Microbial hotspots in soils such as the rhizosphere, detritusphere, biopores, hyphasphere, aggregate surfaces, charsphere, etc., are characterized by high activity and fast rates of such process as soil organic matter (SOM) turnover, nutrient mobilization, litter decomposition, respiration, organic matter stabilization, greenhouse gas emission, acidification, etc. The turnover intensity of microbial biomass and SOM as well as nutrient cycling in such hotspots is at least one order of magnitude higher than in the bulk soil.
This session invites contributions to: 1) Various aspects of microbial activity, interactions, communities composition and distribution in hotspots; 2) Factors influencing (micro)biological nutrient (re)cycling including biotic and abiotic controls; 3) New developments to assess and simulate the crucial microbial mechanisms that underpin biogeochemical processes in hotspots (e.g. new approaches and imaging methods); and 4) Combination of experimental, theoretical and modelling approaches to predict the fate and functions of microorganisms in hotspots.

Convener: Bahar S. Razavi | Co-conveners: Yakov Kuzyakov, Joshua Schimel, Bettina Weber
| Attendance Fri, 08 May, 14:00–15:45 (CEST)

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Chat time: Friday, 8 May 2020, 14:00–15:45

D1791 |
| solicited
Andrea Carminati, Pascal Benard, Mohsen Zarebanadkouki, and Mutez A Ahmed

Plant roots and bacteria alter the soil properties by releasing a polymeric blend of substances (e.g. mucilage and extracellular polymeric substances EPS). Despite extensive knowledge of their ecological importance, the physical mechanisms by which these polymers alter the spatial configuration of the liquid phase and the related hydraulic and biogeochemical properties remain unclear.

Here we show that upon drying in porous media polymer solutions form one-dimensional filaments and two-dimensional interconnected structures spanning across multiple pores. Unlike water, primarily shaped by surface tension, these structures remain connected upon drying thanks to their high viscosity. The integrity of one-dimensional structures is explained by the high viscosity and low surface tension of the polymer solutions (elegantly characterized by the Ohnesorge number). The formation of two-dimensional structures requires consideration of the interaction of the polymer solution with the solid surfaces and external drivers, such as the drying rate.

The implications of these physical processes for life in soils are manifold. After their deposition they enhance water retention by acting as a new solid matrix delaying the air entry, they maintain the connectivity of the liquid phase, thus enhancing the unsaturated hydraulic conductivity, diffusion and enzyme activity. Upon rewetting, the formation of extensive two-dimensional structures corresponds to a sudden increase in soil water repellency, which reduces the rewetting kinetics and maintains gas diffusion preventing sudden water saturation. In summary, these structures buffer fluctuations in soil water contents, protecting roots and soil microorganisms against severe drying and sudden rewetting in soil hotspots.

How to cite: Carminati, A., Benard, P., Zarebanadkouki, M., and Ahmed, M. A.: High viscosity of polymer solutions supports life in soil hotspots, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4089, https://doi.org/10.5194/egusphere-egu2020-4089, 2020.

D1792 |
| solicited
Hannes Schmidt, Stefan Gorka, David Seki, Arno Schintlmeister, and Dagmar Woebken

Our current understanding of microbial hotspots such as the rhizosphere mainly stems from observations through measurements at the macroscopic scale, integrating a multitude of microbial cells and taxa into a few measured variables. Consequently, we still lack an understanding of the individual participants that actively contribute to processes. Identifying microorganisms and relating their activity to these processes within the soil-plant interface on a microscopic scale represent a missing link in understanding nutrient flux in agriculturally important ecosystems such as rice cultivation.

I will present a novel workflow for single-cell isotope imaging in the rhizosphere that combines fluorescence in situ hybridization, gold-targeted secondary electron microscopy, and nano-scale secondary ion mass spectrometry. Based on correlative microscopy and hotspot detection, this approach now allows to (i) identify single bacteria on root surfaces that actively incorporate stable isotopes, (ii) quantify their contribution to processes of interest within a given population, and (iii) potentially trace nutrient fluxes among plants and bacteria on a microscale.

Illuminating plant-microorganism interactions on a microscale provides the potential to evaluate the actual impact of bio-inoculants applied as fertilizers and to engineer plant-microorganism associations which may be essential to increase the production of major staple crops for a growing world population.

How to cite: Schmidt, H., Gorka, S., Seki, D., Schintlmeister, A., and Woebken, D.: Zooming in: a single-cell perspective on nitrogen fixation in the rhizosphere of rice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19045, https://doi.org/10.5194/egusphere-egu2020-19045, 2020.

D1793 |
Nicole Rudolph-Mohr, Sarah Bereswill, Christian Tötzke, Nikolay Kardjilov, and Sascha E. Oswald

Dynamic processes occurring at the soil-root interface crucially influence soil physical, chemical, and biological properties at local scale around the roots that are technically challenging to capture in situ. Combining 2D optodes and 3D neutron laminography, we developed a new imaging approach capable of simultaneously quantifying H2O-, O2-, and pH-distribution around living plant roots while additionally capturing the root system architecture in 3D. The interrelated patterns of root growth and distribution in soil, root respiration, root exudation, and root water uptake can be studied non-destructively at high temporal and spatial resolution.

Neutron computed laminography (NCL), a tomographic approach specially adapted to samples with large lateral extension (here 15 x 15 x 1.5 cm) was applied to visualize the root architecture and soil water content three-dimensionally. Optodes, sensitive to pH and O2 changes, were attached at the inner-sides of thin boron-less glass-containers where one maize plant was grown in each container. Knowledge about the distance of the roots from the container walls and thus from the optodes, support the interpretation of the optical images.

Neutron laminography made it possible to visualize and quantify the 3D root system architecture in association with the observed H2O, pH and oxygen patterns. The older part of the root system with higher root length density was associated with fast decrease of water content and rapid change in oxygen concentration. Lateral roots acidified their rhizosphere by a quarter of a pH unit and crown root even induced acidification of up to one pH unit compared to bulk soil. The benefit of neutron laminography is that we can extract the root structure in 3D, identify root age and root types and relate this to spatiotemporal changes in water content distribution, oxygen concentration and pH values.

How to cite: Rudolph-Mohr, N., Bereswill, S., Tötzke, C., Kardjilov, N., and Oswald, S. E.: Imaging biogeochemical gradients in the rhizosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20074, https://doi.org/10.5194/egusphere-egu2020-20074, 2020.

D1794 |
Siul Ruiz, Daniel McKay Fletcher, Andrea Boghi, Katherine Williams, Simon Duncan, Callum Scotson, Chiara Petroselli, Tiago Dias, Dave Chadwick, David Jones, and Tiina Roose

Soil microbial communities contribute many ecosystem services including soil structure maintenance, crop synergy, and carbon sequestration. However, it is not fully understood how the health of microbial communities is effected by fertilization at the pore scale. This study investigates the nature of nitrogen (N) transport and reactions at the soil pore scale in order to better understand the influence of soil structure and moisture content on microbial community health. Using X-ray Computed Tomography (XRCT) scans, we reconstructed a microscale description of a dry soil-pore geometry as a computational mesh. Solving two-phase water/air models produced pore-scale water distributions at 15, 30 and 70% water-filled pore volume. The model considers ammonium (NH4+), nitrate (NO3-) and dissolved organic N (DON), and includes N immobilization, ammonification and nitrification processes, as well as diffusion in soil-solution. We simulated the dissolution of a fertilizer pellet and a pore scale N cycle at the three different water saturation conditions. To aid interpretation of the model results, microbial activity at a range of N concentrations was quantified experimentally using labelled C to infer microbial activity based on CO2 respiration measurements in bulk soil. The pore-scale model showed that the diffusion and concentration of N in water films is critically dependent upon soil moisture and N species. We predicted that the maximum NH4+ and NO3- concentrations in soil solution around the pellet under low water saturation conditions (15%) are in the order of 1x103 and 1x104 mol m-3 respectively (1-10 M), and under higher water saturation conditions (70%) where on the order of 2x102 and 1x103 mol m-3, respectively (0.1-1 M). Supporting experimental evidence regarding microbial respiration suggests that these concentrations at the pore-scale would be sufficient to reduce microbial activity in the zone immediately around the fertilizer pellet (ranging from 0.9 to 3.8 mm depending on soil moisture status), causing a major loss of soil biological activity by up to 90%. This model demonstrates the importance of pore-scale processes in regulating N movement in soil with special capability to predict the effects of fertilizers on rhizosphere-scale processes and the root microbiome.

How to cite: Ruiz, S., McKay Fletcher, D., Boghi, A., Williams, K., Duncan, S., Scotson, C., Petroselli, C., Dias, T., Chadwick, D., Jones, D., and Roose, T.: Image-based model quantification of pore-scale nitrogen diffusion and potential microbial ‘dead zones’ induced by fertilization application , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8648, https://doi.org/10.5194/egusphere-egu2020-8648, 2020.

D1795 |
Mingyue Yuan, Meng Na, Lettice Hicks, and Johannes Rousk

Soil microorganisms play a crucial role in the regulation of nutrient cycling, and are thought to be either limited by low nutrient availability, or by labile carbon supplied by nutrient limited plant productivity. It remains unknown how climate change will affect the rate-limiting resources for decomposer microorganisms in the Arctic, rendering feedbacks to climate change highly uncertain. In this study, we focused on the responses of soil microbial community processes to simulated climate change in a subarctic tundra system in Abisko, Sweden, using litter additions to represent arctic greening and inorganic N fertilizer additions to represent a faster nutrient cycling due to arctic warming. We hypothesized that 1) the plant community would shift and plant productivity would increase in response to N fertilization, 2) microbial process rates would be stimulated by both plant litter and fertilizer additions, and 3) the growth limiting factors for decomposer microorganisms would shift toward nutrient limitation in response to higher plant material input, and towards C-limitation in response to N-fertilizer additions.


We assessed the responses of the plant community composition (vegetation surveys) and productivity (NDVI), microbial processes (bacterial growth, fungal growth, C and N mineralization) along with an assessment of the limiting factors for fungal and bacterial growth. The growth-limiting factors were determined by full factorial additions of nutrients (C, N, P), with measurement of microbial growth and respiration following brief incubations in the laboratory. We found that plant productivity was ca. 15% higher in the N fertilized plots. However, field-treatments had limited effects on bacterial growth, fungal growth and the fungal-to-bacterial growth ratio in soils. Field-treatments also had no significant effect on the rate of soil C mineralization, but did affect rates of gross N mineralization. Gross N mineralization was twice as high in N fertilized plots compared to the control. In control soils, bacterial growth increased 4-fold in response to C, indicating that bacterial growth was C limited. Bacterial growth remained C limited in soils from all field-treatments. However, in the N fertilized soils, the C limitation was 1.8-times greater than the control, while in soils with litter input, the C limitation was 0.83-times the control, suggesting that the N fertilized soils were moving towards stronger C-limitation and the litter addition soils were becoming less C-limited. The limiting factor for fungal growth was difficult to resolve. We presumed that the competition of fungi with bacteria decreased our resolution to detect the limiting factor. Therefore, factorial nutrient addition were combined with low amount of bacterial specific inhibitors.

How to cite: Yuan, M., Na, M., Hicks, L., and Rousk, J.: Limiting factors for soil microbial growth in climate change simulation treatments in the Subarctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5352, https://doi.org/10.5194/egusphere-egu2020-5352, 2020.

D1796 |
Evert van Schaik, Samuel Mondy, Melanie Lelievre, Marine Martin, Solene Perrin, Laura Meredith, Aurore Kaisermann, Samuel Jones, Olivier Rue, Valentin Loux, and Lisa Wingate

Recent interest in the seasonal and spatial variability of atmospheric COS has intensified as its use as an atmospheric tracer of biosphere productivity in the carbon cycle has recently been demonstrated. The key link between the COS and CO2 cycles in the biosphere is a family of enzymes called the carbonic anhydrases (CA) that catalyse both the hydration of CO2 and the hydrolysis of COS in both plants and soil microbes. Recently studies have demonstrated that the variability in soil COS and CO2 fluxes are modified significantly by fertilisation with inorganic N, indicating a strong coupling between soil carbon (C), nitrogen (N) and sulphur (S) cycling (Kaisermann et al., 2018). However, it is currently not clear whether the observed changes in COS and CO2 gas exchange were principally driven by important shifts in the microbial community size, structure or function or some combination of the three.

To elucidate the underlying mechanism(s) we used a functional metagenomic and metatranscriptomic approach coupled with climate controlled gas exchange measurements on soils. A set of 6 soils collected from boreal and temperate sites were sieved and re-packed in microcosms and incubated in the lab for 2 weeks at 23oC and 30% water holding capacity in the dark. For each site half the microcosms were fertilised with 5 mg N in the form of NH4NO3 at the start of the incubation period. At the end of the incubation period soil COS, CO2 fluxes were measured, and soil samples transported at -80oC to the Genosol platform for DNA and RNA extraction.  For each soil microcosm we quantified the abundance of bacterial, fungal and algal genes in each community using 16S, 18S and 23S amplicon sequencing. After assembling and cross-mapping the metagenomes and metatranscriptomes we used a HMM model (Meredith et al. 2018) to estimate and comparatively assess the abundance of CA genes between the different sites and treatments.

Our results indicate that the N treatment caused a relative increase in the abundance of fungi in N treated soils compared to those in the control. Generally, we also found that the total number of CAs in soils shifted when treated with N compared to the controls and that the β-D CA sub-family were the most prevalent CAs in all of the soils. In our presentation we will demonstrate how both the community structure and the abundance of CAs were modified upon N fertilisation and provide vital clues on the most likely mechanism(s) controlling COS and CO2 fluxes in soil communities and the significance of these results for interpreting atmospheric signals.

Kaisermann, Aurore, Sam P. Jones, Steven Wohl, Jérôme Ogée, and Lisa Wingate. 2018 Nitrogen Fertilization Reduces the Capacity of Soils to take up Atmospheric Carbonyl Sulphide. Soil Systems 2 (4), 62 doi.org/10.3390/soilsystems2040062

Meredith, Laura K, Jérôme Ogée, Kristin Boye, Esther Singer, Lisa Wingate, Christian von Sperber, Aditi Sengupta, et al. 2018. “Soil Exchange Rates of COS and CO18O Differ with the Diversity of Microbial Communities and Their Carbonic Anhydrase Enzymes.” ISME Journal, 2018. https://doi.org/10.1038/s41396-018-0270-2.

How to cite: van Schaik, E., Mondy, S., Lelievre, M., Martin, M., Perrin, S., Meredith, L., Kaisermann, A., Jones, S., Rue, O., Loux, V., and Wingate, L.: Revealing how nitrogen fertilisation regulates the fluxes of COS and CO2 between soil communities and the atmosphere using a functional metagenomic and metatranscriptomic approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21605, https://doi.org/10.5194/egusphere-egu2020-21605, 2020.

D1797 |
Khatab Abdalla, Mutez Ahmed, and Johanna Pausch

The projected global warming risks due to high emissions of greenhouse gases, mainly from anthropogenic activities, increases the need for an agricultural practice with high carbon sink capacity and low water requirements without compromising on environment and productivity. On one hand, it’s well accepted that soil moisture directly affects microbial activity, whereas on the other hand, drought stress was recently postulated to increase root exudates, which in turn will accelerate soil organic matter mineralization “priming effects”. Thus, the objective of this study was to investigate the interplay between soil moisture (well-watered and drought stressed) and maize (Zea mays L.) root exudates on soil CO2 efflux. The experiment consisted of three treatments, which are well-watered, drought stressed maize plus a control (without plants) lysimeters (1 m3), Soil CO2 efflux, soil temperature and moisture content were measured weekly during the growing season (April to September) and monthly in the fallow period. Under well-watered conditions, the annual average of CO2 efflux was 0.12 g CO2-C m-2 hr-1, which was 24.5 and 20% significantly higher than under drought stressed and the control, respectively. Moreover, well-watered treatment had significantly greater primed carbon than drought stressed maize. Soil temperature in deeper soil layers (25, 50 and 75 cm) correlated positively (with the CO2 efflux, while soil moisture correlated negatively at the 5 cm and 25 cm. Overall, these results suggested that the root exudates decreased under drought conditions, which decreasing soil respiration. Drought tolerance varieties could be an option to decrease soil respiration and maintain productivity.

How to cite: Abdalla, K., Ahmed, M., and Pausch, J.: Does rhizosphere priming effect explain the greater soil respiration in well-watered and drought stressed maize? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18874, https://doi.org/10.5194/egusphere-egu2020-18874, 2020.

D1798 |
Michaela Dippold, Sara Halicki, Mutez Ahmed, Hongcui Dai, Jie Zhou, Natalyia Bilyera, Xuechen Zhang, Sandra Spielvogel, Duyen Hoang, and Callum Banfield

Hotspots in agricultural soils, which include rhizosphere, detritusphere and drilosphere, are characterized by strongly different dynamics than those of natural ecosystems. This involves hotspot properties such as element cycling intensity, microbial activation, lifetime or spatial extension. Evidence from studies around the globe suggests that key hotspot characteristics intensify or increase under strongly limiting cropping conditions e.g. low-input agriculture: i) nutrient mining is more intensive around roots in infertile soils, ii) root exudates decompose more slowly under water limitation, and iii) the rhizo-hyphosphere forms a more spatially extended hyphal network under P deficiency. These examples suggest that smart management of hotspots might be a sustainable strategy to overcome soil limitations, not only for crop production on marginal soils but also as a strategy to save resources for future agriculture.

Here, we will present a set of studies applying management strategies, which actively modify hotspot intensity, lifetime or spatial extension with the aim to manipulate biogeochemical cycles of the respective agroecosystem. Most traditional, tillage enlarges the topsoil detritusphere or moves it to lower soil depths. Rather novel but increasingly studied approaches seek to modify rhizosphere properties: applying genotypes with i) specific root traits such as an optimized root morphology (e.g. modified root hairs or deeper fine root system) or ii) modified root exudate compositions and resulting rhizosphere microbiomes. Such approaches need to be applied site- and agroecosystem-specifically to optimize resource utilization. Moreover, as agroecosystems are under long-term controls, hotspot management strategies are not limited to one growing season but can stretch over years of cultivation. The generation of specific biopores – the root channels - created by e.g. tap-rooted or deep-rooting cover crops is a management practise inducing a rhizosphere-detritusphere-rhizosphere transition over time. ‘Re-activated’ hotspots feature unique biogeochemical conditions for young roots as well as microbial communities. Such ‘highways to subsoil’ foster rhizosphere establishment in subsoils, where i) hotspots remain moist and thus active under drought and ii) where gradients from hotspots to bulk soils are for magnitudes higher compared to topsoils. All these aspects present a unique, however largely unexploited potential for future agriculture, yet.

By a novel set of methodological approaches and their combinations, comprising multi-isotope applications, in-situ imaging techniques, biomarkers and microbial activity measures with high spatial resolution, we will provide new insights into the potential of hotspot management in agroecosystems. We will discuss implications for crop production under resource limitation up to the potential for a sustainable development of future agricultural production systems especially in the face of projected climate change.

How to cite: Dippold, M., Halicki, S., Ahmed, M., Dai, H., Zhou, J., Bilyera, N., Zhang, X., Spielvogel, S., Hoang, D., and Banfield, C.: Management of hotspots for sustainable crop production: hotter, deeper, or simply more?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17859, https://doi.org/10.5194/egusphere-egu2020-17859, 2020.

D1799 |
| Highlight
Julia Maschler, Daniel S. Maynard, Devin Routh, Johan van den Hoogen, Zhaolei Li, Shuli Niu, and Thomas W. Crowther

Soil nitrogen is a prominent determinant of plant growth, with nitrogen (N) availability being a key driver of terrestrial carbon sequestration. The local availability of soil N is thus crucial to our understanding of broad-scale trends in soil fertility, productivity, and carbon dynamics. Here, we provide global, high-resolution maps of current and future (2050) potential net nitrogen mineralization (N-min), revealing global patterns in soil N availability. Highest mineralization rates are found in warm and moist tropical regions, leading to a strong latitudinal gradient in N-min. We observed a positive correlation of N-min rates with human population density and net primary productivity. Projected climate conditions for 2050 suggest that N availability will further decrease in areas of low N availability and increase in areas of high N availability, thereby intensifying current global trends. These results shed light on the core processes governing productivity at a global scale, providing an opportunity to improve the accuracy of plant biomass and climate models.

How to cite: Maschler, J., Maynard, D. S., Routh, D., van den Hoogen, J., Li, Z., Niu, S., and Crowther, T. W.: Global maps of current and future nitrogen mineralization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-93, https://doi.org/10.5194/egusphere-egu2020-93, 2020.

D1800 |
Liang Wei

The biogeochemical interfaces are hotspots for organic matter (OM) transformation. However, direct and continuouxiacis tracing of OM transformations and N and P degradation processes are lacking due to the heterogeneous and opaque nature of soil microenvironment. To investigate these processes, a new soil microarray technology (SoilChips) was developed and used. Homogeneous 2-mm-diameter SoilChips were constructed by depositing a dispersed paddy soils with high and low soil organic carbon (SOC) content. A horizon suspension on a patterned glass. Dissolved organic matter from the original soil was added on the SoilChips to mimic biogeochemical processes on interfaces. The chemical composition of biogeochemical interfaces were evaluated via X-ray photoelectron spectroscopy (XPS) and the two-dimensional distribution of enzyme activities in SoilChips were evaluated by zymography. Over 30 days, soil with high SOC content increases microbial nutrition (N and P) requirements than soil with low SOC evidenced by higher hotspots of β-1,4-N-acetaminophen glucosidase, and acid phosphomonoesterases and higher 16S rRNA gene copies. The degree of humification in dissolved organic matter (DOM) was higher and the bioavailability of DOM was poorer in soil with high SOC than soil with low SOC. The poorest bioavailability of DOM was detected at the end of incubation in soil with high SOC. Molecular modeling of OM composition showed that low SOC mainly facilitated the microbial production of glucans but high SOC mainly facilitated the microbial production of proteins. We demonstrated that SOC content or DOM availability for microorganisms modifies the specific OM molecular processing and N and P degradation processes, thereby providing a direct insight into biogeochemical transformation of OM at micro-scale.

How to cite: Wei, L.: Organic matter content controls the N and P degradation process on biogeochemical interfaces: A micro-ecosystem scale study based on SoilChips-XPS-Zymography integrated technique in paddy soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2963, https://doi.org/10.5194/egusphere-egu2020-2963, 2020.

D1801 |
Duyen Hoang Thi Thu

Earthworm catalyzes soil organic matter (SOM) decomposition through their burrowing activity, gut processing of carbon (C) inputs and microorganism stimulation. Specific enzyme is characterized for the decomposition, which is denoted in enzyme activity, substrate turnover and turnover rate of the decomposition. To demonstrate the interaction between earthworms and microbial activities, 14C-labelled plant litter was placed on a soil surface of a mesocosm (10 x 2 x 50 cm) prior to placing earthworms into soil, control soil was set up in mesocosms without earthworms. After 1 month of earthworm presence, soil materials coated on the biopore walls were excavated for another soil incubation to define C turnover by trapping respired CO2 in NaOH 1M. While another subsample was used to define activity of cellobiohydrolase (a cellulolytic enzyme) and its turnover rate. The hypotheses were that i) C turnover by incubation is associated with enzymatic turnover rate but ii) these two turnover rates are depth dependent.

Consequently, activity of cellobiohydrolase was higher in earthworm biopores than control soil regardless of soil depth. The difference in enzyme kinetics between biopores and control soil showed a shift of enzyme system toward higher substrate affinity in the topsoil but lower in the subsoil. This finding can be explained by the distinction in microbial community between topsoil and subsoil in both earthworm biopore and control soil. Substrate turnover time calculated based on saturated substrate concentration and maximum reaction rate velocity. The turnover
rate of substrate decomposition was faster in biopores than bulk soil. The substrate turnover time is depth dependent. We concluded that earthworm biopores are microbial hotspots with demonstrated interactions between microbial functions and microscale features. The decrease of enzyme activities with depth, accompanied by the decrease of catalytic efficiency, implies the microbial production of more efficient enzymes in the top- than in the subsoil. Bioturbation induced by earthworms leads to localization of microorganisms and litter within biopores and plays a crucial role for organic matter processing, its microbial utilization, and turnover. This has direct consequences for C and nutrient cycling.

How to cite: Hoang Thi Thu, D.: Carbon turnover and Turnover rate of enzyme cellobiohydrolase in earthworm biopores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6080, https://doi.org/10.5194/egusphere-egu2020-6080, 2020.

D1802 |
Lingling Shi, Wenting Feng, Xin Jing, Huadong Zang, Peter Edward Mortimer, and Xiaoming Zhou

The roles of soil fungal diversity and community composition in regulating soil respiration when above‐ and below‐ground plant carbon (C) inputs are excluded remain unclear. In the present study, we aimed to examine: (i) how does the exclusion of above‐ and below‐ground plant C inputs affect soil respiration and soil fungi singly and in combination? and (ii) are changes in soil fungal diversity aligned with changes in soil respiration? A field experiment with manipulation of plant C inputs was established in a subtropical forest in southwest China in 2004 with litter removal and tree stem‐girdling to exclude inputs of the above‐ and below‐ground plant C, respectively. In 2009, we measured the rates of soil respiration with an infrared gas analyser and soil fungal community structure using Illumina sequencing. We found that the rates of soil respiration were reduced significantly by litter removal and girdling, by similar magnitudes. However, they were not decreased further by the combination of these two treatments compared to either treatment alone. In contrast, litter removal increased the diversity of soil fungal communities, whereas girdling decreased the abundance of symbiotrophic fungi but increased the abundance of saptrotrophic and pathotrophic fungi. These changes in soil fungal community might initiate CO2 emission from soil C decomposition, offsetting further decline in soil respiration when plant C inputs are excluded. These results revealed that the exclusion of the above‐ and below‐ground plant C inputs led to contrasting soil fungal communities but similar soil function. Our findings suggest that both above‐ and below‐ground plant C are important in regulating soil respiration in subtropical forests, by limiting substrates for soil fungal growth and altering the diversity and composition of soil fungal community.

How to cite: Shi, L., Feng, W., Jing, X., Zang, H., Mortimer, P. E., and Zhou, X.: Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10838, https://doi.org/10.5194/egusphere-egu2020-10838, 2020.

D1803 |
Michael Herre, Bernd Marschner, and Sven Marhan

The distribution of soil organic matter and microbial biomass in subsoils is much more heterogeneous than in the topsoil due to a more localized input of fresh substrate and nutrients from rhizodeposition and preferential flow paths forming hotspots of microbial activity. However, the remaining bulk soil also contains substantial amounts of labile substrates that are readily mineralized during lab incubation experiments. We therefore hypothesized that one reason for this is that potential consumers are spatially separated from these substrates due to the low microbial densities in subsoils. Consequently, hotspots are not only formed through high substrate inputs but also through a higher abundance and diversity of microorganisms compared to the bulk soil due to inputs of cells and spores with the soil solution or through hyphal growth. However, little is known about the colonization potential or dynamics of microorganisms in the subsoil.

In November 2018, we started a field experiment to investigate the re-colonization potential of microorganisms by exposing 24-well microplates containing sterilized soil samples in the field at two different depths (topsoil: 10 cm, subsoil 60 cm) at a beech forest site in northern Germany. After 6 and 12 months, samples from each well and from the intact soil compartments above each well were analyzed for enzyme activities (hydrolytic enzymes using MUF and AMC substrates), microbial activity parameters (soil respiration and SIR using the MicroResp®) and the microbial community structure (quantitative PCR).

We expect (1) different temporal dynamics of re-colonization between top- and subsoil samples; (2) that the recolonization potential is related to the microbial activity in the soil compartments above the exposed samples and (3) that the heterogeneous re-colonization is maintained throughout the field exposure and thus indicates the relevance of preferential flow paths for microbial transport especially in subsoils.

First results of the SIR assays after 6 months of field exposure show that in the topsoil microbial activity has been re-established in all of the wells, but is still below the mean activity in the undisturbed soil above the sterilized samples. In all subsoil samples, the re-established microbial activity was much lower and even below detection limit in some of the wells. In both depths, the SIR assays show a very patchy distribution of wells with higher microbial activities indicating that the influx of organisms is limited to small areas from the soil above the exposed containers.

How to cite: Herre, M., Marschner, B., and Marhan, S.: Re-colonization of sterile soil samples during long term field exposure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16574, https://doi.org/10.5194/egusphere-egu2020-16574, 2020.

D1804 |
Zhang Jiaqi and Liu Yinghui

  With the increasing of nitrogen(N) deposition and changing of precipitation patterns worldwide, large amounts of N are loaded in terrestrial ecosystem, resulting in soil nutrient imbalance and soil nitrous oxide(N2O) flux change. Nitrification and denitrification in soil are two major sources of N2O emission mediated by microorganisms. However, It is still unclear how the soil N2O flux and the abundance of nitrifiers and denitrifiers might change under the addition of N and water(W) in temperate semi-arid steppe. In this study, we established a one-year-long field experiment investigating how soil N2O flux, the abundance of nitrifiers and denitrifiers, and environmental properties, including soil pH, soil moisture, soil dissolved organic carbon content(DOC) and soil available N content responsed when N(NH4NO3 was applied at a rate of 4 g N·m-2·yr-1, which is equivalent to one time the annual nitrogen deposition) and/or W(water was applied at a rate of 112.5 mm·yr-1, which is equivalent to 30% of the annual rainfall) were added to temperate semi-arid steppe in northern China with the natural condition without any treatment as control. Quantitative PCR was used to analyze the abundance of ammonia oxidizers(ammonia-oxidizing bacteria and archaea amoA) and denitrifiers(nirS/nirK and nosZ). Our experimental results demonstrated that soil N2O emission decreased when W was added and W and N were added in temperate semi-arid steppe in northern China. The abundance of nirS and nosZ genes increased when W and N were added. Compared with AOA/AOBamoA and nirK genes, the abundance of nirS and nosZ genes is more sensitive to the addition of N and W. Soil N2O flux was negatively correlated with the abundance of nirS-denitrifier. The nirS gene abundance, soil pH and DOC were the main controls on soil N2O flux and totally explained 78.2% of the variation of soil N2O flux. The results of this study provide a theoretical basis for N cycle mechanism mediated by microorganisms and have practical significance for the prediction of N2O flux change in temperate semi-arid steppe under the background of global change.

How to cite: Jiaqi, Z. and Yinghui, L.: Environmental properties and microbial abundance explain soil nitrous oxide flux variation synergistically under the addition of nitrogen and water in temperate semi-arid steppe , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6270, https://doi.org/10.5194/egusphere-egu2020-6270, 2020.

D1805 |
Xuechen Zhang, Yakov Kuzyakov, Huadong Zang, Michaela A. Dippold, Lingling Shi, Sandra Spielvogel, and Bahar S. Razavi

Among the factors controlling root exudation, root hair proliferation and warming strongly influence exudate release, microbial substrate utilization and enzyme activities. The interactions of these two factors are important but poorly known in the rhizosphere. To clarify these interactions, two maize varieties – a wild type with root hairs and a hairless mutant – were grown at 20 and 30 °C for 2 weeks. We applied a unique combination of zymography to localize hotspots of β-glucosidase with microcalorimetry and substrate-induced respiration from soil sampled in hotspots. This approach enabled monitoring exudate effects on microbial growth strategy, enzyme kinetics (Vmax and Km), heat release and CO2 production in the hotspots in response to warming.

Root hair effects on enzyme activity and efficiency were pronounced only at the elevated temperature: i) β-glucosidase activity of the wild type at 30 °C was higher than that of the hairless maize; ii) temperature shifted the microbial growth strategy, whereas root hairs (i.e. C input) promoted the fraction of growing microbial biomass; iii) Km and the activation energy for β-glucosidase under the hairless mutant was lower than that under wild maize. These results suggest that microorganisms inhabiting hotspots of the wild type synthesized more enzymes to fulfill their higher energy and nutrient demands than those of the hairless mutant. In contrast, at higher temperature the hairless maize produced an enzyme pool with higher efficiencies rather than higher enzyme production, enabling metabolic needs to be met at lower cost. These changes in enzyme kinetics and metabolic shifts confirmed evolutionary theory on tradeoffs of enzyme structure–function and thermal–substrate under warming at the soil hotspot level. We conclude that, if microbial and enzymatic activities are stimulated by more substrate input under warming, then this shift in the microbial community and in enzyme systems to a lower efficiency could offset C losses.

How to cite: Zhang, X., Kuzyakov, Y., Zang, H., Dippold, M. A., Shi, L., Spielvogel, S., and Razavi, B. S.: Rhizosphere hotspots: root hairs and warming control microbial efficiency, carbon utilization and energy production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4140, https://doi.org/10.5194/egusphere-egu2020-4140, 2020.

D1806 |
Rida Sabirova, Michael Makarov, and Maxim Kadulin

Against the climate change there has been an overgrowing of phytocenoses of alpine lichen heath and arctic tundra with dwarf shrubs and shrubs over the past 40 years. Dwarf shrubs roots of Vaccinium vitis-idaea L. forms symbiosis with ericoid mycorrhiza, which may lead to change of soil properties. Mycorrhizal fungi regulate nitrogen, phosphorus and carbon cycles by secretion of active enzymes which depolymerize and mineralize soil organic matter and increase available of mineral nutrition elements for vegetation and microorganisms.

Moreover, in the previous research it was found that moisture was greater under shrubs than under alpine lichen heath. It is known that moisture plays key role in microbial processes in the soil, affect on enzyme activity, nitrification, mineralization and so on. Therefore, the objective of this research is to evaluate the influence of both dwarf shrubs and moisture on the soil characteristics.

Research area is located around 2750 m a.s.l. in the alpine heath of Teberda Nature Reserve, North Caucasus, Karachay-Cherkess Republic where 3 areas with different moisture (15, 21 and 27%) were chosen. In each area samples of mountain-meadow soil were collected from under dwarf shrubs and alpine lichen heath without dwarf shrubs (control) during 10 days of the second part of July and then frozen until laboratory analysis. Firstly, there were analyzed chemical (soil pH, mineral P, organic N, C, inorganic N) and biological (C and N of microbial biomass, basal respiration, mineralization, nitrification and activity of glucosidase, phosphatase, chitinase and leucinaminopeptidase) properties of the soil samples. Furthermore, it was made statistical analysis in Statistica 8.0 program.

 It was found that increase in moisture is accompanied by increase in concentrations of inorganic forms of nitrogen, C and N of microbial biomass, basal respiration and nitrification activity in heath without shrubs, which indicates a growth of microbiota activity. However concentrations of labile organic carbon and nitrogen, and enzymatic activity decrease at the same conditions. Such changes indicate a shift from a community of heath with herbal vegetation to communities dominated by ericoid mycorrhizal plants.

The investigation also revealed that soil acidity is significantly higher under V. vitis-idaea L., however, there is a noticeable decrease in nitrification activity, inorganic nitrogen concentrations, which indicates minor dependence of the dwarf shrubs on mineral compounds in nitrogen nutrition.

Thus, both the presence of V. vitis-idaea L. and various moisture have a significant effect on the soil characteristics. Moreover, the moisture under control plays an essential role, while under the dwarf shrubs many soil properties remain unchanged, therefore, V. vitis-idaea L. creates a microclimate in the soil among roots where moisture has no effect.

How to cite: Sabirova, R., Makarov, M., and Kadulin, M.: Effect of Vaccinium vitis-idaea L. and moisture on mountain-meadow soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-730, https://doi.org/10.5194/egusphere-egu2020-730, 2020.

D1807 |
Gera Van Os, Karin Pepers, Jaap Bloem, Joeke Postma, and Johnny Visser

Worldwide there is an enormous interest in microbial indicators for soil quality, since this reflects the potential capacity for soil ecosystem functions i.e. nutrient cycles, carbon storage, biodiversity and resilience to climate change. Farmers are anxious to measure the effects of different soil management practices in order to improve soil quality and attain sustainable food production. Despite the rapid developments in (molecular) measurement techniques, adequately validated and affordable methods for field measurements on soil microbial activity are still lacking. Nowadays, farmers participate in campaigns to bury cotton undies in order to measure biological activity in their fields (Soil your undies).  If there’s not much left of the undies after a couple of months, this supposedly indicates good soil health. Of course this is by no means a quantitative nor validated indicator.

An elegant, cheap and simple method to measure biological activity in soil is the Tea Bag Index (TBI). This method was developed to determine the global variation in decomposition rate of organic matter by the soil microflora as influenced by abiotic circumstances. The TBI consists of two parameters describing decomposition and stabilization of organic matter by measuring weight loss of green tea and rooibos tea bags that have been buried in the soil for three months. The method is designed to discriminate contrasting ecosystems and, within ecosystems, differences in factors such as soil temperature and moisture content (Keuskamp et al. 2013, doi: 10.1111/2041-210X.12097).

Our research aimed to assess the possibility to use the TBI as an indicator for soil microbial activity, considering its sensitivity and robustness to discriminate between agricultural soil management practices that are known to have a significant impact on soil microbial diversity and activity. The responsiveness to soil pasteurization and organic amendments was investigated under both controlled and field conditions. The TBI decomposition rate differed significantly between both tea varieties (green tea > rooibos tea). Organic amendments had little or no effect. The TBI-results were plotted against some more established biochemical indicators which are sensitive to soil management and often related to microbial biomass, i.e. hot water extractable carbon, potentially mineralizable nitrogen and fungal biomass. Results are discussed, as well as factors which complicate the interpretation of TBI data with respect to soil microbial activity.

How to cite: Van Os, G., Pepers, K., Bloem, J., Postma, J., and Visser, J.: Tea Bag Index as potential indicator for soil microbial activity., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5344, https://doi.org/10.5194/egusphere-egu2020-5344, 2020.

D1808 |
Kyungmin Kim, Andrey Guber, and Alexandra Kravchenko

Soil pore size distribution (PSD) regulates oxygen diffusion and transport of water/mineralized nutrients. Microbial activity, which drives the carbon (C) cycle in the soil system, can react to these physical factors regulated by PSD. In this study, we investigated the contribution of PSD to C-related microbial activity during the switchgrass decomposition. We used two types of soils, which have controlled PSD (dominant pore size of < 10um and > 30 um). 13C labeled switchgrass leaf and root were incorporated into different PSD of soils and incubated for 21 days under 50% water-filled pore space. During the incubation, microbial activity was assessed with several indicators. i) Fate and transport of mineralized switchgrass, ii) Priming effect, iii) Spatial distribution of b-glucosidase and phenol oxidase, and iv) Microbial biomass. Our preliminary results showed that CO2 emission from switchgrass leaf was greater in the soil dominated by < 10 um pores. Higher b -glucosidase activity and mineralized C from switchgrass leaf supported greater C-related activity in such soil. However, interestingly, we observed a greater priming effect in the soil dominated by > 30 um pores. Due to the less mineralization and transport of switchgrass-derived C in such pores, enzymes targeting more complex substrate could be more active in such soil stimulating mineralization of native soil C. Our full results of phenol oxidase, microbial biomass, and more detailed analysis on 13C and C dynamics will help understanding how PSD can affect biochemical reactions in plant decomposition system.

How to cite: Kim, K., Guber, A., and Kravchenko, A.: Pore size effect on soil carbon dynamics during decomposition of switchgrass, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1148, https://doi.org/10.5194/egusphere-egu2020-1148, 2020.

D1809 |
Ali Feizi and Bahar Razavi

Climate change represents a key challenge to the sustainability of global ecosystems and human prosperity in the twenty-first century. The impacts of climate change combined with natural climate variability are predominantly adverse, and often exacerbate other environmental challenges such as degradation of ecosystems, loss of biodiversity, and air, water and land pollution. Besides, rapid industrialization and increasing adaption of agrochemical based crop production practices since green revolution have considerably increased the heavy metal contaminations in the environment.

Assessing the impacts of climate change on our planet and addressing risks and opportunities is essential for taking decisions that will remain robust under future conditions, when many climate change impacts are expected to become more significant.

Here, we established a review survey to assess the impact of biochar amendment and agroforstry system on CO2 sequestration and methaloid remediation.

Our data base showed that Agroforestry-based solutions for carbon dioxide capture and sequestration for climate change mitigation and adaptation in long-term is more practical and realistic options for a sustainable ecosystem and decreasing negative effect of climate change. This was more supported in arid and semi-arid regions as well as area with saline and alkaline soil (20%).

From a soil remediation standpoint, the general trend has been shifting from reduction of the total concentration to reduction of the physic-chemically and/or biologically available fractions of metals. This regulatory shift represents a tremendous saving in remediation cost. While metals are not degradable, their speciation and binding with soil through biochar amending reduced their solubility, mobility, and bioavailability. While agroforestry showed high efficiency in C sequestration (32%), biochar amendment raveled significant mitigation in heavymetals bioavailability (42%). However, studies which coupled both approaches are limited. Thus, we conclude that combined Agroforestry and biochar amendment regulates C sequestration and metalloids remediation more efficiently.

How to cite: Feizi, A. and Razavi, B.: Climate change mitigation and adaptation by biochar: mechanisms and regulatory trend in the rhizosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22654, https://doi.org/10.5194/egusphere-egu2020-22654, 2020.

D1810 |
Nataliya Bilyera, Irina Kuzyakova, Bahar S. Razavi, Sandra Spielvogel, and Yakov Kuzyakov

The recently raised topic of microbial hotspots in soil needs not only visualizations of their spatial distribution and biochemical analyses, but also statistical approaches to segregate these hotspots and separate them from the background.  We hypothesized that each type of hotspots (e.g. hotspots of root exudation, enzyme activities, root water uptake, pesticides accumulation in plant) is a result of processes driven by biotic or abiotic factors, and consequently corresponds to a statistical distribution follows of a composite functions (e.g. normal/Gaussian), which is significantly different from the background. Consequently, the elucidation of microbial hotspots should be based on statistical separation of the distributions or segregate of maximal values within one distribution. As examples, we collected 3 groups of published images: 1) 14C images on carbon input by roots into the rhizosphere, 14C localization in roots and glyphosate accumulation in the plant, 2) zymogram on leucine aminopeptidase, 3) neutron image on root water uptake. Each of the images was analyzed for statistical distribution of activity and its area. In the next step, respective distribution parameters (means and standard deviations) were calculated, the modeled distribution was fit, and the background was removed. For the parameters with one distribution, we identified hotspots as the areas outside of the “Mean+2SD” values (corresponding to the upper ~ 2.5% of activity being over 95.5 % of background values). Finally, images of solely hotspots locations were visualised. Comparison with previously used decisions of the hotspot intensity (i.e. Top-25% intensity) thresholding showed advantages of the “Mean+2SD” approach. The advantages (suitable for “time-specific” hotspots in temporal sequence of images, identification of hotspots with different level of activity, unification of thresholding approach for several imaging methods with different principles of activities distribution) and limitations (loss of hotspot areas at low quality images, several thresholding rounds for two or more distributions at on image) of the suggested approach and the potentials of its further development were discussed. We conclude that objective elucidation and separation of the hotspots is case specific and should be based on statistical tools of distribution analysis, which will also help to understand the processes responsible for the highest activities.

How to cite: Bilyera, N., Kuzyakova, I., S. Razavi, B., Spielvogel, S., and Kuzyakov, Y.: How 'hot' are the hotspots: Statistical approach to localize the high activity areas on soil images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5468, https://doi.org/10.5194/egusphere-egu2020-5468, 2020.

D1811 |
Yi Wang, Shirong Liu, and Junwei Luan

The roles of multiple global change are expected for many terrestrial ecosystems in future. As two main global change factors, the impact of drought and nitrogen deposition and their interaction on soil respiration and its components (R) remains unclear. To explore the responses of soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) to multiple global change factors, we established a field experiment of throughfall reduction and nitrogen additions in a subtropical Moso bamboo (Phyllostachys heterocycla) forest in the Southwest China, using a 4 × 4 completely randomized design. Results showed that bivariate exponential equation with soil temperature (T) and soil moisture (SWC) (R=a.ebT.SWCc) was fitted to predict Rs, Ra and Rh. Throughfall reduction, nitrogen additions and their interaction had no effect on annual mean Rs and Ra, but nitrogen additions significantly depressed annual mean Rh. Nitrogen additions significantly decreased contribution of Rh to Rs and increased contribution of Ra to Rs, however, the contributions were non-responsive under throughfall reduction. The more positive effect of nitrogen additions on the contribution of Ra to Rs was appeared compared with that of throughfall reduction, thereby more negative effect on the contribution of Rh to Rs. The fine root biomass, fine root carbon and nitrogen storage regulated Rs, while fine root phosphorus storage determined Ra. The Rh was negatively correlated with vector lengths, thus suggesting that microbial carbon limitation caused the decline of Rh. Our findings demonstrate that the nitrogen additions played overriding role than throughfall reduction in affecting the contribution of Ra and Rh to Rs. Moreover, the negative response of temperature sensitivity of Rs and Rh to nitrogen additions, suggesting that that the nitrogen additions may weaken the positive response of soil CO2 emission to global climate warming. Our study highlights asymmetrical responses of Rs, Ra and Rh to throughfall reduction and nitrogen additions and could enhance accurate predictions of soil carbon dynamics in response to multiple global climate change in future.

How to cite: Wang, Y., Liu, S., and Luan, J.: Soil respiration and its components respond asymmetrically to throughfall reduction and nitrogen additions in a subtropical Moso bamboo forest in the Southwest China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6262, https://doi.org/10.5194/egusphere-egu2020-6262, 2020.

D1812 |
| Highlight
Sisi Lin and Guillermo Hernandez Ramirez

Thaw-induced N2O emissions have been shown to account for 30-90% of N2O emissions in agricultural fields. Due to the climate change, increased precipitatio is expected in fall and winter seasons for certain regions. As a result, this would in turn enhance the thaw-induced N2O emissions and aggravate climate change. A mesocosm study was conducted to investigate N2O production and sources from soils under elevated soil moisture contents in response to a simulated fall-freeze-thaw cycle. Treatments included two levels of N addition (urea versus control) and two different management histories [with (SW) and without (CT) manure additions]. Our results showed that at least 92% of the N2O emissions during the study were produced during the simulated thawing across all treatments. The thaw-induced N2O emissions increased with increasing soil water content. The fall-applied urea increased the soil-derived N2O emissions during thawing, indicating an excessive mineralization of soil organic N. Compared to the CT soils, the SW soils induced more soil-derived N2O emissions. This could be because the SW soil had more easily decomposable organic matter which was likely due to historical manure additions. Regarding to the daily primed N2O fluxes, different soil water contents impacted the dynamics of daily priming effect. At the high water content, the soils experienced a shift in daily primed N2O fluxes from positive to negative and eventually back to positive throughout the simulated thawing, while the soils at lower water contents underwent positive primed fluxes in general. The shift in daily primed fluxes was probably driven by the preference of soil microbes on the labile N substrates. When the microbes switched from easily to moderately decomposed substrates (e.g., from dissolved organic N to plant residuals), they started to uptake inorganic N from the soil due to a relatively high C:N ratio of plant residuals. Therefore, a net N immobilization and negative primed N2O production occur in the short term in the soils at the high water content.

How to cite: Lin, S. and Ramirez, G. H.: Nitrous oxide production and sources in response to a simulated fall-freeze-thaw cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6227, https://doi.org/10.5194/egusphere-egu2020-6227, 2020.

D1813 |
Shibin Liu, Yakov Kuzyakov, Shengyan Pu, and Bahar Razavi

Manure application has been considerably emphasized to mitigate global soil degradation and improve soil fertility. Though there have been investigations on the contribution of manure application on soil properties in comparison with mineral fertilization, a comprehensive understanding of manure application on soil organic matter (SOM), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) and activities of 7 enzymes is yet to be identified. This study extensively quantified the response of soil biochemical properties to manure application based on a meta-analysis of 83 articles including 460 observations with time span from days to years. The impact of explanatory factors (i.e. climatic factors, experimental types, soil properties and manure characteristics) was also elucidated. Manure application increased SOM, TN, MBC and MBN by 27 ± 3% and 41 ± 5.3%, 87 ± 4.3% and 88 ± 6.7 %. Soil C/N ratio did not vary but MBC/MBN ratio decreased after manure application, indicating a shift in microbial community. The activities of β-glucosidase, dehydrogenase, acid phosphatase, alkaline phosphatase, N-acetyl-β-D-glucosaminidase, urease and sulfatase were also elevated by 150%, 110%, 40%, 110%, 59%, 106% and 221%, respectively. Besides, all soils were neutralized following manure application, suggesting that manure accelerates soil nutrient cycling by adjusting pH to optimum. When mean annual temperature is within the range of 10-20 °C or initial soil pH within 6-8, the highest increase of enzyme activities was revealed. Furthermore, composting manure has stronger impact on soil enzyme activities compared to non-composted manure, which was attributed to beneficial microbial community composition as well as favourable soil organic compound composition in the compost. Contrarily, combined application of manure with mineral fertilizers induces an antagonistic effect and weakens the impact of manure on soil biochemical properties as compared to only manure application. This weakening effect may mitigate the competition between microbes and plant roots for nutrients. In conclusion, necessary differentiation of only manure and manure + chemical fertilizers application is required when developing and modeling the influence of management practices on arable lands.

How to cite: Liu, S., Kuzyakov, Y., Pu, S., and Razavi, B.: Combined application of manure and mineral fertilizers weakens the impact of manure on soil biochemical properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6893, https://doi.org/10.5194/egusphere-egu2020-6893, 2020.

D1814 |
Leandro Paulino, Nelson Beas, Dorota Dec, Felipe Zúñiga, Oscar Thiers, Oscar Martínez, and José Dörner

Aquands are shallow depth and frequently waterlogged volcanic ash soils, presenting seasonal dynamics of water content in the soil profile. Land use change and management are expected to alter the Aquands biological activity due to their impact to water/air relationships as well as nutrient dynamics and greenhouse gases emissions. In southern Chile (41°26’S;73°07’W; 70 m a.s.l.), soil biological processes related to C- and N cycles, as well as greenhouse gas effluxes were assessed in relation to historical land use change and a drainage set in a naturalized grassland for animal husbandry. Disturbed soil samples were obtained in order to evaluate soil respiration, N mineral dynamics (NH4+ and NO3-), denitrification, nitrate reductase activity. Static-closed chambers were installed in the field to assess fluxes of CO2, N2O and CH4 from the soil surface at different seasons of the year with contrasting water table depths. Soil respiration responded to the historical land use change and draining effects. The aerobic and anaerobic biological processes related to soil nitrogen dynamics were less sensitive than respiration, and showed arbitrary effects according to the current use and management of the Aquand. Soil surface fluxes of greenhouse gases showed similar patterns, where CO2 emissions responded temporarily to land use, while N2O and CH4 did not respond conclusively. The content of soil organic carbon associated to the structural changes derived from land use change (e.g. fire clearance) and soil management (e.g. animal trampling) are plausible parameters to explain the variations of CO2 emissions from Aquand soils surface, while other elements such as microbial community and the ferrous wheel hypothesis, should be investigated in order to explain the biological responses and trace greenhouse gases emissions.

How to cite: Paulino, L., Beas, N., Dec, D., Zúñiga, F., Thiers, O., Martínez, O., and Dörner, J.: Land use change and management of a Duric Histic Placaquand in Southern Chile: effects on biological properties and greenhouse gas emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11995, https://doi.org/10.5194/egusphere-egu2020-11995, 2020.

D1815 |
Joann Whalen and Hicham Benslim

Earthworms create hotspots that support microbial diversity and activity in soil. These hotspots may be internal to the earthworm, such as in their intestinal tract, or external to the earthworm in the biopores, casts and middens they create on the soil surface and within the soil profile. This presentation summarizes some of the key hotspots associated with earthworms, and how the biostimulated microbial community in these areas contributes to soil nitrogen cycling. We will present observations about the diversity and activity of nitrogen-cycling microorganisms that live within the earthworm and in its built environments, as well as the population- and community-level contributions of earthworms to denitrification, nitrogen mineralization, and the soil nitrogen supply in temperate agroecosystems.

How to cite: Whalen, J. and Benslim, H.: Hotspots created by earthworms, and their contribution to soil nitrogen cycling , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9434, https://doi.org/10.5194/egusphere-egu2020-9434, 2020.

D1816 |
Mehdi Rashtbari and Ali Akbar Safari Sinegani

Annually, millions of tons of antibiotics in the world are used in medicine, veterinary and agriculture, and their excessive application have negative impacts on soil microorganisms and biological processes. In the present study, the effect of releasing the mostly used antibiotic in veterinary and ameliorative impact of organic and non-organic amendments was studied in which treatments include (control (without antibiotic), gentamicin, oxytetracycline and penicillin) and different concentrations (50, 100 and 200 mg/kg dry soil) with and without organic and mineral conditioners (cow manure, biochar and nano-zeolite) on soil urease (URE) and alkaline phosphatase (ALP) enzyme activity and their resistance and resilience indices at three time periods including 1-7, 7-30 and 30-90 days during a 90-day incubation time in a split-factorial design which soil conditioners were considered as the main plots and antibiotic types and concentration were as experimental factors. Resistance (RS) and resilience (RL) indices were calculated for enzymes activity. Results showed that in control treatment (without conditioner), application of gentamicin at 200 mg/kg caused a 68.9 percent decrease in soil ALP activity compared to control (without antibiotic), while a decrease in ALP activity in tetracycline-treated soils compared to control (without conditioner), manure, biochar, and nano-zeolite was 17.5, 13.8, 17.5 and 16 percent, respectively. URE enzyme activity at 30-90-days during incubation the period had an increasing trend from 1-7 days and the highest enzyme activity was measured on the 90th day of incubation. According to results, soil enzymes responded differently to antibiotics and conditioners in soil, so that penicillin and oxytetracycline had no considerable negative impact on ALP enzyme activity, while gentamicin and oxytetracycline at all applied concentrations significantly decreased URE activity. To sum up, findings showed that application of soil conditioners could alleviate negative impacts of antibiotics in soil and could improve resistance and resilience indexes of soil enzymes activities in soil.

How to cite: Rashtbari, M. and Safari Sinegani, A. A.: Enzymes Activity in Response to Veterinary Antibiotics in Presence of Organic (Biochar and Manure) and Mineral (Nano-Zeolite) amendment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10264, https://doi.org/10.5194/egusphere-egu2020-10264, 2020.

D1817 |
Wioleta Stelmach-Kardel, Magdalena Frąc, Agata Gryta, and Bahar S. Razavi

Among many factors controlling root exudation, root hairs proliferation and warming have strong influence on exudate release as well as microbial substrate utilization and enzyme activities. Thus, the interactions of these two factors are important but least known in the rhizosphere. Phosphorus (P) is the most important growth limiting nutrient in soils. Concerns about a depleting supply of P as fertilizer has boosted research efforts on understanding P cycling and fluxes, as a breakdown of P availability would have disastrous global consequences. Efficient P recycling in temperate ecosystems provides an excellent possibility to study all kind of biogeochemical P transformations – those mobilizing low available P species and those recycling available P – maintaining a high level of microbial biomass P in the ecosystem. Such microbial cycling has been successfully shown for individual C compounds or within compound classes. P recycling, especially within microbial communities, has not been investigated so far. Microbial necromass as a source of available C and N affect microbial P utilization. However, the mechanisms underlying this alteration of biogeochemical transformations within the P cycle are not understood. To clarify these interactions for 21 days, rhizoboxes with Maize wildtype and mutant (rth3, no root hairs) under 20 and 30 °C, with and without necromass addition were incubated. The spatial distribution of acid phosphatase was assessed with MUF-based Zymography. Phosphatase activity as well as enzyme kinetics parameters (Vmax and Km) were determined in bulk and rhizosphere soil of all treatments. 
Our result showed that necromass addition accelerated microbial activity and phosphates hotspots at high temperature ranges. Necromass had no influence on rhizosphere size but increased hotspots independent of temperature. In treatment without necromass amendment, root-hairs effects on enzyme activity and efficiency was pronounced only at elevated temperature. Necromass addition caused formation of roots with special morphology comparable to root hairs in mutant type (hairless root). This was plant strategy to compensate P limitation and acquire more P under competition with soil microbiome. Consequently, P content in plant biomass after changes of root morphology increased while MBP decreased. This, shows that microbial necromass was decomposed and used as a source of P by plant. Thus, plant by adaptation of their morphology over compete microorganisms for more efficient P uptake.

How to cite: Stelmach-Kardel, W., Frąc, M., Gryta, A., and S. Razavi, B.: Microbial necromass shaped plant traits in a warmer condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10754, https://doi.org/10.5194/egusphere-egu2020-10754, 2020.

D1818 |
Joana Séneca, Andrea Söllinger, Alexander Tveit, Petra Pjevac, Craig Herbold, Tim Urich, Josep Peñuelas, Ivan Janssens, Michael Wagner, Bjarni Sigurdsson, and Andreas Richter

Soil microorganisms control the breakdown (depolymerization) of high molecular weight organic matter in soil and its mineralization and release as CO2 to the atmosphere. The enzymatic reactions involved in these steps are known to be temperature sensitive. Therefore, increasing global temperatures are expected to accelerate microbial activity and ecosystem processes and stimulate further CO2 emissions, potentially causing a positive feedback to climate change. On the other hand, higher turnover rates demand an increased amount of energy allocated for growth, enzyme production and maintenance, which can progressively deplete soils from substrate, forcing a reduction of microbial biomass and/or activity and a higher metabolic investment in resource acquisition.

The response of ecosystems to warming has been shown to be related with its duration and magnitude. In this study, we analyzed soils from long-term (>50 years) and short-term (8 years) warmed plots at the natural geothermal warming experiment ForHot (https://forhot.is), located in a sub-arctic grassland in Iceland. Previous studies at this warming experiment have shown an accelerated C cycle in response to warming, with decreased soil carbon stocks, and higher rates of decomposition of labile and recalcitrant organic matter, regardless of the warming duration. In addition to carbon losses, increased N losses from soils were found, but no change in the N content of the vegetation along the temperature gradient. Additionally, both ammonification and nitrification rates were shown to increase under warming, pointing to higher N losses from warmed soils.

In this study, we tested the hypothesis that under warming microorganisms become progressively limited in organic substrates, leading to a higher microbial investment in organic N decomposing enzymes to mine the existing organic N sources present in their surroundings. This hypothesis is based on previous data, that showed that microbial turnover was increased in the warmed plots. Under this assumption, we expected to observe higher expression levels of genes coding for organic N mining extracellular enzymes in warmed plots.

We analyzed the metatranscriptome from a total of 16 soil samples representative of ambient (n=4) and +6°C warmed (n=4) soils, for both grassland types. Additionally, we sequenced the metagenomes of 4 soil samples, representative of each condition, to allow for transcript mapping and differential gene expression analysis.

We used Hidden Markov models to screen the assembled metatranscriptomes for genes involved in the degradation of chitin, proteinaceous compounds, nucleic acids and microbial cell walls. The subcellular location and presence/absence of signal peptides was assessed with Psort and SignalP to discriminate transcripts involved in internal recycling from those targeted for secretion. First results show a general up-regulation of all transcripts involved in organic N degradation in the grassland subjected to long-term warming, whereas this trend is less clear in the short-term warmed grassland. Further work includes cross-referencing gene expression patterns with potential changes in active community composition.

We conclude that an acceleration in microbial turnover rates in response to warming is coupled to a higher investment in N acquisition enzymes, as indicated by an up-regulation of genes involved in upstream processes of organic N degradation.

How to cite: Séneca, J., Söllinger, A., Tveit, A., Pjevac, P., Herbold, C., Urich, T., Peñuelas, J., Janssens, I., Wagner, M., Sigurdsson, B., and Richter, A.: Soil warming leads to an up-regulation of genes involved in the decomposition of organic N in a subarctic grassland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13985, https://doi.org/10.5194/egusphere-egu2020-13985, 2020.

D1819 |
Onurcan Ozbolat

How agroforestry systems influence the abundance of nitrogen-cycle contributing microbial genes under Mediterranean conditions?


Onurcan Özbolat *,1, Irene Ollio1, Eva Lloret1, Marcos Egea2, Raul Zornoza1


1 Sustainable Use, Management and Reclamation of Soil and Water Research Group, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain.


2 Institute of Plant Biotechnology (IBV), Campus Muralla del Mar, Edificio I+D+I, Universidad Politécnica de Cartagena, 30202, Cartagena, Spain.






Agroforestry systems represent cropping systems in which woody crops are intercropped with alley crops to increase land productivity and enhance the delivery of ecosystem services. Avoiding bare soils in the alleys and cultivation of different annual or perennial species, with shifts in tillage and/or irrigation patterns, will have an influence in organic matter turnover and nutrient cycling, mostly carbon and nitrogen, mediated by soil microbial communities. The ability of the soil to conduct a healthy relation with the microbiome and the crops is one of the most important soil quality indicators. In this study, soil samples from two different case studies where different diversification systems were applied are examined in perspective of ammonia oxidizing (amoA) and denitrifying (nirK and narG) gene abundances through quantitative-PCR assays to assess how nitrogen cycle can be modified by agroforestry systems compared to tree monocultures. The first case study included an almond orchard intercropped weather with Capparis spinosa or Thymus hyemalis. The second case study represented a mandarin orchard intercropped with a rotation of fava bean and vetch/barley or a rotation of several vegetables and vetch/barley. Abundances of amoA, nirK and narG genes significantly decreased in all intercropped systems with respect to monocultures. Thus, the special root-microorganisms and plant-plant interactions in the diversified systems contributed to soil N-cycle by decreasing the functional gene abundances. Decreasing nitrification and denitrification through management is desirable to decrease N losses and increase N fertilizer use efficiency. Thus, agroforestry systems seem more efficient in N turnover than tree monocultures where alleys remain bare most of the year.

How to cite: Ozbolat, O.: How agroforestry systems influence the abundance of nitrogen-cycle contributing microbial genes under Mediterranean conditions?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21485, https://doi.org/10.5194/egusphere-egu2020-21485, 2020.

D1820 |
Dalia López, Francisco Matus, and Carolina Merino

Temperate rain forest soils (>8000 mm yr -1 ) of south of Chile in the East Andes range are
intensively affected by increasing freezing and thawing cycles (FTC) due to increasing
climate variability in the last 20 years. Most of these volcanic forests soils are unpolluted
(pristine) and receive seasonal snow-cover. In spite of pollutant free precipitations, the
snow cover in these ecosystems contains aerosols, nutrients and microorganisms from
circumpolar south west winds. These inputs and FTC generate specific conditions at the
shallow layer at the soil surface for soil microbiology and biochemistry. The objectives of
the study were to compare (micro)biological and chemical properties of topsoil and snow
cover in an pristine forest and after clear-cut. The organic matter mineralization was
monitored in a microcosm experiment to explore the effects of FTC and snow melting on
redox potential and other topsoil parameters. FTC for soil+snow released more CO 2 in
closed forest (81.9 mg CO 2 kg -1 ) than that after clear-cut (20.5 mg CO 2 kg -1 ). Soil texture
and soil organic matter accumulation played a crucial role for organic matter mineralization
and CO 2 fluxes. Gradually increase of temperature after freezing reveled that loamy soils
with certain amount of available C maintain active microbial population that response very
fast to temperature change. Sandy soils with very low C content showed the opposite
results – very slow response of microbial community and CO 2 fluxes. In conclusion,
microbial community structure and functions have distinct transition from snow to the soil
in temperate snow-covered forest ecosystem. FTC showed that different microbial groups

are responsible for organic matter mineralization in soil under forest and clear-cut, because
the pH and redox potential are influenced by snow melting.

How to cite: López, D., Matus, F., and Merino, C.: Effects of snow cover on CO 2 production and microbial composition in a thin topsoil layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22683, https://doi.org/10.5194/egusphere-egu2020-22683, 2020.

D1821 |
Ming Wang

Hummock-hollow microtopography is a common feature in northern peatlands. It
creates microsites of variable hydrology, vegetation, and soil biogeochemistry, thus affect soil C
cycling in peatlands at the local scale. This study investigated effects of microtopography on soil
enzyme (β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG), acid phosphatase (AP)
and peroxidase (PER)) activities and environment variables as well as their relationships in a
typical sedge peatland in Changbai Mountain, northeast of China. Our results showed that the
enzyme activities in the sedge peatland significantly varied across seasons and microtopographical
positions. Soil enzyme activities in hummocks exhibited more obvious seasonal variation than
hollows, with the βG, AP and PER activities presented a distinct valley in summer and the
maximum values occurred in Spring or Autumn. Soil hydrolase (βG, NAG and AP) activities in
hummocks were significantly higher compared to hollows, while soil oxidase (PER enzyme)
activity in hollows was higher than hummocks. The NMDS analysis revealed that the influence
degree of microtopography on the enzyme activities was higher than that of seasonal variation.
Redundancy analysis (RDA) indicated that the variations of soil enzyme activities in the peatland
were related to environmental variables, especially to water table depth (WTD), soil temperature
(ST), SOC, N availability and P availability. Furthermore, correlation analysis showed that the
three hydrolase (BG, NAG and AP) activities were positively correlated with soil TN, SOC and
C/N, and negatively correlated with WTD and TP. On the contrast, the PER activities were
positively correlated with TP, and negatively correlated with ST, SOC and C/N. The present
study demonstrated that small scale topographic heterogeneity created by hummock cause habitat
heterogeneity and thus lead to significant difference of soil enzyme activity between hummock
and hollow in the sedge peatlands. This finding provides further evidence of the importance of
peatland microtopography to C cycling and has direct implications for scaling biogeochemical
processes to the ecosystem level.

How to cite: Wang, M.: The response of soil enzyme activity to seasonal and microtopographical variations in the sedge peatlands in Changbai Mountain, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22531, https://doi.org/10.5194/egusphere-egu2020-22531, 2020.