SSS4.7

Copper-based fungicides are commonly applied in vineyards to control fungal diseases that can severely affect grapevine productivity. Continuous application of this type of fungicides contributes to Cu accumulation in surface horizons of the soil, which can generate toxicity problems in plants, regardless of being an essential nutrient. Several strategies have been proposed to immobilize or counteract the effect of soil contaminants, such as plant inoculation with arbuscular mycorrhizal fungi (AMF). However, depending on the element concentration, this may not be sufficient to avoid its excessive accumulation in belowground and/or aboveground organs. Since Fe is known to have an antagonistic interaction with Cu in plants, Fe application, as an amendment, in vineyard soils, could be a good strategy to avoid excessive Cu uptake by grapevines growing in Cu-contaminated soils. However, little information is available on the combined effects of both strategies.

In order to reveal the possible beneficial effects of plant mycorrhization and Fe application in Cu-contaminated soils on grapevine growth and nutrition, a mesocosm experiment was established under controlled conditions. Two-year-old plants, previously inoculated or not with two different AMF, were grown in pots filled with 6.5 kg of an Arenosol collected from a wine-growing region. These plants were subjected to three soil treatments: 1) soil contamination with Cu, where the grapevines were watered with a solution containing 5.89 mg/L CuSO₄ to ensure that the soil in each container reached 300 mg Cu/kg; 2) soil contamination with Cu + Fe addition, where the plants were watered with a solution that contained the same amount of CuSO₄ plus 0.38 mg/L of FeNaEDTA·3H₂O to achieve 100 mg of Fe/kg soil; and 3) non-contaminated soil watered with deionized water. Four months later, at the end of the growing season, plant vegetative growth as well as leaf and root nutrient contents were analyzed.

Grapevines inoculated with AMF demonstrated a good level of tolerance to high Cu concentrations in soil, as they presented significantly higher root biomass than non-inoculated plants and Cu was mainly accumulated in the roots avoiding its translocation to the aerial part. However, when the Cu-contaminated soil was amended with Fe, a significant decrease was observed in root biomass in all mycorrhizal inoculation treatments and Cu was accumulated in grapevine leaves. Contrastingly, Fe application helped to avoid the excessive increase of Mn concentrations in leaf and roots that is commonly induced in Cu contaminated soils, which can be detrimental for grapevine growth.

These results demonstrated that mycorrhizal inoculation is a suitable strategy to promote grapevine growth in Cu-contaminated soils. However, special attention needs to be taken when applying amendments to correct Cu contamination, as the mycorrhizal status of plants may alter the expected outcome.

How to cite: Nogales, A., S. Santos, E., Victorino, G., Viegas, W., and Abreu, M. M.: Mycorrhizal inoculation and application of Fe correction in the soil for ameliorating grapevine performance in a copper-contaminated soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4254, https://doi.org/10.5194/egusphere-egu21-4254, 2021.

Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.

We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.

We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 µm d^-1 at 20% volumetric water content.

We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.

We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.

How to cite: Bitterlich, M. and Pauwels, R.: Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4564, https://doi.org/10.5194/egusphere-egu21-4564, 2021.

Alkaline Fe ore tailings are by far one of the most challenging environmental issue facing the global mining industry, which is ranked 4^th globally in terms of their discharge volumes in storage dams. These tailings possess poor physical structures and adverse chemical properties (e.g., alkaline pH and deficiencies of organic carbon and nutrients) and it is hard for sustainable colonization of plants and microbial communities. Eco-engineering tailings into soil-like substrate in situ is a promising technology to achieve sustainable rehabilitation of tailing landscape. The formation of water stable aggregates (WSA) in tailings primed with eco-engineering inpiuts (e.g., plant biomass organic matter and fertilisers) is indicative of the first milestone of soil formaiton, resulting from bio-geochemically driven mineral weathering and cementation. WSAs are basic physical units underpinning soil structure and functions, such as the porosity and hydraulic conductivity, gas exchange and water retention, biological activities of microbes and roots. The further development and evolution may be enhanced by Arbuscular mycorrhizal (AM) fungi associated with plants colonising infertile soil (such as tailing-soil), because of their role in generating organic cements and organo-mineral interactions. Our previous study found that AM fungi were present in the Fe ore mine tailing site, associated with colonising native plants. In the present study, we have investigated the role of AM symbiosis (Glomus spp. in association with Sorghum spp.) in aggregate formation and organic matter sequestration in Fe ore tailings eco-engineered with organic matter amendment and pioneer plant colonization. The results showed that AM fungi formed symbiotic association with Sorghum spp. plant roots (with mycorrhizal colonization intensity above 80%) in the eco-engineered tailings. Quantitatively, AM symbiosis enhanced the formation of micro-aggregates (53~250 um) rather than macro-aggregate aggregates (250 um~2000 um) formation, which may be partially due to the direct role of extra-radical mycelium as revealed by FE-SEM analysis. Qualitatively, AM symbiosis increased the amount of organic carbon and nitrogen associated with mineral particles in the macro-aggregates. Those organic carbon associated with minerals was found to be rich in carboxyl C and alkyl C, as revealed by synchrotron based C 1s X-ray absorption near edge structure (NEXAFS, conducted in Australia Synchrotron) and the Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra. Overall, the study revealed the role of AM fungi in advancing the formation of microaggregates and increasing the sequestration of organic C and N in macroaggregates in the eco-engineered Fe ore tailings. These suggest that AM fungi inoculum be added to pioneer plants to not only enhance plant growth via improved nutrient and water acquisition, but also to advance aggregate formation and quality via increased organic C and N sequestration with impacted mineral particles.

How to cite: Li, Z., Wu, S., and Huang, L.: Arbuscular Mycorrhizal symbiosis enhances aggregate formation and organic matter sequestration in alkaline Fe ore tailings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4658, https://doi.org/10.5194/egusphere-egu21-4658, 2021.

Since industrialization, the global average temperature increases with far reaching consequences for the world climate. One phenomenon is the current occurrence of more heavy and long droughts in Middle Europe, which lead to extensive tree die-off and shows that we need a better understanding of the forest-soil ecosystem in times of climate change.

Within the interdisciplinary Kranzberg Roof Experiment, we study the drought resistance and drought recovery of mature Norway spruce (Picea abies) and European beech (Fagus sylvatica). The trees experienced a rainfall exclusion for five years during the vegetation period and were rewetted by drip irrigation in summer 2019. Our interest focuses in the functional role of ectomycorrhizal and overall fungal communities on tree drought resistance and recovery. Particularly, we hypothesized the rewetting event will lead to a shift in community structure because of steeply rising water and nutrient availabilities.

To get insights to the development of the fungal communities right after the rewetting period, we sequenced the fungal ITS2 region of fine root DNA extracts. The roots were taken from soil cores before and at several time-points after irrigation.

We found that the fungal communities stayed quite similar to each other during the time-frame of recovery we investigated (84 days), while the amount of new root tips strongly increased directly after the rewetting. Surprisingly, the organic material which had accumulated as it was not degraded during the years of drought, did not lead to a shift in community composition. In particular, there were no changes in the relative amounts of saprotroph fungi in the phase after the rewetting.

Therefore, root fungal communities – the interface between trees and soil – seemingly did not experience a strong pressure to adapt their composition to the new condition, which matches their resistant behavior during the long drought phase before (cf. abstract 2937).

How to cite: Danzberger, J., Werner, R., Weikl, F., and Pritsch, K.: Unperturbed root fungal communities in a temperate forest recovering from five years of reoccurring droughts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6334, https://doi.org/10.5194/egusphere-egu21-6334, 2021.

Plant roots are usually colonized by various arbuscular mycorrhizal (AM) fungal species, which vary in morphological, physiological, and genetic traits. This colonization constitutes the mycorrhizal nutrient uptake pathway (MP) and supplements the pathway through roots. Simultaneously, the extraradical hyphae of each AM fungus is associated with a community of bacteria. However, whether the community structure and function of the microbiome on the extraradical hyphae differ between AM fungal species remains unknown. In order to understand the community structure and the predicted functions of the microbiome associated with different AM fungal species, a splitroot compartmented rhizobox cultivation system, which allowed us to inoculate two AM fungal species separately in two root compartments, was used. We inoculated two separate AM fungal species combinations, (i) Funneliformis mosseae and Gigaspora margarita and (ii) Rhizophagus intraradices and G. margarita, on a single root system of cotton. The hyphal exudate-fed, active microbiome was measured by combining ¹³C-DNA stable isotope probing with MiSeq sequencing. We found that different AM fungal species, which were simultaneously colonizing a single root system, hosted active microbiomes that were distinct from one another. Moreover, the predicted potential functions of the different microbiomes were distinct. We conclude that the arbuscular mycorrhizal fungal component of the system is responsible for the recruitment of distinct microbiomes in the hyphosphere. We found that arbuscular mycorrhizal fungi cocolonizing on single plant roots recruit their own specific microbiomes, which should be considered in evaluating plant microbiome form and function. Our findings demonstrate the importance of understanding trophic interactions in order to gain insight into the plant-AM fungus-bacterium symbiosis

How to cite: Zhou, J., Chai, X., Zhang, L., George, T., Wang, F., and Feng, G.: Different Arbuscular Mycorrhizal Fungi Cocolonizing on a Single Plant Root System Recruit Distinct Microbiomes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9524, https://doi.org/10.5194/egusphere-egu21-9524, 2021.

Soil organic matter (SOM) is any material produced by living organisms at various stages of decomposition. SOM enhances soil fertility and quality and influences soil’s ability to fight against soil-borne diseases. Atmospheric CO₂ sequestration into SOM through improved agricultural management practices has been suggested to be a cost effective way to mitigate climate change.

The build-up of SOM is largely regulated by soil microbial activity. Soil microbes use most plant-derived C and either produce CO₂ or incorporate C into their biomass and after death microbial necromass may contribute to stable SOM. Arbuscular mycorrhizal (AM) fungi are one of the root colonizing soil microbes important in nutrient cycling, plant nutrition, growth and composition and maybe soil aggregation. The benefits of microbes including AM fungi should be thus utilized for climate friendly agriculture by magnifying their benefits via better agricultural management.

Cover crops use is one of the climate friendly agricultural practices. Cover crops if managed right, can provide several benefits e.g. enhanced soil C sequestration, reduced emissions from fertilizer production, weed suppression, better soil moisture retention and microbial activity. Moreover, use of diverse cover crops may favor higher soil biodiversity leading to high SOM content. In this project, plant diversity impacts on soil and root fungal community composition and microbial activity related to soil C sequestration were studied in a field experiment. In addition, special attention was given to AM fungi.

The field experiment was started in May, 2019 in Viikki Research farm, University of Helsinki. The experiment consists of seven treatments comparing four different levels of biodiversity to conventional monoculture treatments and bare fallow. Eight different species of cover crops representing four functional traits were sown under barley: 1) nitrogen (N₂)-fixing + shallow rooting , 2) deep rooting, 3) N₂-fixing +deep rooting and 4) no N₂-fixing and shallow rooting. Barley and cover crop root samples and soil samples were collected from two growing seasons 2019 and 2020. Root samples were analyzed for AM fungal colonization %. Soil samples were analyzed for soil microbial biomass and microbial respiration in different seasons. Preliminary results showed no significant cover crop diversity effect on AM fungal colonization % in barley root in 2019. Soil microbial biomass and soil microbial respiration showed seasonal variations but not significant cover crop diversity effect. Therefore, fungal communities in soil and root will be examined using Illumina (MiSeq) sequencing targeting the fungal internal transcribed spacer (ITS) region. Soil enzyme activities and carbon use efficiency will be performed to gain insight into microbial activity. Obtained results will show if microbial community and activity is affected by either plant family composition or plant diversity.

How to cite: Shrestha, R., Huusko, K., Salonen, A.-R., and Heinonsalo, J.: Climate-smart agriculture: microbiological impacts of plant diversity to soil carbon (C) sequestration., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13588, https://doi.org/10.5194/egusphere-egu21-13588, 2021.

Ectomycorrhizal fungi (EMF) play a key role in the cycling of nitrogen (N) and carbon (C) in boreal forests. Trees receive growth-limiting N in exchange for allocating C to their mycorrhizal symbionts, but supplying the fungi with C can also cause N immobilization, which hampers tree growth. We present results from field and greenhouse experiments combined with mathematical modelling, showing that these are not conflicting outcomes.

Under N limitation, which is the general case in boreal forests, the plant host has been observed to continue supplying its ectomycorrhizal partner with C, and even increasing this C investment, while the fungus reduces mobilization of N to its host (Corrêa et al. 2008, 2010). N is thus withheld under conditions of limiting availability, and the host tree cannot unlock it by supplying the EMF with more C, because such an investment results in further diminishing N returns. Critical to this question is the observation that more than one fungus can form mycorrhiza on a given tree and that several trees can be connected to a given fungal individual (Southworth et al. 2005).

We hypothesize that plants sharing common ectomycorrhizal symbionts compete with each other for N by exporting C to the EMF network, and vice versa for a fungus. The fungi making up the EMF network export N to hosts if it is absorbed in excess of their own growth demand, which is limited by C; Exporting more than this would reduce their growth, exporting less would reduce their competitiveness for plant C (Näsholm 2013, Franklin 2014). This hypothesis has specific and predictable implications for relationship between plant C export to EMF and N uptake: At the community level, increasing plant C supply to EMF would increase both fungal N uptake and N use, but as soil N availability gradually becomes limiting, uptake should saturate while EMF N use continued to increase, leading to declining N export to plants.

We conducted two experiments, one in potted mesocosms and the other in a boreal forest setting. Belowground C flux was reduced by shading and/or stem strangling, which is a treatment whereby the flow of C to the root system is physically restricted by blocking transport through the phloem in the stem (Björkman 1944; Henriksson et al. 2015). Strangling a subset of seedlings growing in the same pot accomplishes two things: 1) the total belowground C flux is decreased, and 2) each seedling’s relative contribution to that flux is altered.

Based on measurements and mathematical modelling, we conclude that belowground C allocation by trees can indeed fuel N immobilization, reducing the amount of N to be distributed among the trees. But we also found that individual trees received nutritional benefits in proportion to their C contribution to the fungal network. We illustrate the evolutionary underpinnings of this situation by drawing on the analogous tragedy of the commons (Hardin 1968), where the shared mycorrhizal network is the commons, and explain how rising atmospheric CO₂ may lead to greater nitrogen immobilization in the future.

How to cite: Henriksson, N., Franklin, O., Tarvainen, L., Marshall, J., Lundberg-Felten, J., Eilertsen, L., and Näsholm, T.: The mycorrhizal tragedy of the commons, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15571, https://doi.org/10.5194/egusphere-egu21-15571, 2021.

The anthropogenic impact on soil microbiota in polar climate remains overlooked and the comparison between microbiota in urban and natural soils in polar regions are highly interesting. Fungi are the key components of soil microbiota, responsible for improtant functions and ecsystem services and highly senstive to direct (e.g., pollution) and indirect (e.g., urban heat island) anthropogenic effects. Urban soils of Murmanks (68.967 N, 33.083 E) – the biggest polar city in the world – were studied in comparison to Podzols of the natural forest-tundra area. Soil fungi in urban and natural soils were analyzed by luminescence microscopy and PCR real time.

The fungal biomass in the upper horizon of Technosol varied from 0.50 to 0.75 mg/g of soil, which was 1.5-2 times less than in Podzol. Different profile distribution of fungal biomass was shown for urban and natural soils. In natural Podzol, the highest fungal biomass was observed in the upper organic O horizon, then decreased in the topsoil mineral elluvial E horizon, and then slightly increased in the subsoil mineral illuvial Bs horizon. In urban soils, the second maximum of number of fungi in the soil profile was not found. The biomass of fungi decreased exponentially in the soil profile.

The number of ITS ribosomal gene copies of fungi in the topsoil organic horizon of natural Podzol reached 10¹⁰gene copies/g of soil. In urban soils, there was a decrease in their number by 6 or more times. The number of fungal gene copies decreased sharply down the soil profile in both urban and natural soils. So, if the number of fungi in topsoil horizons was about 10⁸-10¹⁰ gene copies /g of soil, in subsoil horizons it was 10⁶-10⁷ gene copies/g of soil. First of all, this may be due to the mycorrhizal mycobiota, which has the largest extent of mycelium in the topsoil horizons of soil. In forest soil, the number of gene copies in horizon E was 37 times less than in the topsoil horizon; in urban soil, the content of gene copies in the subsoil BC horizon is 10 times less than in the topsoil horizon.

The proportion of fungal mycelium varied from 28 to 80%. A minimum of mycelium was found in the subsoil horizons, while the topsoil horizons were abundant with fungal hyphae, the length of which in them reached more than 160 m/g of soil. The maximum amount of mycelium (581.72 m/g of soil) was observed in natural Podzol. The number of single-celled fungal propagules (spores and yeasts) was 10⁴-10⁵ cells/g of soil. Most of the propagules are represented by small-sized forms (2-3 microns), the proportion of which increased from the topsoil horizons (68-93%) to the deep ones (up to 100%). This trend was observed for both urban and background soils. Large propagules with a diameter of 5-7 microns were found exclusively in the topsoil horizons, and their number is no more than 10³ cells/g of soil.

Acknowledgements This research was supported by state task AAAA-A18-118021490070-5 and Russian Foundation for Basic Research project № 19-29-05187.

How to cite: Korneykova, M., Nikitin, D., Dolgikh, A., and Vasenev, V.: Biomass and number of gene copies of fungi in the polar urban soils, Murmansk, Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10864, https://doi.org/10.5194/egusphere-egu21-10864, 2021.

Our knowledge about the role of microbial organisms as drivers of soil biogeochemical cycles is mainly based on soil analyses, and the physiological information that exists for few microbial model organisms. In soil, measurements of process rates and element contents can be related to the apparent activity of the microbial community, though conclusions are often indirect - actual microbial physiology and diversity remains hidden. By contrast, analyses of microbial physiology under controlled conditions are hardly representative of the vast diversity of microorganisms in soil, and a transfer of these findings to complex soil systems is challenging. Thus, we argue that a better exchange among these ecological disciplines will lead to a valuable transfer of relevant questions, knowledge and improved understanding of the role of microbes in soil and its responses to environmental change.
Here, we provide examples of an evaluation of microbial parameters relevant in soil biogeochemical cycles, analysing traits in a collection of 31 saprobic fungi in response to varying substrate conditions. The large dataset allowed to test several assumptions and conclusions derived from soil system analyses exemplarily for soil fungi. Specifically, we (1) evaluated the optimum C:N:P (carbon:nitrogen:phosphorus) substrate ratio for fungal growth and activity, (2) assessed the responses in carbon-use efficiency and enzyme activity to N deficiency, (3) analyzed the relevance of C versus N supply for fungal growth and activity under varying substrate conditions and (4) tested the assumption of microbial stoichiometric homeostasis, that represents a basic principle in soil ecological stoichiometry.
Fungal responses to changes in N and C availability were partly consistent with expectations, e.g. regarding general nutrient demands, though as often discussed C availability appeared more relevant for growth especially in complex substrates. Enzymatic activity and respiration also positively correlated with N availability, resulting in decreased carbon-use efficiency at high N supply. These findings, for example, contradict certain conclusions in soil analyses, namely that N limitations will result in “N mining” (high enzymatic activity), while the excess of C causes “overflow respiration” and reduced CUE. Regarding fungal C:N:P ratios, those were only related to nutrient demands when growing in simple media, while in soil substrate such relations seem more complex. Contradicting the assumption of microbial homeostasis in soil, fungal individuals showed more flexible C:N:P ratios than expected, though the degree of flexibility varied among isolates. In general, the results also reveal a large trait variation among different isolates, with several traits showing a phylogenetic signal, indicating variations in microbial activity depending on community composition.
Finally, we want to raise and discuss several emerging questions: How relevant is a deeper understanding of microbial physiology to understand soil biogeochemical processes? How do we include the variability of traits in diverse soil communities – are average values informative, or can we proceed with useful categories? And how can methods in soil science and microbial ecology be merged best to allow fruitful knowledge transfer?

How to cite: Camenzind, T., Lehmann, J., Lehmann, A., Aguilar-Trigueros, C. A., and Rillig, M. C.: How relevant are microbial traits to understand soil biogeochemical cycles?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11186, https://doi.org/10.5194/egusphere-egu21-11186, 2021.

Soils are characterized by their largely varying microhabitats that determine their microbial communities and functions such as nutrient cycling. Microbes, and especially fungi, do not only react to those microhabitats but also contribute to shaping them.

We used transparent, microstructured chips simulating the internal pore space of soils, to microscopically study fungal mycelia at the hyphal scale. We investigated the variety of fungal morphologies in maze structures, and hyphal interactions with their biotic and abiotic microenvironments. We studied both a variety of laboratory strains including an arbuscular mycorrhizal fungus and natural soil inocula, and we quantified their growth strategies in different microstructures and their interactions with bacteria, protists and soil mineral particles.

We could observe how the rigid hyphae of fungi opened up passages through chip- or soil solids and aggregates, increasing the spatial availability of the pore space. They, on the other hand, also filled up pores and pore necks with their biomass, creatingbarriers for both organisms, flow of water and sedimentation of matter, and thus changing the pore size distribution and -connectivity. Hyphae also increased the wettability of pores, which led to a higher connectivity of water films across air pockets and thus benefiting the dispersal of water-dwelling microorganisms, a phenomenon earlier termed “fungal highways”. We found the abundance of both bacteria and protists strongly increased in pore spaces containing hyphae in comparison to those without, dispersal events via fungal hyphae that happened frequently and were quantifiable in the high internal replication of our chip’s pore space channels. This allowed us to conclude on a high relevance of this mode of dispersal in soils with intermediate moisture. Fungal hyphae had thus a strong and obvious effect on their surrounding microenvironments and organisms.

We consider the study of microbial behaviour and interactions at the cellular scale in microhabitats to be essential for a better understanding of soil functions, and to gain mechanistic insight into phenomena observable at macroscale.

How to cite: Hammer, E., Mafla Endara, M. P., Arellano Caicedo, C. G., Pucetaite, M., Aleklett Kadish, K., and Ohlsson, P.: Fungi as Ecosystem Engineers in the Soil Pore Space, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13098, https://doi.org/10.5194/egusphere-egu21-13098, 2021.

Altered temperature and precipitation regimes particularly prolonged drought periods when combined with heat strongly affect forests in the last decades. However, neither did all trees die nor even stop growing at all sites. We are interested in the question if below ground interaction with ectomycorrhizal fungi could be partly mediating strong soil drought. For this purpose, we established sampling sites with Fagus sylvatica, Picea abies or Pinus sylvestris along a natural precipitation gradient of 400 km length in Bavaria (Germany). We hypothesized root associated fungal communities to reflect long-term adaptation to local edaphic and climate conditions and that the resulting tree-fungal partnerships have distinct compositional patterns.

How to cite: Pritsch, K., Roth, M., and Weikl, F.: Ectomycorrhizal communities along a precipitation gradient in Bavaria (Germany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6176, https://doi.org/10.5194/egusphere-egu21-6176, 2021.

Microbial communities are major players in carbon and nitrogen cycling globally and are of particular importance for plant communities in the nutrient poor soils of boreal forests. Especially relevant are the fungal communities in the soil that interact with the plants in multiple ways, indirectly through their pivotal role in the breakdown of organic matter and, more directly, through mycorrhizal symbiosis with plant roots. Large-scale disturbances of these complex microbial communities can lead to shifts in soil carbon storage with unknown and global-scale long-term consequences. To understand the dynamics of these communities and their relationship to associated plants in response to climate change and anthropogenic influence, we need a better understanding of how modern “omics” methods can help us to understand compositional and functional shifts of these microbiomes. Microbial gene expression and functional activity can be assayed with RNA sequencing (RNA-Seq) data from environmental samples. In contrast, currently phylogenetic marker gene amplicon sequencing data is generally used to assess taxonomic composition and community structure of the microbiome. Few studies have considered how much of this structural and taxonomic information is included in RNA-Seq transcriptomic data from matched samples. Here we describe fungal communities using both RNA-Seq and fungal ITS1 DNA amplicon sequencing to compare the outcomes between the methods. We used a panel of root and needle samples from mature stands of the coniferous tree species Picea abies (Norway spruce) growing in untreated (nutrient deficient) and nutrient enriched plots at the Flakaliden forest research site in boreal northern Sweden. We created an assembly-based, reproducible and hardware agnostic workflow to taxonomically and functionally annotate fungal RNA-Seq data obtained from Norway spruce roots, which we compared to matching ITS amplicon sequencing data. We show that the community structure indicated by the fungal transcriptome is in agreement with that generated by the ITS data, while also identifying limitations imposed by current database coverage. Furthermore, we show examples to demonstrate how metatranscriptomics data additionally provides biologically informative functional insight at the community and individual species level. These findings highlight the potential of metatranscriptomics to advance our understanding of interaction, response and effect both between host plants and their associated microbial communities, and among the members of microbial communities in environmental samples in general.

How to cite: Schneider, A., Sundh, J., Sundström, G., Richau, K., Delhomme, N., Grabherr, M., Hurry, V., and Street, N.: Comparative fungal community analyses using metatranscriptomics and ITS-amplicon sequencing from Norway spruce, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7249, https://doi.org/10.5194/egusphere-egu21-7249, 2021.

Middle Europe’s forests face an increasing risk of recurring summer droughts. To explore the impact of such conditions, trees in a mature spruce-beech forest were exposed to five successive years of extreme summer drought during the Kranzberg Roof Experiment located in Bavaria (Grams et al. 2021, DOI: 10.1002/ecs2.3399).

Those trees (Picea abies and Fagus sylvatica) heavily depend on their ectomycorrhizal fungal symbiosis partners (ECMf) belowground. Thus, we set out to identify modes of compositional and functional adaptation in these communities.

We monitored ECMf communities via metabarcoding and analysed the functionality of morphotyped ectomycorrhizae via testing their enzyme activities.

To our surprise, most effects were quantitative throughout the whole period. Total enzyme activities strongly declined alongside the numbers of vital root tips of drought treated trees, while enzyme activities per surviving root tip remained remarkably similar to controls. Likewise, ECMf communities only experienced minor shifts that only slightly increased during the years, although different capacities for drought tolerance in ECMf have previously been hypothesised.

Summed up: Along with most tree individuals, their fungal partners showed a strong ability to resist the applied extreme drought scenario, at the cost of severely diminished capacities at the ecosystems level.

Speculatively, individual root tips could be seen as surviving insulae whose fungal communities only experienced indirect and moderated drought effects. Therefore, the ECM system may rather show an inherent resistance to drought, with observable qualitative adaptation requiring a still longer time-frame.

How to cite: Weikl, F. and Pritsch, K.: Are ectomycorrhizal fungi actually adapting to 5 years of extreme summer drought in Middle European forests?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2937, https://doi.org/10.5194/egusphere-egu21-2937, 2021.

Fungal community in the soil plays a central role in natural systems and agroecosystems, therefore it attracted much research interests. However, the fungal microbiota of aromatic plants, such as Salvia sclarea L., especially in trace-element (TE) polluted conditions and within the framework of phytomanagement approaches, remains unexplored. The presence of high concentrations of TE in the soil is likely to negatively affect not only microbial diversity and community structures, but also plant establishment and growth. The objective of this study is to investigate the soil fungal and arbuscular mycorrhizal fungi (AMF) community structure and their changes over time in TE-polluted soils in the vicinity of a former lead smelter and under the cultivation of clary sage. We used Illumina MiSeq amplicon sequencing to evaluate the effects of in situ clary sage cultivation during two successive years, combined or not with an exogenous AMF inoculation, on the rhizospheric soil and root fungal communities. We obtained 1239 and 569 fungal amplicon sequence variants (ASV) respectively in the rhizospheric soil and roots of S. sclarea in TE-polluted conditions. Remarkably, 69 AMF species were detected in our experimental site, belonging to 12 AMF genera. Besides, the inoculation treatment significantly shaped the fungal communities in soil, and increased the number of AMF ASVs in clary sage roots. In addition, successive years of clary sage cultivation also significantly shaped both fungal and AMF communities in the soil and root biotopes. Our data provide new insights on fungal and AMF communities in the rhizospheric soil and roots of clary sage grown in TE-polluted agricultural soil.

Keywords: Trace Elements-polluted soils, fungal microbiota, Salvia sclarea, arbuscular mycorrhizal fungi

How to cite: Raveau, R., Fontaine, J., Hijri, M., and Lounès Hadj-Sahraoui, A.: Clary sage cultivation and mycorrhizal inoculation influence rhizosphere fungal community structure over time in a trace-element polluted site, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12862, https://doi.org/10.5194/egusphere-egu21-12862, 2021.

Millipedes are among the largest and most important invertebrates, with over 12,000 identified and 80,000 expected species worldwide. Millipedes are detritivores living on leaf litter, deadwood, or soil. Because of the poor nature of their diets, millipedes compensate through high food consumption. Thanks to this, they are keystone species in many terrestrial ecosystems. In fact, in tropical and temperate zones, they rank the third most essential macrodetritivores after termites and earthworms and consume 10-36% of the annual litter. Thus, they contribute to soil formation and are essential forest ecosystem engineers. Despite their ecological importance, it remains unclear what role does their microbiome play in their diet.

We studied the gut microbiota of 11 millipede species and measured key physicochemical conditions (redox, pH and O₂ levels). We found that the bacterial and archaeal communities were phylogenetically conserved while the fungi matched the diet. Methanogenic millipedes had a distinct community dominated by fermenting and syntrophic microorganisms. Follow-up experiments on the methanogenic and non-methanogenic species Epibolus pulchripes and Glomeris connexa, respectively, showed that both could survive prolonged antibiotic treatment, although with some disruption of their digestion. Antibiotics treatment significantly reduced the faecal bacterial colony counts after seven days in both species. Additionally, methane production dropped by 74% in the group treated with antibiotics and 52%, in the group that received sterile feed without antibiotics.

Microbiome analysis of these groups showed major shifts of the community composition in response to antibiotics, but less so with sterile feed. Apart from the presence of methanogens, high methane production correlated with a high relative abundance of Bacteroidia, while Gammaproteobacteria dominated the guts of millipedes with low, or no, methane production.

By supplementing the millipedes' diet with BES, methane production could be suppressed entirely within 21 days. Microscopic analysis of the faeces (using CARD-FISH) revealed methanogens from the orders Methanobacteriales and Methanomassiliicoccales associated with ciliates. These methanogens persisted even in the absence of methane production.

Our results indicate a significant gut microbiome activity in cellulolytic, fermentative and methanogenic litter decomposition processes, however,  unlike in ruminants and termites with a limited nutritional contribution to the host.

How to cite: Angel, R., Šustr, V., Eyiuche Nweze, J., Gupta, S., Horváthová, T., M. Ardestani, M., Petrová, E., and Faktorová, L.: Millipedes cluster into distinct ecophysiological guilds based on their microbiome, with clear ecosystem implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12016, https://doi.org/10.5194/egusphere-egu21-12016, 2021.

Peatlands are globally valued for the ecosystem services they deliver, including water quality regulation and carbon sequestration. In the UK, blanket bogs are the main peatland habitat and previous work has linked blanket bog management, especially rotational burning of heather vegetation on grousemoors, to impacts on these ecosystem services. However, we still lack a mechanistic, process-level understanding of how peatland management and habitat status is linked to ecosystem service provision, which is mostly driven by soil microbial processes.

Here we examine bacterial and fungal communities across a spectrum of “intact” to degraded UK blanket bogs and under different vegetation management strategies. Sites included grousemoors under burnt and alternative mown or uncut management along with further locations including 'near intact', degraded and restored sites across a UK climatic gradient ranging from Exmoor (South UK), the Peak District (Mid) to the Flow Country (North). Moreover, an experiment was setup at the University of York with peat mesocosms taken from all sites and management/habitat conditions to allow a comparison between field and controlled conditions and assessing root-mediated processes. Using a structural equation model, we linked grousemoor management to specific fungal/bacterial functional groups, and have started to relate this to changes in water quality provision and carbon cycle aspects. This represents a significant step in the effort to use microbial communities as indicators of peatland habitat condition in UK upland blanket bogs. 

How to cite: Burn, W., Heinemeyer, A., Helgason, T., Glaves, D., and Morecroft, M.: The Hidden Half: Linking microbial communities to habitat condition and vegetation management in UK blanket bogs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11861, https://doi.org/10.5194/egusphere-egu21-11861, 2021.

Soil microorganisms are an essential component of forest ecosystems being directly involved in the decomposition of organic matter and the mineralization of nutrients. Anthropogenic disturbances such as logging and livestock modify the structure and composition of forests and also the structure and diversity of soil microbial communities changing critical biogeochemical processes in the soil. In this research we evaluated the effect of anthropic disturbance on the soil in a degradation gradient of Andean temperate forest. This gradient comprises mature forest stands dominated by Nothofagus dombeyii, secondary forests dominated by Nothofagus alpina with medium degradation, a highly degraded forests dominated by Nothofagus obliqua and a highly degraded grassland. We evaluate the reservoir of the main soil nutrients (TC, TN, NO₃^-, NH₄⁺) and the structure, diversity and functions of the soil microbial community (bacteria and fungi) via NGS-Illumina sequencing and metagenomic análisis with DADA2 pipeline in R-project. The results show a higher amount of TC, TN, NO₃^- and C:N ratio in the most degraded condition (degraded grassland). There are no significant differences in the amount of TC, TN and NH₄⁺ along the forest degradation gradient. This reflects a C:N:P stoichiometry that tends to decrease as forest degradation increases. The soil bacteria community was mainly dominated by Phyla Proteobacteria (45.35%), Acidobacteria (20.73%), Actinobacteria (12.59%) and Bacteroidetes (7.32%). At genus level there are significant differences, Bradyrhizobium has a higher relative abundance in the condition of mature forest which tends to decrease along the gradient of degradation forest. The soil fungi community was dominated by the Phyla Ascomycota (42.11%), Mortierellomycota (28.74%), Basidiomycota (24.61%) and Mucoromycota (2.06%). At genus level the condition of degraded grassland has significantly lower relative abundance of the genera Mortierella and Cortinarius. The degraded grassland soil microbial community is significantly less diverse in terms of bacteria (D' = 0.47±0.04) however it is significantly more diverse in terms of fungi (H' = 5.11±0.33).

How to cite: Atenas, A., Aburto, F., Hasbun, R., and Merino, C.: Effects of anthropogenic degradation of an Andean temperate forest on the soil nutrients and on the diversity and function of the soil microbial community, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14004, https://doi.org/10.5194/egusphere-egu21-14004, 2021.

Forest parks play an important role in the sustainable functioning of urban ecosystems. In contrast to natural forests, urban forests are under continuous anthropogenic pressure, affecting the soil microbial community functioning and its capacity to provide many ecosystem services. Moreover, another significant factor determining such functioning is bioclimatic conditions, i.e., city geographic location. Our study aims to examine the effect of urbanization on soil microbial biomass and functional diversity along a latitudinal gradient of European Russia. Urban forest parks (UFP) were chosen in Moscow, Tula, and Belgorod cities located in mixed coniferous-broadleaved forests, deciduous forests, and forest-steppe biomes of European Russia, respectively (17 sites). Outside of the cities the reference suburban forests (SUF) were selected (12 sites). When selecting sites, we considered the following criteria: i) same soil reference group within the biome (Retisols, Luvisols, Phaeozems in mixed coniferous-broadleaved forests, deciduous forests, and forest-steppe, respectively), ii) loam parent materials, and iii) forest aged ≥60 years. In each UFP and SUF, five spatially distributed plots were chosen, in which soil samples were taken from the upper 10 cm layer without litter (totally 85 and 60 for UFP and SUF). For freshly collected soil samples, microbial biomass carbon content (MBC, substrate-induced respiration method) and basal respiration (BR; rate of CO₂ release) were measured, then the ratio BR / MBC = qCO₂ was calculated. The community level physiological profile of soil microorganisms (CLPP, MicroResp^TM technique) indicating the microbial ability to utilize different organic substrates (carbohydrates, acids: amino, carboxylic, phenolic, 14 totally) was tested. CLPP data were used to calculate the Shannon–Wiener diversity index (H_CLPP).

It was found that soil BR decreased on average from SUF to USP in all studied biomes, while the MBC content did not change significantly. A significant increase of MBC in USP and SUF soils was observed from north to south (from mixed coniferous-broadleaved forests to forest-steppe), and for qCO₂ – decreasing. The CLPP of the studied soils were dominated by microorganisms consuming carboxylic acids (ascorbic and citric) and carbohydrates (glucose, fructose, galactose). Cluster analysis identified two groups that differed by soil CLPP: i) mixed coniferous-broadleaved forests and deciduous forests (Moscow, Tula) and ii) forest-steppe (Belgorod). Soil H_CLPP index didn’t significantly differ between SUF and UFP in all studied biomes. Two-way ANOVA showed that soil MBC, qCO₂, and H_CLPP changes were more associated with bioclimatic conditions (18-47% of explained variance, P <0.05) than urbanization (P> 0.05). On contrary, soil BR was more sensitive to urbanization (4% of explained variance, P <0.05) than to the change of bioclimatic conditions (P> 0.05). Notably, driving factors of spatial variation for the studied soil microbial properties within each city (53-92% unexplained variance) have yet to be identified.

This study was supported by the Russian Foundation for Basic Research, project No. 20-04-00148.

How to cite: Ananyeva, N., Khatit, R., Sushko, S., Buyvolova, A., Dolgikh, A., Zhuravleva, A., Selezneva, A., Vasenev, V., and Ivashchenko, K.: Soil microbial biomass and functional diversity in urban forest parks and suburban forests of various biomes in European Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14784, https://doi.org/10.5194/egusphere-egu21-14784, 2021.

Soil enzymes catalyse the hydrolysis of various soil compounds leading to an increase in the availability of nutrients for plants and microorganisms, but the increase in mobility might also lead to losses by leaching. Sources of extracellular soil enzymes in soil include release by soil microorganisms such as bacteria and fungi and plant roots but also microbial necromass. Irrespective of their source, the released enzymes can accumulate in the soil by becoming stabilized on mineral and organic surfaces. It is generally assumed that 40 to 60% of measured enzyme activity originate from stabilized enzymes. As such they directly affect the ability of a soil to fulfil its numerous functions, including the provision of nutrients to plants, the cleaning of percolating water and climate regulation.

Although measurements of soil enzyme activity are increasingly recognised as sensitive indicators of soil health, variations and inconsistencies between existing methods make it difficult to compare the results of different studies. Most commonly, soil enzyme activities are assessed using destructive biochemical laboratory incubations, thus altering the natural soil conditions.

Therefore, based on the principle of soil zymography, a membrane based method to map the heterogeneity of enzymatic activity on exposed soil surfaces, we developed a portative, hand-held sensor allowing rapid measurement of the soil enzymatic activity in-situ (Digit Soil; https://www.digit-soil.com/). In this presentation, we will compare the performance of our sensor to laboratory incubations for the application on various types of soils differing in basic properties such as pH, texture and soil organic matter content at different moisture conditions.

Based on the results, we will discuss the prospects this new sensor offers for rapid in-situ evaluation of soil health in the framework of precision agriculture and sustainability labels.

How to cite: Iven, H., Meller, S., Luster, J., and Frossard, E.: A novel in-situ soil enzymatic activity sensor- expanding soil precision measurements to indicator of soil health., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10708, https://doi.org/10.5194/egusphere-egu21-10708, 2021.