Displays

A sustainable agricultural management can contribute to promoting soil biodiversity performance, thereby preserving soil functions and ensuring the provision of soil biota-induced ecosystem services. In order to make the best possible use of these services for the benefit of agricultural production, a better understanding of interlinkages between management measures, ecosystem service/disservice balance and soil self-regulation potential is essential. In this context, it is well known that the reduction of soil tillage intensity combined with mulching techniques, on the one hand, promote the survival, development and spread of plant pathogenic mycotoxin-producing soil-borne fungi, but, on the other hand, enhance the diversity of antagonistic mycotoxin-degrading fungivorous soil animals. However, up to now it is still unclear, which ecosystem service/disservice balance results from both pathways and which self-regulation mechanisms are involved.

To analyse and assess the bioregulation potential of fungivorous soil faunal key species (earthworms: Lumbricus terrestris, collembolans: Proisotoma minuta, enchytraeids: Enchytraeus crypticus and E. christenseni) on economically relevant plant pathogenic species of the fungal genus Fusarium (F. graminearum, F. culmorum, F. verticillioides) and its mycotoxins (deoxynivalenol (DON), zearalenon (ZEN), 3-acetyl-deoxynivalenol (3AcDON) and fumonisin B1 (FB1)) in maize residues, field and laboratory experiments were performed as part of the EU BiodivERsA project SoilMan. Based on these studies the following hypotheses were tested: (1) soil faunal key organisms supress Fusarium species and reduce their mycotoxins in maize residues, (2) the bioregulation potential depends on substrate size and soil texture (3) interactions between fungivorous key species affect their bioregulation potential, (4) leaching of mycotoxins represents a potential risk for arable soils.

The results reflect that soil faunal key species regulate amounts of F. graminearum and F. culmorum in maize residues depending on substrate size and soil texture, but did not affect amounts of F. verticillioides. Fungivorous soil animals significantly accelerate degradation rates of Fusarium mycotoxins by up to 300%, depending on soil faunal species, respective mycotoxin and soil texture. In particular, primary decomposers within the earthworm community (L. terrestris) are pivotal for the bioregulation of Fusarium species and their mycotoxins in the mulch layer. The bioregulation potential of the mesofauna (collembolans and enchytraeids) strongly depends on soil faunal interactions. The findings further indicate that the mycotoxins DON and ZEN leach from infected maize residues.

The present studies contribute to improve understanding of the complex interrelations between arable management and ecosystem service/disservice balance in agroecosystems.

How to cite: van Capelle, C., Meyer-Wolfarth, F., Meiners, T., Sandor, M., and Schrader, S.: Soil fauna regulates the ecosystem service/disservice balance in mulched soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6545, https://doi.org/10.5194/egusphere-egu2020-6545, 2020.

Past studies have praised earthworms for improving soil structure and fertility, but criticized earthworms for increasing the leaching of nutrients and soil greenhouse gas emissions. Therefore, in order to maximize the environmental benefits and reduce the environmental costs of earthworms, it is important to determine the factors controlling the structure of earthworm communities at local, landscape and continental scales. We first hypothesized that forested riparian buffer strips (FRBS) within agricultural landscapes would be a refuge for earthworms, due to higher soil moisture and organic matter compared to adjacent agricultural fields (“treatment” = FRBS vs. Field).  Within sites, we hypothesized that earthworms would be most abundant where the chemical quality of above- and belowground plant litter is high, or where soil disturbance is low. At the continental scale, we hypothesized that total summer precipitation interacts with regional and local scale factors in controlling earthworm community structure.  A field survey was conducted to quantify earthworm species abundances in FRBS and adjacent agricultural fields across Eastern Canada and Central Europe (two “bioregions” differing in rainfall). At each of 77 sites, we collected and identified earthworms from three plots within FRBS and adjacent agricultural fields, and noted the tree species, understory vegetation, drainage class, agricultural crop as well as five soil physicochemical variables (texture, pH, total C, total N and % organic matter). In each bioregion and treatment, we found proportionately more endogeic than anecic or epigeic earthworm species. In Eastern Canada there were proportionately fewer anecic and more epigeic individuals in FRBS than in fields, whereas in Central Europe there were fewer endogeic and more anecic earthworms in FRBS than in fields. We also found significant interactions between bioregion and treatment on total earthworm abundance and biomass, and on soil moisture. More specifically, in Eastern Canada we found higher earthworm abundance and biomass, soil moisture and organic matter in FRBS. Conversely, in Central Europe we found higher earthworm abundance and biomass in fields, no treatment effects on soil moisture, and higher soil organic matter in FRBS. The different earthworm distribution patterns in each bioregion were not related to the types of agricultural crops, but rather to differences in precipitation and soil moisture across bioregions. Within FRBS in Eastern Canada, earthworm abundance in deciduous and mixedwood stands were higher than in coniferous stands; in Central Europe, earthworm abundance was higher in deciduous stands only. Within FRBS in Eastern Canada, the abundance of the prominent endogeic species Apporectodia rosea was correlated with herbaceous plants, notably ferns and graminoids. Conditional regression tree analysis revealed positive relationships between earthworms and soil clay content, pH, moisture and organic matter. Our results suggest that local and landscape patterns in earthworm diversity can be predicted by soil and vegetation attributes, but the relative importance of these factors change across continual scales due to climate.  Comparing the distributions of earthworms across different scales provides insights into the potential of different species to spread into new habitats with climate change.

How to cite: Cameron, A., Bradley, R., Benetkova, P., Józefowska, A., Boilard, G., Šimek, M., Whalen, J., and Thevathasan, N.: Local, landscape and continental scale factors controlling earthworm community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-274, https://doi.org/10.5194/egusphere-egu2020-274, 2020.

Over the last decades, reduced tillage became more and more important as a suitable soil management practice. Moreover, reduced tillage is expected to promote a healthy and active soil life as a feature of sustainable agricultural. The determination of soil microbial biomass and microbial indices are suitable indicators for estimating soil quality. This study follows a regional approach and focusses at four different countries with varying environmental conditions at long-term experimental field-sites (LTE´s) across Europe. Soil microbial biomass carbon (SMB-C), the metabolic quotient (qCO₂) and the ratio of SMB-C to soil organic carbon (SOC) were measured as microbial properties.

Our contribution to the ongoing discussion of the effectiveness of non-conventional tillage systems is (i) the comparison between conventional ploughing (CT) and minimum tillage (MT), (ii) the comparison of inversion vs. not inversion tillage at the same working depth, (iii) the comparison of ploughing vs. no-tillage (NT), (iv) the comparison between reduced tillage systems with each other (MT vs. NT).

We found a significant difference of SMB-C for CT and MT between 0 and 10 cm in Germany and Sweden, but no difference between tillage treatments for the sampled soil profile (0-30 cm). We highlight that tillage changed the vertical distribution of SMB-C, showing similar values among soil depths under CT and a depth gradient with decreasing values for MT.

The comparison of inversion vs. not inversion tillage at the same working depth in Romania showed no differences between CT and MT at all. This suggests that humus-rich soils seem to be more resistant to tillage-related disturbances. The working depth might have a greater impact for both, inversion and non-inversion tillage than the type of the tillage system itself.

For the comparison of CT and NT, we used the field-sites in Spain and Sweden. In Spain, NT was clearly of advantage for microbial biomass and activity, compared to CT. This was true for the whole sampled soil profile (0-30 cm) whereas in Sweden differences could only be detected between SMB-C levels in two soil depths. Our results indicate that the effect of tillage seems to be smaller in cold-temperate areas.

Comparing MT and NT in Sweden, we found no difference in SMB-C between these two forms of conservation tillage, neither in the first centimeters, nor in the whole sampled profile. Consequently, minimum tillage seems to be an alternative in cold and moist regions if no-tillage is not possible to apply without reducing soil quality or crop yields.

We conclude that even if minimum and no-tillage are generally beneficial for microorganisms, there is a big variance between the different forms of reduced tillage systems. Thus, statements cannot be made across different soils and machine types, but have to be made on a regional scale.

How to cite: Schmoock, I., Linsler, D., Sandor, M., Joergensen, R. G., and Potthoff, M.: Long-term effects of tillage intensity on the distribution of microbial biomass and activity in four arable field-sites across Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9043, https://doi.org/10.5194/egusphere-egu2020-9043, 2020.

The type of soil organic amendment selected can have profound implications for carbon cycling processes in soils. Understanding the link between this choice and its effect on the soil microbiome will improve our understanding of the capacity of these materials to improve carbon sequestration and cycling dynamics. Understanding and facilitating the lifestyle strategies of microorganisms processing organic matter is essential to improving our understanding of the terrestrial carbon cycle. This research focuses on utilising organic amendments to alter the indigenous soil microbial community composition and function to improve the capacity of the soil to cycle and store carbon in horticultural soils.  The effects of annual application of various organic fertilisers (peat, bracken, bark, horse manure, garden compost) in a long-term (10year) field experiment were explored. Sampling was completed pre and post application of organic matter within one season (following 10 years of applications) to identify which organic amendment was more effective in producing benefits to plants through improved soil organic matter and which amendments provide the greatest legacy effect on carbon cycling. The response of the soil microbial community composition (phospholipid fatty acid analysis) and carbon functional cycling dynamics (respiration using MicroResp™) were determined with a view to improving our understanding of the interaction between the materials applied and microbial processes. PCA of the MicroResp™ data identified that all treatments had a different functional profile compared to the control[PM1]  with peat being significantly different from all other treatments. Horse manure and bark differed significantly within a single growing season; prior and post organic matter addition in spring 2019.  Microbial biomass measurements for garden compost and horse manure were significantly higher following organic matter addition compared to all other treatments and the control[PM2] .  All treatments had a significant effect [PM3] on hot water extractable carbon and total carbon. Peat had a significantly different effect[PM4] , when compared to other treatments, on the soil PLFA profile and bark application significantly increased [PM5] the neutral lipid (NLFA) biomarker 16:1ω5.  Bark and horse manure application both significantly increased PLFA fungal biomarker 18:2ω6,9. No significant differences were found between the fungal/bacterial ratios of the organic matter additions prior to being added to the soil. These findings show that altering the resources available to the soil microbial community has a significant impact on soil microbial community composition and microbially mediated carbon cycling functionality. Increasing our understanding of how soil functions are altered by land management decisions will enable better informed predictions of the long-term benefits of organic matter applications on carbon sequestration and cycling dynamics.

How to cite: hasler, R., pawlett, M., harris, J., bostock, H., and redmile-gordon, M.: Organic matter additions to soil and effects on microbially mediated carbon cycling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11209, https://doi.org/10.5194/egusphere-egu2020-11209, 2020.

Soil, the living skin of the Earth, provides ecosystem services critical for life: soil acts as a water filter and a growing medium, offers habitat for billions of organisms, and supplies most of the antibiotics. In places, it may take a hundred years to form one cm of soil, but it can be degraded only in a few years or less by a number of natural and anthropogenic factors, including climate change. Presently, one third of all land is degraded to some extent, and fertile soil is lost every year. Droughts are becoming more common, also in humid climates, and the combination of erratic weather patterns with an increased pressure on land by human activities leads to soil degradation. Soil degradation results in a loss of fertile topsoil, thereby altering the soil hydrology completely. As the consequences, soil water holding capacity decreases, hydrophobicity increases, and more runoff is observed, that leads to further soil degradation. Thus, soil hydrology is the key for a healthy functioning topsoil/soil ecosystem. We are in urgent need for novel solutions for improving soil hydraulic properties that will lead to restoration of degraded soils.

In this study we investigate a possibility of restoring degraded soil using microorganisms. The hypothesis is that microorganisms can improve soil hydraulic properties such as infiltration and water retention, and reduce hydrophobicity that will facilitate further ecosystem restoration. Such strategy is based on combining the research fields of microbiology and soil physics that to date have hardly been combined. To test this hypothesis, we have inoculated sandy soil with a bacterium Bacillus mycoides and then measured its hydraulic properties using evaporation and pressure plate methods. We have also made efforts of standardizing this methodology by testing incubation time and inoculum concentrations on the hydraulic properties of the soil. Evaluation of an effect of bacteria addition on the soil water holding capacities and unsaturated water conductivity have been conducted as a comparison between inoculated soil and uninoculated (control). Results of this ongoing study will be presented here.

How to cite: Coban, O., de Deyn, G., and van der Ploeg, M.: From soil degradation to restoration via soil microorganisms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10283, https://doi.org/10.5194/egusphere-egu2020-10283, 2020.

The high diversity of densely packed organisms occurring in small volumes of soils has long been intriguing and we still poorly understand what drives such diversity. Exploring the role of small scale physical structure of the soil, constituting the habitat of these organisms offers unprecedented clues for explaining how organisms interact, notably through trophic interactions and how, in turn, these interactions drive this extraordinary diversity. We review here how restrictions on soil organisms’ ability to sense (e.g. volatiles) and access food resources/prey imposed by the soil physical structure and aqueous habitats within are important drivers for trophic interactions, and consequently, of soil biodiversity. Examples from micro- to macrofauna are presented, focusing on organisms unable to create their own pore space, such as bacteria, fungi, protists, nematodes and microarthropods. Finally, we discuss interdisciplinary challenges to develop research merging soil physics and soil food web ecology.

How to cite: Erktan, A., Or, D., and Scheu, S.: Into the soil labyrinth: soil physical structure as a driver of trophic interactions and soil biodiversity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4802, https://doi.org/10.5194/egusphere-egu2020-4802, 2020.

Soils contain a vast diversity of microorganisms including millions of cells and thousands of species. Many of those species encode for similar functions which is known as functional redundancy. From an ecosystem perspective, it remains unknown how many of such species are contributing to processes and are actually necessary to perform functions. Not knowing about the number and type of taxa of a soil sample a priori, let alone of the interaction between those taxa or the chemical environment of their habitats, hampers the reproducibility of soil ecological research and renders a targeted experimentation virtually impossible. This is one of the most important reasons why linking microbial identity to processes at the soil scale has proven to be everything but easy.

A promising avenue to overcome these limitations are model ecosystems that allow to identify principles of community functioning via standardised experimentation. Here, we will present a synthetic ecology approach using artificial soil mimicking the structural and chemical complexity of a soil and a synthetic microbial community to investigate microbial functioning in soil. Our approach includes genome-guided in silico design of synthetic communities to reproduce the functionality of soil heterotrophic bacteria and fungi, while largely decreasing the number of individual taxa for laboratory experimentation.

Initial experiments suggested that our synthetic community was able to establish in artificial soil and sterilized natural soil and to perform a range of simple soil processes, as evident through potential enzymatic activities, heterotrophic respiration, and changes in organic and inorganic soil components. Molecular analysis of the community composition over time demonstrated high similarities of the established community among replicates, indicating low effects of stochasticity on community assembly, a major requirement for reproducible experimentation. These promising preliminary data indicate that our model system could indeed represent the experimental platform for targeted experimentation in soil ecological research in the future.

How to cite: Schmidt, H., Horak, J., Kits, K. D., Canarini, A., Hadziabdic, L., and Richter, A.: Towards standardized experimentation in soil research – a synthetic ecology approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19246, https://doi.org/10.5194/egusphere-egu2020-19246, 2020.

Understanding how ecosystem function depends on temperature is important in understanding ecosystem resilience to climate change. The response to warming at a species level is relatively well understood, through the metabolic theory of ecology, which captures the temperature dependence of biological processes. However, when multiple species are present, interactions between the species are important too. Therefore, to understand community function, we must understand the response of the individual species, and the interactions between them. These interactions may depend on temperature, and can be split into two main mechanisms: selection and complementarity. Both of these processes are likely to depend on the number of species present; the biodiversity of the ecosystem. Currently, the response of communities to temperature change, and how changes in diversity may increase or buffer impacts, is poorly understood.

Our understanding of ecosystem function can be improved by using mathematical models to constrain the mechanisms underlying key processes. Using data from laboratory experiments, we model communities of heterotrophs responding to temperature change. To model selection, we use a simple model of a community sharing a resource, with parameters measured empirically. Without complementarity, the model underestimates community function. Complementarity is included through a single parameter, which determines to what extent different taxa share the same resource pool. This parameter is difficult to measure directly, so must be fitted using empirical community function data. Through our model, we show that the strength of complementarity within a community depends on both diversity and temperature. Interestingly, we also find that complementarity is strongest at higher and lower temperatures, and more dependent on diversity at medium temperatures.

How to cite: Millington, R., Cox, P. M., García, F. C., and Yvon-Durocher, G.: Modelling the role of selection and complementarity in ecosystem function under climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16475, https://doi.org/10.5194/egusphere-egu2020-16475, 2020.

The vital role of soil microorganisms as catalysts for soil organic matter (SOM) formation has long been recognised. Plant residues are now considered to be transformed by soil microorganisms who use the plant litter as a carbon source for microbial biomass formation. How much carbon is retained as microbial biomass during transformation of plant material, critically depends on substrate availability, carbon use efficiency of the microorganisms, and maximum microbial growth. In addition, microorganisms presumably recycle biomass building blocks from plant or microbial material to avoid energy expenditure for biomass synthesis. After cell death, a part of the microbial necromass is cycling through the microbial food web; the other part is stabilised in soil (Miltner et al., 2012). Potential stabilisation mechanisms are similar to those for SOM in general, with organo-mineral interactions, in particular encapsulation and physical isolation, being important mechanisms. Independent of which pathway the plant-derived carbon goes, SOM constitutes a continuum of plant and microbial necromass at various stages of decay. The contribution of microbial necromass to the topsoil organic matter pool has recently been estimated to range from 30 to 60% (Liang et al., 2019). Such high contributions of microbial necromass have a number of important implications for understanding SOM transformation and sequestration processes. Most obviously, the chemical identity of the organic material changes. For example, while retaining a substantial part of the carbon, the elemental stoichiometry changes substantially. Some microbial necromass materials are rather long-lasting in soil. In general, cell envelope residues have a higher stability than bulk biomass carbon. Proteins have also been shown to be rather persistent in soil, presumably due to conformational changes and the spatial arrangement of microbial necromass material, e.g. fragments of cell envelopes presumably pile up in multiple layers and the material forms clusters of macromolecular size. Residual electron-shuttle biomolecules (e.g. oxidoreductases, Fe-S-cluster, quinoid complexes of respiratory chains) may persist and retain some activity and thus contribute to redox reactions in soil. In addition, the necromass is expected to cover soil particle surfaces and thus determine the surface properties of these particles. In particular, these materials contribute to the water storage potential. They affect water retention and nutrient diffusion as well as microbial motility. Adaption of microbes to water stress changes their cell surface properties and molecular composition and thus may determine overall soil wettability. Knowledge on the contribution of microbial necromass to SOM would thus be essential for modelling SOM formation and optimising soil management practices for maintaining soil functions.

References:

Miltner A, Bombach P, Schmidt-Brücken B, Kästner M (2012) SOM genesis: Microbial biomass as a significant source. Biogeochemistry 111: 41-55.

Liang C, Amelung W, Lehmann J, Kästner M (2019) Quantitative assessment of microbial necromass contribution to soil organic matter. Global Change Biology 25: 3578-3590.

How to cite: Miltner, A., Zheng, T., Liang, C., and Kästner, M.: Microbial necromass as a source for soil organic matter formation - implications for soil processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13094, https://doi.org/10.5194/egusphere-egu2020-13094, 2020.

During the decomposition of organic matter (OM), microorganisms use the assimilated carbon (C) for biomass production or respiration, and the fraction of growth to total assimilation defines the microbial carbon-use efficiency (CUE). Therefore, microbial CUEs have direct consequences for the balance of C between atmosphere and soil, and is as such a central parameter to represent the global C cycle well in Global Cycling Models (GCMs). Despite its enormous leverage this factor remains critically underexplored. Based on the physiology of cultured microorganisms, it is anticipated that (H1) high nutrient availabilities will increase microbial CUE, (H2) that higher quality substrate will increase microbial CUE, (H3) that microbial communities more dominated by fungi will have higher CUE, and (H4) that microbial CUE will decrease in response to environmental stress. We combined extensive field surveys with experimental treatments in microcosms to assess our hypotheses. We sampled temperate forest soils, temperate agricultural soils, and subarctic forest soils, encompassing a wide range of soil pHs (4.0-7.1), nutrient availabilities (10<soil C/N<33), and soil OM qualities (7-fold differences in respiration per SOM). We also surveyed environmental pollution gradients where metallurgy had contaminated soil with high heavy metal concentrations in boreal forest and temperate grassland sites. We also subjected selected soils to microcosm experiments where soil pH (liming), mineral N (50 kg N ha^-1), OM quality (plant litter), or heavy metal stress were manipulated and the resulting bacterial and fungal growth, respiration, and CUE were monitored over the course of 2 months.

Fungal-to-bacterial growth ratios (F:B) ranged from 0.02 to 0.44 across the studied ecosystems, and that the fungal dominance was higher in soils with lower C:N ratio and higher C-quality. CUE ranged from 0.03 to 0.30, and values clustered most strongly according to site rather than level of soil N. CUE was higher in soil with high C:N ratios and high C-qualities. However, within each land-use type, a high mineral N-content did result in lower F:B and higher resulting CUE. In the microcosm experiments, plant litter addition stimulated the growth of fungi more than bacteria, while increasing soil pH stimulated bacteria more than fungi. Mineral N additions inhibited bacterial growth and stimulated fungal growth. This resulted in microbial CUE estimates in real time that ranged from ca 0.05 to 0.55, and where increased pH and litter increased values while mineral N supplements decreased values. Long-term exposure to heavy metals decreased microbial CUE, but only marginally, even at very high rates of metal exposure. Short-term exposure to metal stimulated microbial CUE in soil from contaminated sites, while CUE was reduced in soil with no history of metal contamination. In conclusion, a higher site soil C-quality coincided with lower F:B and higher CUE across the surveyed sites, while a higher N availability did not. A higher site N availability resulted in higher CUE and lower F:B within each site, while mineral N supplements in the microcosm induced the opposite response, suggesting that site-specific differences associated with fertility such as the effect of plant communities, overrode the influence of mineral N-availability.

How to cite: Rousk, J.: Soil microbial growth and carbon-use efficiency: ecological control mechanisms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2166, https://doi.org/10.5194/egusphere-egu2020-2166, 2020.

How to cite: Domeignoz-Horta, L. A., Pold, G., Liu, X.-A., Frey, S. D., Melillo, J. M., and DeAngelis, K. M.: Microbial diversity drives carbon use efficiency in a model soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20248, https://doi.org/10.5194/egusphere-egu2020-20248, 2020.

Carbon use efficiency (CUE) is theorized to be positively associated with the formation of microbially-derived, mineral-associated soil carbon.  Yet few empirical studies have directly tested this relationship. Moreover, it is unclear: (1) how differences between distinct soil microbial communities (for example, differences in competitive interactions and/or growth rate among rhizosphere, detritusphere, and bulk soil communities) may yield different relationships between carbon-use efficiency and soil carbon formation, and (2) how microbial ecophysiology – such as physiological changes induced by drought – may modulate the strength and/or direction of the CUE-soil carbon relationship.

To investigate these questions, we conducted a 12-week ¹³C tracer study to track the movement of two dominant sources of plant carbon – rhizodeposition and root detritus – into soil microbial communities and carbon pools under normal moisture vs drought conditions. Using a continuous ¹³CO₂-labeling system, we grew the Mediterranean annual grass Avena barbata in controlled growth chambers and measured the formation of organic matter from ¹³C-enriched rhizodeposition. As the plants grew, we harvested rhizosphere and bulk soil at three time points (4, 8, and 12 weeks) to capture changes in soil carbon pools and microbial community dynamics. In parallel microcosms, we tracked the formation of soil carbon derived from ¹³C-enriched A. barbata root detritus during 12 weeks of decomposition; harvesting detritusphere and bulk soil at 4,8, and 12 weeks. In all microcosms, we manipulated soil moisture to generate drought (7.8 ± 2.1 % soil moisture) and ‘normal moisture’ (15.1 ± 4.2 % soil moisture) treatments.

In all samples (over 150 observations), we measured CUE via the ¹⁸O-H₂O method, and quantified the formation of different ¹³C-soil organic carbon pools via density fractionation. Here we will present data on how soil moisture influences CUE in rhizosphere, detritusphere, and bulk soil communities, and whether differences in CUE are correlated with the formation of mineral-associated soil organic carbon. These results will help to illustrate whether CUE acts as a lynchpin variable with predictive power for stable soil carbon formation, or whether other microbial traits may require consideration.

How to cite: Sokol, N., Blazewicz, S., Foley, M., Greenlon, A., and Pett-Ridge, J.: How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13148, https://doi.org/10.5194/egusphere-egu2020-13148, 2020.

The ¹⁸O-labelling method is a powerful tool for studying soil microbial carbon use efficiency (CUE), as the label itself does not affect the soil microbial carbon metabolism. Beside parameters of soil microbial activity, the DNA extracted within this method can be used to gain information on soil microbial metagenome, e.g. community composition. Amongst others, the ¹⁸O-CUE method can support studies on the impact of land use change on the soil microbial metabolism and thus soil carbon dynamics.

As soil sample handling and length of incubation prior to analysis have been shown to affect measured parameters of soil microbial activity (e.g. Birch-effect) and community, different sample preparation measures are recommended in the literature depending on the focus of the study. However, so far the sensitivity of CUE and associated parameters to sample pre-treatment is unknown. We therefore tested i) how different sample pre-treatments (freezing, drying, and fresh) affect the parameters of soil microbial metabolism and community measured within the ¹⁸O-CUE method. In order to determine the potential to use the ¹⁸O-CUE in land use change studies we tested ii) if mentioned parameters of the two compared systems forest and cropland were - if applicable -affected in a similar way.

Based on five different paired sites (cropland and forest each), we evaluated the effects on the CUE and associated parameters (respiration, soil microbial biomass C, DNA extracted, abundance of fungi, bacteria and archaea) of six pre-treatments for soil samples via the ¹⁸O-CUE method: (i) direct analysis of field-fresh soil samples, analysis after pre-incubation of (ii) field-fresh, (iii) air-dried, (iv) oven-dried, (v) frozen at -20°C and (vi) in-situ frozen soil samples (dry ice and subsequently liquid N₂).

Among all pre-treatments, the pre- incubation of 14 days as such had the strongest effect on metabolic parameters. Furthermore, while individual parameters (respiration, microbial biomass C) were influenced by the pre-treatment the ¹⁸O-CUE was relatively insensitive. We therefore conclude that not only fresh but also archived, dried soil samples can be used to obtain representative CUE values. Drying soil samples and rewetting led to increased fungal abundance in the forest soil, while this was not the case for croplands.

How to cite: Schroeder, J., Kammann, L., Tebbe, C. C., and Poeplau, C.: Impact of soil sample pre-treatment on microbial carbon use efficiency and associated parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9254, https://doi.org/10.5194/egusphere-egu2020-9254, 2020.

As the global hydrological cycle intensifies with future warming, more severe droughts will alter the terrestrial biogeochemical carbon (C) cycle. As soil microbial physiology controls the large fluxes of C from soil to the atmosphere, improving our ability to accurately quantify microbial physiological parameters in soil is essential. However, currently available methods to determine microbial C metabolism in soil require the addition of water, which makes it practically impossible to measure microbial physiology in dry soil samples without stimulating microbial growth and respiration (namely, the “Birch effect”).

We developed a new method based on in vivo ¹⁸O water vapor equilibration to minimize soil re-wetting effects. This method allows the isotopic labelling of soil water without any liquid water or dissolved substrate addition to the sample. This was compared to the main current method (¹⁸O-water application method) in soil samples either at near-optimal water holding capacity or in air dry soils. We generated time curves of the isotopic equilibration between liquid soil water and water vapor and calculated the average atom percent ¹⁸O excess over incubation time, which is necessary to calculate microbial growth rates. We tested isotopic equilibration patterns in nine different soils (natural and artificially constructed ones) covering a wide range of soil texture and organic matter content. We then measured microbial growth, respiration and carbon use efficiency in three natural soils (either dry or at near-optimal water holding capacity). The proposed ¹⁸O vapor equilibration method provides similar results as the currently widely used method of liquid ¹⁸O water addition to determine microbial growth when used a near-optimal water holding capacity. However, when applied to dry soils the liquid ¹⁸O water addition method overestimated growth by up to 250%, respiration by up to 500%, and underestimated carbon use efficiency by up to 40%.

Finally, we applied the new method to undisturbed biocrust samples, at field water content (1-3%), and show for the first time real microbial growth rates and CUE values in such arid ecosystems. We describe new insights into biogeochemical cycling of C that the new method can help uncover and consider the wide range of questions regarding microbial physiology and its response to global change that can now be proposed and addressed.

How to cite: Canarini, A., Wanek, W., Watzka, M., Sandén, T., Spiegel, H., Imminger, S., Woebken, D., Šantrůček, J., and Schnecker, J.: Quantifying microbial growth and carbon use efficiency in dry soil environments via 18O water vapor equilibration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14553, https://doi.org/10.5194/egusphere-egu2020-14553, 2020.

Soil organic carbon (SOC) represents both a source of energy (catabolism) and a building material for biosynthesis (anabolism) for microorganisms. Microbial carbon use efficiency (CUE) – the ratio of C used for biosynthesis over C consumed – measures the partitioning between anabolic and catabolic processes. While most work on CUE has been based on C mass flows, the role of SOC energy content, microbial energy demand, and general energy flows on CUE have been rarely considered. Thus, a bioenergetics perspective on CUE could provide new insights on how microorganisms utilize C substrates and ultimately allow C to be stabilized in soils.

The microbial growth reactions are generally associated with a negative enthalpy change, which results in heat dissipation from the system. This heat can be measured using an isothermal calorimeter, which is often coupled with respiration measurements. This coupled system allows studying energy and C exchanges, and calculating their ratio referred to as the calorespirometric ratio (CR). Here, we formulate a coupled mass and energy balance model for microbial growth and provide a generalized relationship between CUE and CR. In the model, we consider two types of organic C in soils, the added substrate (i.e., glucose) and the native SOC. Furthermore, we assume that glucose is taken up via aerobic (AE) and two fermentation metabolic pathways – glucose to ethanol (F1) and glucose to lactic acid (F2); for simplicity, only aerobic growth on the native SOC was adopted. We use this model as a framework to generalize previous formulations and generate hypotheses on the expected variations in CR as a function of substrate type, metabolic pathways, and microbial properties (specifically CUE). In turn, the same equations can be used to estimate CUE from measured CR.

Our results show that in a non-growing system, CR depends only on the rates of different metabolic pathways (AE, F1, and F2). While in growing systems, CR is a function of rates as well as growth yields for these metabolic pathways. Under purely aerobic conditions, our model predicts that CUE increases with increasing CR when the degree of reduction of the substrate is higher than that of the microbial biomass. Similarly, CUE decreases with increasing CR when the degree of reduction of substrate is lower than that of the biomass. In the case of combined metabolism – aerobic and fermentation simultaneously – CUE is not only a function of CR and the degree of reduction of substrates but also the rates and growth yields of all metabolic pathways involved. To summarize, in this contribution we illustrate how calorespirometry can become an efficient tool to evaluate CUE and the role of different metabolic pathways in soil systems.

How to cite: Chakrawal, A., M. Herrmann, A., and Manzoni, S.: New insights on carbon use efficiency using calorespirometry – a bioenergetics-based model , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5450, https://doi.org/10.5194/egusphere-egu2020-5450, 2020.

Energy crops are grown at low cost and low maintenance used in making biofuels, such as bioethanol, or combusted to generate electricity or heat. Production of energy crops as an alternative to fossil fuels will help to reduce CO₂ emission, thus leading to large scale changes in agricultural landscapes. Increase in the cultivation of annual energy crops such as maize (Zea mays) is assumed to decrease biodiversity in the agrarian landscape. This may lead to changes in soil properties, thereby affecting the soil biodiversity and its ecosystem functions and services like for instance soil microarthropod communities and their contribution to decomposition of plant litter. Perennial crops such as field grass (a mixture of Festulolium,  Dactylis glomerate, Loliuim perenne, Festuca pratensis and Festuca arundinacea) and cup plant (Silphium perfoliatum) are assumed to protect and promote soil biodiversity through less intensive management. The relationship between decomposer diversity and ecosystem functioning is little understood. So far, the role of soil microarthropods in decomposition is the most disputed aspect due to scarce empirical data.

The main aim of this field study was to assess the effect of soil microarthropods on litter of maize, field grass and cup plant, via decomposition using litter bags with 2 different mesh sizes (0.02 mm and 0.5 mm) for a period of 3 months during the vegetation period. At the end of the experiment, the decomposition rate was higher in cup plant followed by maize and field grass in the coarse mesh size, and higher in the cup plant followed by field grass and maize in the fine mesh size. A total of 55,464 soil microarthropods (73% mites, 25% collembola and 2% others) were extracted from the litter bags. The diversity and abundance of soil microarthropods was higher under cup plant cultivation followed by field grass and maize.

How to cite: Dioh Lobe, P. and Schrader, S.: How energy crops (Maize, Field grass, Cup Plant) affect soil microarthropods and their decomposition services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6624, https://doi.org/10.5194/egusphere-egu2020-6624, 2020.

Soil acidification is a serious problem on a global scale, about 30% of land surface is occupied by acidic soils (pH≤ 5.5). Recent research indicates, that more than 50% of arable soils in Poland have too low pH. Acid soils are characterised the ability to mobilize toxic metals and increased plant uptake as well as decreased microbial activity in the soil. Progressive acidification leads to degradation of soils and caused that they are marginal for agricultural production. Soil acidification is a naturally occurring process, but only when natural factors are supported by intensive human activity, especially by nitrogen fertilisers application, intensive degradation is observed. Traditionally method to increase soil pH is the application of lime materials e.g. calcite, burnt lime or dolomite. The liming efficiency depends on lime material type (primarily chemical form of calcium compounds), the neutralising value, lime application method, soil properties and the particle size distribution of lime. The aim of this research was to determine the rate of action and influence of ultra-fine powdered calcium carbonate on selected chemical and microbiological soil properties.

The incubation studies were conducted on the three soils (G1, G2 – silt loam and G3 – sandy loam). Soil samples were taken from the 0-20 cm layer. Soil properties were measured after 7, 14, 30, 60 and 120 days of incubation. The liming factor was ultra-fine powdered calcium carbonate with particle size distribution < 0.08 mm. The application dose was calculated for 0.5 soil hydrolytic acidity. In the soil samples pH_KCl, buffer capacity, microbial biomass carbon and dissolved organic carbon content were measured.

Application of lime caused an increase of pH value in all studied soils. The highest increase of the pH_KCl was noted between 0 to 7^th day of incubation. Afterward, the pH_KCl decreased slowly for the soil G1 and G2. However, in the soil G3 significantly decreased just after 7^th to 14^th day, and afterward, the pH_KCl decreased slowly to the end of the incubation period. As a result of liming long-term changes in soil buffer capacity were not noted. The studied soils were characterised by the higher buffer capacity in alkaline than in acidic range. The microbial biomass carbon content was varied during the incubation in all studied soils. The dissolved organic carbon content increased during the incubation, starting from the 7^th to the 120^th day of incubation for G2 and G3 soils and from 14^th to last day of incubation for G1 soil. Application of lime caused an increase of the dissolved organic carbon content in all studied soils. These studies show that application of ultra-fine powdered calcium carbonate is an effective and fast way to improve soil properties.

How to cite: Woźnica, K., Gąsiorek, M., Sokołowska, J., Józefowska, A., and Zaleski, T.: Dynamics of selected chemical and microbiological properties changes in soils after application of ultra-fine powdered calcium carbonate – incubation studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7128, https://doi.org/10.5194/egusphere-egu2020-7128, 2020.

The Polish Carpathian Mountains characterise the unique landscape containing high valuable seminatural mountain meadows. However, due to land abonnement, especially decrease agriculture and pasture activity, land cover changes occur. As a result of such changes, natural forest succession in the Carpathians become more and more widespread process. Despite, landscape transformations the natural forest succession is an important issue of science in the context of carbon sequestration. It is well known, that soil organic carbon is the largest terrestrial organic carbon pool in the world. Land cover transformations are regarded as the most dynamic factors of soil organic carbon changes. So far, studies have presented no clear organic carbon accumulation pattern, there is a lack of study covered different land use conversions.

Soil microbiota is the major factor influence on decomposition and transformation of organic matter in the soil. One of the predominantly measured parameters of microbial activity is soil respiration. Moreover, soil respiration is widely used as an indicator of soil quality, degree of development and especially the carbon cycling dynamics. Furthermore, understanding the mechanism controlling microbial respiration is critical to efforts to model carbon cycling at a regional and global scale. The purpose of this study was to investigate the influence of natural forest succession on microbial respiration.

The study area was located in Bieszczady National Park in south-eastern Poland. The samples from two layers (0-10 cm and 10-20 cm) in the four transects each consisted of a meadow, a succession (covered by 30-60 years trees) and a forest (more than 150 years old trees) were taken. Microbial respiration was determined by the incubation method. Respiration was measured for 5 weeks in closed vials. During the three days, the soil was carried in the vial with the small baker containing NaOH and hermetically closed. After this period the baker was removed and trapped CO₂ was quantified by titration with HCl and with participation BaCl₂. Additionally, based on the first-order kinetic model of microbial respiration cumulative respiration, the content of carbon available for microbial respiration present at the start of the experiment and the rate constant were calculated. Moreover, other microbiological, chemical and physical soil properties were determined in previous research.

Soil respiration C-CO₂ after the first week of incubation was significantly higher in the 0-10 cm layer compare to 10-20 cm, however, after the fifth week of incubation differences between investigated layers were no significant differences. In the 0-10 cm layer, the highest cumulative respiration was observed in succession (74.9 mgC-CO₂ g^-1 h^-24) and the lowest in forest (51.9 mgC-CO₂ g^-1 h^-24). However, in the 10-20 cm layer meadow characterised the highest cumulative respiration (42.0 mgC-CO₂ g^-1 h^-24) and forest the lowest (26.8 mgC-CO₂ g^-1 h^-24). Following cumulative respiration, significant the highest content of carbon available for microbial respiration was observed in succession and meadow, in the 0-10 and 10-20 cm layers respectively. Cumulative respiration of investigated soils was positively correlated with total nitrogen content, microbial biomass carbon as well as dehydrogenase and cellulase activity.

How to cite: Sokołowska, J., Józefowska, A., Woźnica, K., and Zaleski, T.: The effects of natural forest succession on soil respiration in Bieszczady National Park (south-eastern Poland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7130, https://doi.org/10.5194/egusphere-egu2020-7130, 2020.

Maize (Zea mays) is the most commonly cultivated energy crop throughout Europe. However, its cultivation has severe negative effects such as loss of biodiversity and its delivery of ecosystem services, soil compaction and enhanced greenhouse gas emissions. These negative effects tend to be even more pronounced in wet soils such as pseudogleys. As an alternative to annual maize, the perennial cup plant (Silphium perfoliatum) is known to produce a similar yield, especially under waterlogging conditions, while management impacts of its cultivation are assumed to be less harmful to soil biota. Therefore, the aim of the present study was to quantify the provision of ecosystem services (here: control of the soil water balance) delivered by earthworm communities in wet soils under cultivation of cup plant compared with maize and to assess the ecological impact of both energy crops.

Fieldwork was conducted cup plant and maize fields (n = 4) in South Western Germany in spring and autumn 2019. The overall soil type was pseudo gleyic luvisol. All fields are managed for commercial purposes by farmers in the area. Sampling included earthworm extraction with allyl isothiocyanate (AITC) while the infiltration rate was measured simultaneously. Afterwards, hand sorting completed the earthworm sampling. Earthworm species, their abundance and biomass (live weight) were determined.

On average, earthworm abundance and biomass were higher in cup plant fields than in maize fields. In addition, variations in earthworm communities were found. While endogeic earthworms, especially of the genus Aporrectodea, were present in all fields, anecic earthworms were more abundant in cup plant fields. Higher infiltration rates were measured in maize fields. Hints to a correlation between the infiltration rates and the functional earthworm groups were found.

Our results suggest that cup plant fields host overall more diverse earthworm communities. These communities are able to produce a wider range of ecosystem services, even though the link between the infiltration and the crops studied in this stud is not yet validated.

How to cite: Wöhl, L. and Schrader, S.: Effects of earthworm communities on water infiltration in wet soils with energy crops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7628, https://doi.org/10.5194/egusphere-egu2020-7628, 2020.

European ground squirrels (EGS) are members of the soil megafauna and part of the ecosystem engineers that shape physical, chemical, and biological characteristics of soil ecosystems in European grasslands. Thanks to their strict protection their abundance and distribution have been surveyed systematically and annually in Hungary. The results of their 20 year monitoring indicate that their population is declining, there are sudden extinctions of local populations, and a desynchronized variation of the abundance of local populations occur either spatially or temporally.

The monitoring protocol involves the estimation of their abundance in each colony by a strip-transect method and the habitat-colony area by visual observations or digital maps. Both approaches use animal burrows as proxies for either their presence (colony area) or density (colony size). These estimation methods, however, consist of systematical errors: first, they consider the animals’ density to be even over the entire habitat-area, second, they conjecture that animals occupy the habitable area completely, and third, evenly. If we were able to survey distribution and abundance of EGS more accurately, frequently, and efficiently, we could better intervene in time when local populations begin to decline or before they disappear. In addition, we could better estimate the effects (+ or -) of management strategies in real time.

The primary aims of our study were to develop a non-invasive, semi-automated method for (1) estimating abundance of EGS in the area of occupation of a colony, and (2) delineating their occupancy within the habitable area. We have defined burrow openings and mounds as quantitative proxies for the presence of animals. We have started to develop a monitoring technique to identify, locate, and count objects of interest in images automatically and to delineate the area of occupancy by identifying those objects of interest from the surroundings. To survey EGS colonies and habitats we have used a multirotor platform UAV equipped with either an RGB visible-range or a hyperspectral sensor.

To test our method several pilot areas with different vegetation and relief were surveyed. Acquired aerial images have been processed by photogrammetric software and resulting high spatial resolution orthomosaics are classified by machine-learning algorithms (randomforest, CART, C5.0) implemented in a custom R script. As detection of mounds and openings are visually restricted by vegetation height (e.g. grass, shrubs, weeds, herbs), we have studied the effect of grass height on detection success. Preliminary results suggest that successful classification can be performed either on RGB visible-range and hyperspectral images. However, the appropriate spatial resolution (below cm range) and the presence of high grass are more important key factors than number of spectral bands.

Detecting EGS burrow openings and mounds is based on surface characteristics of EGS burrow openings and mounds consequently the method is being developed for EGS specifically but can be modified to the characteristics of other burrowing mammals of this size (e.g. mole-rats, moles).

How to cite: Árvai, M., Mészáros, J., Kovács, Z., Brevik, E. C., Pásztor, L., and Gedeon, C. I.: Automatic detection and mapping of European ground squirrel burrows on UAV-based multi- and hyperspectral imagery with classification methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8773, https://doi.org/10.5194/egusphere-egu2020-8773, 2020.

Reduced tillage is assumed to be a suitable practice to maintain and promote microbial biomass and microbial activity in the soil. The microbial biomass in particular is considered as a sensitive indicator for detecting soil disturbances. The objective of this study was to quantify the influence of different tillage practices on microbial parameters in the soil. Furthermore, we analyzed the relation of those microbial parameters with site-specific conditions.

To get a deeper insight in that topic, soils from different fields of agricultural farms with different tillage practices in France (12 fields), Romania (15 fields) and Sweden (17 fields) were examined within the “SoilMan project”. The tillage practices were no-tillage (absence of any tillage), minimum tillage (non-inversion tillage for instance by chisel plough or cultivator) and conventional tillage (inversion tillage by ploughing), all of which were carried out for at least five years prior to sampling. Soil samples were taken in spring 2018 from all fields under winter wheat (Triticum aestivum) at three soil depths (0-10 cm, 10-20 cm, 20-30 cm). As microbial parameters we measured microbial biomass carbon and nitrogen contents, ergosterol contents (as proxy for fungi) and basal respiration rates. For site-specific conditions we measured soil organic carbon, total nitrogen and total phosphorus contents, texture, pH and the soil water content.

Results show that microbial biomass carbon and nitrogen were more affected by soil type and soil texture as well as climatic conditions (mean precipitation and temperature) than by tillage practices. For instance, an increased clay content had a positive effect on the microbial biomass and, in addition to the higher average annual temperature, explained the generally low values ​​in France. The lack of inversion tillage primarily led to stratified levels of soil organic carbon, microbial biomass carbon and ergosterol contents, which can be explained by the lack of crop residue incorporation. There were hardly any differences in microbial indicators between the tillage intensities when looking at the whole of the sampled soil profile (0-30 cm). In France, the microbial biomass carbon / soil organic carbon ratio was lower for no-tillage than for conventional tillage, which may indicate, among other things, that the mechanically ground organic matter incorporated into the soil under conventional tillage was better colonized by microorganisms. However, this effect could not be confirmed in the other countries. The metabolic quotient was generally increased at the lowest sampled depth (20-30 cm), irrespective of the cultivation.

We can conclude that the soil tillage intensity influenced the distribution of microbial biomass carbon and soil organic carbon contents more strongly than the total amounts in the sampled soil profile and that the soil texture had a greater impact on microbial soil properties than the agricultural management practice.

How to cite: Linsler, D., Gerigk, J., Schmoock, I., Jörgensen, R. G., and Potthoff, M.: Microbial properties in European arable soils with different tillage systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10240, https://doi.org/10.5194/egusphere-egu2020-10240, 2020.

Traditionally, soil quality has been assessed through physical, chemical and biological properties without paying attention to soil biota and the different associated ecosystem services provided (Tyler, 2019). To fill that gap, the european BiodivERsA “SoilMan” project (Ecosystem services driven by the diversity of soil biota – understanding and management in agriculture) is focused on the relations among soil management, soil biodiversity, and ecosystem services, at seven different management gradients in agricultural long term observations (LTO’s) trials across Europe (France “SOERE-PROs EFELE” and “SOERE-ACBB Lusigan”, Romania “Turda”, Sweden “Angermanland” and “Säby-Uppland”, Germany “Garte Süd” and Spain “La Hampa”). Management gradients covered different tillage regimes (zero, minimum and conventional) and different crop rotations (crop types and duration).

In the present study, we characterised the bacterial and fungal communities of soils from the different countries and agricultural managements in arable land. The samplings were carried out following the same methodology in all the countries during 2017-2018 when wheat was sown in the LTO’s. The soil DNA was extracted and subjected to metabarcoding analysis of 16S and Internal Transcribed Spacer (ITS) ribosomal RNA (rRNA) for bacterial and fungal community analysis, respectively.

Different alpha diversity metrics, including number of OTUs, Simpsons and Shannon indexes, as well as beta diversity distances (weighted and unweighted UNIFRAC, Jaccard and Bray-Curtis) were calculated. Multidimensional Scaling ordination plots (PCoA) were used to visualize the existence of community gradients among locations and soil managements. All the statistical data  procedure  was analysed using the vegan R package (Oksanen, 2011).

In general terms, results show that alpha diversity for both bacteria and fungi, clearly differs among countries while soil management effects are less defined among and within countries. Concerning the beta diversity indexes, communities tend to cluster more according to the spatial location than due to the soil management regimen. This is especially true for fungal communities. Further analysis will identify possible correlations of bacterial and fungal communities with environmental variables and other physicochemical and biological soil properties.

References:

Oksanen, J. (2011). Multivariate Analysis of Ecological Communities in R: vegan tutorial.

Tyler, H. L. (2019). Bacterial community composition under long-term reduced tillage and no till management. Journal of Applied Microbiology, 126(6), 1797–1807. https://doi.org/10.1111/jam.14267

How to cite: Arias, L. F., Guzmán, G., Gómez, J. A., Anguita-Maeso, M., Dascalu, D., Linsler, D., Morvan, T., Öpik, M., Pérès, G., Potthoff, M., Sandor, M., Taylor, A., Torppa, K., Vahter, T., and Landa, B. B.: Effects of agricultural soil management practices on soil microbiota across Europe – investigations in seven long term field experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11299, https://doi.org/10.5194/egusphere-egu2020-11299, 2020.

Soil microorganism are an essential component of forest ecosystem. Microbes and plant release enzymes that catalyse reactions needed to decomposed soil organic matter and crucial to release nutrient in available forms. Therefore, soil enzymes are relevant indicators of microbial activity and nutrient cycling in forest ecosystems. Anthropic disturbances in natural forest, such as logging and exotic livestock, modify the structure and composition of forest thereby altering the structure and activities of soil microbial communities.

Here we determine the effect of these disturbances on the enzymatic activity (Dehydrogenase-DHA; Phosphatase Acid-AP; Ureasa-UA) and the microbial diversity using a forest degradation gradient of native temperate forest dominated by Nothofagus dombeyi, Nothofagus obliqua and Nothofagus alpina. In addition we quantify C:N:P nutrient reservoirs, stoichiometry and available pools. Preliminary results suggest a higher activity of the DHA enzyme in degraded forest dominated by N. obliqua. AP and UA showed no relationship with the phosphorus and total nitrogen reservoirs. Forest degradation modify microbial communities, C:N:P stoichiometry, total and available nutrient pools, where the biggest pool of total C and N was registered on low degraded condition and decrease as degradation condition increase from medium to high degraded forest (74.44%; 65.35%; 48.05% for total C and 3.71; 3.41; 3.24 for total N respectively). Inverse relation was registered for total P pool were the highest pool was registered on high degraded condition (14963ppm; 13092ppm and 11299ppm from high to low degraded condition). Degraded sites were dominated mainly by members of Gammaproteobacteria, Alfaproteobacteria, Acidobacteria and Bacteroidia. Chitinophagaceae and Burkholderiacea were not detected in degraded plots, which suggest that some of the specialised functions carried by this groups could be lost. With respect to fungi Ascomycota and Basidomicota Phylum dominated the soil profiles. A species of the genus Clonostachys (Bionectriaceae) was identified, an endophyte fungus that acts as a saprophyte, also known to be a parasite of other fungi and some nematodes.

This research contributes to a better understanding of the direct effects of anthropic disturbances on the biogeochemical functioning of temperate forests and their relationship to the activity and composition of microbial communities.

Acknowledgment: Proyecto Reforestación Enel – UdeC

How to cite: Atenas, A., Aburto, F., Hasbun, R., and Merino, C.: Evaluation of the enzymatic activity and diversity of soil microorganism in Andean temperate forests degradation gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21058, https://doi.org/10.5194/egusphere-egu2020-21058, 2020.

In contrast to taxonomic diversity of soil microbiome, the distribution patterns of functional diversity for various ecosystems, including along an altitudinal gradient, is poorly understood. Consequently, the study focuses on finding out the spatial distribution features of microbial functional diversity in mountainous soils along elevation through forests and meadows ecosystems. We hypothesized that soil microbial functional diversity is increasing along the altitudinal gradient in conjunction with plant diversity. In Northwestern Caucasus (Karachay-Cherkess Republic, Russia) the north-eastern mountain slope was studied across mixed, fir and deciduous forests, subalpine and alpine meadows located from 1260 to 2480 m above sea level. Twelve plots (0.25 m² each) were randomly chosen within each ecosystem (total 60). Plant species composition and Shannon plant diversity index (H) were assessed for the plots. Topsoil samples (0-10 cm) were taken from the plots in August for assessment microbial functional diversity through community level physiological profile (CLPP). It was determined by microbial respiration response on amino, carboxylic, phenolic acids and carbohydrates (MicroResp). Shannon's functional diversity index based on the CLPP (H_CLPP) was calculated. Edaphic properties as moisture, temperature, pH, total carbon (C) and nitrogen (N) contents were determined as possible drivers of CLPP. As expected, plant diversity was increased along the elevation gradient with the lowest H value in the mixed forest (0.6) and the highest – in the alpine meadow (1.9). The H_CLPP did not differ among studied ecosystems and reached on average 2.4 for each. Microbial respiration response on amino acids was mainly contributed to dissimilarities between studied ecosystems and increased on average by 1.3 times with elevation from mixed to fir and deciduous forests. Along this elevation row, the soil N content was the most significant driver compared to other edaphic properties. Among subalpine and alpine meadows the differences between microbial responses on studied carbon substrates were not found.

Considering that elevation didn’t contribute to distribution patterns of soil H_CLPP at the inter-ecosystems level, consequently, the hypothesis of our study was rejected. Plant diversity was not related to H_CLPP as expected. Meanwhile, the distribution patterns of soil microbial community, utilizing amino acids, along the altitudinal gradient was found.

The current research was financially supported by RFBR No 20-34-70121

How to cite: Ivashchenko, K., Seleznyova, A., Sushko, S., Zhuravleva, A., Tronin, A., Ananyeva, N., and Kudeyarov, V.: Soil microbial functional diversity along an elevation gradient in Northwestern Caucasus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21272, https://doi.org/10.5194/egusphere-egu2020-21272, 2020.

Soil regulates plant productivity in terrestrial ecosystems and maintains the balance of biogeochemical cycles through biotransformations mediated by living organisms, which are responsible for 80 to 90% of these functions. Therefore, it is necessary to evaluate whether restoration/natural regeneration processes in land degraded areas may allow the soil to partially or fully recover its microbial functions reflecting thus, in the fertility of these soils and consequently in the regeneration of forests. The use of microbiological attributes combined with infrared spectroscopy (FTIR) offers many opportunities to understand temporal dynamics and spatial variability in the recovery of important ecosystems during forest regeneration stages.The present work aims to evaluate the evolution of microbial quality in soils under three Atlantic Forest areas at different stages of regeneration (R40 - advanced, R12 - intermediate and RP - early regeneration pasture area) located in São Paulo state, Brazil. We used as indicators of the soil microbial quality the number of colony-forming units (CFU) of total bacteria and fungi, spore density and root colonization by arbuscular mycorrhizal fungi (AMF). We also analyzed these soils by Fourier Transform Infrared Spectroscopy (FTIR-UATR). For each area, seven soil samples and plant roots were randomly collected at a depth of 0-20 cm at the end of the dry season (October 2019). In terms of dry soil, the CFU bacteria for each area was, respectively, 7.7, 4.6 and 3.2 x 10⁵ CFU g^-1; fungi, 1.2, 1.0 and 0.6 x 10³ g^-1, and AMF spore density, 39, 33 and 27 spores 50 ml^-1. On average, AMF root colonization was 26 (R40), 25 (R12) and 21% (PR). For the FTIR spectrum, the major bands and their assignments were identified as a 3.370 cm^-1 wide band assigned to the O-H groupings; a peak at 1.635 cm^-1 attributed to aromatic C=C vibration, with contribution of C=O of the COO^- and a peak at 1.072 cm^-1 attributed to the carbohydrate C-O bond. No difference was attributed to the composition of the main functional groups (O-H, C=O, COO- and C-O) between the soils from R40 and R12, but this difference was more evident when compared to the RP area.  The microbiological results show good similarity between the tree areas in terms of spores, fungi and root colonization. However, in terms of bacteria, there is a more pronounced difference between the recent (RP) and the older regeneration areas (R12 and RP). Similar pattern was pointed by the FTIR results. Considering pasture as a strongly degrading area, these results are interesting since they show the differences in the soil quality between the three areas is not highly pronounced. They also show that in twelve years of regeneration, in many aspects’ soils become similar to the area with forty years regeneration. Given these results, a further investigation on soil physics of these areas is being developed to relate soil regeneration processes and soil physical properties such as porosity, density and water retention capacity, all of them important to the maintenance of vegetation and ecosystem services of water and climate regulation.

How to cite: Borma, L., Pupin, B., and Sakani, K.: Microbiological and FTIR applications in Atlantic forest regeneration areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22032, https://doi.org/10.5194/egusphere-egu2020-22032, 2020.

Fertilisation is a common practise in grass production systems performed to increase primary production, a supporting ecosystem service essential for other services. However, different fungal groups, like saprothropic fungi (SF) and the obligate symbionts arbuscular mycorrhizal fungi (AMF), have potential differential response to the fertilizer concentration and composition. Three controlled field experiments were utilised in our study, two medium-term (6 years) in the south of Sweden (SE) and one long-term experiment (46 year) in Switzerland (CH), all sampled in 2018. The Swedish sites included the same two factor treatment, i.e. four different plant mixtures and two (SE-Lanna) or three (SE-Alnarp) nitrogen fertilization levels (0, 60, 120 kg ha^-1 yr^-1); while the Swiss experiment  included different proportions of N, P and K fertilization under different cutting regimes (CH-Bremgarten). The PLFA and NLFA (phospholipid- and neutral lipid fatty acid) analysis was used to estimate the fungal biomass (SF+AMF). The application of N was associated with a decrease in the AMF biomass, with significant effects with the application of 60 and 120 kg N ha^-1 in SE-Alnarp, and 75 and 150 kg N ha^-1 in CH-Bremgarten. On the other hand, the SF biomass was only negatively affected by the N fertilization in SE-Lanna (60 kg N ha^-1) under the plant mixture that showed the biggest SF biomass in the unfertilized plot; and by the highest application of N in CH-Bremgarten. Our findings indicate that nitrogen fertilization influences microbial community structure and reduces the abundance of AMF, with these being more sensitive than SF to fertilizer application.

How to cite: Barreiro, A., Fox, A., Lüscher, A., Widmer, F., and Dimitrova Mårtersson, L.-M.: Fertilization effects on the fungal biomass in grasslands , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16110, https://doi.org/10.5194/egusphere-egu2020-16110, 2020.

Studying the soil seed bank is a time and space-consuming task, and therefore only a small fraction of the soil is sampled. It is then critical to optimize sampling effort to reliably estimate soil seed bank properties. Here, we test whether the spatial patterns of species richness in the soil seed bank differ under increasing sampling effort. For this, we used data of germination from soils in a mediterranean shrubland in Central Spain. Two data sets were used, one of the seedlings emerging after heating the soil to break dormancy, and one with the combined germinations of heated and non-heated soil subsamples. We simulated increased sampling effort with sample-based rarefaction curves, extrapolating the species richness corresponding to a 2x and 3x increase in the number of individuals (seedlings) per sample. We then analyzed the spatial pattern of the original and extrapolated species richness using linear regression and semivariograms. Species richness increased by 34% and 52% in the 2x and 3x estimations, however the spatial pattern of species richness remained largely unchanged. For the long-distance spatial pattern, the slope of the plot-scale trend (i.e., the regression coefficient) increased only slightly with increasing sampling effort, while the adjusted R-squared of the regression decreased with increasing sampling effort. For the short-distance spatial pattern we could only fit spherical model semivariograms to the data from soils exposed to a heat shock, and the intensity of the spatial pattern (spatial dependence) increased very slightly with increased sampling effort. These results suggest that even with a doubled or tripled sampling effort, as provided by the simulations, the spatial pattern of species richness would have remained unchanged. We argue that increased effort in detecting species in the seed bank needs not necessarily improve the detection of spatial pattern.

How to cite: Torres, I. and Moreno, J. M.: Relating sampling effort to the detection of spatial patterns of species richness in the soil seed bank of a mediterranean shrubland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18218, https://doi.org/10.5194/egusphere-egu2020-18218, 2020.

Soil biodiversity is essential to sustain healthy ecosystems supporting the maintenance of the environment and agricultural practices. Soils provide vital habitat for microorganisms which play determinant roles through organic matter transformation and nutrient cycling, which have a great impact in agriculture and food production and climate regulation. Understanding soil microbiome is becoming a relevant matter for supporting plant productivity and plant health. Unravelling the function and structure of microbial communities prevailing in soils is essential for a better understanding of plant development. However, the vast majority of soil microorganisms remain unknown and their variability at regional and temporal seasonal scale is still an unexplored field. In this study, soils associated to the rhizosphere of three olive varieties were sampled during autumn 2018 and spring 2019 in three olive orchards with differences in physicochemical soil characteristics and climate, located in the provinces of Jaén, Córdoba and Málaga, in Andalusia, Southern Spain. Bacterial and fungal populations were analysed using Illumina MiSeq platform to determine the structure and diversity of soil microbial communities and how those environmental factors may affect them. Sequencing data resulted in a total of 730 bacteria OTUs, distributed in 23 phyla and 312 genera while there were 553 fungal OTUs divided in 8 phyla and 280 genera. Proteobacteria was the most abundant bacterial phylum across olive orchard location (30.37%-5.52%) followed by Actinobacteria (10.72%-5.49%) and Bacteroidetes (7.73%-0.89%). There was circa 50% abundance reduction of these phyla on samples taken in autumn compared to that sampled in the spring. Unique bacterial genera differed according to field location in Jaén (72), Córdoba (45) and Málaga (48) while the shared bacteria genera among plots was 82. Fungi results showed Ascomycota (49.13%-3.13%) and Basidiomycota (25.64%-2.79%) as the two most abundant phyla in all olive orchards. A reduction on the abundance of Ascomycota was noticed on samples from autumn to spring (37.84% and 20.42%, respectively), while Basidiomycota displayed a distinct behavior (11.89% to 20.27%). Exclusive fungal genera varied from Jaén (50), Córdoba (7) and Málaga (14), whereas the core fungal genera among fields was 28. This information can contribute to generate new knowledge regarding temporal and spatial scale insights on soil microbiome associated to olive crop that may be considered to increase plant health and soil biodiversity.

Study supported by Projects 01LC1620 SOILMAN, XF-ACTORS 727987 (EU-H2020) and AGL2016-75606-R (MICINN Spain and FEDER-EU).

How to cite: Anguita-Maeso, M., Rivas, J. C., León, G., Estudillo, C., Navas-Cortés, J. A., and Landa, B. B.: Soil microbial communities from olive cultivars are shaped by seasonality and geographical scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4224, https://doi.org/10.5194/egusphere-egu2020-4224, 2020.

Litter decomposition is a crucial ecosystem process that driven carbon and nutrient cycling, which can be determined by the diversity of biota that involved in decomposition process. Forest ecosystems at globally have been or being expected to experience drought stress and cause dieback, consequently may lead losses of tree species and soil biota. However, how projected drought affect litter decomposition and its relationship with biodiversity is less understood. We hypothesize that 1) drought depressed the activity of soil biota and retard litter decomposition, while biodiversity loss at both plant and soil organism levels exacerbated the drought induced retarding of litter decomposition; 2) soil biota interaction or the top down control of ecosystem process can be relieved under drought stress. In our study, throughfall reduction experiments were conducted in five locations representing different forest types (i.e., temperate broadleaf-Korean pine mixed forest, warm-temperate oak forest, subtropical bamboo forest, south subtropical evergreen forest, tropical rainforest) along a climate gradient in China. In each location, leaf litter from 4 common native plants and 11 mixtures of these litter types were enclosed in three types of nylon mesh screens litterbags, and were placed in the field of throughfall reduction and control treatments replicated five times. Different combination of litter types represent diversity of litters, and mesh size of litterbags represent diversity of functional group of soil biota (i.e., microorganism, medium-sized fauna, large-bodied fauna) participate into decomposition. The litterbags were incubated in situ for a period of time and were collected, all litter samples were separated into the constituent species immediately after litter retrieval, mass loss, C and N loss of each sample was determined. Thereby the hypothesizes can be testified.

How to cite: Luan, J., Liu, S., Li, S., Wang, Y., Lu, H., Zhang, J., Han, S., Wang, H., Chen, L., Zhou, W., and Zhang, Y.: Litter decomposition under drought related with litter and decomposer diversity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6297, https://doi.org/10.5194/egusphere-egu2020-6297, 2020.

Paddy soil as a major component of cropland, plays an important role in the global carbon (C) cycle and favors carbon sequestration especially in southern China. Soil microorganisms are central to the conversion of organic matter into SOC, yet the mechanisms underlying the paddy management at long time scales remain largely unknown, including microbial enzyme and functional potential kinetics, microbial growth and turnover. Here, using observations from a 2000-year-old paddy chronosequence since reclamation from tidal wetland at two different soil depths (0-20 cm and 20-50 cm) in the Yangtze River Delta, China, we show how paddy soil C sequestration is driven by the relationship between short-term responses in microbial physiology and long-term changes in biogeochemical soil properties. The samples were analyzed for nutrient pools, microbial biomass and growth, microbial activity and community composition, functional gene abundances, as well as microbially mediated nitrogen (N) cycling rate to determine how these microbial functionalities and processes affect microbial carbon use efficiency (CUE), an important indicator for microbial C sequestration. Across multiple time-scales ranging from decades to millennia, SOC in topsoil was increased by 65% during the first 50 years and reached the steady-state condition until 700-year, then was largely accumulated by 169% and 125% in 1000- and 2000-year, respectively, while C loss appeared in subsoil after 700 years of paddy cultivation. For topsoil and subsoil, microbial CUE reached to the highest values in 1000- and 700-year (0.46 and 0.36, respectively, while only 0.20 in the tidal wetland), along with microbial growth which both increased 5.2- and 3.3-fold in 1000-year, respectively. We found the similar increasing trends between microbial CUE and soil C:P and N:P ratios, the reduction of N limitation and functional potentials including N- and P-cycling, C degradation, C-fixation (acsA gene), microbial community homogenization and microbial biomass across soil chronosequence in topsoil. Moreover, the structural equation model revealed that with longer paddy management, the decline in soil pH had positive effects on microbial functional potentials and microbial biomass carbon. The enhanced functional potentials directly positively affected microbial growth, and thereby on microbial biomass carbon. Finally, the prolonged paddy cultivation increased SOC content via its direct positive effect and indirect positive influence on microbial biomass carbon. We conclude that longer paddy management captures the cumulative microbial anabolism on SOC sequestration in the plough layer, with the shifts in abiotic and biotic conditions towards increased nutrient availability and homogenous microbial community with higher functional potentials.

How to cite: Bi, Q., Lin, X., Wanek, W., Zhang, S., Canarini, A., Richter, A., and Zhu, Y.-G.: Microbial and abiotic interactions driven higher microbial anabolism on organic carbon accumulation during 2000 years of paddy soil development in the Yangtze River Delta, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12665, https://doi.org/10.5194/egusphere-egu2020-12665, 2020.