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SSS4.8

Plant-Microorganism-Soil interactions in the rhizosphere: from chemical, biological, and physical perspectives to an interlinked understanding of processes

The rhizosphere is regarded as the soil compartment with the highest level of nutrient flux through a multitude of interactions between plants, soil, and (micro)biota. Roots and associated (micro)organisms interact with heterogeneous soil environments that provide habitats for biota on various scales. High metabolic activity and nutrient cycling can be observed from single root tips to whole root systems which makes the rhizosphere of central importance for ecosystem functioning.
The main knowledge-gaps in rhizosphere research are related to the difficulty in mechanistically linking the physical, chemical and biological processes, taking place at different scales (nm to cm) in the rhizosphere and to the challenge of upscaling these processes to the scale of the root system and the soil profile. The key for overcoming these knowledge gaps is to understand rates of matter flux, and to link the spatial arrangement of the different interconnected components of the rhizosphere with their temporal dynamics. This requires concerted efforts to combine methods from different disciplines like plant genomics, imaging, soil physics, chemistry and microbiology.
We welcome experimental and modelling studies on rhizosphere functioning that aim at revealing spatial gradients of e.g. functional biodiversity of microorganisms, uptake and release patterns by roots, soil structure modification by root growth (and vice versa) as well as feedbacks between those processes in order to improve our mechanistic understanding of emerging properties like water acquisition, nutrient cycling, plant health, soil structure development and feedbacks among them.

Convener: Evgenia Blagodatskaya | Co-convener: Hannes Schmidt
Presentations
| Tue, 24 May, 11:05–11:50 (CEST), 13:20–14:50 (CEST)
 
Room 0.49/50

Tue, 24 May, 10:20–11:50

Chairpersons: Evgenia Blagodatskaya, Hannes Schmidt

11:05–11:08
Introduction

11:08–11:15
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EGU22-3344
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Highlight
Alexandra Kravchenko et al.

Greater plant diversity facilitates soil C gains, yet the exact mechanisms of this effect are still under intensive discussion. Whether a plant grows in monoculture or in an inter-cropped mixture can affect allocation of plant assimilates, belowground exudation, and microbial stimulation. The goal of this study was to examine the effects of inter-cropping on a previously overlooked aspect of plant-soil interactions, namely, on locations where plant assimilated C is allocated within the soil pore system and its subsequent fate in relation to soil pores. The soil for the study originated from a greenhouse experiment with switchgrass (Panicum virgatum L.) (var. Cave'n'Rock) (SW), big bluestem (Andropogon gerardii Vitman) (BB), and wild  bergamot (Monarda fistulosa L.) (WB) grown in monocultures and in inter-cropped pairs and subjected to species specific C pulse labeling (Kravchenko et al., 2021). Intact soil cores (8 mm Ø) were collected from the experimental pots, subjected to a short-term (10 day) incubation, X-ray computed micro-tomography (μCT) scanning, and soil C micro-sampling "geo-referenced" to μCT images. Results indicated that in the plant systems with demonstrated interplant C transfer soil C was positively correlated with <10 μm Ø pores immediately after plant termination and with 20-80 μmØ pores after the incubation. In the systems without marked interplant C transfer, soil C was positively correlated with 20-30 μm Ø pores, however, the correlations disappeared after the incubation. Soils from the systems with demonstrated belowground C transfer displayed lower losses of root-derived C during incubation than the systems where interplant C transfer was negligible. These differences suggest dissimilarities in the possible mechanisms of adding photoassimilated C to the soil: via mycorrhizal hyphae into small sized pores vs. via roots into mediumsized pores. In the latter case the plant-derived C was quickly lost during subsequent incubation. Our findings indicate that greater losses of plant assimilated C from the soil often reported during comparisons of monocultures with inter-cropped plant mixtures are related not only to monoculture vs. polyculture dichotomy, but to the route of plant C additions to the soil and its localization within the soil pores.

How to cite: Kravchenko, A., Zheng, H., Kuzyakov, Y., and Guber, A.: Inter-plant C Transfer and Associations between Plant-assimilated C Inputs and Soil Pores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3344, https://doi.org/10.5194/egusphere-egu22-3344, 2022.

11:15–11:22
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EGU22-651
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ECS
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Highlight
Olivera Topalović and Stefan Geisen

Soil is a reservoir of a myriad of plant-beneficial to plant-hostile (micro)organisms. Plant-parasitic nematodes (PPN), which contribute to around 15% of annual global yield losses, are particularly important soil-borne pests. Several bio-products based on specific microbial strains with PPN-antagonistic properties have appeared on the market as an alternative to the environmentally harmful chemical pesticides, but the efficiency of these bio-products is usually low in the field. By contrast, we know nothing about the potential and antagonistic mechanisms of complex assemblages of soil microorganisms and of free-living nematodes as the most abundant animals on Earth in regulating PPN damage on plants. Here we present how the microbiome associates with PPN in soil and explore the potential of free-living nematodes to boost the antagonistic effects of these microbiomes. We show that the soil-borne stages of PPN acquire specific microbiomes on their surface and that different factors including the soil type, nematode designation, microbial density and competition affect the outcome of microbial attachment to nematodes. We also show that some of these microbiomes suppress PPN and reduce their root-invasion rate. In addition to a direct antagonism, we demonstrate that some PPN-attached microorganisms are able to trigger pathogen-associated pattern-triggered immunity in plants upon nematode penetration into the roots. We are currently expanding these results by elucidating how the biological action of nematode-antagonistic microbes can be increased in a native soil system that is dominated by free-living nematodes. Together we show the importance of the complexity of soil biodiversity as a potent player in the suppression of PPN and therefore as a potential measure to increase sustainability in agriculture.

How to cite: Topalović, O. and Geisen, S.: Exploring the contribution of free-living nematodes in soil to plant health, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-651, https://doi.org/10.5194/egusphere-egu22-651, 2022.

11:22–11:29
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EGU22-3419
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ECS
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Highlight
Tino Colombi and Arjun Chakrawal

Plant roots are essential for acquiring water and nutrients from soils and constitute a major input source for soil organic matter. Plants invest a significant proportion of the photosynthetically fixed carbon into the growth and maintenance of their root system. The carbon supplied from the shoot fuels both anabolic (i.e., biosynthesis including root growth) and catabolic (i.e., respiration and fermentation) processes in roots. The partitioning of carbon between anabolic and catabolic processes can be expressed as the carbon use efficiency of roots. Root carbon use efficiency determines how much of the total carbon allocated to roots remains in the plant-soil system in the form of root biomass and how much carbon is lost via catabolic pathways. Hence, the carbon use efficiency of roots plays a pivotal yet underexplored role for root growth and associated ecosystem functions such as primary production and carbon sequestration. Here, we present a conceptual framework to assess carbon allocation patterns in plant-soil systems that explicitly accounts for the interactions among root physiology, root trait plasticity, whole plant growth, and soil conditions. Using our framework, we illustrate how soil conditions such as soil aeration, soil moisture, and soil strength interfere with root carbon use efficiency and carbon allocation patterns between different plant organs. We show how edaphic stress and the resulting decrease in root carbon use efficiency may limit root growth, thereby reducing whole plant productivity and inputs of organic matter to soil. Moreover, we provide theoretical and experimental evidence that the plasticity of root structural traits such as cortical cell size and cortical cell number enables plants to maintain their growth upon decreased carbon use efficiency of roots. This suggests that root trait plasticity is a key mechanism that allows plants to adjust to edaphic stress and heterogenous soil environemnts. We, therefore, propose that the framework presented here may provide new insights into the complex interactions between root physiology, soil (micro-)environments, and associated soil functions.

How to cite: Colombi, T. and Chakrawal, A.: The role of root physiological and structural plasticity for carbon allocation in plant-soil systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3419, https://doi.org/10.5194/egusphere-egu22-3419, 2022.

11:29–11:36
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EGU22-5201
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ECS
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Highlight
Mutez Ali Ahmed et al.

Although the impact of root hairs (RHs) in nutrients uptake is well documented, their role in water uptake and drought tolerance remains controversial. Maize wild type and its hair-defective mutant (rth3) were grown in two contrasting soil textures (sand and loam). We used a novel root pressure chamber to measure the relation between transpiration rate (E) and leaf xylem water potential (ψleaf_x) during soil drying. The hypotheses were: 1) RHs extend the root-soil contact and reduce the decline in ψleaf_x at high E in dry soils; 2) the impact of RHs is more pronounced in sand; and 3) mutants partly compensate for the lack of RHs by producing longer and/or thicker roots. The ψleaf_x(E) relation was linear in wet conditions and became nonlinear as the soils dried. The nonlinearity of the relation occurred more abruptly and at less negative matric potentials in sand (ca. -10 kPa) than in loam (ca. -100 kPa). At slightly more negative soil matric potentials, soil hydraulic conductance became smaller than root hydraulic conductance in both soils. Both genotypes exhibited ca. 1.7 times longer roots in loam, but 1.6 times thicker roots in sand. No differences were observed in the ψleaf_x(E) relation and active root length between the two genotypes. Root hairs had no contribution to soil-plant hydraulics in maize in both sand and loam. These results suggest that the role of root hairs cannot be easily generalized across species and the response of root hydraulics to soil drying is remarkably affected by soil textures.

How to cite: Ahmed, M. A., Gaochao, C., Duddek, P., Abdalla, M., and Carminati, A.: Advances in understanding the efficacy of root hairs in water uptake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5201, https://doi.org/10.5194/egusphere-egu22-5201, 2022.

11:36–11:43
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EGU22-7241
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ECS
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Chaoqun Wang et al.

Biogeochemical cycles of phosphorus (P) and iron (Fe) are tightly intertwined, especially in highly weathered and acidic subtropical and tropical soils rich in ferric Fe (Fe(III))oxides. In low-redox and P-deficient paddy soils, the quantitative contribution of the reductive dissolution of Fe(III)-bound P (Fe-P) to the demands of rice plants (Oryza sativa L.) and microorganisms remains unclear. We hypothesized that Fe(III) reductive dissolution can cover the P demand of microorganisms but not of rice plants during the initial growth stages, when P demand is high but the root system is still limited. We grew pre-germinated rice plants for 33 days in flooded rhizoboxes filled with a paddy soil of poor P availability. 32P-labeled orthophosphate sorbed to ferrihydrite (80 kg ha-1) was supplied either (1) in polyamide mesh bags (30 μm mesh size) to prevent roots from directly mobilizing Fe-P (Pellets-mesh bag treatment), or (2) in the form of pellets directly to the soil without mesh bags to enable roots’ accessing the Fe-P (Pellets-no-mesh bag treatment). With the application of Fe-P directly to the soil, P was more available resulting in the increases in microbial biomass carbon (MBC) by 18–55% and nitrogen (MBN) by 4–108% in rooted soil as compared to the pellet not available to roots directly. The maximum enzyme activities (Vmax) of phosphomonoesterase and β-glucosidase followed this pattern. During rice root growth, MBC and microbial biomass phosphorus (MBP) in both rooted and bottom bulk soil gradually decreased by 28–56% and 47–49%, respectively. In contrast to our hypothesis, the contribution of Fe-P to MBP strongly decreased from 4.5% to almost zero during 10–33 days after rice transplantation, while Fe-P compensated up to 16% of the plant P uptake 33 days after rice transplantation, thus outcompeting microorganisms.

How to cite: Wang, C., Dippold, M., Guggenberger, G., and Dorodnikov, M.: Can ferric iron reduction in paddy soils compensate phosphorus limitation of rice plants and microorganisms?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7241, https://doi.org/10.5194/egusphere-egu22-7241, 2022.

11:43–11:50
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EGU22-12193
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ECS
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Chris McCloskey et al.

While rhizosphere priming effects are well-documented under laboratory and controlled-environment conditions, their significance in undisturbed systems under field conditions is less clear. This is in part because it is impracticable to measure rates of rhizodeposition in the field with high resolution over a substantial period. We propose that photosynthesis, closely linked to rhizodeposition, can be used as a proxy for plant root activity.

We have used a field system containing 24 0.8-m diameter, 1-m deep lysimeters holding naturally-structured soil monoliths from two contrasting C3 soils sown with a C4 grass (Bouteloua dactyloides) to measure carbon (C) fluxes at a high temporal resolution, exploiting isotopic differences to allow partitioning of plant and soil fluxes. These fluxes are coupled to high-resolution measurements of soil temperature and moisture, alongside atmospheric temperature and solar radiation. This system has allowed measurement of both ecosystem resolution and net ecosystem exchange, and the partitioning of respiration between plant and soil sources using stable isotope methods. Using this system we have generated a dataset of measured and modelled respiration and photosynthesis fluxes over two years.

Our dataset has revealed clear seasonal and diurnal patterns in plant and soil fluxes. We have assessed the relationship between diurnal patterns in soil respiration and potential drivers, and examined whether model estimates of soil respiration are improved by the inclusion of photosynthesis as an explanatory variable alongside soil moisture and temperature. We found a significant positive relationship between photosynthesis and soil respiration, and inclusion of photosynthesis improves models of soil respiration. This is best explained by rhizosphere priming enhancing soil C turnover.

How to cite: McCloskey, C., Kirk, G., Otten, W., and Paterson, E.: Tight coupling between photosynthesis and soil carbon turnover indicative of rhizosphere priming in the field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12193, https://doi.org/10.5194/egusphere-egu22-12193, 2022.

Tue, 24 May, 13:20–14:50

Chairpersons: Hannes Schmidt, Evgenia Blagodatskaya

13:20–13:30
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EGU22-1208
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solicited
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Highlight
Maire Holz and Johanna Pausch

Soil C priming is a short-term change in the turnover of soil organic matter caused by the addition of easily available organic C to the soil. The increase in SOM decomposition during priming is likely to affect not only C- but also gross N mineralization from SOM because large amounts of soil N is stored in SOM that is decomposed during priming. In order to assess whether soil C priming results in an increase in gross and mineralization and finally in enhanced plant N availability and uptake, we searched the literature for studies relating soil C priming to soil N cycling. In order to assess the effect of soil priming on soil N cycling we included studies quantifying soil C priming (PE) and gross N mineralization (GNM) in plant systems and in incubation setups. Secondly, we searched for studies measuring GNM in dependence to addition of C to the system. The third data set comprised studies, quantifying PE and the % of soil N derived N uptake as well as total N uptake of plants. Finally we included studies that quantified soil priming and enzyme activities in the respective soil samples. In order to be able to compare PE to GNM, % of soil N derived N uptake and soil enzyme activities respectively, we calculated the excess of GNM, % of soil N derived N uptake and soil enzyme activities by subtracting the parameter values of the control from the treatment values. We found a significant positive relation between soil C priming and GNM for studies with plants (R2=0.21) indicating that soil priming caused by root exudation increased soil N mineralization. In agreement with this, activities of enzymes related to the N cycle were positively related to priming (p=0.09), though, due to the small number of studies, the enzyme results must be interpreted with caution. In contrast to plant studies, the relation between soil C priming and GNM was significantly negative for incubation studies (R2=0.06). These contrasting results for plant and incubation studies indicate that incubation studies might not adequately reflect processes occurring in the rhizosphere. It is possible that plants attract particularly N mineralizing microbes for example by exudation of signaling compounds, a process that would not be reflected in incubation studies. We also found a significant positive relation between soil C priming and the % of soil N derived N uptake by plants (R2=0.56) and total plant N uptake (R²=0.21) indicating that at least part of the N mineralized during priming was available to, and taken up by the plants. In conclusion, the results of our meta-analysis indicate that rhizosphere C priming positively feeds back to plant N nutrition by causing increased N mineralization in the rhizosphere that facilitates plant N uptake.

How to cite: Holz, M. and Pausch, J.: Rhizosphere carbon priming: a plant mechanisms to enhance soil nitrogen accessibility?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1208, https://doi.org/10.5194/egusphere-egu22-1208, 2022.

13:30–13:37
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EGU22-4940
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ECS
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Hao Chen et al.

Nitrogen (N) lost from the agricultural field as leachate and nitrous oxide (N2O) gas causes water pollution, accelerates global warming and decreases agricultural N use efficiency. Soil amendments with straw and nitrification inhibitors are used to combat these problems by increasing microbial N immobilization and suppressing nitrification, respectively. The potential N competition between soil microorganisms and subsequent crops under the incorporation of pre-crop straw can be moderated by seasonal temperature variation, but this interfering factor is insufficiently studied. A 99-days mesocosm experiment that simulated the seasonal temperature variation was conducted, to investigate the effects of wheat straw amendment (WSA) and nitrification inhibitor (NI) on the competition for soil N between soil microbes and winter barley under three N fertilization levels (N0 as control, N1 as low N fertilizer, N2 as high N fertilizer), and N lost from soil as N2O and leachate. Strong mineralization was detected after the cooling-warming cycle, which happens in early spring frequently in Germany. Soil NH4+ of all treatments were increased by 34-138 % and soil NO3 of N2 levels were increased by 42-133 % during this process, providing mineral N for barley growth but also imposing the risk of N losses. Straw incorporation stimulated immobilization of N by soil microorganisms, increased soil microbial biomass C and N by 45-123 % till the end of experiment, thus decreased the total N lost by 41 % on average by decreasing N leaching (43-91 %), NI mitigated N2O emission by 40 % in N2 levels, the combination of WSA and NI could mitigate N losses and global warming. However, the immobilized N under WSA was not remineralized timely during barley growth, therefore, barley shoot biomass (by 23-34 %) and N (by 28-46 %) decreased in N0 and N1 fertilizer levels, the shoot nitrogen use efficiency (NUE) decreased in N1 (by 53 %) and N2 (by 30 %) fertilizer levels. Considering the strong (long term) N immobilization induced by straw, we suggest applying straw and N fertilizer separately to avoid N competition between soil microorganisms and crops.

How to cite: Chen, H., Blagodatsky, S., Rosinger, C., Reichel, R., Li, B., Kumar, A., Rothardt, S., Luo, J., Brüggemann, N., Kage, H., and Bonkowski, M.: Straw amendment as a double-edge sword controlling N losses and immobilization over winter cooling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4940, https://doi.org/10.5194/egusphere-egu22-4940, 2022.

13:44–13:51
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EGU22-6207
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ECS
Chaturanga Bandara et al.

Correct image segmentation is the pre-requisite for identifying classes of objects in microscopic datasets in order to determine relationships between them. We recently reported on a novel embedding protocol for rhizosphere samples based on the hydrophilic acrylic LR-white resin.1 X-ray µ-CT data measured on such embedded samples shows only minimal contrast between root and resin which renders segmentation of these data is difficult or even impossible using common methods based on thresholding of histograms or detection of edges.

Here, we demonstrate how this barrier can be overcome using deep learning of convolutional neural networks based on U-Net architecture.2 We show successfully segmented roots from resin, where classical machine learning approach Random Forest was not successful in our attempts. Firstly, the embedded samples were characterised by X-ray µ-CT and cut by a water-jet. Roots on the exposed 2D section were identified using epifluorescence and helium ion microscopy. The analysed 2D image plane was then correlated with the X-ray µ-CT data for accurate classification of training 3D image pixels. With a given input image (in this case a greyscale micrograph of resin embedded soil), a trained U-Net model with minimal labelled pixels, semantically segmented the X-ray data set showing roots, soil and pores. Using multiple deep learning algorithms, the U-Net was the most promising architecture to segment rhizosphere X-ray µ-CT and we show the different input parameters which can improve the segmentation process. The deep learning experiment was carried out with the ORS dragonfly image processing software. We show an accurate and fast approach that can be used to segment LR-white embedded rhizosphere X-ray CT data to roots-soil-and pores for further correlative microscopy analysis to interpret complex rhizosphere processes in the future.

Author Contributions: CB embedded the soil samples and trained the deep learning algorithms, Eva Lippold acquired and reconstructed CT data, Matthias Schmidt acquired helium ion microscopy data and discussions on improving data segmentation.

Acknowledgement: This work was conducted within the framework of the priority program 2089, “Rhizosphere spatiotemporal organization-a key to rhizosphere functions” funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number RI-903/7-1. Funding is acquired by Niculina Musat and Hans Richnow. Authors acknowledge the analytical facilities of the Centre for Chemical Microscopy (ProVIS) at the Helmholtz Centre for Environmental Research, Leipzig, Germany, which is supported by the European Regional Development Funds (EFRE - Europe funds Saxony) and the Helmholtz Association. Authors thank Object Research Systems for providing a free Dragonfly commercial licence for use in this work.

References

  • Bandara, C. D.; Schmidt, M.;  Davoudpour, Y.;  Stryhanyuk, H.;  Richnow, H. H.; Musat, N., Microbial Identification, High-Resolution Microscopy and Spectrometry of the Rhizosphere in Its Native Spatial Context. Frontiers in Plant Science 2021, 12 (1195).
  • Ronneberger, O., Fischer, P., Brox, T. U-Net: Convolutional Networks for Biomedical Image Segmentation 2015.

How to cite: Bandara, C., Lippold, E., and Schmidt, M.: A Novel Deep Learning Approach for Complete Segmentation of Roots, Soil and Pores in X-ray Tomography Data of Acrylic Resin Embedded Rhizosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6207, https://doi.org/10.5194/egusphere-egu22-6207, 2022.

13:51–13:58
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EGU22-10091
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ECS
Maik Lucas et al.

Carbon inputs into soil take place primarily through rhizodeposition and root decay. Spatial inaccessibility of organic matter to organisms, i.e., physical protection, is a key factor for stabilizing such carbon in soils. Protection is governed by soil structure, i.e., the spatial arrangement of solids and voids, thus, differences in root distribution and in their rhizosphere physical properties influence carbon sequestration. This structure, in turn, is affected by roots, which explore the soil by rearranging existing soil particles and thus may compact the rhizosphere, especially, when the soil does not contain a well connected macropore system.

Here we conducted a split root experiment to determine how plant roots grow into soil depending on the structure they encounter and how this affects the fate and distribution of SOM. Soil cores, with four different structures, either intact or destroyed by sieving, from monoculture switchgrass and prairie systems were incorporated into containers planted with Panicum virgatum L. (Switchgrass) and Rudbeckia hirta L. (Black-eyed Susan), plants with contrasting root characteristics.

The cores were X-ray µCT scanned before and after plant growth, enabling explorations of the feedback interactions between roots and soil structure through analysis of pore size distributions, root distributions, and rhizosphere physical properties. To assess the fate of the plant-derived C, the plants were labelled by 14CO2; and presence of 14C in roots, rhizosphere, and rhizoplanes was examined. The cores were incubated for 30 days and 14CO2 and CO2 respiration was measured. Soil solution from pores of different sizes was collected by centrifugation and analyzed for 14C. This enabled to investigate the fate and distribution of carbon in correlation to the interactions of roots and structure derived from image analysis.

Results suggest root soil contact as a universal driver that stimulates greater allocations of photo assimilated C (14C) to roots and to their immediate surroundings. When roots were growing into the dense soil matrix, greater 14C was detected within the roots, rhizosphere, and rhizoplane. In addition, more 14C was found as DOC. Although most of this carbon was released fast, in total more 14C also remained in the soil after the 30 day incubation. While the majority of roots from Black-Eyed-Susan grow into the dense soil matrix, Switchgrass roots, in contrast, preferentially grew into macropores (especially into switchgrass created biopores). When that happened, roots and rhizosphere had low quantities of freshly assimilated C (i.e., 14C), yet, surprisingly more 14C was found at greater distances from the roots in microsamples, which may be linked to mycorrhizae.

The study is founded in part by the NSF DEB Program (Award # 1904267) and by the Great Lakes Bioenergy Research Center (Award # DE-SC0018409).

How to cite: Lucas, M., Guber, A., and Kravchenko, A.: The soil structure roots encounter affects root activity and the fate of carbon in the rhizosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10091, https://doi.org/10.5194/egusphere-egu22-10091, 2022.

13:58–14:08
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EGU22-4428
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solicited
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Highlight
Andrey Guber and Alexandra Kravchenko

Colloids are known to facilitate transport of a broad variety of chemicals and microorganisms in soils. Extracellular hydrolytic enzymes, produced by many soil microorganisms and plant roots, have high affinity to clay and silt particles constituting soil mineral colloids (SMC). Therefore, those enzymes can be released jointly with colloids from soil matrix during high water flow events and transported convectively attached to the colloids carried by the water flow. At the same time hydrolytic enzymes are often considered as free-mobile proteins with a self-propelled diffusion mechanism. Current literature lacks any information on enzyme transport in soils, and it is not clear whether enzymes are transported and, if so, whether they are transported in free- or colloid-associated form. Studying enzyme transport in soils is challenging due to infeasibility of their enumeration in soil solutions and suspensions, differences in activity of free and colloid-associated enzymes, the influence of colloid size and composition, pH and ionic strength in the colloidal suspensions on the enzyme activity. This study presents the first experimental evidence of enzyme transport in soils facilitated by SMC in sandy, loamy and two sandy-loam soils. Its results suggest from 50 to 80% of transported hydrolytic enzymes are associated with transport of coarse SMC. The remaining 20 to 50% of enzymes are likely transported by organic colloids and fine SMC (Ø < 1 mm). The ionic strength played a dual role in the joined enzyme and colloidal transport: (1) by affecting dispersion and release of SMC colloids from soil; and (2) modifying optimum pH of enzymatic activity in released colloidal suspensions. Our results provided insights into factors governing plant-soil-microbial interactions through the transport and activity of hydrolytic enzymes. Support for this research was provided by the NSF LTER Program (DEB 1027253) at the Kellogg Biological Station, by USDA NC1187 project, by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award Number DE-SC0018409.

How to cite: Guber, A. and Kravchenko, A.: Colloid-facilitated transport of hydrolytic enzymes in soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4428, https://doi.org/10.5194/egusphere-egu22-4428, 2022.

14:08–14:15
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EGU22-5070
Zeeshan Ibrahim et al.

The labile organic compounds provided by roots remove the nutrient limitation and thus stimulate microbial activity and facilitate biochemical process rates into the soil, forming microbial hotspots. However, the extent of root effect and the functional properties of microorganisms are dependent on the root morphology and can vary with the distance from the root. The objective of this study was 1) to investigate whether biochemical processes mediated by hydrolytic enzymes that are involved in C, N, and P cycling, are overlapping in the rhizosphere hotspots or whether they are hotspot-specific and 2) to evaluate the effect of plant genotype on the kinetic parameters in the hotspots. We identified the hotspots from two maize (Zea mays L.) plant genotypes (wild type and root hair deficient mutant) by applying zymography of β-glucosidase, acid phosphatase, and leucine aminopeptidase. Soil samples were taken at 1, 1-2, and >2mm from the hotspots epi-centrum.  The Vmax of β-glucosidase was 1.7 times higher at a 1mm distance from roots than 1-2mm and was 4 times higher than >2mm distance. The Vmax of β-glucosidase was significantly higher in the wild type versus root hair-deficient mutant at a 1mm distance from the root. Acid phosphatase and leucine aminopeptidase in both 96-well microplate and image processing indicated higher enzymes activity at the epi-centrum than outside the hotspot. In general, the microplate assay demonstrated similar trends with soil zymography, but the latter ensured better statistical significance. The Km values indicated similar enzyme systems within and outside the hotspots across the plant roots. The Km values suggested that root hair deficiency was compensated by higher affinity of enzymes acquiring C, N and P for the plant. In contrast, wild type of maize attracts microorganisms with broader spectrum of functional traits compared to root hair-deficient mutant. This work was conducted within the framework of the priority program 2089 “Rhizosphere spatiotemporal organization – a key to rhizosphere functions”, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number: 403664478. Seeds of the maize were provided by Caroline Marcon and Frank Hochholdinger (University of Bonn).

Keywords: Zymorgaphy, Enzyme activity, Enzyme affinity

How to cite: Ibrahim, Z., Ghaderi, N., and Blagodatskaya, E.: Enzyme activity gradients across the maize roots, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5070, https://doi.org/10.5194/egusphere-egu22-5070, 2022.

14:15–14:22
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EGU22-7128
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ECS
Negar Ghaderi et al.

Enzymes are secreted by microbial cells into the soil to catalyze the acquisition of carbon or nutrients like nitrogen and phosphorus from soil organic matter. Apart from microorganisms and soil fauna, roots also secrete enzymes to mobilize nutrients from the soil nutrient pool. Thus, living plants and microorganisms are considered the main sources of soil enzymes in agroecosystems. To understand how exo-enzymes are distributed in soil microhabitats, and whether enzymatic activity is higher in soil solution or on particle surfaces, we visualized enzymatic activity at the corresponding scale. Visualization of enzymatic activity links microbial functioning to localization in heterogeneous soil habitats. To assess enzymatic reactions in soil at the microscopic level, we developed a micro-zymography approach based on fluorogenically-labeled substrate (phosphomonoesterase) in the rhizosphere soil of Zea mays L. For this, first we compared different fixatives required to prevent sample drying and found super transparent silicon as the most appropriate one. Then we evaluated micro-zymography i) on individual soil aggregates, ii) on thin layers of aggregates (≈ 500 µm) to assess the dynamics of phosphomonoesterase activity, and iii) on maize roots under laser scanning microscope. The results demonstrated that the main fluorescence signal shifted from the soil solution to the interface between the soil solution and aggregates within 30 min after substrate addition and was finally only detectable on the surface of a few aggregates. This was probably due to higher microbial abundance and enzymatic activity on the soil aggregates compared to the soil solution. The enzymatic activity appeared patchy on the aggregate surfaces indicating heterogeneous distribution of microorganisms. Similarly, a patchy distribution of enzymatic activity was detected on maize root surfaces. This work was conducted within the framework of the priority program 2089 “Rhizosphere spatiotemporal organization – a key to rhizosphere functions”, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number: 403664478. Seeds of the maize were provided by Caroline Marcon and Frank Hochholdinger (University of Bonn).

Keywords: exo-enzyme, micro-zymography, fixative

How to cite: Ghaderi, N., Schmidt, H., Schlüter, S., Banfield, C., and Blagodatskaya, E.: Development of micro-zymography: microscopic visualization of enzymatic activity in soil aggregates and Zea mays L. root, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7128, https://doi.org/10.5194/egusphere-egu22-7128, 2022.

14:22–14:29
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EGU22-9125
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ECS
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guoting shen et al.

The combination of two non-destructive 2D imaging methods: amino-mapping and zymography have been developed and applied to monitor organic nitrogen allocation in the rhizosphere of Zea mays L.  under contrasting nutrient treatments. Amino-mapping was based on the fluorescent reaction of o-phthaldialdehyde and β-mercaptoethanol enabling to estimate the content of labile organic N, playing an important role in soil nitrogen cycling. Amino-mapping was coupled with leucine-aminopeptidase zymography to quantify the amino-N release in the rhizosphere of maize grown under climate chamber conditions for 3 weeks. The combination of the two approaches enabled visualization of organic N hotspots either distinctly separated or overlapped with the hotspots of enzymatic activity. This work was conducted within the framework of the priority program 2089 “Rhizosphere spatiotemporal organization – a key to rhizosphere functions”, funded by German Research Foundation (DFG – Project number: 403664478). Seeds of the maize were provided by Caroline Marcon and Frank Hochholdinger (University of Bonn).

How to cite: shen, G., Khosrozadeh, S., Ghaderi, N., Guber, A., and Blagodatskaya, E.: Mapping the organic N distribution in the rhizosphere of maize, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9125, https://doi.org/10.5194/egusphere-egu22-9125, 2022.

14:29–14:36
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EGU22-12700
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ECS
Claudio Cacace et al.

In an era characterized by land degradation, climate change, and a growing population, ensuring high-yield productions with limited resources is of utmost importance. In this context, the use of novel soil amendments and the exploitation of plant growth-promoting microorganism’s potential are considered promising tools for developing a more sustainable primary production. In fact, several soil properties are positively influenced after the addition of organic amendments, as the organic matter content that represents a limiting factor for the growth and production of crops in the Mediterranean basin. In this regard, bread and bakery products represent up to 20% of the total daily food waste produced, and only a little quantity is reused, mainly to feed livestock. In this study, a bioprocessed wasted bread, obtained by an enzymatic treatment coupled with fermentation using a selected lactic acid bacterium, together with unprocessed wasted bread were used as amendments in a pot trial, with and without plants. An integrated analytical plan aimed at assessing i) the modification of the physicochemical properties of a typical Mediterranean alkaline agricultural soil, and ii) the plant growth-promoting effect on escarole (Cichorium endivia var. Cuartana), used as indicator crop, was carried out. Compared to the unamended soils, the use of biomasses raised the soil organic carbon content (up to 37%) and total nitrogen content (up to 40%). Moreover, the lower pH and the higher organic acid content, especially in bioprocessed wasted bread, determined a major availability of micronutrients in amended soils. In contrast, the availability of P was reduced by the treatments. The escaroles from pots amended with raw and bioprocessed bread had a number of leaves 1.7- and 1.4-fold higher than plants cultivated on unamended pots, respectively. In addition, the yield of escarole resulted 1.95 and 1.70 times higher in the amended pots with raw and bioprocessed bread, respectively, than control soils. Therefore, no apparent phytotoxicity has been observed, confirming the possible re-utilization of such residual biomasses as agriculture amendments. Finally, since lactic acid bacteria cause an acidification of biomasses, the latter are suitable for the application as alkaline soil amendment through beneficial effects on the bioavailability of several nutrients.

How to cite: Cacace, C., Rizzello, C. G., Verni, M., Brunetti, G., De Mastro, F., Traversa, A., and Cocozza, C.: Reuse of wasted bread, bioprocessed and not, as soil amendment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12700, https://doi.org/10.5194/egusphere-egu22-12700, 2022.

14:36–14:43
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EGU22-7526
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ECS
Vusal Guliyev et al.

Expanding the use of environmentally friendly materials to protect the environment is one of the key factors in maintaining a sustainable ecological balance. Polybutylene succinate (PBS) and polybutylene succinate-co-adipate (PBSA) are considered the most promising biobased and biodegradable plastics for the future with a high number of applications. We used stable isotope techniques to partition plastic- and soil-originated C in the CO2 released in the course of PBSA plastic decomposition in the soil as dependent on nitrogen availability. Our 90 days laboratory experiment was conducted using a Haplic Chernozem soil from the conventional farming plot of the Global Change Experimental Facility (GCEF), Bad Lauchstädt, Central Germany. The experiment was designed as 4 treatments: two controls (non-amended soil and soil amended with (NH4)2SO4) and two plastic amendments (with (PSN) and without (PS) N). Nitrogen facilitated plastic decomposition by 6 weeks, increased the amount of decomposed plastic by 10% and reduced the priming effect by 26% during the experiment.

How to cite: Guliyev, V., Tanunchai, B., Udovenko, M., Glaser, B., Purahong, W., and Blagodatskaya, E.: Decomposition of a bio-based plastic in soil: CO 2 source partitioning approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7526, https://doi.org/10.5194/egusphere-egu22-7526, 2022.

14:43–14:50
Discussion