Deep incorporation of organic amendments into soils of a 'Calardis Musqué' vineyard: effects on greenhouse gas emissions, vine vigor, and grape quality.

Background: Traditional wine growing regions are increasingly endangered by climatic alterations. One promising approach to mitigate advancing climate change could be an increase of soil organic matter. Here, especially subsoils are of interest as they provide higher carbon storage potential than topsoils. In this context, vineyard subsoils could be particularly suitable since they are deeply cultivated once before planting and afterwards, left at rest for several decades due to the perennial nature of grapevines. Methods: For this purpose, a biochar compost substrate and greenwaste compost were incorporated in up to 0.6 m depth before planting a new experimental vineyard with the fungus-resistant grapevine cultivar 'Calardis Musqué'. The influence of this deep incorporation on greenhouse gas emissions and grapevine performance was evaluated and compared to a non-amended control using sensor-based analyses. Results: Increased CO2 emissions and lower N2O emissions were found for the incorporation treatments compared to the control, but these differences were not statistically significant due to high spatial variability. Only few plant traits like chlorophyll content or berry cuticle characteristics were significantly affected in some of the experimental years. Over the course of the study, annual climatic conditions had a much stronger influence on plant vigor and grape quality than the incorporated organic amendments. Discussion: In summary, organic soil amendments and their deep incorporation did not have any significant effect on greenhouse gas emissions and no measurable or only negligible effect on grapevine vigor, and grape quality parameters. Thus, according to our study the deposition of organic amendments in vineyard subsoils seems to be an option for viticulture to contribute to carbon storage in soils in order to mitigate climate change.

Biochar addition reduces non-CO2 greenhouse gas emissions during composting of human excreta and cattle manure.

Ecological sanitation combined with thermophilic composting is a viable option to transform human excreta into a stabilized, pathogen-free, and nutrient-rich fertilizer. In combination with suitable bulking materials such as sawdust and straw, and additives such as biochar, this could also be a suitable waste management strategy for reducing greenhouse gas (GHG) emissions. In this study, we conducted a 143-days thermophilic composting of human excreta or cattle manure together with teff straw, organic waste, and biochar to investigate the effect that biochar has on GHG (CO2 , N2 O, and CH4 ) and NH3 emissions. The composting was performed in wooden boxes (1.5 × 1.5 × 1.4 m3 ), GHG were measured by using a portable FTIR gas analyzer and NH3 was sampled as ammonium in an H2 SO4 trap. We found that the addition of biochar significantly reduced CH4 emissions by 91% in the cattle manure compost, and N2 O emissions by 56%-57% in both humanure and cattle manure composts. Overall, non-CO2 GHG emissions were reduced by 51%-71%. In contrast, we did not observe a significant biochar effect on CO2 and NH3 emissions. Previous data already showed that it is possible to sanitize human fecal material when using this composting method. Our results suggest that thermophilic composting with biochar addition is a safe and cost-effective waste management practice for producing a nutrient-rich fertilizer from human excreta, while reducing GHG emissions at the same time.

Fate of Horizontal-Gene-Transfer Markers and Beta-Lactamase Genes during Thermophilic Composting of Human Excreta.

Thermophilic composting is a suitable treatment for the recycling of organic wastes for agriculture. However, using human excreta as feedstock for composting raises concerns about antibiotic resistances. We analyzed samples from the start and end of a thermophilic composting trial of human excreta, together with green cuttings and straw, with and without biochar. Beta-lactamase genes blaCTX-M, blaIMP, and blaTEM conferring resistance to broad-spectrum beta-lactam antibiotics, as well as horizontal gene transfer marker genes, intI1 and korB, were quantified using qPCR. We found low concentrations of the beta-lactamase genes in all samples, with non-significant mean decreases in blaCTX-M and blaTEM copy numbers and a mean increase in blaIMP copy numbers. The decrease in both intI1 and korB genes from start to end of composting indicated that thermophilic composting can decrease the horizontal spread of resistance genes. Thus, thermophilic composting can be a suitable treatment for the recycling of human excreta.

Straw amendment and nitrification inhibitor controlling N losses and immobilization in a soil cooling-warming experiment.

It is common practice in agriculture to apply high­carbon amendments, e.g. straw, or nitrification inhibitors (NI) to reduce soil nitrogen (N) losses. However, little is known on the combined effects of straw and NI and how seasonal soil temperature variations further affect N immobilization. We conducted a 113-day mesocosm experiment with different levels of 15N-fertilizer application (N0: control; N1: 125 kg N ha-1; N2: 250 kg N ha-1) in an agricultural soil, amended with either wheat straw, NI or a combination of both in order to investigate N retention and loss from soil after a cooling-warming phase simulating a seasonal temperature shift, i.e., 30 days cooling phase at 7 °C and 10 days warming phase at 21 °C. Subsequently, soils were planted with barley as phytometers to study 15N-transfer to a following crop. Straw addition significantly reduced soil N-losses due to microbial N immobilization. Although carbon added as straw led to increased N2O emissions at high N fertilization, this was partly counterbalanced by NI. Soil cooling-warming strongly increased ammonification (+77 %), while nitrification was suppressed, and straw-induced microbial N immobilization dominated. N immobilized after straw addition was mineralized at the end of the experiment as indicated by structural equation models. Re-mineralization in N2 was sufficient, but still suboptimal in N0 and N1 at critical times of early barley growth. N-use efficiency of the 15N tracer decreased with fertilization intensity from 50 % in N1 to 35 % in N2, and straw amendment reduced NUE to 25 % at both fertilization rates. Straw amendment was most powerful in reducing N-losses (-41 %), in particular under variable soil temperature conditions, but NI enforced its effects by reducing N2O emission (-40 %) in N2 treatment. Sufficient N-fertilization coupled with straw application is required to adjust the timely re-mineralization of N for subsequent crops.

Functional, not Taxonomic, Composition of Soil Fungi Reestablishes to Pre-mining Initial State After 52 Years of Recultivation.

Open-cast mining leads to the loss of naturally developed soils and their ecosystem functions and services. Soil restoration after mining aims to restore the agricultural productivity in which the functions of the fungal community play a crucial role. Whether fungi reach a comparable functional state as in the soil before mining within half a century of recultivation is still unanswered. Here, we characterised the soil fungal community using ITS amplicon Illumina sequencing across a 52-year chronosequence of agricultural recultivation after open-cast mining in northern Europe. Both taxonomic and functional community composition showed profound shifts over time, which could be attributed to the changes in nutrient status, especially phosphorus availability. However, taxonomic composition did not reach the pre-mining state, whereas functional composition did. Importantly, we identified a positive development of arbuscular mycorrhizal root fungal symbionts after the initial three years of alfalfa cultivation, followed by a decline after conversion to conventional farming, with arbuscular mycorrhizal fungi being replaced by soil saprobes. We conclude that appropriate agricultural management can steer the fungal community to its functional pre-mining state despite stochasticity in the reestablishment of soil fungal communities. Nonetheless, conventional agricultural management results in the loss of plant symbionts, favouring non-symbiotic fungi.

Improving nitrogen retention of cattle slurry with oxidized biochar: An incubation study with three different soils.

The application of livestock slurry in soils can lead to nitrogen (N) losses through ammonia (NH3 ) emission or nitrate (NO3 - ) leaching. Oxidized biochar has great potential to mitigate N losses due to its strong adsorption capacity; however, the effects of oxidized biochar in different soils treated with slurry are currently unclear. Here, we investigated the effect of untreated and oxidized biochar (applied at a rate of 50 kg C m-3 slurry) on reducing N losses in a laboratory experiment with three different soils (loamy sand, sandy loam, loam) amended with cattle slurry at an application rate of 73 kg N ha-1 . Oxidized biochar reduced NH3 emissions by 64-75% in all soils, whereas untreated biochar reduced NH3 emissions by 61% only in the loamy sand. Oxidized biochar significantly reduced the NO3 - content in the soil solution of the loamy sand in the early phase of the incubation and led to a significantly higher NO3 - concentration in the same soil compared with the slurry-only treatment at the end of the experiment, indicating a significant increase in NO3 - retention in this organic C-poor soil. We conclude that oxidized biochar can reduce N losses, both in the form of NH3 emission and NO3 - leaching, from cattle slurry applied to soil, particularly in soil with soil organic carbon content <1% and pH <5 (i.e., oxidized biochar can serve as a means for improving the quality of marginal and acidic soils).

Fenton oxidation of biochar improves retention of cattle slurry nitrogen.

Nitrogen (N) losses during fertilization with livestock slurry, mainly in the form of ammonia (NH3 ), can cause environmental problems and reduce fertilizer efficiency. Leonardite, which is characterized by oxygen-rich functional groups and low pH, has been found to decrease losses of slurry N. However, leonardite, as a byproduct of open-cast lignite mining, is not a renewable resource. The objective of this study was to modify biochar by chemical surface oxidation in order to find a sustainable but similarly effective substitute for leonardite. Biochar was produced from spruce sawdust in a pyrolysis oven at a maximum temperature of 610 °C. Then the biochar was oxidized using the Fenton reaction, with a ratio of Fe2+ /H2 O2 of 1:1,000, as a source of highly reactive HO· radicals to introduce oxygen-rich functional groups to the biochar surface. The ammonium (NH4 + ) adsorption capacity of biochar, oxidized biochar, and leonardite was tested in ammonium sulfate [(NH4 )2 SO4 ] solution, pH-adjusted (NH4 )2 SO4 solution, and cattle slurry. The results showed that biochar had the highest total NH4 + adsorption of 1.4 mg N g-1 in (NH4 )2 SO4 solution, whereas oxidized biochar had the highest reversible NH4 + adsorption of 0.8 mg N g-1 . In the pH-adjusted ammonium solution, all materials reduced NH3 emissions by ≥90%, and oxidized biochar reduced NH3 emissions by 99.99%. In contrast, leonardite reduced NH3 emissions the most in cattle slurry, and oxidation of biochar increased the reduction in NH3 emissions from 22 to 67% compared with non-oxidized biochar. In conclusion, biochar oxidized by means of the Fenton reaction greatly decreased NH3 emissions by increased adsorption of NH4 + in cattle slurry compared with non-oxidized biochar, indicating the great potential of oxidized biochar for reducing N losses during slurry application.

Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms: An interlaboratory comparison of three common measurement approaches.

RATIONALE: Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (Ni ) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ15 N in NO3 - and NH4 + and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. METHODS: Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ15 N in NO3 - and NH4 + . The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms Ni to either N2 O (CM-N2 O) or N2 (CM-N2 ), and (c) the denitrifier (DN) methods. RESULTS: The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2 O performing superior for both NO3 - and NH4 + , followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%15 N of Ni of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO3 - and ± 32.9‰ for NH4 + ; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered. CONCLUSIONS: The inconsistency among all methods and laboratories raises concern about reported δ15 N values particularly from environmental samples.

Metagenomic Insights Into the Changes of Antibiotic Resistance and Pathogenicity Factor Pools Upon Thermophilic Composting of Human Excreta.

In times of climate change, practicing a form of sustainable, climate-resilient and productive agriculture is of primordial importance. Compost could be one form of sustainable fertilizer, which is increasing humus, water holding capacity, and nutrient contents of soils. It could thereby strengthen agriculture toward the adverse effects of climate change, especially when additionally combined with biochar. To get access to sufficient amounts of suitable materials for composting, resources, which are currently treated as waste, such as human excreta, could be a promising option. However, the safety of the produced compost regarding human pathogens, pharmaceuticals (like antibiotics) and related resistance genes must be considered. In this context, we have investigated the effect of 140- and 154-days of thermophilic composting on the hygienization of human excreta and saw dust from dry toilets together with straw and green cuttings with and without addition of biochar. Compost samples were taken at the beginning and end of the composting process and metagenomic analysis was conducted to assess the fate of antibiotic resistance genes (ARGs) and pathogenicity factors of the microbial community over composting. Potential ARGs conferring resistance to major classes of antibiotics, such as beta-lactam antibiotics, vancomycin, the MLSB group, aminoglycosides, tetracyclines and quinolones were detected in all samples. However, relative abundance of ARGs decreased from the beginning to the end of composting. This trend was also found for genes encoding type III, type IV, and type VI secretion systems, that are involved in pathogenicity, protein effector transport into eukaryotic cells and horizontal gene transfer between bacteria, respectively. The results suggest that the occurrence of potentially pathogenic microorganisms harboring ARGs declines during thermophilic composting. Nevertheless, ARG levels did not decline below the detection limit of quantitative PCR (qPCR). Thresholds for the usage of compost regarding acceptable resistance gene levels are yet to be evaluated and defined.

Thermophilic Composting of Human Feces: Development of Bacterial Community Composition and Antimicrobial Resistance Gene Pool.

In times of climate change, practicing sustainable, climate-resilient, and productive agriculture is of primordial importance. Compost from different resources, now treated as wastes, could be one form of sustainable fertilizer creating a resilience of agriculture to the adverse effects of climate change. However, the safety of the produced compost regarding human pathogens, pharmaceuticals, and related resistance genes must be considered. We have assessed the effect of thermophilic composting of dry toilet contents, green cuttings, and straw, with and without biochar, on fecal indicators, the bacterial community, and antibiotic resistance genes (ARGs). Mature compost samples were analyzed regarding fecal indicator organisms, revealing low levels of Escherichia coli that are in line with German regulations for fertilizers. However, one finding of Salmonella spp. exceeded the threshold value. Cultivation of bacteria from the mature compost resulted in 200 isolates with 36.5% of biosafety level 2 (BSL-2) species. The majority is known as opportunistic pathogens that likewise occur in different environments. A quarter of the isolated BSL-2 strains exhibited multiresistance to different classes of antibiotics. Molecular analysis of total DNA before and after composting revealed changes in bacterial community composition and ARGs. 16S rRNA gene amplicon sequencing showed a decline of the two most abundant phyla Proteobacteria (start: 36-48%, end: 27-30%) and Firmicutes (start: 13-33%, end: 12-16%), whereas the abundance of Chloroflexi, Gemmatimonadetes, and Planctomycetes rose. Groups containing many human pathogens decreased during composting, like Pseudomonadales, Bacilli with Bacillus spp., or Staphylococcaceae and Enterococcaceae. Gene-specific PCR showed a decline in the number of detectable ARGs from 15 before to 8 after composting. The results reveal the importance of sufficiently high temperatures lasting for a sufficiently long period during the thermophilic phase of composting for reducing Salmonella to levels matching the criteria for fertilizers. However, most severe human pathogens that were targeted by isolation conditions were not detected. Cultivation-independent analyses also indicated a decline in bacterial orders comprising many pathogenic bacteria, as well as a decrease in ARGs. In summary, thermophilic composting could be a promising approach for producing hygienically safe organic fertilizer from ecological sanitation.

Nutrient dynamics during composting of human excreta, cattle manure, and organic waste affected by biochar.

Ecological sanitation via thermophilic composting could be a promising solution to the lack of sanitation and limited access to fertilizers, particularly in developing countries. Here, we conducted a 185-d thermophilic composting experiment with human excreta, and separately with cattle manure, mixed with kitchen scraps, teff [Eragrostis tef (Zuccagni) Trotter] straw, sawdust, and biochar (BC) by using an appropriate-technology approach. We followed the dynamics of the most important macronutrients (N, P, K), temperature, moisture, pH, electrical conductivity, cation exchange capacity, as well as content of organic matter, organic C, Ca, Mg, and micronutrients throughout the process. Low N (<47%), P (<9%), K (<11%), Ca (<18%), and Mg (<21%) losses and the temperature profile indicated a well-functioning thermophilic composting process. Compost temperature was >60 °C for 7, 6, 5, and 8 consecutive days for treatments containing human excreta, human excreta amended with BC, cattle manure, and cattle manure amended with BC, respectively, suggesting a final compost product free of pathogens. The compost mixture with cattle manure and BC reached a significantly higher temperature than the same variant without BC, with a maximum value of 65.9 °C on Day 6. For all treatments, final germination index values >100% indicated compost maturity and the absence of phytotoxic substances. Biochar addition reduced losses of organic matter (18-23%), C (33-42%), and N (49-100%) and decreased the amount of extractable NO3 - (32-36%) in the final compost. The tested ecological sanitation concept via thermophilic composting is thus a promising strategy to improve access to cheap fertilizer by safe and sustainable sanitation and waste management.

Soil type affects not only magnitude but also thermal sensitivity of N2O emissions in subtropical mountain area.

It is a concern whether the effect of soil type on N2O emissions has to be considered for regional mitigation strategies and emission estimates in mountainous areas with inherent spatial heterogeneities of soil type. To date, there were few field experiments which investigated soil type effects on N2O emissions. Thus a 2-year field study was conducted to measure N2O emissions and soil environmental variables from three different soils that were formed from similar parental rock under the same climate. Seasonal N2O fluxes ranged from 0.18 to 0.40 kg N ha-1 for wheat seasons and 0.40 to 1.50 kg N ha-1 for maize seasons across different experimental soils. The intra- and inter-annual variations in N2O emissions were mainly triggered by temporal dynamics of soil temperature and moisture conditions. On average, seasonal N2O fluxes for acidic soils were significantly lower than for neutral and alkaline soils in cold-dry wheat seasons while significantly greater than for neutral and alkaline soils in warm-wet maize seasons. These determined differences of N2O emissions were mainly caused by differences of initial soil properties across different soils. Moreover, seasonal N2O fluxes were positively correlated with soil pH in wheat seasons, but negatively correlated in maize seasons. The temperature sensitivity coefficient (Q10) of soil N2O emissions for acidic soil (4.06) were significantly greater than those for neutral (1.82) and alkaline (1.15) soils. Overall, N2O emissions for acidic soils were not only higher than those for neutral and alkaline soils but also more sensitive to changing temperature. The present study highlights that soil type is needed to be carefully considered for regional estimate and proposing mitigation strategy of N2O emissions especially in subtropical mountain regions with inherent great heterogeneity of soil type.

Ecotrons: Powerful and versatile ecosystem analysers for ecology, agronomy and environmental science.

Ecosystems integrity and services are threatened by anthropogenic global changes. Mitigating and adapting to these changes require knowledge of ecosystem functioning in the expected novel environments, informed in large part through experimentation and modelling. This paper describes 13 advanced controlled environment facilities for experimental ecosystem studies, herein termed ecotrons, open to the international community. Ecotrons enable simulation of a wide range of natural environmental conditions in replicated and independent experimental units while measuring various ecosystem processes. This capacity to realistically control ecosystem environments is used to emulate a variety of climatic scenarios and soil conditions, in natural sunlight or through broad-spectrum lighting. The use of large ecosystem samples, intact or reconstructed, minimizes border effects and increases biological and physical complexity. Measurements of concentrations of greenhouse trace gases as well as their net exchange between the ecosystem and the atmosphere are performed in most ecotrons, often quasi continuously. The flow of matter is often tracked with the use of stable isotope tracers of carbon and other elements. Equipment is available for measurements of soil water status as well as root and canopy growth. The experiments ran so far emphasize the diversity of the hosted research. Half of them concern global changes, often with a manipulation of more than one driver. About a quarter deal with the impact of biodiversity loss on ecosystem functioning and one quarter with ecosystem or plant physiology. We discuss how the methodology for environmental simulation and process measurements, especially in soil, can be improved and stress the need to establish stronger links with modelling in future projects. These developments will enable further improvements in mechanistic understanding and predictive capacity of ecotron research which will play, in complementarity with field experimentation and monitoring, a crucial role in exploring the ecosystem consequences of environmental changes.

Dolerite Fines Used as a Calcium Source for Microbially Induced Calcite Precipitation Reduce the Environmental Carbon Cost in Sandy Soil.

Microbial-Induced Calcite Precipitation (MICP) stimulates soil microbiota to induce a cementation of the soil matrix. Urea, calcium and simple carbon nutrients are supplied to produce carbonates via urea hydrolysis and induce the precipitation of the mineral calcite. Calcium chloride (CaCl2) is typically used as a source for calcium, but basic silicate rocks and other materials have been investigated as alternatives. Weathering of calcium-rich silicate rocks (e.g., basalt and dolerite) releases calcium, magnesium and iron; this process is associated with sequestration of atmospheric CO2 and formation of pedogenic carbonates. We investigated atmospheric carbon fluxes of a MICP treated sandy soil using CaCl2 and dolerite fines applied on the soil surface as sources for calcium. Soil-atmosphere carbon fluxes were monitored over 2 months and determined with an infrared gas analyser connected to a soil chamber. Soil inorganic carbon content and isotopic composition were determined with isotope-ratio mass spectrometry. In addition, soil-atmosphere CO2 fluxes during chemical weathering of dolerite fines were investigated in incubation experiments with gas chromatography. Larger CO2 emissions resulted from the application of dolerite fines (116 g CO2-C m-2) compared to CaCl2 (79 g CO2-C m-2) but larger inorganic carbon precipitation also occurred (172.8 and 76.9 g C m-2, respectively). Normalising to the emitted carbon to precipitated carbon, the environmental carbon cost was reduced with dolerite fines (0.67) compared to the traditional MICP treatment (1.01). The carbon isotopic signature indicated pedogenic carbonates (δ13Cav = -8.2 ± 5.0‰) formed when dolerite was applied and carbon originating from urea (δ13Cav = -46.4 ± 1.0‰) precipitated when CaCl2 was used. Dolerite fines had a large but short-lived (<2 d) carbon sequestration potential, and results indicated peak CO2 emissions during MICP could be balanced optimising the application of dolerite fines.

Altered energy partitioning across terrestrial ecosystems in the European drought year 2018.

Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004-2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

52 years of ecological restoration following a major disturbance by opencast lignite mining does not reassemble microbiome structures of the original arable soils.

Opencast mining for lignite continuously creates areas of land that require restoration. Here we applied a chronosequence approach to investigate the development of soil bacterial communities during 52 years as influenced by the restoration process and subsequent changes in soil physico-chemical conditions starting from the initial reclamation of the sites. By comparison with the unaffected soils near the mine, we were able to address the question if soil bacterial communities have reached a steady state within 52 years, which is comparable to the original soil. Our study revealed three distinct phases of the restoration process, each with a specific bacterial community composition. The effect size of these changes was similar to the one observed for seasonal dynamics at our sites. At the beginning of the restoration process Flavobacteriaceae, Cytophagaceae and Sphingobacteriaceae were found as typical members of the bacterial community as well as Rhizobiales as a result of the cultivation of alfalfa on the restored plots. At later stage the families Peptostreptococcaceae, Desulfurellaceae as well as Streptomycetaceae increased in relative abundance and became dominant members of the bacterial community. Even though overall bacterial abundance and richness exhibited values comparable to the original soil already 5 years after the start of the restoration process, main responder analyses reveal differences in the bacterial community structure even 52 years after the start of the restoration process. Mostly Nitrospirae were reduced in abundance in the soils restored for 52 years compared to the original soils. To broaden the significance of our study, we compared our data bioinformatically with published results from other restored areas, which were previously affected by opencast mining. Despite different durations of the different restoration phase, we could observe a large degree of conformity when bacterial patterns of succession were compared indicating common modes of action of ecological restoration tools for bacterial communities.

Decoupling of impact factors reveals the response of German winter wheat yields to climatic changes.

Yield development of agricultural crops over time is not merely the result of genetic and agronomic factors, but also the outcome of a complex interaction between climatic and site-specific soil conditions. However, the influence of past climatic changes on yield trends remains unclear, particularly under consideration of different soil conditions. In this study, we determine the effects of single agrometeorological factors on the evolution of German winter wheat yields between 1958 and 2015 from 298 published nitrogen (N)-fertilization experiments. For this purpose, we separate climatic from genetic and agronomic yield effects using linear mixed effect models and estimate the climatic influence based on a coefficient of determination for these models. We found earlier occurrence of wheat growth stages, and shortened development phases except for the phase of stem elongation. Agrometeorological factors are defined as climate covariates related to the growth of winter wheat. Our results indicate a general and strong effect of agroclimatic changes on yield development, in particular due to increasing mean temperatures and heat stress events during the grain-filling period. Except for heat stress days with more than 31°C, yields at sites with higher yield potential were less prone to adverse weather effects than at sites with lower yield potential. Our data furthermore reveal that a potential yield levelling, as found for many West-European countries, predominantly occurred at sites with relatively low yield potential and about one decade earlier (mid-1980s) compared to averaged yield data for the whole of Germany. Interestingly, effects related to high precipitation events were less relevant than temperature-related effects and became relevant particularly during the vegetative growth phase. Overall, this study emphasizes the sensitivity of yield productivity to past climatic conditions, under consideration of regional differences, and underlines the necessity of finding adaptation strategies for food production under ongoing and expected climate change.

Investigating the root plasticity response of Centaurea jacea to soil water availability changes from isotopic analysis.

Root water uptake is a key ecohydrological process for which a physically based understanding has been developed in the past decades. However, due to methodological constraints, knowledge gaps remain about the plastic response of whole plant root systems to a rapidly changing environment. We designed a laboratory system for nondestructive monitoring of stable isotopic composition in plant transpiration of a herbaceous species (Centaurea jacea) and of soil water across depths, taking advantage of newly developed in situ methods. Daily root water uptake profiles were obtained using a statistical Bayesian multisource mixing model. Fast shifts in the isotopic composition of both soil and transpiration water could be observed with the setup and translated into dynamic and pronounced shifts of the root water uptake profile, even in well watered conditions. The incorporation of plant physiological and soil physical information into statistical modelling improved the model output. A simple exercise of water balance closure underlined the nonunique relationship between root water uptake profile on the one hand, and water content and root distribution profiles on the other, illustrating the continuous adaption of the plant water uptake as a function of its root hydraulic architecture and soil water availability during the experiment.

Quantifying N2O reduction to N2 during denitrification in soils via isotopic mapping approach: Model evaluation and uncertainty analysis.

The last step of denitrification, i.e. the reduction of N2O to N2, has been intensively studied in the laboratory to understand the denitrification process, predict nitrogen fertiliser losses, and to establish mitigation strategies for N2O. However, assessing N2 production via denitrification at large spatial scales is still not possible due to lack of reliable quantitative approaches. Here, we present a novel numerical "mapping approach" model using the δ15Nsp/δ18O slope that has been proposed to potentially be used to indirectly quantify N2O reduction to N2 at field or larger spatial scales. We evaluate the model using data obtained from seven independent soil incubation studies conducted under a He-O2 atmosphere. Furthermore, we analyse the contribution of different parameters to the uncertainty of the model. The model performance strongly differed between studies and incubation conditions. Re-evaluation of the previous data set demonstrated that using soils-specific instead of default endmember values could largely improve model performance. Since the uncertainty of modelled N2O reduction was relatively high, further improvements to estimate model parameters to obtain more precise estimations remain an on-going matter, e.g. by determination of soil-specific isotope fractionation factors and isotopocule endmember values of N2O production processes using controlled laboratory incubations. The applicability of the mapping approach model is promising with an increasing availability of real-time and field based analysis of N2O isotope signatures.

Low yield and abiotic origin of N2O formed by the complete nitrifier Nitrospira inopinata.

Nitrous oxide (N2O) and nitric oxide (NO) are atmospheric trace gases that contribute to climate change and affect stratospheric and ground-level ozone concentrations. Ammonia oxidizing bacteria (AOB) and archaea (AOA) are key players in the nitrogen cycle and major producers of N2O and NO globally. However, nothing is known about N2O and NO production by the recently discovered and widely distributed complete ammonia oxidizers (comammox). Here, we show that the comammox bacterium Nitrospira inopinata is sensitive to inhibition by an NO scavenger, cannot denitrify to N2O, and emits N2O at levels that are comparable to AOA but much lower than AOB. Furthermore, we demonstrate that N2O formed by N. inopinata formed under varying oxygen regimes originates from abiotic conversion of hydroxylamine. Our findings indicate that comammox microbes may produce less N2O during nitrification than AOB.