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We present field data on the effects of heavy rainfall after drought on the mobility of glyphosate and redox conditions in a clayey floodplain soil. By applying glyphosate together with deuterated water as conservative tracer in combination with time resolved

The turnover and stabilization of soil organic matter (SOM) is the key to highly productive agriculture and to climate change mitigation. The pathways of matter and energy use by soil microorganisms are controlled by their functional traits and interactions. We present the concept of a novel data-driven bioenergetic soil organic matter model and shed light on integrating ecological trait-based ecological frameworks with process-based models. The model links SOM thermodynamics with key microbial traits, corresponding substrate-specific degradation pathways and extracellular enzymatic depolymerization processes. Carbon and energy flows will be quantitatively traced by modeling mass fractions of specific C source pools, C isotopologues and thermodynamic properties (degree of reduction) as dynamic state variables. The model uses functional microbial pools (generalists, specialists and stress tolerators) with specific trait trade-offs to reflect microbial life and growth strategies in line with current ecological theory. We use microbial transition state theory to reflect microbial growth kinetics and test this approach compared to empirical Monod kinetics. Resource use (i.e., enzyme synthesis) is modeled assuming that microbes are naturally selected to maximize their reproductive success (i.e., growth rate). Using a case study, we further demonstrate the applicability of a constraint-based model conditioning method for simulating microbial SOM processing. Based on this, we explain how constraint-based model conditioning could be used to parameterize bioenergetic models for predicting SOM stabilization in agroecosystems.

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 synthesis, we argue, that the soil-plant-atmosphere continuum, 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 soil-plant-atmosphere-continuum – are key to understand the effect of drought stress 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 soil-plant-atmosphere-continuum 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.

Drought alters carbon (C) allocation within trees, thereby impairing tree growth. Recovery of root and leaf functioning and prioritized C supply to sink tissues after drought may compensate for drought -induced reduction of assimilation and growth. It remains unclear if C allocation to sink tissues during and following drought is controlled by altered sink metabolic activities or by the availability of new assimilates. Understanding such mechanisms is required to predict forests' resilience to a changing climate. We investigated the impact of drought and drought release on C allocation in a 100-y-old Scots pine forest. We applied (CO2)-C-13 pulse labeling to naturally dry control and long-term irrigated trees and tracked the fate of the label in aboveand belowground C pools and fluxes. Allocation of new assimilates belowground was ca. 53% lower under nonirrigated conditions. A short rainfall event, which led to a temporary increase in the soil water content (SWC) in the topsoil, strongly increased the amounts of C transported belowground in the nonirrigated plots to values comparable to those in the irrigated plots. This switch in allocation patterns was congruent with a tipping point at around 15% SWC in the response of the respiratory activity of soil microbes. These results indicate that the metabolic sink activity in the rhizosphere and its modulation by soil moisture can drive C allocation within adult trees and ecosystems. Even a subtle increase in soil moisture can lead to a rapid recovery of belowground functions that in turn affects the direction of C transport in trees.

Deadwood may alter the chemical and microbial properties of forest soils. However, it is unclear how downed deadwood (logs) of different tree species affect nutrients, microbial activity and biomass in different forest soils and regions. We investigated the effect of logs on underlying soils after 8 years of decomposition in an experiment consisting of 13 log tree species replicated at 30 forest sites across three German regions with distinct climate and geology. Soils beneath logs were compared to soils without recognizable influence of deadwood (control) 8 m away. Carbon, nitrogen, phosphorous and calcium concentrations increased by 5–18% in the soils under logs, whereas soil potassium, magnesium, iron, manganese and aluminum were not or slightly negatively affected by logs. Soils beneath logs exhibited 33%, 18% and 54% higher carbon mineralization, microbial biomass and ergosterol (component of fungal cell membranes) contents, respectively. Despite major differences in decay rates, the effect on soil properties hardly differed among the 13 log tree species. The effect of logs on microbial and chemical soil parameters increased with decreasing concentration of carbon, nitrogen, phosphorous and pH in the prevailing forest soils. Consequently, the strongest effects of logs on soil parameters occurred in plots with low soil nutrient contents and low soil pH. Our results suggest that logs of all tree species primarily increase the microbial activity and nutrient contents of acidic and nutrient-poor soils.

Exchangeable sodium can have pronounced influences on physicochemical soil properties whereas the combined impact on microbial turnover of organic carbon (OC) remains elusive. In this work, we aimed to differentiate the effects of exchangeable sodium and soil pH on microbially mediated aggregate formation and turnover of cattle slurry. We incubated the soils under controlled laboratory conditions using artificial soil model minerals containing quartz grains, montmorillonite and goethite. The montmorillonite was pre-treated with NaCl solutions of sodium adsorption ratios (SAR) 0, 1 and 5 which resulted in exchangeable sodium percentages (ESP) of 1, 7 and 19 on average. The soil pH was adjusted within two treatments to 7.5 and 8.5 for each ESP at the start of the incubation. We incubated these six treatments with and without cattle slurry ground to < 200 µm after addition of a combined microbial inoculum, extracted from a Cambisol (pHH2O 7.5, Germany) and a Calcaric Solonchak (pHH2O 9.3, Spain) added to all samples. The microcosms were incubated with three replicates over a period of 30 days at constant pF of 2.2. The CO2 emission measurements of the microcosms with exchangeable sodium indicated a delayed respiration. The respiration under ESP 19 increased rapidly within the first days of incubation, whereas it was more delayed under ESP 7 until 15 days of incubation. The delayed CO2 respiration might be related to inhibited structural formation in treatments with higher exchangeable sodium. To test this, we are investigating the data on water-stable aggregation by wet sieving. The delayed CO2 respiration was reflected in lower microbial biomass, extracted after the incubation. The microbial biomass under ESP 19 and pH 8.5 was highest whereas the amount of leached C after two rainfall events (at day 7 and 15) was lowest, which could be related to a higher microbially mediated OC sequestration. The composition of exchangeable cations was monitored before and after the whole incubation which might help explaining the processes of microbially mediated aggregate formation and microbial carbon turnover under different levels of exchangeable sodium.

Climate is changing and predicted future scenarios include both changes in long-term 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 CO

Litter-derived dissolved organic carbon (DOC) is considered to be a major source of stabilised C in soil. Here we investigated the microbial utilisation of litter-derived DOC within an entire soil profile using a stable isotope labelling experiment in a temperate beech forest. The natural litter layer of a Dystric Cambisol was replaced by 13C enriched litter within three areas of each 6.57 m−2 for 22 months and then replaced again by natural litter (switching-off the 13C input). Samples were taken continuously from 0 to 180 cm depths directly after the replacement of the labelled litter, and 6 and 18 months thereafter. We followed the pulse of 13C derived from aboveground litter into soil microorganisms through depth and over time by analysing 13C incorporation into microbial biomass and phospholipid fatty acids. Throughout the sampling period, most of the litter-derived microbial C was found in the top cm of the profile and only minor quantities were translocated to deeper soil. The microbial 13C stocks below 30 cm soil depth at the different samplings accounted constantly for only 6–12% of the respective microbial 13C stocks of the entire profile. The peak in proportional enrichment of 13C in subsoil microorganisms moved from upper (≤ 80 cm soil depth) to lower subsoil (80–160 cm soil depth) within a period of 6 months after switch-off, and nearly disappeared in microbial biomass after 18 months (< 1%), indicating little long-term utilisation of litter-derived C by subsoil microorganisms. Among the different microbial groups, a higher maximum proportion of litter-derived C was found in fungi (up to 6%) than in bacteria (2%), indicating greater fungal than bacterial dependency on litter-derived C in subsoil. However, in contrast to topsoil, fungi in subsoil had only a temporarily restricted increase in litter C incorporation, while in the Gram-positive bacteria, the C incorporation in subsoil raised moderately over time increasingly contributing to the group-specific C stock of the entire profile (up to 9%). Overall, this study demonstrated that microorganisms in topsoil of a Dystric Cambisol process most of the recently deposited aboveground litter C, while microbial litter-derived C assimilation in subsoil is low.

Despite all legislative efforts, pesticides persist in soils at low concentrations and are leached to groundwater. This environmental issue has previously been associated with control factors relevant in natural soils but elusive in lab experiments and standard modeling approaches. One such factor is the small-scale spatial distribution of pesticide-degrading microorganisms in soil. Microbes are distributed heterogeneously in natural soils. They are aggregated in biogeochemical “hotspots” at the centimeter scale. The aim of our study is to investigate the relevance of such aggregation for pesticide degradation. For this, we upscaled the effect of the heterogeneity-induced accessibility limitations to degradation to the soil-column scale and analyzed kinetic constraints and amplifying factors under contrasting unsaturated flow regimes.We performed a 2D spatially explicit, site-specific model-based scenario analysis for bioreactive transport of the model pesticide 4-chloro-2-methylphenoxyacetic acid (MCPA) in an arable soil (Luvisol). Stochastic centimeter-scale spatial distributions of microbial degraders were simulated with a spatial statistical model (log Gaussian Cox process), parametrized to meet experimentally observed spatial distribution metrics. Three heterogeneity levels were considered, representing homogenized soil conditions, and the lower and upper limit of expected microbial spatial aggregation in natural soils. Additionally, two contrasting precipitation scenarios (continuous light rain vs. heavy rain events directly following MCPA application) were assessed. A reactive transport model was set up to simulate a 0.3 m x 0.9 m soil column based on hydraulic and bioreactive measurements from a soil monitoring station (Germany, SM#3/ DFG CRC 1253 CAMPOS).Our simulations revealed that heavy precipitation events were the main driver of pesticide leaching. Leached amounts from the topsoil increased by two to five orders of magnitude compared to the light rain scenario and at max. ca. 20 ng was leached from 90 cm after one year. With the increasing spatial aggregation of microbial degraders, upscaled pesticide degradation rates decreased, and considerable differences emerged between homogeneous and highly aggregated scenarios. In the latter, leaching from the plow layer into the subsoil was more pronounced and MCPA was detectable (LOD = 4 µg/kg) 5-6 times longer. In heterogeneous scenarios, degradation in microbial hotspots was mainly diffusion-limited during “hot moments” (times of high substrate availability), with a fraction of MCPA simultaneously “locked in” in coldspots with low microbial abundance. During intense precipitation events MCPA was remobilised from these coldspots by advective-dispersive transport, thereby increasing pesticide accessibility.Our results indicate that predicted environmental concentrations and detectability of pesticides might be underestimated if spatial heterogeneity of microbial degraders is neglected, and they highlight the importance of heavy rain events as drivers of leaching and substrate accessibility.

Soil microbial functional traits control carbon (C) decomposition and stabilization in soil. Integrating metabolic trade-offs and life-history strategies of microbial communities into models enhances the representation of feedbacks between microbial diversity and soil biogeochemical functions. This has great potential to improve our understanding of microbial C allocation and how microbial processes affect C storage and use efficiency in soil. The current challenge is, however, to quantify and identify ecologically meaningful microbial traits. This study utilizes data from a 13C pulse-labelling litter decomposition experiment to inform a new soil C turnover model that captures microbial life-history traits and dormancy in combination with soil organic matter accessibility. Quantitative data from 13C DNA stable isotope probing and high-throughput sequencing is used to parameterize the C utilization of copiotrophic and oligotrophic microorganisms. The new model is then applied to quantify C utilization of functional microbial groups and C turnover in soil. In scenario analyses we investigate the sensitivity of functional microbial groups and its feedback on C cycling to C input.

We present a multi-proxy approach to reconstruct Middle Bronze Age (MBA, 1600-1250 BCE) land use practices in the north-western Alpine foreland (SW Germany, Hegau). We combined biogeochemical proxies from multi-layered colluvial deposits and archaeobotanical and archaeozoological data within and in the surrounding of the archaeologically well-documented settlement site of Anselfingen. Offsite pollen data from two peat bogs were used to place the onsite and near-site vegetation and land use data to a regional context.Phases of colluvial deposition were reconstructed by optically stimulated luminescence (OSL) and radiocarbon (AMS 14C) dating. The first phase of major colluviation could be correlated with MBA land use followed by phases of colluvial deposition during the Iron Age, the Medieval period, and modern times. Charcoal spectra from colluvial deposits and archaeological structures indicate MBA forest management favoring Quercus in the surrounding area north of the settlement. The analysis of faecal biomarker (5ß-stanols up to 40 %) and excavated pig bones (up to 14 %) suggest the presence of a forest pasture mainly used for pig farming. In the surrounding area south of the settlement, an arable field with a buried MBA plough horizon (2Apb) could be verified by soil micromorphological features such as very dusty clay coatings and a banded microstructure and by high concentrations of grass phytoliths from leaves and stems. Agricultural practices (e.g. ploughing) focused on five staple cereal crops (Hordeum distichon/vulgare, Triticum dicoccum, Triticum monococcum, Triticum spelta, Triticum aestivum/turgidum) as indicated by the onsite archaeobotanical records. Stilted pantries, reconstructed from MBA post-holes, were interpreted as storage facilities, while excavated heat stones are likely to indicate post-harvest processing of cereal crops and other agrarian products. Higher levels of urease activity compared to microbial biomass carbon (up to 2.1 µg N µg Cmic-1), and input of herbivorous animal faeces indicate livestock husbandry on fallow land or manuring practices. The suites of polycyclic aromatic hydrocarbons (PAHs) and their spatial distribution indicate the use of fire for various purposes, e.g. for landscape opening and maintenance, for domestic burning and for technical applications. The offsite pollen data support the onsite and near-site vegetation change. During the MBA, fire played a major role in shaping the landscape (peak of micro-charcoal during the MBA in the offsite pollen records) and anthropogenic activities promoted oak dominated forest vegetation at the expense of natural beech forests. This approves a broad regional human influence in the north-western Alpine foreland during the MBA.Our data allow in-depth insights into the MBA subsistence economy on a local and regional scale, which was not limited to settlements at lakeshore sites. The MBA in the north-western Alpine foreland was a period of establishing settlements with sophisticated land management and land use practices also at low and mid altitude inland sites. We could further show that colluvial deposits are promising archives for the reconstruction of past land use practices.

This paper aims to reconstruct Middle Bronze Age (MBA; 1600–1250 BCE) land use practices in the northwestern Alpine foreland (SW Germany, Hegau). We used a multi-proxy approach including the analysis of biogeochemical proxies from colluvial deposits and buried topsoils in the surroundings of the well-documented settlement site of Anselfingen and off-site pollen data from two peat bogs. This approach allowed for in-depth insights into the MBA subsistence economy and shows that the MBA in the northwestern Alpine foreland was a period of establishing settlements with sophisticated land management and land use practices. The reconstruction of phases of colluvial deposition was based on ages from optically stimulated luminescence (OSL) and radiocarbon (AMS14C) dating from multi-layered colluvial deposits and supports the local archaeological record with the first phase of major colluvial deposition occurring during the MBA followed by phases of colluvial deposition during the Iron Age, the Medieval period and modern times. The on-site deposition of charred archaeobotanical remains and animal bones from archaeological features, as well as polycyclic aromatic hydrocarbons (PAHs), charcoal spectra, phytoliths, soil microstructure, urease enzymatic activity, microbial biomass carbon (Cmic) and heavy metal contents from colluvial deposits, were used as proxies for on-site and near-site land use practices. The charcoal spectra indicate MBA forest management which favored the dominance of Quercus in the woodland vegetation in the surrounding area north of the settlement site. Increased levels of 5β stanols (up to 40 %) and the occurrence of pig bones (up to 14 %) support the presence of a forest pasture mainly used for pig farming. In the surrounding area south of the settlement, an arable field with a buried MBA plow horizon (2Apb) could be verified by soil micromorphological investigations and high concentrations of grass phytoliths from leaves and stems. Agricultural practices (e.g., plowing) focussed on five staple crops (Hordeum distichon/vulgare, Triticum dicoccum, Triticum monococcum, Triticum spelta, Triticum aestivum/turgidum), while the presence of stilted pantries as storage facilities and of heat stones indicate post-harvest processing of cereal crops and other agrarian products within the settlement. In the area surrounding the settlement, increased levels of urease activity, compared to microbial biomass carbon (up to 2.1 µg N µg Cmic-1), and input of herbivorous and omnivorous animal faeces indicate livestock husbandry on fallow land. The PAH suites and their spatial distribution support the use of fire for various purposes, e.g., for opening and maintaining the landscape, for domestic burning and for technical applications. The off-site palynological data support the observed change in on-site and near-site vegetation as well as the occurrence of related land use practices. During the Early and Middle Bronze Age, fire played a major role in shaping the landscape (peak of micro-charcoal during the MBA), and anthropogenic activities promoted Quercus-dominated forest ecosystems at the expense of natural beech forests. This indicates a broader regional human influence in the northwestern Alpine foreland at low- and mid-altitude inland sites during the Middle Bronze Age.

The objective of our study was to test whether limited microbial degradation at low pesticide concentrations could explain the discrepancy between overall degradability demonstrated in laboratory tests and their actual persistence in the environment. Studies on pesticide degradation are often performed using unrealistically high application rates seldom found in natural environments. Nevertheless, biodegradation rates determined for higher pesticide doses cannot necessarily be extrapolated to lower concentrations. In this context, we wanted to (i) compare the kinetics of pesticide degradation at different concentrations in arable land and (ii) clarify whether there is a concentration threshold below which the expression of the functional genes involved in the degradation pathway is inhibited without further pesticide degradation taking place. We set up an incubation experiment for four weeks using 14C-ring labeled 2-methyl-4-chlorophenoxyacetic acid (MCPA) as a model compound in concentrations from 30 to 20,000 μg kg–1 soil. To quantify the abundance of putative microorganisms involved in MCPA degradation and their degradation activity, tfdA gene copy numbers (DNA) and transcripts (mRNA) were determined by quantitative real-time PCR. Mineralization dynamics of MCPA derived-C were analyzed by monitoring 14CO2 production and 14C assimilation by soil microorganisms. We identified two different concentration thresholds for growth and activity with respect to MCPA degradation using tfdA gene and mRNA transcript abundance as growth and activity indices, respectively. The tfdA gene expression started to increase between 1,000 and 5,000 μg MCPA kg–1 dry soil, but an actual increase in tfdA sequences could only be determined at a concentration of 20,000 μg. Accordingly, we observed a clear shift from catabolic to anabolic utilization of MCPA-derived C in the concentration range of 1,000 to 5,000 μg kg–1. Concentrations ≥1,000 μg kg–1 were mainly associated with delayed mineralization, while concentrations ≤1,000 μg kg–1 showed rapid absolute dissipation. The persistence of pesticides at low concentrations cannot, therefore, be explained by the absence of functional gene expression. Nevertheless, significant differences in the degradation kinetics of MCPA between low and high pesticide concentrations illustrate the need for studies investigating pesticide degradation at environmentally relevant concentrations.

Increasing air and soil temperatures and changes in precipitation patterns as consequences of climate change will affect crop production in agricultural ecosystems. The combined effects of soil warming and altered precipitation on the productivity and product quality of oil crops are not yet well studied. Winter oilseed rape (OSR) (Brassica napus L., cv. Mercedes) was field-grown under elevated soil temperature (+2.5 &deg, C), reduced precipitation amount (&minus, 25%), reduced precipitation frequency (&minus, 50%) both separately and in combination in order to investigate effects on crop development, seed yield, and seed quality. Soil warming accelerated crop development during early plant growth and during spring. At maturity, however, plants in all treatments were similar in quantitative (aboveground biomass, seed yield) and qualitative (protein and oil content, amino acids, fatty acids) parameters. We observed the long-term effects of the precipitation manipulation on leaf size, leaf senescence and biomass allocation. Seed yield was not affected by the altered climatic factors, perhaps due to adaptation of soil microorganisms to permanent soil warming and to relatively wet conditions during the seed-filling period. Overall, OSR performed well under moderate changes in soil temperature and precipitation patterns, thus, we observed stable seed yield without negative impacts on nutritive seed quality.

Soil organic carbon (SOC) losses under a changing climate are driven by the temperature sensitivity of SOC mineralization (usually expressed as Q10, the multiplier of activity with 10 °C temperature increase). The activation energy theory (AET) suggests that, due to higher activation energies, the more complex the carbon, the higher is mineralization Q10. However, studies on Q10 have been inconsistent with regard to AET. Measurements of potential soil enzymes activity Q10 even contradicted AET: Phenoloxidase (representing complex carbon) had consistently lower Q10 than the more labile xylanase and glucosidase. This study used two approaches of examining Q10 in SOC modeling: 1) Bayesian calibration (BC) and 2) using different measured enzyme Q10 as proxies for mineralization Q10 of different SOC pools. The SOC model was DAISY (S. Hansen et al., 2012). BC informed Q10 by field measured data, while the second approach tested if directly using enzyme Q10 (of phenoloxidase, glucosidase and xylanase) for DAISY pools improved simulation results. Both approaches used the temperature sensitive measurements of CO2 evolution and soil microbial biomass. The measured enzyme Q10 were from field manipulation experiments with bare fallow and vegetated plots in the two regions of Kraichgau and Swabian Jura in Southwest Germany. The enzyme-derived Q10 were used for modelling those fields and furthermore for in‑situ litterbag decomposition experiments at 20 sites in the same region. Two further laboratory experiments with temperature manipulation were included: an incubation of the field residues into soil and an incubation of bare soil from the start and year 50 of a long duration bare fallow (from Ultuna). The BC made use of CO2 and microbial data to inform about the range of Q10 of different carbon pools for the individual experiments and combined data.The BC of the residue incubation experiment constrained Q10 for metabolic (~3) and structural litter (~2). Estimated 95% credibility intervals did not overlap. The BC for Ultuna could constrain the slow and fast SOC pool with Q10 ~2.8 and ~3, respectively, but credibility intervals of both pools overlapped. The Q10 of field experiments, which had most abundant data, could not be constrained by BC, probably because their annual temparature variability was too low. However, the model errors of the field experiment could be reduced by the second approach, when the Q10 of phenoloxidase was used for to the structural litter pool as well as for the fast and slow SOC pools. Thus regional enzyme Q10 improved the model fit but only for regional simulations. Therefore, they could be useful proxies when natural temperature range is too small to inform temperature sensitivity by BC. Any trends found in this study contradicted AET, both from measured enzymes and BC of the incubation experiments. This calls for alternative Q10 hypotheses and the need for individual Q10 values for different SOC pool rather than a general one. BC approaches would benefit from a wider temperature range of field experiments and understanding what causes variable enzyme Q10 could help to improve future SOC models.

Aim: The aim of this study was to investigate the effects of integrated (INT), organic (ORG) and biodynamic (BD) management systems with similar C- and N-inputs on soil microbiology in a viticultural long-term field trial.Methods and results: Within the systems comparison, soil samples were taken 10 years after conversion, throughout the growing season. To gather information about microbial community structure, the activity of five soil enzymes was measured, and phospholipid fatty acids (PLFA) and neutral lipids fatty acids (NLFA) profiles were analysed accompanied by comprehensive soil analysis. pH associated with BD was significantly higher compared to INT soil. Copper and N-min values in INT were significantly lower compared to the organic systems. BD and ORG were characterised by a higher b-D-glucosidase and urease activity and a higher abundance of fungi and bacteria. INT had larger quantities of mycorrhizae indicator NLFAs.Significance and impact: Results from this study contribute to a better understanding of the microbial community structure and nutrient cycling under organic and biodynamic viticulture.

Microbial assimilation and stabilization of soil organic carbon (SOC) is an important process in global carbon cycling. For an improved understanding of climate-induced changes in ecosystem C dynamics, it is important to know the group-specific turnover of microbial C. Consequently, we wanted to answer the questions if fungi store newly assimilated C longer than bacteria and if climatic and edaphic properties of different regions affect microbial C assimilation and its subsequent release. This study presents results from a 112-day long field experiment where endogenous microorganisms from two agricultural soils were labeled with 13C labeled glucose to follow the dynamics of newly assimilated C. Both soils were representative for the respective study regions (Kraichgau and Swabian Alb). Whereas, microbial assimilation of newly added C was higher in Kraichgau than in Swabian Alb, the opposite result was obtained for the mean residence time (MRT) of microbial biomass C (76 days in Kraichgau and 93 days in Swabian Alb). The accelerated turnover rates of microbial C in the warmer soil of Kraichgau with lower clay content might be an important mechanism explaining the differences in SOC content between both regions. Gram-positive bacteria assimilated more 13C-glucose into their biomass than fungi and the MRT of C was higher in bacteria as compared to fungi in both regions. Beside these dynamic substrate utilization strategies, we observed possible cross feeding by gram-negative bacteria. Carbon MRT in fungi was region specific and was best represented by a two-pool model; the initial MRT ranged between 5 and 39 days and was, in the end, higher than 4 years. This hints toward a functional separation of the fungal community; fast growing fungi dominant in the early phase and internal redistribution of C in the second phase of decomposition. Our study identified microbial group and region specific MRT of freshly assimilated C as an important parameter, which might help to explain the commonly found variation in soil respiration and SOC stabilization.

Trait-based models have improved the understanding and prediction of soil organic matter dynamics in terrestrial ecosystems. Microscopic observations and pore scale models are now increasingly used to quantify and elucidate the effects of soil heterogeneity on microbial processes. Combining both approaches provides a promising way to accurately capture spatial microbial-physicochemical interactions and to predict overall system behavior. The present study aims to quantify controls on carbon (C) turnover in soil due to the mm-scale spatial distribution of microbial decomposer communities in soil. A new spatially explicit trait-based model (SpatC) has been developed that captures the combined dynamics of microbes and soil organic matter (SOM) by taking into account microbial life-history traits and SOM accessibility. Samples of spatial distributions of microbes at µm-scale resolution were generated using a spatial statistical model based on Log Gaussian Cox Processes which was originally used to analyze distributions of bacterial cells in soil thin sections. These µm-scale distribution patterns were then aggregated to derive distributions of microorganisms at mm-scale. We performed Monte-Carlo simulations with microbial distributions that differ in mm-scale spatial heterogeneity and functional community composition (oligotrophs, copiotrophs and copiotrophic cheaters). Our modelling approach revealed that the spatial distribution of soil microorganisms triggers spatiotemporal patterns of C utilization and microbial succession. Only strong spatial clustering of decomposer communities induces a diffusion limitation of the substrate supply on the microhabitat scale, which significantly reduces the total decomposition of C compounds and the overall microbial growth. However, decomposer communities act as functionally redundant microbial guilds with only slight changes in C utilization. The combined statistical and process-based modelling approach derives distribution patterns of microorganisms at the mm-scale from microbial biogeography at microhabitat scale (µm) and quantifies the emergent macroscopic (cm) microbial and C dynamics. Thus, it effectively links observable process dynamics to the spatial control by microbial communities. Our study highlights a powerful approach that can provide further insights into the biological control of soil organic matter turnover.

Complex interactions between biodegradation and mass transfer of organic compounds drive the fate of pesticides in soil ecosystems. We hypothesized that, at the small-scale, co-location of degraders and pollutants in soils may be a prerequisite for efficient biodegradation of these chemicals. In non-co-localized micro-environments, however, diffusive and advective solute transport as well as active transport of microbial degraders towards their corresponding substrate may improve the accessibility of microbial substrates. The objective of this study was to test whether water flow can accelerate microbial pesticide degradation by facilitating the encounter of spatially separated pesticides and bacterial degraders at the millimeter scale. Combining natural and sterilized soil aggregates, we built soil cores with different spatial localizations of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) and microbial degraders: (i) homogeneous distribution of microorganisms and 2,4-D throughout the soil core, (ii) co-localized microorganisms and 2,4-D in a mm3 soil location, and iii) separated microorganisms and 2,4-D in two mm3 soil locations spaced 1 cm apart. Following the fate of 14C labelled 2,4-D (mineralization, extractable and non-extractable residues) as well as the abundance of bacterial 2,4-D degraders harboring the tfdA gene over an incubation period of 24 days, we observed decreased biodegradation of 2,4-D with increasing spatial separation between substrate and bacterial degraders. We found evidence that advection is a key process controlling the accessibility of 2,4-D and pesticide degraders. Advective solute transport induced leaching of about 50% of the initially applied 2,4-D regardless of initial spatial distribution patterns. Simultaneously, advective transport of 2,4-D and bacterial degraders triggered their re-encounter and compensated for the leaching-induced separation of initially co-localized microorganisms and 2,4-D. This resulted in effective biodegradation of 2,4-D, comparable to the homogeneous treatment. Similarly, advective transport processes brought substrate and degraders into contact if both were initially separated. Thus, advection more effectively removed bioaccessibility limitations to pesticide degradation than diffusive transport alone. These results emphasize the importance of considering spatial microbial ecology as well as biogeophysics at the mm scale to better understand the fate of pesticides at larger scales in soil.

There has been growing interest in fluorescence-based microplate methods to measure enzyme activities due to the sensitivity of fluorimetric detection and the potential for simultaneous and rapid assaying of multiple enzyme activities in the same soil suspension. However, micro-scale methods could introduce considerable operator error such as: 1) the requirement to put soil samples into a suspension; 2) the very small amounts of soil placed in each microplate well; 3) pipetting error because μL volumes are required; and 4) the need for standard curve calibration with every sample to account for quenching. For valid data comparison and interpretation, there is clearly a need to have a strict and agreed-upon enzyme assay protocol to standardize the microplate-based method. Therefore, the objectives were to: 1) determine the reproducibility and comparability of the standard p-nitrophenol bench-scale and 4-methylumbelliferone microplate enzyme assays measured by five laboratories for β-glucosidase (EC 3.2.1.21) and acid phosphomonoesterase (EC 3.1.3.2) on the same soil samples; and 2) determine the degree and the sources of variability associated with the assays within and among the laboratories. The results showed that overall variability was highest for replication on the microplate (n = 4), whereas suspension replication had low CVs. This suggests an important source of variation is from pipetting not variability from soil suspensions. A major effort was made to control for methodological differences by using air-dried soils (therefore more stable over varying storage periods) and operator consistency for each task across the labs (e.g. preheated reagents, microplate reader sensitivity set to the highest standard, readings taken within an hour of reaction termination, and controls for substrate autohydrolysis). As a result, the differences among labs were much smaller than differences due to soil type for the microplate method, indicating operator error can be minimized by following the same strict protocol. At the molar level, enzyme activity rates measured across the five labs were not the same between bench and MUF microplate methods (although they were within an order of magnitude), but were quite similar in terms of ranking of soil management treatments and soil types ( Table 2 ). Correlations between bench and microplate assays were strong for both enzymes, although slightly stronger for acid phosphomonoesterase (r = 0.93) than β-glucosidase (r = 0.81). Additionally, for both acid phosphomonoesterase and β-glucosidase, correlation r values were mostly similar for MUF microplate and PNP bench method correlation with EL-FAME biomarkers, suggesting both methods were measuring activity originating from the same microbial groups. We conclude that different labs using the same MUF microplate protocol tested, gives reasonably similar absolute activity values, variability, and ranking of treatments (highest to lowest). We propose that the MUF microplate method described in this study be considered as a standard protocol for assaying soil enzyme activities, providing that the buffer pH for the incubation be adjusted to the optimal pH according to the enzyme of interest.

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 (Q10) of soil respiration and enzymes (β-glucosidase and xylanase) at two scales: landscape (two individual areas, each approximately 27 km2) 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 (Q10) 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 Q10. Soil properties controlling soil enzymes (Q10) were scale-specific. We found pH to be the main factor affecting β-glucosidase Q10 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.

Global environmental change is causing increases in soil temperatures and alternations in precipitation patterns, which are affecting soil biota in natural and managed systems. Arable soils, generally disturbed due to management practice, are particularly sensitive to a changing environment. However, little is known how warming interacts with precipitation pattern to affect soil fauna and thereby ecosystem functions. In an arable system, we investigated the interactions of soil warming and altered precipitation amount and frequency on soil conditions and health using nematodes as bioindicators. Our findings showed that the nematode population density was significantly increased by warming and decreased by reduced precipitation frequency. Warming mainly fostered the density of fungal feeders and obligatory plant parasites, with the latter suggesting higher crop damage. Root-associated plant feeders were further affected by changes in precipitation pattern; their density declined with reduced precipitation frequency and increased with the alternated precipitation amount. The nematode abundance was generally low in the arable ecosystem and remained stable under the simulated environmental change. In response to warming, the major soil decomposition channel via bacteria was reduced, and the fungal mediated pathway fostered, implying more fungal dominated depleted and degraded soil conditions. Soil decomposition pathways were not affected by altered precipitation pattern, neither by amount nor by frequency. Overall, warming and precipitation independently altered the soil nematode fauna and the functioning of belowground food webs. Therefore, our study highlights the need for more research considering the interactions of environmental variables to see if this lack is a general pattern and to develop strategies for agroecosystem's management under climate change.

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.

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 (Rs ), 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 N2 O 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 N2 O emissions under warming limit the GHG mitigation potential of biochar.

The effects of biochar amendments under elevated soil temperatures on the dynamics of soil organic matter are largely unknown. The objective of this study was to analyze the effect of biochar application and elevated soil temperature on the amount and composition of organic matter (OM) associated with soil fractions of different OM turnover rates. Samples were taken from four treatments of the Hohenheim Climate Change Experiment with the factors temperature (ambient or elevated by 2.5 °C, initiated in 2008) and biochar (control and 30 t ha−1Miscanthus pyrolysis biochar, corresponding to approximately 12.4–13.9 g biochar kg−1 soil, applied in 2013) in two depths (0–5 and 5–15 cm) in August 2014. Microbial biomass C (Cmic) and basal respiration were analyzed within an incubation experiment. Aggregate-size fractions were separated by wet-sieving and the free light (fLF), occluded light (oLF) and heavy fractions were isolated by density fractionation. All fractions were analyzed for organic carbon (OC), δ13C and by infrared spectroscopy. Cmic was significantly (p ≤ 0.05) increased by elevated temperature in both depths and no biochar-C was found in the microbial biomass. Biochar significantly increased basal respiration by 24–68%. Biochar and elevated temperature had no significant effects on the OC associated with aggregate-size classes, although small amounts of biochar were incorporated into all fractions already after one year of application. Biochar application markedly increased the OC associated with the fLF and oLF. The proportion of CO groups of the aggregates >250 μm and 250–53 μm and of the oLF was significantly increased in the biochar treatments. The results suggest that already within one year, biochar-mineral interactions had occurred which had led to an aggregate occlusion of the applied biochar as revealed by the results for the oLF. At least in the short-term, the effects of biochar on the amount and composition of OM associated with different aggregate-size and density fractions do not seem to be affected by elevated soil temperatures.

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.

Anthropogenic climate change is altering the functioning of terrestrial ecosystems. Agricultural systems are particularly vulnerable to climate change as they are frequently disturbed by intensified management practices. This also threatens belowground organisms that are responsible for providing crucial ecosystem functions and services, such as nutrient cycling and plant disease suppression. Amongst these organisms, earthworms are of particular importance as they can modulate the effects of climate change on soil organisms by modifying the biotic and abiotic soil conditions. However, they are also known to decline under intensified management, justifying their use as key biotic indicators of intensified agriculture. Yet, our knowledge of the responses of belowground species to the interacting effects of warming and land-use intensification (simulated by earthworm reduction in the experimental setup) remains limited. Here, we tested the interactive effects of soil warming and reduced earthworm densities on soil protists, nematodes, meso- and macrofauna, and their diversity in a common barley system in the Hohenheim Climate Change Experiment. We found that belowground species richness was lowest at elevated temperature and reduced earthworm densities, indicating that earthworms can buffer warming effects on belowground biodiversity. Furthermore, warming increased the densities of plant-feeding nematodes, and herbivorous macrofauna benefitted from reduced earthworm densities. Our results indicate that warming and reduced earthworm densities may simultaneously modify the functioning and service provisioning of soils via shifts in diversity and density of soil biota that would likely lead to simplified belowground food webs. These findings thus highlight the importance of maintaining greater densities of ecosystem engineers like earthworms that may help buffering the detrimental effects of climate warming in agricultural systems.

The life sciences comprise numerous disciplines; these study physiology, anatomy, behavior, development, evolution, ecology and disorders of living organisms as well as the use of organisms in natural or technical procedures. Life sciences include biology, biomedical research and pharmaceutics, biochemistry, biophysics, bioinformatics, agricultural and nutritional science as well as food technologies, bio-based economy and the use of biogenic resources. The life sciences contribute not only to our understanding of basic mechanisms of living organisms and ecological systems; new research opens up novel possibilities to elucidate and treat human diseases as well as securing food for a growing world population.

Colluvial deposits are considered as sedimentary archives for the reconstruction of the sedimentation and climate history, past pedogenesis and phases of land use. However, the human contribution to the formation of colluvial deposits is mainly based on assumptions derived from the local chronostratigraphy and archaeology. For this reason, there is often a substantial gap in the identification of specific land use practices that promoted prehistoric soil erosion and sedimentation processes. We use an archaeopedological multi-proxy approach on a multi-layered colluvial deposit (six colluvial horizons) at the prehistoric site of Furstenberg (Southwest Germany) to gain detailed insights into the sedimentation history, past pedogenesis and land use practices since the Neolithic. Soil and geochemical analyses such as X-ray fluorescence (XRF), X-ray diffraction (XRD), pedogenic oxides, pH-value and calcium carbonate content support the chronostratigraphy based on ages from optically stimulated luminescence (OSL) and AMS 14C dating. Further, biogeochemical analyses of phytoliths, charcoal spectra, black carbon (BC), soil organic matter (SOM) composition by using pyrolysis-field ionization mass spectroscopy (Py-FIMS), urease activity, steroid biomarker and heavy metals (HM) are used as land use proxies. The OSL and 14C ages and the local archaeological record indicate six phases of colluvial deposition that occurred through five phases of land use comprising the Early to Younger Neolithic, the Urnfield to Hallstatt period, the Iron to Roman Age, the High Middle Ages, and the pre-modern period. The soil and geochemical proxies correlate with a phase of geomorphodynamic stability between the Early to Younger Neolithic and the Urnfield to Hallstatt period. The high abundance of grass morphotypes since the Neolithic and the increase of Juniperus since the Urnfield to Hallstatt period indicate a persistent anthropogenic impact on the vegetation. Considerable amounts of burned OM (up to 676 g BC kg−1 SOC, also identified as thermally stabilized SOM compounds by Py-FIMS) in colluvial horizons provide information that fire clearing (e.g. slash-and-burn) was especially used to open and maintain the landscape until the Roman Age. The absence of phytolith species originating from cereals, the occurrence of Juniperus and the evidence from the analysis of urease activity and faecal biomarkers indicate that the slopes of the Furstenberg were mainly used for livestock farming and wood procurement. Thus, the application of specific soil-biogeochemical proxies to colluvial deposits provide new information on the nature of past land use practices that caused the formation of colluvial deposits at that time. In general, archaeopedological multi-proxy analyses of colluvial deposits, integrating the local archaeological record, contributes to a refined understanding of how humans have shaped the landscape since the Neolithic.

The direction and magnitude of change of soil organic carbon (SOC) stocks due to global warming depend strongly on the temperature sensitivity (e.g., Q10) of carbon mineralization. To date, most multi-pool SOC models assume a general Q10 of 2 despite experimental evidence suggesting different Q10 for different carbon fractions. The aim of this study was to test if the use of experimentally derived pool specific Q10 values improves the performance of SOC models. Five contrasting data sets from three field experiments and two laboratory incubations were used to study the link between carbon pool recalcitrance and Q10 using two different approaches: a) Bayesian calibration of the Daisy SOC model parameters to infer Q10 of SOC and crop-litter pools, and b) using measured Q10 values of carbon degrading enzymes as proxies for Q10 of different Daisy pools. Namely β-glucosidase (median Q10 of 1.82) was assigned to metabolic litter and phenol/peroxidase (1.35) to structural litter and both SOC pools. To partition litter-carbon and SOC into model pools, the lignin-to-nitrogen ratio and the ratio of aliphatic/aromatic-carboxylate carbon were used, respectively. Measurements included soil microbial biomass, soil carbon dioxide (CO2) evolution and remaining carbon in soils and crop-litter. In the Bayesian calibration, strong differences in inferred Q10 values of the same pools between experiments suggested that intrinsic substrate recalcitrance was not the main driver of temperature sensitivity. For field experiment simulations, both the Q10 values derived by Bayesian calibration and measured enzyme Q10 were centered around values below 2, contrasting with high Q10 values for mineralization under laboratory incubations (close to 3). Furthermore, assigning measured phenol/peroxidase Q10 values to the slow crop-litter as well as both SOC pools and β-glucosidase to the fast crop-litter pool (approach b), could significantly improve model performance compared to using the default Q10 value of 2 for all pools. Root-mean-squared-deviation reductions were between 3 and 10% for field experiments, with no change in the laboratory experiments. Thus, site specific Q10 values of soil enzymes show potential as proxies for pool specific Q10. We present a new conceptual framework to explain the observed differences in temperature sensitivities between experiments as a result of two fundamental driving factors classified in a) state variables, that fluctuate in time, and b) soil properties, that are constant over decades. Measured enzyme Q10 values were interpreted as a proxy incorporating both factors. More than intrinsic substrate recalcitrance, the state variables such as physical protection, substrate abundance and unfavorable conditions for microorganisms control temperature sensitivity of mineralization. To reduce the uncertainty in global SOC simulations under a changing climate, their relative contributions should be disentangled and then implemented into SOC models.

The mechanistic integration of microbial behavior remains a major challenge in biogeochemical modeling of organic matter turnover in soil. We recently introduced dynamic feedbacks between specific microbial groups and their micro-environment in a biogeochemical model (Pagel et al., 2014). Here, the model was applied in a case study to simulate pesticide degradation coupled to carbon (C) turnover in the detritusphere. We aimed at unravelling the effects of litter-derived substrate supply on the spatiotemporal dynamics of the microbial community and the resulting biogeochemical processes at the mm-scale in soil. We linked genetic information on abundances of bacteria, fungi and specific pesticide degraders to the biogeochemical dynamics of C and a generic model compound (MCPA, 4-chloro-2-methylphenoxyacetic acid) in soil by multiobjective calibration. We observed and simulated increased dissolved organic and microbial C as well as accelerated MCPA degradation in soil up to a 6 mm distance to litter. We found that, whereas transport and sorption processes act as extrinsic control on the encounter of microorganisms and substrates, microbial traits such as substrate preference or metabolic capabilities intrinsically determine turnover rates triggering feedback effects on physicochemical processes such as diffusion. A process analysis revealed that C cycling and pesticide degradation in the detritusphere were strongly controlled by fungal dynamics. Our study demonstrates that integrating mathematical modeling with experiments provides comprehensive insight into the microbial regulation of matter cycling in soil.

Hydraulic redistribution (HR) of water from wet to dry soil compartments by non-differentiated mycelium was recently shown for the saprotrophic fungus Agaricus bisporus. The redistributed water triggered the carbon (C) mineralization in the dry soil. The potential of other saprotrophic fungal species and their mycelia networks for HR in soils is unknown. Here, we tested the potential for HR of the mycelial cord forming species Schizophyllum commune, compared it to capillary water transport in a sandy soil and assessed the impact of HR on C mineralization and enzyme activities in mesocosm experiments with dry and wet soil compartments using labeled water (2H) and labeled organic substrate (13C, 15N). Further, we determined nitrogen (N) translocation between the soil compartments by the mycelium of S. commune and A. bisporus. The flow velocity of redistributed water in single hyphae of S. commune was about 0.43 cm min−1 which is 1.5–2 times higher than in hyphae of A. bisporus, suggesting that cords enhance fungal HR. The amount of redistributed water was similar to capillary transport in the sterile sandy soil. Despite greater potential for HR, S. commune only slightly increased C mineralization and enzyme activity in the dry soil within 7 days. S. commune translocated N towards the organic substrate in the dry soil and used it for hyphal growth whereas A. bisporus redistributed N within the mycelial network towards the wet soil. Our results suggest that fungal hyphae have the potential to overcome capillary barriers between dry and wet soil compartments via HR and that the impact of fungal HR on C mineralization and N translocation is related to the foraging strategy and the resource usage of the fungus species.

Our understanding of the interactions between minerals, organic matter, and microorganisms at so-called biogeochemical interfaces in soil is still hampered by the inherent complexity of these systems. Artificial soil maturation experiments can help to bridge a gap in complexity between simple abiotic sorption experiments and larger-scale field experiments. By controlling other soil-forming factors, the effect of a particular variable can be identified in a simplified system. Here, we review the findings of a series of artificial soil incubation experiments with the aim of revealing general trends and conclusions. The artificial soils were designed to determine the effect of mineral composition and charcoal presence on the development of abiotic and biotic soil properties during maturation. In particular, the development of soil aggregates, organic matter (OM) composition and turnover, sorption properties, and the establishment of microbial community composition and function were considered. The main objectives of the research were to determine (1) how surface properties and sorption of chemicals modify biogeochemical interfaces ; (2) how much time is required to form aggregates from mixtures of pure minerals, OM, and a microbial inoculum ; and (3) how the presence of different mineral and charcoal surfaces affects aggregation, OM turnover, and the development of microbial community composition.

The amendment of biochar to agricultural soils is presumed to mitigate global warming through long-term carbon (C) sequestration. In addition, biochar may support microbial biomass and diversity as well as plant growth by the improvement of soil properties. So far, no information is available on the stability of biochar and the effects of biochar on soil microbial and plant properties under predicted soil warming at the field scale. We investigated the impacts of biochar addition (Miscanthus pyrochar, 30 t ha−1, August 2013) and long-term soil warming (+2.5 °C, since July 2008) and their interactive effects on microbial biochar-C utilization and physical, chemical and microbial soil properties of a silty-loamy stagnic Luvisol in a temperate agroecosystem (Stuttgart, Germany) over one year under winter rapeseed (Brassica napus). Three months after biochar application (November 2013), microbial abundances remained unaffected, indicating that readily available C from fresh biochar had been consumed before sampling. However, we found evidence for initial decomposition of more recalcitrant biochar-C by fungi under soil warming after three months. We suggest that the added biochar was very stable, since increased biochar degradation by fungi could not be detected after seven and twelve months. Nevertheless, during spring 2014, biochar reduced water loss in warmed soil by 16 % and decreased negative effects of soil dryness on microbial abundances by up to 80 %. In addition, the positive effect of biochar on soil moisture affected canopy height of winter rapeseed in the non-warmed plots in the early growth stages, although it did not change the final aboveground biomass in the first year after biochar application. Overall, biochar could be an appropriate tool for C sequestration by improving or maintaining soil fertility and productivity in temperate agroecosystems under future elevated temperatures.

Decomposition rates of coarse woody debris (CWD) have been investigated in many studies, however data on fungal biomass and the related enzymatic activities in decomposing CWD are scarce. Here, we investigated the relations between fungal biomass, enzyme activities and CWD properties in sap- and heartwood of decomposing logs of 13 different temperate European tree species, exposed for 6 years on the ground. Fungal biomass was significantly higher in sapwood than in heartwood and higher in deciduous than in coniferous species, and represented 0.3–4.4% of CWD dry mass. In deciduous sapwood, fungal biomass may represent up to 29% of the total N stock in CWD. Fungal biomass correlated positively with the N content of CWD and, in heartwood, negatively with extractives. Enzyme activities were higher in deciduous than in coniferous CWD and for hydrolases higher in sapwood than in heartwood. Correlations between enzyme activities and the ergosterol content were generally weak. Hydrolytic enzymes were frequently found in all decaying tree species, whereas ligninolytic oxidoreductases showed high variability specifically in deciduous wood. Fungal biomass and enzymatic activities confirm the assumption that, in the initial stage, the decomposition of deciduous CWD is faster than of coniferous CWD under comparable conditions.

The response of agroecosystem carbon (C) respiration fluxes to environmental changes needs to be better understood as respiration subcomponents may respond differently to management and seasonal weather dynamics, which is important for soil organic matter (SOM) modeling. Respiration measurements at two different spatial and temporal scales (eddy covariance (EC) and soil chambers) were used to ascertain the relationship between temperature and CO2 flux of different ecosystem respiration components (ecosystem (Reco), soil and root combined, and soil). Further, different model approaches (static versus dynamic reference CO2 rate (rb) and activation energy type parameter (E0) with an Arrhenius-like function) in order to partition Reco into above- and belowground autotrophic (RA_above, RA_below) and heterotrophic respiration (RH_SOM) were tested. Canopy level CO2 fluxes in winter wheat and silage maize were measured by EC stations and soil surface CO2 flux by a handheld chamber analyzer in arable fields in Southwest Germany over a period of three growing seasons (2009, 2010, and 2012). Additionally, successive bare fallow plots were installed at the beginning of each growing season to partition soil respiration between autotrophic and heterotrophic sources (including “labile” soil C (newest bare fallow) as the difference to the oldest bare fallow). Stepwise model building was tested with keeping rb and E0 constant (static method) and then by varying rb and E0 each individually or together by time period (dynamic method) over the whole growing season (15, 10 or 7 days for Reco, measurement periods for soil chamber measurements). The dynamic models were superior as measured by Aaike Information Criteria (AIC) and coefficient of determination (average R2, 0.15 for the static model and 0.50 for the dynamic model). In the best fitting model for each crop-year (lowest AIC), rb was successfully estimated in each time period (relative standard error

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.

Understanding in situ enzyme activities could help clarify the fate of soil organic carbon (SOC), one of the largest uncertainties in predicting future climate. Here, we explored the role of soil temperature and moisture on SOM decomposition by using, for the first time, modelled in situ enzyme activities as a proxy to explain seasonal variation in soil respiration. We measured temperature sensitivities (Q 10 ) of three enzymes (β-glucosidase, xylanase and phenoloxidase) and moisture sensitivity of β-glucosidase from agricultural soils in southwest Germany. Significant seasonal variation was found in potential activities of β-glucosidase, xylanase and phenoloxidase and in Q 10 for β-glucosidase and phenoloxidase activities but not for xylanase. We measured moisture sensitivity of β-glucosidase activity at four moisture levels (12%–32%), and fitted a saturation function reflecting increasing substrate limitation due to limited substrate diffusion at low water contents. The moisture response function of β-glucosidase activity remained stable throughout the year. Sensitivity of enzymes to temperature and moisture remains one of the greatest uncertainties in C models. We therefore used the response functions to model temperature-based and temperature and moisture-based in situ enzyme activities to characterize seasonal variation in SOC decomposition. We found temperature to be the main factor controlling in situ enzyme activities. To prove the relevance of our modelling approach, we compared the modelled in situ enzyme activities with soil respiration data measured weekly. Temperature-based in situ enzyme activities explained seasonal variability in soil respiration well, with model efficiencies between 0.35 and 0.78. Fitting an exponential response function to in situ soil temperature explained soil respiration to a lesser extent than our enzyme-based approach. Adding soil moisture as a co-factor improved model efficiencies only partly. Our results demonstrate the potential of this new approach to explain seasonal variation of enzyme related processes.