• The common soil nutrient enrichment (nitrogen, N; phosphorus, P) typical of the agro-pasture ecotone may impact plants-arbuscular mycorrhizal fungi (AMF) symbiotic relationships. However, the stoichiometric responses of plants to increased soil nutrient availability and AMF are not yet clear.
• Thus, we carried a 3-year in situ study to understand how AMF as well as N and P additon alter the dominant plant ecological stoichiometry in a P-impoverished grassland in Northwest China. The grassland type is desert stepp. The soil type is light sierozem, with 1.8 mg kg⁻¹ soil available P and 6.7 mg kg⁻¹ soil inorganic N. A randomized block design (three-way factors) was conducted with four fertilization treatments: control, N input (N), P input (P), and combined N and P input (NP). Each fertilization treatment comprised two AMF treatments: a non-benomyl and a benomyl treatment. N input was provided as an NH₄NO₃ fertilizer (10 g N m⁻² year⁻¹) evenly input by hand to N and NP plots in late June (early growing season) in each year. P input was provided as a Ca(H₂PO₄)₂ fertilizer (10 g P m⁻² year⁻¹), similarly distributed as the N input.
• Overall, our study indicated that P input considerably exacerbated plant P limitations by diminishing their C:P and N:P; the impact of P input on plant C:P and N:P was higher than that of AMF and N input. This observed reduction in plant N:P and C:P owing to the P supply might be due to the higher soil available P level and quick increase in plant P concentration by P input. Conversely, N input and AMF suppression decreased two dominant grasses C:N ratios by increasing their N concentration. Accordingly, plant and soil available N:P could predict plant biomass changes under N and P addition in P-deficient grasslands.
• Our findings highlight that the importance of P input, but not AMF, in changing plant C:N:P stoichiometry in P-impoverished grasslands.

How to cite: Yang, X.: Phosphorus addition, rather than mycorrhizal fungi or nitrogen addition, alleviate plant phosphorus deficits in phosphorus-impoverished grassland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5305, https://doi.org/10.5194/egusphere-egu26-5305, 2026.

Fungal symbionts play essential roles in ecosystems by shaping plant development and biodiversity. Among these, mycorrhizal fungi can form common mycorrhizal networks (CMNs) where a single fungus connects the roots of two or more plants through a continuous extraradical mycelium, facilitating transfer of resources, including nitrogen and carbon, between the connected plants.
Remaining understudied, there is another group of fungal mutualists known as endophytes, which are relatively phylogenetically and morphologically distinct from mycorrhizal fungi. Endophytic fungi also support plant development and may form common endophyte networks (CENs). Whether endophytes can transfer soil resources like nitrogen, carbon, and water through such networks remains an open question. To test this, we established a CEN experiment in split petri dishes using Arabidopsis thaliana hosts and three phylogenetically diverse endophytes (Trichoderma viride, Mucor hiemalis, and Fusarium temperatum) to test if isotopically labelled amino acid ¹⁵ nitrogen (N), amino acid ¹³ carbon, ¹⁵ N-ammonium, or deuterated water can be transferred from a donor plants soil to receiver plants connected via a CEN. We show that the tested endophytes can form CENs and transfer growth limiting resources from donor plant soil to receiver plant tissues. F. temperatum boosted plant growth by 38% relative to the uninoculated control, and it enriched plant ¹⁵ N content derived from amino acids by 55%. Surprisingly, we also observed amino acid-derived ¹³ carbon transport from donor plant soil to receiver plant tissues by T. viride (+ 2.83% > control). We also demonstrate that soil resource transfer by all three endophytes shifted in the presence of two versus a single host plant even when root systems were physically separated to avoid competition, underscoring that endophytic functioning, not just that of plants, also shifts when CENs are formed. Our results demonstrate that non-mycorrhizal fungi, in particular endophytes, can form networks similar to the idea of CMNs and transfer plant growth relevant resources. Endophytes display a broad array of symbiotic functions with their hosts, and formation of CENs may be a newly discovered component of their symbiotic tool kit.

How to cite: Spiegel, P., Waschk, P., and Anthony, M.: Evidence for resource transfer via common endophytic networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6787, https://doi.org/10.5194/egusphere-egu26-6787, 2026.

Temperate forests in Central Europe are largely dominated by ectomycorrhizal (ECM) trees, with arbuscular mycorrhizal (AM) species currently representing a lesser proportion. Climate-driven forest dieback has prompted management strategies to diversify species composition and foster structural complexity to enhance ecosystem resilience. In Brandenburg, eastern Germany, forest transformation efforts primarily promote native ECM-associated trees to increase structural and compositional diversity, while concurrently the AM tree species Prunus serotina has expanded in the understory through natural regeneration. Rising temperatures may increase the prevalence of AM symbiotic systems, yet the consequences for belowground fungal communities in ECM-dominated forests, particularly for symbiotic fungi, remain poorly understood.

We asked whether AM-dominated understory reorganizes communities of AM fungi in ECM-dominated forests, and to what extent forest structure and microclimate explain variation in biomass and community composition of AM fungi relative to other fungal groups. We collected soil samples from 40 plots in a managed forest in Brandenburg, Germany, in Scots pine and mixed conifer–deciduous stands, each with or without AM-dominated understory. AM fungal and total fungal biomass were quantified using neutral and phospholipid fatty acid analysis. Fungal diversity and community composition were assessed by DNA metabarcoding targeting the ITS2 region for the total fungal community and an 18S rRNA region specific for AM fungi. Stand structural metrics derived from laser scanning and microclimatic variables were included as continuous explanatory factors.

Preliminary results indicate that AM-dominated understory increased biomass and beta diversity of AM fungi across pine and mixed conifer-deciduous stands, while alpha and gamma diversity of AM fungi declined. That suggests dominance-driven community reorganization rather than a net increase in diversity. Forest structure and microclimate explained little variation. The total fungal community composition and biomass remained largely unaffected by the presence of AM-dominated understory. In these dry and nutrient-poor Podzol soils, a higher proportion of AM symbiotic systems may add complementary pathways of water and nutrient acquisition to those provided by ECM fungi. This functional diversification could contribute to forest resilience and may become increasingly important under a changing climate.

How to cite: Brunschweiger, B., Zuev, A. G., Weikl, F., Bain, H., Jansen, M., and Annighöfer, P.: Arbuscular mycorrhiza understory alters AM fungal community composition with little effect on other soil fungi in an ectomycorrhizal-dominated forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6998, https://doi.org/10.5194/egusphere-egu26-6998, 2026.

Aim: Investigate the functional diversity of top- and subsoil arbuscular mycorrhizal fungi (AMF) communities as well as specific functional traits regarding nutrient mobilization.
Method: In the first experiment, five plant species with distinct functional traits were grown in top- and subsoil cores in a mesocosm experiment. Roots AMF communities’ composition was analyzed by DNA amplicon sequencing of the ITS rRNA gene. In the second experiment, we used 15N and 33P isotope tracers to test the ability of selected distinct AMF communities to stimulate nutrient mobilization from organic matter.
Results: AMF richness is consistently greater in topsoil regardless of plant species (p < 0.001). Both AMF taxonomic and phylogenetic beta diversity show more diversity among subsoil communities than topsoil communities. Furthermore, subsoil AMF communities are hypothesized to be more capable of stimulating N and P mobilization from organic matter than topsoil communities.
Conclusion: These results suggest that AMF communities’ composition is shaped by both plant species and soil depths. Despite topsoil AMF communities supporting greater richness, subsoil communities display greater taxonomic and phylogenetic diversity.

How to cite: Ziche, Z. I., Shi, L., and Stock, S.: From Roots to Depths: Unveiling Functional Traits and Diversity of Arbuscular Mycorrhizal Fungi in Agricultural Top- vs. Subsoil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7855, https://doi.org/10.5194/egusphere-egu26-7855, 2026.

Fungi are a major component of soil microbial communities in forest ecosystems and regulate a wide range of biogeochemical processes. Saprotrophic fungi decompose dead organic matter, pathogenic fungi can influence plant fitness, and symbiotic mycorrhizal fungi support plant nutrient acquisition in exchange for photosynthetically derived carbon. Beyond their functional diversity, fungal biomass represents a substantial pool of soil organic carbon through living fungal tissues and extensive mycelial networks. Soil fungi further interact with other microbial groups, thereby influencing nutrient turnover and overall ecosystem functioning. Here, we investigate how forest stands differ in soil fungal biomass and which environmental parameters best predict variability in fungal biomass. We further test how net nitrogen mineralization, a process often associated with bacteria-dominated nitrogen transformations, relates to fungal biomass. Soil samples were collected from 60 mature European beech stands distributed across the Vienna Woods, Austria. Fungal biomass was estimated by quantifying ergosterol concentrations extracted from soil samples taken from the organic layer and from three depths in the mineral soil (0–10, 10–20, and 20–50 cm). Net nitrogen mineralization rates were determined by measuring ammonium and nitrate concentrations before and after a 12-day laboratory incubation. Fungal biomass was related to nitrogen mineralization rates as well as a wide range of stand-, soil-, and site-level variables. First results are presented and discussed in the context of soil carbon storage and nitrogen availability.

How to cite: Konrad, D., Friedl, N., Keiblinger, K., Berger, T. W., and Mayer, M.: Soil fungal biomass and nitrogen cycling in European beech stands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10448, https://doi.org/10.5194/egusphere-egu26-10448, 2026.

Trees are the dominant primary producers in forest ecosystems and play a central role in global carbon (C) cycling. A substantial fraction of tree-assimilated C enters the soil as leaf litter, where it is decomposed by diverse microbial consortia. Whether C from litter is rapidly mineralized to CO₂ or accumulates as soil organic matter largely depends on the functional traits and activities of soil microbes. Understanding the factors shaping litter-decomposing microbiomes is therefore essential for predicting the capacity of forest soils to act as C-sinks.

Most tree species form symbiotic associations with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi. Litter from AM-associated trees typically contains more accessible nutrients and decomposes faster than the more recalcitrant litter from ECM-associated trees. ECM fungi possess broad enzymatic repertoires and, in some taxa, oxidative mechanisms for nutrient mobilization, whereas AM fungi largely depend on interactions with other microbial taxa. Although these contrasts are well established, the multipartite interactions among trees, mycorrhizae, and other soil microorganisms, and particularly the functional differences of decomposer microbiomes in AM- and ECM-dominated forests, remain insufficiently understood.

To address this, we conducted an in-situ incubation experiment using litter from Acer saccharum (AM-associating) and Quercus alba (ECM-associating) in AM- and ECM-dominated forest stands in south-central Indiana, USA. We assessed the changes in the composition of decomposer microbiomes with progressing litter decay and seasonal dynamics in the litter and adjacent soil by metabarcoding of the 16S rRNA and ITS2 regions after 1, 3, 6, and 12 months. Additionally, we performed metatranscriptomic analyses for decomposer communities after 3 months. Combined with existing metagenomic data, these approaches will enable us to identify microbial taxa and processes driving litter decomposition, C- and nutrient processing across contrasting mycorrhizal contexts.

Initial results indicate that fast-growing, opportunistic Aspergillaceae, known to utilize readily available, labile substrates, dominated the early decomposition of AM-litter. In contrast, Sordariomycetes, capable of degrading recalcitrant compounds, were more abundant in ECM-litter. These patterns are consistent with our expectations and demonstrate the potential of our experimental setup to resolve the functions of microbiome members beyond mycorrhizal fungi. Ultimately, this study will enhance our understanding of the microbial taxa that are critical for C cycling in forests and of how decomposer microbiome dynamics are shaped by dominating mycorrhizal types.

How to cite: Tyborski, N., Kurbel, V. B., Huenupi, E., Phillips, R. P., and Pausch, J.: Leaf litter decomposition by microbial communities compared among forest stands dominated by arbuscular versus ectomycorrhizal fungi, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6573, https://doi.org/10.5194/egusphere-egu26-6573, 2026.

In temperate forest ecosystems, ectomycorrhizal fungi (EMF) are key regulators of global carbon cycling. Up to 70% of the carbon accumulation in the organic soil layer originates from roots and mycorrhizal fungi rather than from aboveground litter deposition. A significant fraction of the photosynthetically fixed carbon that EMF receive from trees is directed toward production of extraradical mycelium, the main fungal component responsible for nutrient uptake. Despite the importance of EMF mycelium, the processes regulating its growth and functioning remain poorly understood in the face of climate change. Even less is known about the role of bacteria in regulating ectomycorrhizal physiology under altered environmental conditions. To address this, carbon-free in-growth sand bags used to "bait" ECM fungi were buried in the soil at two beech forests in Switzerland in an experimental climate warming x drought field study. In-growth mesh bags provide a powerful method for investigating this critical component of the belowground carbon stock, allowing targeted assessment of extraradical mycelium biomass production and turnover, and to study the bacteria associated with EMF mycelium. We quantified fungal and associated bacterial biomass within the sand bags using phospholipid fatty acids (PLFA) analysis, and we compared the composition and potential functions of the bacterial biome using DNA metabarcoding and metatranscriptomics. Across treatments and sampling windows, bacterial biomass was positively correlated with EMF biomass, indicating a tight coupling between extraradical mycelium and associated bacterial communities under climate stress. After the entire growing season, drought reduced the fungal-to-bacterial biomass ratio, while warming and the combined warming × drought treatment had weaker effects. This suggests that bacteria associated with the extraradical mycelium of ectomycorrhizal fungi are relatively more tolerant to drought stress than the fungi themselves. At finer taxonomic resolution, response ratios revealed group-specific and site-dependent responses of bacterial and fungal functional groups to climate treatments. While single stressors usually reduced the biomass of Gram-positive, Gram-negative, actinobacteria and fungi in both experimental sites, the combined warming × drought treatment frequently resulted in contrasting non-additive responses, especially in one of the two sites, indicating complex interactions between climate drivers. Overall, our results highlight that extraradical mycelium-associated bacterial communities remain tightly linked to ectomycorrhizal fungi under climate stress but with distinct tolerances that may shift bacterial contributions which support EMF functioning.

How to cite: Cantini, G., Zarsav, A., Spiegel, P., and Anthony, M.: Responses of ectomycorrhizal extraradical mycelium and associated bacteria to drought and warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13699, https://doi.org/10.5194/egusphere-egu26-13699, 2026.

The ectomycorrhizal (ECM) symbiosis underpins forest nutrient cycling through tightly regulated exchange of carbon and nutrients at the plant–fungal interface. Despite their ecological importance, the spatial chemistry of this interface remains poorly characterised. Here, we apply optical photothermal infrared (O-PTIR) spectroscopy to chemically map ECM root tip cryosections, with the aim of visualising potential transfer or storage compounds directly at the mycorrhizal interface.

Spectral mapping reveals consistent spatial patterns across multiple ECM root tip cross sections. Distinct spectral bands are associated with the plant stele and the hyphal mantle, suggesting the presence of tissue-specific spectral bands at the ECM interface. Correspondingly, multivariate analysis shows a clear separation between plant and fungal tissues. In contrast, spectra from a putative Hartig net region overlap with both domains, consistent with a chemically heterogeneous interface where plant and fungal molecular signatures converge.

These first data demonstrate the feasibility of O-PTIR for resolving chemically distinct domains within ECM root tips. This approach provides a promising foundation for investigating the spatial organisation of metabolites at the ECM interface and highlights the potential of high-resolution vibrational spectroscopy for studying nutrient exchange at biologically complex interfaces.

How to cite: Gorka, S., Imminger, S., Schintlmeister, A., and Kaiser, C.: Chemical mapping of the ectomycorrhizal interface using optical photothermal infrared spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13969, https://doi.org/10.5194/egusphere-egu26-13969, 2026.

Many agroecosystems experience soil nitrogen (N), phosphorus (P), or potassium (K) deficiencies due to imbalanced fertilization or insufficient replenishment of nutrients withdrawn by biomass harvest. Nutrient deficiencies affect both arbuscular mycorrhizal fungi (AMF) and their associated plant hosts. Since AMF and plant communities are interconnected by their symbiosis, soil nutrient deficiencies can indirectly influence AMF communities through changes in plant community composition and vice versa. Furthermore, changes in soil nutrient availability alter soil physicochemical properties, thereby affecting both AMF and plant communities.

This study examined the coupled responses of AMF and belowground plant communities to long-term soil N, P and K deficiencies in a managed grassland. Additionally, we evaluated the associations between AMF and belowground plant communities, particularly at the genus and functional guild levels, while controlling for edaphic factors.

The study was conducted in a long-term managed grassland experiment in Admont (Styria, Austria), where N, P, and K, as well as lime and organic fertilizers, have been applied in different combinations for more than 70 years. Aboveground vegetation was harvested three times annually for over seven decades, resulting in long-term nutrient depletion of specific nutrients in non-fertilized plots. AMF communities in soil and roots were characterized using RNA- and DNA-based amplicon sequencing of the 18S rRNA gene, respectively. Belowground plant community composition was evaluated by amplicon sequencing of the chloroplast rbcL (RuBisCo large subunit) gene region from mixed root samples.

Our analysis shows that AMF and belowground plant community compositions differed significantly between plots receiving lime and organic fertilizers, and those fertilized with inorganic treatments. N, P, and K deficiencies affected both soil AMF and plant community compositions, whereas root-associated AMF community compositions responded significantly to only K deficiency. Since pH exerted the strongest influence on soil and root AMF as well as belowground plant community compositions, we performed Partial Mantel tests controlling for pH to examine associations between AMF and plant communities. Both soil and root AMF communities were significantly correlated with belowground plant community composition, with comparable correlation strengths for soil AMF (r=0.20, p<0.01) and root AMF (r=0.21, p<0.01). Partial correlation (controlling for pH) analyses between plant and AMF genera showed that more correlations were observed between root-associated AMF and plant genera than between soil AMF and plant genera. Additionally, all AMF genera showing correlations with plant genera belonged to the rhizophilic functional guild, which is characterized by a higher proportion of intraradical relative to extraradical hyphae.

Our findings suggest that long-term soil nutrient depletion influences AMF and plant community composition both directly and indirectly, through shifts in soil parameters and plant–AMF associations. They further indicate that rhizophilic AMF play a central role in mediating plant–AMF associations. These findings highlight that integrating the ecology of subsurface AMF communities—often overlooked beyond monoculture frameworks—can substantially enhance our understanding of plant community responses in a changing environment.

How to cite: Jenab, K., Guseva, K., Schmidt, H., Pötsch, E. M., Richter, A., Jansa, J., and Kaiser, C.: Long-term soil nutrient deficiencies reshape connections between arbuscular mycorrhizal fungi and plant communities in a managed grassland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17487, https://doi.org/10.5194/egusphere-egu26-17487, 2026.

Ectomycorrhizal fungi (ECM) form mutualistic associations with tree roots, enhancing nutrient and water uptake and improving tree resistance to drought stress. ECM associations generally improve plant performance but act as strong carbon sinks, altering carbon allocation within the root system and modifying its architecture. A high degree of ECM colonization has been associated with increased root branching and the formation of short, swollen root tips. However, the role of ECM in shaping root system functional architectural traits remains unclear.

For instance, root diameter is a key trait differentiating fundamentally different functions, with fine roots mainly serving resource uptake and coarse roots mainly serving axial transport. Yet, studies observed ECM colonization leading to both stimulation and suppression of fine‑root production. These contrasting findings might derive from the widespread use of the <2 mm diameter threshold to define fine roots, a broad range lumping together root structures that differ both anatomically and functionally.

In this study, we distinguish two functionally different components of the fine-root system: ultrafine, absorptive feeder roots (diameter <0.5 mm) and thicker, transport/structural fine roots (0.5–2 mm). We then determine whether the degree of ECM colonization is associated with relative changes in ultrafine (<0.5 mm) root abundance.

We collected root samples from oak (Quercus petraea), beech (Fagus sylvatica), and larch (Larix decidua) saplings planted in 2024 at three sites in Northern Luxembourg that differ in land‑use history. At planting, half of the saplings received a commercial mycorrhizal inoculant. We stained root system subsamples with lactophenol cotton blue to facilitate ECM detection and counted the colonized root tips under a digital microscope. All root samples were later imaged using a flatbed scanner, and images were analyzed with WinRhizo software to quantify root length distribution across seven diameter classes (from <0.1 mm to 0.6-2 mm, in 0.1 mm increments). We then assessed relationships between ECM colonization and the proportion of ultrafine roots (< 0.5 mm) for each root sample.

The analysis revealed an overall negative correlation between ECM colonization and ultrafine root proportion. However, when examining sites separately, this trend was not observed at the site with former pasture land use. There, inoculated saplings showed both relatively high ECM colonization and high ultrafine root proportion. As the other two sites were former spruce stands (typically nutrient-poor), we argue that the greater nutrient availability at the ex-pasture site promoted the production of ultrafine roots, whereas high ECM colonization may reflect the legacy of the inoculation treatment rather than indicating substantial hyphal activity. Ongoing soil nutrient analyses will help confirm this interpretation.

Overall, the results suggest that, in nutrient poor soils, root systems may adjust their ultrafine feeder root proportion according to the degree of mycorrhization. We argue that this adjustment may potentially allow plants to maximize the benefits of the ECM association by reducing investment in short-lived feeder roots, whose function can be replaced by ECM.

How to cite: Ceolin, S., Schymanski, S., Gerekens, J., Juilleret, J., and Hissler, C.: Ectomycorrhizal colonization reduces ultra-fine root abundance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20261, https://doi.org/10.5194/egusphere-egu26-20261, 2026.

Urbanization highly impacts soil properties and microbial communities in remaining soil patches. Tiny Forests, small densely planted native forest patches, represent an increasingly widespread nature-based solution to restore urban biodiversity. However, empirical data on their soil microbial communities remain scarce.

In this study we assessed fungal communities in ten Tiny Forests and ten paired adjacent urban open spaces (control sites) in Berlin and Frankfurt, Germany, using DNA metabarcoding.

We could show, that urban soils harbored high fungal diversity, with significant variation between Tiny Forests and control sites as well as among individual sites. Tiny Forests supported fungal communities specialized in decomposition and nutrient cycling, while control sites showed higher overall species richness. Community composition differed between Tiny Forests and control sites, yet site-specific patterns revealed that local environmental conditions highly shape fungal communities alongside land use effects.

Taxonomic patterns indicated that differences between Tiny Forests and control sites were not limited to community structure but also involved shifts in dominant taxa. Control sites showed higher abundances of plant-associated and potentially pathogenic fungi, whereas Tiny Forests were characterized by saprotrophic taxa linked to organic matter turnover and nutrient mobilization. In addition, regional differences between Berlin and Frankfurt contributed to community composition, emphasizing the combined influence of vegetation, soil conditions, and local environmental context.

These findings show that Tiny Forests harbor distinct fungal communities compared to adjacent control sites, with a shift toward saprotrophic taxa involved in decomposition and nutrient cycling. Our results indicate that Tiny Forests can alter urban soil fungal communities, though the strong site-specific variation highlights that local environmental conditions play an equally important role in shaping these communities.

How to cite: Schalamun, M., Scharfe, S., Pjevac, P., and Hinterdobler, W.: Fungal Community Responses in Tiny Forests in Urban Areas in Germany , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20953, https://doi.org/10.5194/egusphere-egu26-20953, 2026.