Globally soil fauna can consume about half of litter fall. Important question is how this activity affect mineralization and stabilization of soil organic matter. Here we explore how much fauna effect litter decomposition and organic matter stabilization in soils of various ages supplied by litter of various quality.   Laboratory mesocosm consist from litter and mineral layer mineral soil originated either from spruce and alder stand which were growing either on post mining soils (young soil) or from soil in close vicinity of post mining sites (mature soil), mineral soils were supplied by matching litter, mesocosms were either without fauna or supplied by two individuals of earthworm Aporectodea rosea. Results show significant effect of tree, soil age and earthworm; alder respire more than spruce, young soil respire more than old soil, and mesocosms with earthworms respire more than without earthworms.  Earthworm effect show statistically significant interaction with tree and soil age, earthworms always increase respiration in alder soil, but in spruce only in mature soil while opposite was true for young soil.  In general earthworms promote removal of litter from soil surface and its accumulation in mineral soil. Earthworms promote C storage in MAOM  namely in young spruce soil. Results indicate that in young soils which are far from saturation (spruce on post mining soil) earthworm activity promote soil C storage most likely by promoting C storage in MAOM, in the contrary in mature,  C saturated soils, earthworms rather promote soil respiration.

How to cite: Frouz, J. and Irshad, S.: How the effect of earthworms on soil organic matter mineralization and stabilization is affected, by litter quality and stage of soil development., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1118, https://doi.org/10.5194/egusphere-egu23-1118, 2023.

Among the high diversity of urban soils, of particular interest are soil constructures (Technosols) created by man to solve certain problems: landscaping and recultivation. Microorganisms quickly respond to external influences and are indicators of changes occurring in ecosystems. Microfungi determine the soil health, and the activity of saprotrophic microscopic fungi can lead to improved soil properties associated with soil fertility.

The aim of the study was to evaluate the quantitative indicators of soil fungal communities of 2-years-old Technosols, created on the basis of peat, sand and loam, in different climatic zones in comparison with background soils.

The studies were carried out in cities located in different climatic zones: subarctic (Apatity), temperate continental with a humid climate (Moscow), and temperate continental with a dry climate (Rostov-on-Don). Soil sampling was carried out at stations with soil constructures of a composition universal for all regions: peat/sand/loam in the ratio 1/1/1.

Quantitative assessment of the content of ribosomal genes of fungi was performed by real-time polymerase chain reaction (PCR). The fungal biomass was determined by luminescence microscopy method.

The predominance of fungal biomass over that of prokaryotes was revealed in all climatic zones, both in background soils and in Technosols. The fungal biomass in Technosols of different climatic zones varied from 0.073 to 0.790 mg/g of soil. In Apatity and Moscow, its values 2 years after the creation of Technosols were lower than in the background soil; in Rostov, the values were close. In the Technosols of Apatity and Moscow, microfungi were mainly in the form of mycelium, while in Rostov-on-Don, spores prevailed over mycelium. However, small spores prevailed in all zones, both in background soils and in Technosols. Over the 2-years period of Technosols development in the subarctic and the temperate zone, similar trends in the state of the fungal community were noted, while in the area with a warmer climate, other patterns were revealed.

The number of the fungal ITS rRNA ribosomal genes copies in the soils varied from 5.95×10⁸ in the Technosols of Apatity to 3.39×10⁹ gene copies/g soil in the background soil of the Moscow region. According to the quantitative content of fungal genes copies over a two-year period, the Technosols of Rostov-on-Don correspond to the background soils and slightly exceed the values of the latter. In the subarctic, the values of this indicator are also comparable for Technosols and background soils, while in Moscow, the number of copies of Technosols genes is 2.5 times less.

Thus, the change in the quantitative indicators of soil fungal communities over time makes it possible to judge the dynamics of the development of Technosols in different climatic zones. However, for such a short period (2 years), the state of fungal communities does not reach the state of the background ecosystems in any of the regions. We can only talk about trends in the parameters of the fungal community in the direction of background ecosystems.

How to cite: Korneykova, M., Nikitin, D., Vasilieva, M., and Vasenev, V.: Microscopis fungi of Technosols in cities of different climatic zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2092, https://doi.org/10.5194/egusphere-egu23-2092, 2023.

It is widely known that natural soils under different land use provide a heterogenous environment regarding nutrient availability. This affects plants as well as microorganisms such as arbuscular mycorrhizal fungi (AMF).  It can have an impact on the abundance and amount of root colonization by AMF. These complex systems are often studied in experimental setups, while the wider scope of natural systems shaping entire landscapes so far received less attention.

To unravel the impact of land use and the soil parent material (including the typical periglacial layering along slopes in the area) on nutrient availability and thus AMF root colonization and total abundance, two forest-grassland-creek catenae were selected in the low mountain region of the eastern Bavarian Forest (Germany). This landscape is characterized by the uniformity of the bedrock and its weathering product (saprolite), which decisively shapes the landscape. One of the two catenae was extensively used for feed production with 2-3 cuts per year. It received slurry twice a year as well as carbonic magnesium lime. The other catena had always been used as part of a deer browsing area with low stocking density. It has never been fertilized (apart from deer excretions) or limed and is mulched once per year. Soil profiles along both catenae were sampled and suction cups placed according to the periglacial layering, to investigate the nutrients in percolation- and interflow water coming downslope. Moreover, samples were taken for the investigation of AMF colonization and abundance according to the catena-profiles.

We will present our results on the nutrient dynamics observation along the two catenae. These consist of nutrient concentrations in slope water from the suction cups as well as carbon, nitrogen and phosphorus contents along the catenae. Moreover, we will show the corresponding AMF root colonization and AMF abundance data. We expect these data to show a correlation of nutrient dynamics along the slope with AMF colonization and abundance as well as a difference between the two sites in nutrient dynamics and resulting AMF occurrence, according to the divergent land use.

To summarize, we will provide a field-based observation of the impact of land use regimes and landscape-shaping geological disposition on nutrient dynamics along grassland slopes in the Bavarian Forest, which influence AMF colonization and abundance.

How to cite: Holmer, A. S., Lei, K., van Grinsven, S., and Völkel, J.: Nutrient Dynamics in Soil and Soil Water impact Arbuscular Mycorrhizal Fungi (AMF) Colonization and Abundance on Grassland Slopes in Eastern Bavaria, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6338, https://doi.org/10.5194/egusphere-egu23-6338, 2023.

In nature, complex organismic communities have evolved for optimal colonization of habitats. Interkingdom interactions between fungi and bacteria can be mutualistic, but also parasitic. Ongoing research reveals an increasing number of fungi inhabited by bacteria, which results in diverse phenotypic alterations in fungi. Therefore, we were interested, how widespread the presence of endofungal bacteria is in strains of the genus Trichoderma, which fulfil a variety of ecological functions – from beneficial plant interaction and mycoparasitism on pathogenic fungi to degradation of cellulosic litter.

We found evidence for the presence of endohyphal bacteria of different species in the majority of Trichoderma strains tested. Interestingly, we did not detect a preference of specific bacterial species for a fungal species or vice versa. In the saprophyte Trichoderma reesei, we detected endohyphal bacteria by confocal microscopy and specific staining. We could confirm the presence of a Methylobacterium species in the hyphae by sequencing of 16S rRNA. After curing T. reesei QM6a from the bacteria using antibiotics, re-sequencing of the 16S rRNA and whole genome sequencing of the isolated bacterium confirmed its identity. Again, the association with Methylobacterium turned out to be strain specific with strains from different tropic habitats than species specific. Isolation of the bacterium from T. reesei QM6a showed that it is not obligate biotroph and both the bacterium and the fungus are viable individually.

In order to evaluate the interrelationship of Methylobacterium and T. reesei, we applied phenotype microarrays to assess metabolic contributions of the bacterium and performed functional assays. Antagonism against pathogenic fungi on plates was not perturbed in the absence of Methylobacterium from T. reesei on no general growth defect was obvious. However, BIOLOG analysis clearly showed a light dependent alteration of growth in the cured strain especially on xylitol, an intermediate of hemicellulose degradation and D-mannitol, a carbohydrate with important roles in stress response and carbon storage.

Accordingly, comparative transcriptome analysis between wild-type and cured fungal strains indicates an influence of the endohyphal Methylobacterium of T. reesei QM6a on diverse metabolic pathways, with different patterns upon growth in light or in darkness. The hypothesis, that the endohyphal bacterium of T. reesei QM6a supports the metabolic adaptation of the fungus to growth in light is corroborated by sequencing the genome of Methylobacterium, which comprises multiple genes with light-response associated protein domains.

In summary, we discovered an intriguing new physiological aspect of T. reesei, which opens up a new field of research with high potential for gaining an in depth understanding of interkingdom interaction of fungi with their prokaryotic inhabitants. On a broader scale, our findings highlight the abundance and important interaction of soil fungi with their endohyphal bacteria for ecosystem functions like carbon degradation, which is currently hardly considered in microbiome research and warrants further studies into the role of such interkingdom interactions in microbial communities.

How to cite: Schmoll, M., Schalamun, M., Beier, S., Scalmani, I., Compant, S., and Hinterdobler, W.: An endohyphal bacterium impacts growth and metabolism of carbohydrates associated with storage and hemicellulose degradation of its fungal host, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8071, https://doi.org/10.5194/egusphere-egu23-8071, 2023.

Lytic bacteriophages are major drivers of bacterial mortality and biogeochemical cycles in several ecosystems, roles that have also been hypothesized in soil. Phage particles have no metabolism of their own, yet to achieve sustainable replication they must travel from one host to the next through the surrounding environment. Evidence from soil physics and phage biology suggests that this is a hazardous journey for unprotected phages, especially under the prevailing assumption that dispersal occurs by diffusion. However, many other viruses overcome dispersal challenges by taking advantage of vectors – third-party organisms that carry the virus from one host to the next. We hypothesized that bacterivorous nematodes play this role in soil, picking up phages while feeding on bacteria and transferring them to uninfected bacteria while foraging. We postulated that nematodes would provide active and directed transport of phages between bacterial patches via two possible mechanisms. First, nematode intestines could temporarily harbour infected bacteria during nematode movement. Second, nematodes could carry phages through external attachment to the nematode cuticle. Using experiments with model nematodes (C. elegans) and bacteria (E. coli, P. putida) along with phages (T7, Phi Ppu-W11) we confirmed that transfer occurs at high frequency when facilitated by nematodes, and does not occur without nematodes. Resource availability was found to influence the transfer by modulating nematode behaviour in agar, but this effect was not found in structured compost habitats. Based on these results we propose that vectors are crucial for soil phage dispersal, suggesting that phage roles in soil function are mediated by interactions with local fauna.

How to cite: Mason-Jones, K., Dietz, C., Zwart, M., Helder, J., and van Sluijs, L.: Nematode hitchhiking in soil bacteriophage dispersal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10742, https://doi.org/10.5194/egusphere-egu23-10742, 2023.

Animal grazing is known to affect both, soil carbon storage and above and belowground biodiversity. However, we lack a more detailed understanding how specific soil properties might determine biodiversity and soil carbon storage as affected by grazing. Thus, in the present work we aim to connect the geo- and biodiversity with organic matter decomposition functionalities of the soil community, and thus identify how this regulates soil carbon and nitrogen storage. Therefore, we analysed aboveground plant biodiversity, soil microbial functional diversity, and soil organic matter (SOM) characteristics on a summer grazed island (Eskilsø) in a Danish fjord. Specifically, plant biodiversity analyses were conducted and topsoils sampled at thirty plots (4 replicated soil samples per plot) on the ca. 140 ha island. The plots cover the island’s main habitats: salt meadows, meadows, and developing dry grasslands. Soils were analysed for organic carbon (OC), total nitrogen (TN), organic phosphorus (OP), inorganic phosphorus (IP), and pH. Additionally, community level physiological profiles (CLPP) were analysed using the Microresp technique to make inferences about soil microbial functional diversity and activities. 
We are able to demonstrate that plant biodiverse plots contained greater contents and stocks of SOM. This also correlates with an increased soil microbial functional diversity. The findings are in line with the often observed positive interaction between aboveground diversity and belowground functionality of the soil biome in grassland ecosystems, partly due to increased amounts and diversity of rhizodeposits. As microbial activity is important for mediating the turnover of plant derived organic matter into more stable soil OM pools, this reflects the correlation with higher soil OC stocks and thus links to soil carbon persistence. For the studied island ecosystem we are able to demonstrate how the fate of soil organic matter is functionally linked to the interactions between above- and below-ground components of the ecosystem. 

How to cite: O'Keeffe, J., Aagaard Kristensen, J., Fløjgaard, C., and Müller, C. W.: Interplay between aboveground plant biodiversity, soil organic matter, and soil microbial functional diversity in a grazed Danish island ecosystem, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11680, https://doi.org/10.5194/egusphere-egu23-11680, 2023.

Root fungal endophytes are present in most plants and co-occur with other mycorrhizal fungi. Their intraradical colonization suggests a special, differentiated relationship with host plants and increases opportunities for close interactions between hosts and fungal symbionts (e.g., carbon to nutrient exchange or hormone signalling). During the symbiosis between plant and arbuscular mycorrhizal fungi (AMF), specific trading features are established. These features have been incorporated into the biological market hypothesis, where dynamics of carbon to nutrient trading in the plant‐mycorrhizal fungal mutualism are compared to trades in a market economy. Multiple examples of similar dynamics have been shown for root endophytic fungi: soil nutrients are transported to the plant in exchange for carbon. However, plants have been shown to be able to reward AMF that exchange larger amount of nutrients (and vice versa), while at least some root fungal endophytes have been described as “by-product mutualists”, where the fungal symbiont enhances the performance and fitness of their host plant by providing benefits, but not requiring major investments from the host. Whereas AMF have received large attention, the role of fungal endophytes in carbon to nutrient exchange with plants remains largely uninvestigated.

In this study we aimed at developing a controlled system to evaluate effects of multiple fungal endophytes (Colletotrichum tofieldiae and Cladophialophora chaetospira) on a model plant species (Lotus japonicus) and their role in the carbon to nitrogen exchange in the presence of different nitrogen sources (organic and inorganic). We further developed this controlled system to include plants colonized by AMF. Two-compartment petri dishes were used to achieve plant root colonization in a nutrient limited compartment and allow separation of nutrient sources only accessible by the fungal endophytes. We performed dual ¹⁵N and ¹³CO₂ pulse-labelling experiments to trace the fate of plant carbon into fungal biomass and of different nitrogen sources into plant aboveground tissues. We analysed root for RNA sequencing to gain insights into the genetic controls over the observed dynamics.

We successfully established a controlled system and found that C. tofieldiae can elicit positive effects on plant growth and nitrogen acquisition. These effects are dependent on the nutrient source to which the fungus has access to, with positive effects displayed in the presence of organic nitrogen. Plants exchange relatively less carbon to C. tofieldiae accessing organic nitrogen. Root transcriptome shows specific changes in response to root fungal colonization which are dependent on the nitrogen source available to the fungal endophyte. Furthermore, the presence of AMF did not modify the observed carbon to nitrogen exchange dynamics.

In conclusion we show that the root fungal endophyte C. tofieldiae can play an important role for plant nutrient acquisition in the presence of organic nitrogen. The trade of nitrogen for plant carbon displays different features from the AMF symbiosis (i.e., higher amount of nitrogen is not rewarded with plant carbon investment) and different gene regulations are involved. Our results indicate complementarity between C. tofieldiae and AMF during root colonization, offering mechanistic explanations for the concomitant presence of AMF and fungal endophytes in terrestrial ecosystems.

How to cite: Canarini, A., Zheng, J., Koba, K., Séneca, J., Fujii, K., Furukawa, S., Honjo, M., Kudoh, H., Nishino, T., Kobae, Y., Hiruma, K., Narisawa, K., Field, K., Huang, Y.-T., Kiers, T., and Toju, H.: Fungal root endophytes and their role in carbon to nitrogen exchange with plants, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12246, https://doi.org/10.5194/egusphere-egu23-12246, 2023.

Arctic soils store nearly half of the global soil organic carbon, but what will happen with this large carbon pool if soil macrofauna, able to ingest organic matter accumulated at depths in the soil, establish in the Arctic? The question is justified as emerging evidence suggests that low soil organic carbon (SOC) turnover rates in high latitude ecosystems could, in addition to abiotic factors, partly be due to the current lack of larger detritivores that can stimulate the breakdown of organic matter. Earthworms are large detritivores increasing their distribution into arctic ecosystems. With potential to both increase stabilisation and decomposition of SOC, but also enhance plant productivity, it has been difficult to determine what net effect earthworms have on ecosystem C storage. The scientific debate around this ‘earthworm dilemma’ has however primarily focused on the fate of SOC in response to earthworms, leaving cascading effects on plant productivity largely undiscussed.

Here, we use a four-year outdoor experiment to study the effects of introducing earthworms to tundra vegetation types on both plant biomass (above and belowground) and SOC. We found that earthworms invasive to the Arctic: i) reduced the SOC pool beneath herb dominated tundra while they increased the SOC pool under dwarf-shrub dominated tundra; ii) increased the below ground biomass in both vegetation types; and iii) increased the total plant biomass C to the degree that it offset the SOC losses from the herb dominated soil. In the dwarf-shrub vegetation, earthworms increased both the plant C pool and the SOC pool resulting in a net increase of the ecosystem C stock. We highlight that the effect on root growth seems of great importance when predicting how ecosystem C sequestering responds to invasive earthworms. Both through increased plant biomass C but also through increased deposition of persistent root-derived organic matter.

How to cite: Jonsson, H., Blume-Werry, G., Wackett, A., Arvidsson, E., Lundgren, O., and Klaminder, J.: Increased tundra root biomass offset invasive earthworm effects on SOC decomposition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14905, https://doi.org/10.5194/egusphere-egu23-14905, 2023.

Wood decomposition has been studied extensively due to its importance in wood deterioration and carbon cycling processes. Wood decaying fungi are categorised into white rot, soft rot and brown rot. White rot fungi have an enzymatic mechanism by which they can digest lignin and crystalline cellulose. Instead, brown rot fungi lack the enzymes to digest lignin and crystalline cellulose. Several hypotheses have been made on the mechanism by which brown rot fungi mine carbon out without the required enzymes mainly focussing on extracellular metabolites and metal ions. Here, we investigate chemical and structural modifications on cellulose produced by saprotrophic fungi using Raman specrtroscopy under different conditions. In additions, known modifications introduced by chemicals on cellulose will also be compared to fungal changes on cellulose.

How to cite: Ahlawat, A. and Floudas, D.: Characterization of cellulose decomposed by saprotrophic fungi using Raman spectroscopy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16494, https://doi.org/10.5194/egusphere-egu23-16494, 2023.

Mycorrhizal fungi play a vital role in soil processes and form a large part of belowground biodiversity in tropic ecosystems. Unlike temperate forests, many tree species in tropical stands are dominated by arbuscular mycorrhizal fungi (AMF), which form high amount of extraradical mycelium and even rhizomorphs, penetrating both soil and leaf litter. The quantification of mycelium biomass in natural systems often being conducted with the use of sand filled in-growth mesh bags made of nylon mesh [1]. The use of plastic polymer for mesh bags in temperate systems is justified by low bioavailability of the material that can be hardly decomposed by soil bacteria and fungi or penetrated by roots or soil invertebrates. In a number of tropical forests, the activity of invertebrates is more aggressive, mostly due to the termites foraging, resulting in the disruption of the integrity of the mesh bags and consequent samples loss.

Here we introduce the use of dual-walled in-growth mesh bags made of nylon and stainless steel. Its relevance was attested in Dong Nai (Cat Tien) National Park in Southern Vietnam. The harvested biomass of extraradical EMF mycelium and taxonomic composition of EMF and AMF fungi was compared in regular and dual-walled in-growth mesh bags across two tropical rainforests, dominated by both EMF and AMF associated tree species. The biomass was accessed with PLFA analysis for fungal biomarkers 18:2ω6,9, 18:1ω9 [2] and 18:0 [3]. The taxonomic composition of extraradical mycelium from harvested in-growth mesh bags was studied with new-generation sequencing, including specific primer pair WANDA/AML2 for the SSU ribosomal RNA gene of AMF fungi and ITS fragment (primer pair ITS3/ITS4) for ectomycorrhizal fungi.

Double-walled mesh bags remained completely intact, while about 40% of regular mesh bags were damaged by termite activity after 180 days of exposure. The biomass of extraradical mycelium of ectomycorrhizal fungi was comparable between forests dominated by EMF and AMF associated trees and reached 114.5 and 122.1 µg of «fungal» carbon g^-1 of substrate respectively. The total amount of the three measured PLFA biomarkers did not differ between both variants of in-growth mesh bags and surrounding soil, while the median values were slightly higher for mesh bags compared to soil (1.9 and 1.6 µg g^-1 of substrate respectively). Application of ITS fragment was 100% positive among harvested mycelium samples from both forests, while AMF fungi were detected in 62% of samples from the forest dominated by AMF-associated trees and 70% samples from the forest dominated by EMF-associated trees.

This study was supported by Alexander von Humboldt Foundation (project 3.4-1071297-RUS-IP).

References:

[1] Wallander H, Nilsson LO, Hagerberg D, Bååth E (2001) Estimation of the biomass and seasonal growth of external mycelium of ectomycorrhizal fungi in the field. New Phytol 151:753–760. https://doi.org/10.1046/j.0028-646x.2001.00199.x

[2] Ruess L, Chamberlain PM (2010) The fat that matters: Soil food web analysis using fatty acids and their carbon stable isotope signature. Soil Biol Biochem 42:1898–1910. https://doi.org/10.1016/j.soilbio.2010.07.020

[3] Chen J, Ferris H, Scow KM, Graham KJ (2001) Fatty acid composition and dynamics of selected fungal-feeding nematodes and fungi. Comp Biochem Physiol B Biochem Mol Biol 130:135–144. https://doi.org/10.1016/S1096-4959(01)00414-6

How to cite: Zuev, A., Schaefer, I., Van Thinh, N., and Zueva, A.: Armored mesh bags: collecting mycelium of mycorrhizal fungi in a tropical rainforest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16888, https://doi.org/10.5194/egusphere-egu23-16888, 2023.