopic composition of HCl-extractable phosphate (δ18OP) and identified differences in P speciation with increasing soil depth using X-ray absorption near-edge structure (XANES) spectroscopy. We further determined microbial oxygen demand with and without nutrient supply at different soil depths to analyse nutrient limitation of microbial growth and used nanoscale secondary ion mass spectrometry (NanoSIMS) to visualize spatial P gradients in the rhizosphere. We found that δ18OP values in the topsoil of all sites were close to the isotopic signal imparted by biological cycling when oxygen isotopes in phosphate are exchanged by enzymatic activity. However, with increasing soil depth and increasing HCl-P concentrations, δ18Ο values continuously decreased towards values expected for primary minerals in parent material at depths below 60 cm at sites with high subsoil P stocks and below more than 2 m at sites with low subsoil P stocks, respectively. For these depths, XANES spectra also indicated the presence of apatite. NanoSIMS images showed an enrichment of P in the rhizosphere in the topsoil of a site with high P stocks, while this P enrichment was absent at a site with low P stocks and in both subsoils. Addition of C, N and P alone or in combination revealed that microbial activity in subsoils of sites with low P stocks was mostly P limited, whereas sites with high P stocks indicated N limitation or N and P co-limitation. We conclude that subsoil P resources are recycled by trees and soil microorganisms. With continued weathering of the bedrock and mobilisation of P from the weathered rocks, P cycling will proceed to greater depths, especially at sites characterised by P limitation. [ABSTRACT FROM AUTHOR]

Contrasting environmental conditions in topsoil and subsoil determine both abundance and function of soil microbial communities, affecting carbon (C) dynamics throughout the entire soil profile. Although the response of soil microorganisms to single factors such as substrate availability or micro-climatic conditions has been frequently studied, fewer studies have focused on complex interactions between substrate availability and environmental conditions. To address this, we employed vertical soil translocations between topsoil and subsoil horizons of an acid and sandy Dystric Cambisol under European beech forest in Lower Saxony, Germany, to investigate the impact of changing habitat conditions on microbial decomposer communities. To follow microbial substrate utilization at different soil depths, we created hot spots of fresh organic matter (OM) by adding 13C-labelled root litter. Soil samples were taken every three months over an experimental period of twelve months (June 2014 to June 2015). Generally, microbial biomass was strongly controlled by C availability throughout the profile. The importance of root litter as a microbial C source increased from topsoil to subsoil, but changes in available C sources affected fungi and bacteria differently. Fungi preferentially used root litter-derived C throughout the entire soil profile, demonstrating that limited access to preferred substrates, rather than micro-climatic conditions, was the main driver of decreasing fungal abundance with soil depth. In contrast, bacteria intensified utilization of root-derived C only in the absence of alternative C sources in the subsoil and were more strongly affected by spatial separation from C sources. Low soil moisture in combination with the highly sandy subsoil environment limited bacterial access to their substrates and, consequently, bacterial growth. In conclusion, fungal C utilization relies mainly on the quantity of recent plant-derived substrates, whereas bacterial access to substrates is additionally controlled by environmental conditions. This study indicates that limited microbial access to their heterogeneously distributed substrates may be an important factor for C accumulation and stabilization in subsoils. • Micro-climatic conditions inhibit bacterial carbon utilization in subsoil. • Substrate limitation is the main driver of low fungal abundance in subsoil. • Altered carbon sources with soil depth affect the microbial community structure. [ABSTRACT FROM AUTHOR]

Dark, that is, nonphototrophic, microbial CO2 fixation occurs in a large range of soils. However, it is still not known whether dark microbial CO2 fixation substantially contributes to the C balance of soils and what factors control this process. Therefore, the objective of this study was to quantitate dark microbial CO2 fixation in temperate forest soils, to determine the relationship between the soil CO2 concentration and dark microbial CO2 fixation, and to estimate the relative contribution of different microbial groups to dark CO2 fixation. For this purpose, we conducted a 13C‐CO2 labeling experiment. We found that the rates of dark microbial CO2 fixation were positively correlated with the CO2 concentration in all soils. Dark microbial CO2 fixation amounted to up to 320 µg C kg−1 soil day−1 in the Ah horizon. The fixation rates were 2.8–8.9 times higher in the Ah horizon than in the Bw1 horizon. Although the rates of dark microbial fixation were small compared to the respiration rate (1.2%–3.9% of the respiration rate), our findings suggest that organic matter formed by microorganisms from CO2 contributes to the soil organic matter pool, especially given that microbial detritus is more stable in soil than plant detritus. Phospholipid fatty acid analyses indicated that CO2 was mostly fixed by gram‐positive bacteria, and not by fungi. In conclusion, our study shows that the dark microbial CO2 fixation rate in temperate forest soils increases in periods of high CO2 concentrations, that dark microbial CO2 fixation is mostly accomplished by gram‐positive bacteria, and that dark microbial CO2 fixation contributes to the formation of soil organic matter. [ABSTRACT FROM AUTHOR]

Summary: Soils provide a heterogeneous environment varying in space and time; consequently, the biodiversity of soil microorganisms also differs spatially and temporally. For soil microbes tightly associated with plant roots, such as arbuscular mycorrhizal fungi (AMF), the diversity of plant partners and seasonal variability in trophic exchanges between the symbionts introduce additional heterogeneity. To clarify the impact of such heterogeneity, we investigated spatiotemporal variation in AMF diversity on a plot scale (10 × 10 m) in a grassland managed at low intensity in southwest Germany. AMF diversity was determined using 18S rDNA pyrosequencing analysis of 360 soil samples taken at six time points within a year. We observed high AMF alpha‐ and beta‐diversity across the plot and at all investigated time points. Relationships were detected between spatiotemporal variation in AMF OTU richness and plant species richness, root biomass, minimal changes in soil texture and pH. The plot was characterized by high AMF turnover rates with a positive spatiotemporal relationship for AMF beta‐diversity. However, environmental variables explained only ≈20% of the variation in AMF communities. This indicates that the observed spatiotemporal richness and community variability of AMF was largely independent of the abiotic environment, but related to plant properties and the cooccurring microbiome. [ABSTRACT FROM AUTHOR]

Summary: Bacteria colonize reactive minerals in soils where they contribute to mineral weathering and transformation. So far, the specificity, patterns and dynamics of mineral colonization have rarely been assessed under natural conditions. High throughput Illumina sequencing was employed to investigate the bacterial communities assembling on illite and goethite during exposure to natural grassland soils. Two different types of organic carbon sources, simple carbon compounds representing root exudates and detritus of two dominant grassland plant species were applied, and their effects on the temporal dynamics of bacterial communities were investigated. The observed temporal patterns suggest that the surfaces of de novo exposed minerals in soils drive the establishment of bacterial communities and override the effect of the type of carbon sources and of other environmental properties. Mineral colonization was selective and specific bacterial sequence variants exhibited distinct colonization patterns, among which early, intermittent, and late colonizers could be distinguished. Based on our results, soil minerals are not only colonized by specific bacterial communities but enable a succession of different bacterial communities. Our results thereby expand the concept of the mineralosphere and provide novel insights into mechanisms of community assembly in the soil ecosystem. [ABSTRACT FROM AUTHOR]

Drivers of ecosystem stability have been a major topic in ecology for decades. Most studies have focused on the influence of species richness on ecosystem stability and found positive diversity‐stability relationships. However, land use and abiotic factors shape species richness and functional composition of plant communities and may override species richness‐stability relations in managed grasslands.We analysed the relative importance of land‐use intensity (LUI), resident plant species richness and functional composition for recovery of plant communities (plant species richness, plant cover, above‐ and below‐ground biomass) and release of soil nutrients after a severe mechanical disturbance. Experimental sward disturbance was applied to 73 grassland sites along a LUI gradient in three German regions. We considered relative (ln(disturbance/control)) and absolute (disturbance − control) treatment effects. Using structural equation modelling, we disentangled direct effects of LUI and resident species richness on recovery and indirect effects via changes in functional richness.Community‐weighted‐mean traits rarely mattered for recovery or nutrient release, while functional richness especially increased relative recovery of plant communities but also relative release of NO3‐N and NH4‐N. These effects were enhanced by increasing resident plant species richness and decreasing LUI. Next to these indirect influences of LUI and resident plant species richness via functional community composition, grasslands of high compared with grasslands of low resident plant species richness generally showed decreased recovery of plant communities. In grasslands of high LUI, absolute recovery of some aspects of plant communities was decreased. We did not find consistent differences between the relative importance of the different drivers of recovery after the first and the second season. Overall, resident species richness seemed most important for relative recovery and less important for absolute recovery, where direct effects of LUI were more common.Synthesis. The stability of ecosystems in managed grasslands depends on more than species richness. Thus, drivers that directly affect species richness and functional community composition have to be considered when studying the stability of real‐world ecosystems. More specifically, in managed grasslands high resident species richness but also high land‐use intensity (LUI) decreased the stability of ecosystem functions, which was partially buffered by increases in functional richness. [ABSTRACT FROM AUTHOR]

Carbon cycling in terrestrial ecosystems provides a feedback mechanism to climate change by releasing or sequestering additional atmospheric CO2. The C balance in soils is mainly determined by the input of plant C and the release of soil organic C (SOC) as CO2, which are both sensitive to global warming. We were, therefore, interested in the impact of soil warming on C cycling in an arable soil. We hypothesized that warming will 1) increase C flow from maize into soil and 2) increase heterotrophic respiration of SOC, resulting in an accelerated C turnover but an unaltered C balance. We used the Hohenheim Climate Change (HoCC) experiment, which was established in summer 2008 on an arable field and increases soil temperature by 2.5°C in 4 cm depth. The experimental plots were planted with maize (Zea mays) in 2018. The C flow from maize into SOC, microbial biomass and CO2 was measured using the difference in 13C signature between maize and C3 plant derived SOC. Preliminary results indicate that warming increased soil respiration, but had only minor effects on the 13C value of the respired CO2. Similarly, the 13C values of extractable organic C and microbial biomass C were only slightly affected by warming. These first results indicate that warming could increase soil derived C loss by heterotrophic respiration while C input via the root system of maize is not affected. If confirmed by the final data evaluation, this bears the risk of a net soil C loss from the investigated arable system, leading to a positive feedback of climate warming. [ABSTRACT FROM AUTHOR]