Ectomycorrhizal fungi in culture respond differently to increased carbon availability

Pisolithus microcarpus isolates with contrasting abilities to colonise Eucalyptus grandis exhibit significant differences in metabolic signalling

Biotic factors in fungal exudates impact plant-fungal symbioses establishment. Mutualistic ectomycorrhizal fungi play various ecological roles in forest soils by interacting with trees. Despite progress in understanding secreted fungal signals, dynamics of signal production in situ before or during direct host root contact remain unclear. We need to better understand how variability in intra-species fungal signaling at these stages impacts symbiosis with host tissues. Using the ECM model Pisolithus microcarpus, we selected two isolates (Si9 and Si14) with different abilities to colonize Eucalyptus grandis roots. Hypothesizing that distinct early signalling and metabolite profiles between these isolates would influence colonization and symbiosis, we used microdialysis to non-destructively collect secreted metabolites from either the fungus, host, or both, capturing the dynamic interplay of pre-symbiotic signalling over 48 hours. Our findings revealed significant differences in metabolite profiles between Si9 and Si14, grown alone or with a host root. Si9, with lower colonization efficiency than Si14, secreted a more diverse range of compounds, including lipids, oligopeptides, and carboxylic acids. In contrast, Si14's secretions, similar to the host's, included more aminoglycosides. This study emphasizes the importance of intra-specific metabolomic diversity in ectomycorrhizal fungi, suggesting that early metabolite secretion is crucial for establishing successful mutualistic relationships.

Environmental dependency of ectomycorrhizal fungi as soil organic matter oxidizers

Forest soils play a pivotal role as global carbon (C) sinks, where the dynamics of soil organic matter (SOM) are significantly influenced by ectomycorrhizal (ECM) fungi. While correlations between ECM fungal community composition and soil C storage have been documented, the underlying mechanisms behind this remain unclear. Here, we conducted controlled experiments using pure cultures growing on naturally complex SOM extracts to test how ECM fungi regulate soil C and nitrogen (N) dynamics in response to varying inorganic N availability, in both monoculture and mixed culture conditions. ECM species dominant in N-poor soils exhibited superior SOM decay capabilities compared with those prevalent in N-rich soils. Inorganic N addition alleviated N limitation for ECM species but exacerbated their C limitation, reflected by reduced N compound decomposition and increased C compound decomposition. In mixed cultures without inorganic N supplementation, ECM species with greater SOM decomposition potential facilitated the persistence of less proficient SOM decomposers. Regardless of inorganic N availability, ECM species in mixed cultures demonstrated a preference for C over N, intensifying relatively labile C compound decomposition. This study highlights the complex interactions between ECM species, their nutritional requirements, the nutritional environment of their habitat, and their role in modifying SOM.

The Conservation and Study of Macromycetes in the Komarov Botanical Institute Basidiomycetes Culture Collection-Their Taxonomical Diversity and Biotechnological Prospects

Culture collections (CCs) play an important role in the ex situ conservation of biological material and maintaining species and strains, which can be used for scientific and practical purposes. The Komarov Botanical Institute Basidiomycetes Culture Collection (LE-BIN) preserves a large number of original dikaryon strains of various taxonomical and ecological groups of fungi from different geographical regions. Started in the late 1950s for the investigation of Basidiomycetes' biological activity, today, in Russia, it has become a unique specialized macromycetes collection, preserving 3680 strains from 776 species of fungi. The Collection's development is aimed at ex situ conservation of fungal diversity, with an emphasis on preserving rare and endangered species, ectomycorrhizal fungi, and strains useful for biotechnology and medicine. The main methods applied in the collection for maintaining and working with cultures are described, and the results are presented. Some problems for the isolation and cultivation of species are discussed. The taxonomical structure and variety of the strains in the collection fund are analyzed, and they show that the taxonomical diversity of fungi in the LE-BIN is commensurable with the largest CCs in the world. The achievements from the ex situ conservation of the diversity of macromycetes and the main results from the screening and investigation of the collection's strains demonstrate that a number of strains can be prospective producers of enzymes (oxidoreductases and proteases), lipids, and biologically active compounds (terpenoids, phthalides, etc.) for biotechnology and medicine.

Carbon availability affects already large species-specific differences in chemical composition of ectomycorrhizal fungal mycelia in pure culture

Although ectomycorrhizal (ECM) contribution to soil organic matter processes receives increased attention, little is known about fundamental differences in chemical composition among species, and how that may be affected by carbon (C) availability. Here, we study how 16 species (incl. 19 isolates) grown in pure culture at three different C:N ratios (10:1, 20:1, and 40:1) vary in chemical structure, using Fourier transform infrared (FTIR) spectroscopy. We hypothesized that C availability impacts directly on chemical composition, expecting increased C availability to lead to more carbohydrates and less proteins in the mycelia. There were strong and significant effects of ECM species (R2 = 0.873 and P = 0.001) and large species-specific differences in chemical composition. Chemical composition also changed significantly with C availability, and increased C led to more polysaccharides and less proteins for many species, but not all. Understanding how chemical composition change with altered C availability is a first step towards understanding their role in organic matter accumulation and decomposition.

Plant productivity response to inter- and intra-symbiont diversity: Mechanisms, manifestations and meta-analyses

Symbiont diversity can have large effects on plant growth but the mechanisms generating this relationship remain opaque. We identify three potential mechanisms underlying symbiont diversity-plant productivity relationships: provisioning with complementary resources, differential impact of symbionts of varying quality and interference between symbionts. We connect these mechanisms to descriptive representations of plant responses to symbiont diversity, develop analytical tests differentiating these patterns and test them using meta-analysis. We find generally positive symbiont diversity-plant productivity relationships, with relationship strength varying with symbiont type. Inoculation with symbionts from different guilds (e.g. mycorrhizal fungi and rhizobia) yields strongly positive relationships, consistent with complementary benefits from functionally distinct symbionts. In contrast, inoculation with symbionts from the same guild yields weak relationships, with co-inoculation not consistently generating greater growth than the best individual symbiont, consistent with sampling effects. The statistical approaches we outline, along with our conceptual framework, can be used to further explore plant productivity and community responses to symbiont diversity, and we identify critical needs for additional research to explore context dependency in these relationships.

Survival and growth of saprotrophic and mycorrhizal fungi in recalcitrant amine, amide and ammonium containing media

The elimination of hazardous compounds in chemical wastes can be a complex and technically demanding task. In the search for environmental-friendly technologies, fungal mediated remediation and removal procedures are of concern. In this study, we investigated whether there are fungal species that can survive and grow on solely amine-containing compounds. One compound containing a primary amine group; 2-diethylaminoethanol, one compound with a primary amide group; 2,6-dichlorobenzamide (BAM), and a third compound containing a quaternary ammonium group; N3-trimethyl(2-oxiranyl)methanaminium chloride, were selected. The choice of these compounds was motivated by their excessive use in large scale manufacturing of protein separation media (2-diethylaminoethanol and the quaternary amine). 2,6-dichlorobenzamide, the degradation product of the herbicide 2,6-dichlorobenzonitrile (dichlobenil), was chosen since it is an extremely recalcitrant compound. Utilising part of the large fungal diversity in Northern European forests, a screening study using 48 fungal isolates from 42 fungal species, including saprotrophic and mycorrhizal fungi, was performed to test for growth responses to the chosen compounds. The ericoid (ERM) mycorrhizal fungus Rhizoscyphus ericae showed the best overall growth on 2-diethylaminoethanol and BAM in the 1-20 g L-1 concentration range, with a 35-fold and 4.5-fold increase in biomass, respectively. For N3-trimethyl(2-oxiranyl)methanaminium chloride, the peak growth occurred at 1 g L-1. In a second experiment, including three of the most promising fungi (Laccaria laccata, Hygrophorus camarophyllus and Rhizoscyphus ericae) from the screening experiment, a simulated process water containing 1.9% (w/v) 2-diethylaminoethanol and 0.8% (w/v) N3-trimethyl(2-oxiranyl)methanaminium chloride was used. Laccaria laccata showed the best biomass increase (380%) relative to a control, while the accumulation for Rhizoscyphus ericae and Hygrophorus camarophyllus were 292% and 136% respectively, indicating that mycorrhizal fungi can use amine- and amide-containing substrates as nutrients. These results show the potential of certain fungal species to be used in alternative green wastewater treatment procedures.

Carbon for nutrient exchange between Lycopodiella inundata and Mucoromycotina fine root endophytes is unresponsive to high atmospheric CO2

Non-vascular plants associating with arbuscular mycorrhizal (AMF) and Mucoromycotina 'fine root endophyte' (MFRE) fungi derive greater benefits from their fungal associates under higher atmospheric [CO₂] (a[CO₂]) than ambient; however, nothing is known about how changes in a[CO₂] affect MFRE function in vascular plants. We measured movement of phosphorus (P), nitrogen (N) and carbon (C) between the lycophyte Lycopodiella inundata and Mucoromycotina fine root endophyte fungi using ³³P-orthophosphate, ¹⁵ N-ammonium chloride and ¹⁴CO₂ isotope tracers under ambient and elevated a[CO₂] concentrations of 440 and 800 ppm, respectively. Transfers of ³³P and ¹⁵ N from MFRE to plants were unaffected by changes in a[CO₂]. There was a slight increase in C transfer from plants to MFRE under elevated a[CO₂]. Our results demonstrate that the exchange of C-for-nutrients between a vascular plant and Mucoromycotina FRE is largely unaffected by changes in a[CO₂]. Unravelling the role of MFRE in host plant nutrition and potential C-for-N trade changes between symbionts under different abiotic conditions is imperative to further our understanding of the past, present and future roles of plant-fungal symbioses in ecosystems.

Suillus mycelia under elevated atmospheric CO2 support increased bacterial communities and scarce nifH gene activity in contrast to Hebeloma mycelia

Bacterial communities associated with mycorrhizal roots are likely to respond to rising atmospheric CO(2) levels in terms of biomass, community composition and activity since they are supported by the carbon (C) flow outside the root tips, especially by exudation of low molecular weight organic compounds. We studied how general bacterial and diazotrophic communities associated with ectomycorrhizal (ECM) fungi respond to different belowground C supply conditions, mediated by elevated atmospheric CO(2) concentration under nitrogen (N) limited conditions. Microcosm systems were constructed using forest soil and Scots pine seedlings, which were either pre-inoculated with one of the ECM fungal species Hebeloma velutipes or Suillus variegatus, or non-inoculated. These fungal species differ in C allocation and exudation patterns. Seedlings were maintained under ambient (380 ppm) or elevated (700 ppm) CO(2) levels for 6 months. Quantitative polymerase chain reaction (PCR) showed a significant increase in 16S rRNA gene copy numbers for Suillus-inoculated microcosms under elevated CO(2) compared to ambient CO(2). The copy numbers of the nitrogenase reductase (nifH) gene were under the detection limit in all samples regardless the CO(2) treatments. Denaturing gradient gel electrophoresis analysis of PCR-amplified nifH genes revealed simple and consistent communities in all samples throughout the incubation period. A nested reverse transcription PCR approach revealed that expression of nifH genes were detected in some microcosms. Our findings suggest that the effect of mycorrhizal fungi on soil bacteria may vary depending on C supply and fungal species.

Intraspecific diversity regulates fungal productivity and respiration

Individuals and not just species are key components of biodiversity, yet the relationship between intraspecific diversity and ecosystem functioning in microbial systems remains largely untested. This limits our ability to understand and predict the effects of altered genetic diversity in regulating key ecosystem processes and functions. Here, we use a model fungal system to test the hypothesis that intraspecific genotypic richness of Paxillus obscurosporus stimulates biomass and CO(2) efflux, but that this is dependent on nitrogen supply. Using controlled experimental microcosms, we show that populations containing several genotypes (maximum 8) of the fungus had greater productivity and produced significantly more CO(2) than those with fewer genotypes. Moreover, intraspecific diversity had a much stronger effect than a four-fold manipulation of the carbon:nitrogen ratio of the growth medium. The effects of intraspecific diversity were underpinned by strong roles of individuals, but overall intraspecific diversity increased the propensity of populations to over-yield, indicating that both complementarity and selection effects can operate within species. Our data demonstrate the importance of intraspecific diversity over a range of nitrogen concentrations, and the need to consider fine scale phylogenetic information of microbial communities in understanding their contribution to ecosystem processes.

Small genetic differences between ericoid mycorrhizal fungi affect nitrogen uptake by Vaccinium

Ericoid mycorrhizal fungi have been shown to differ in their pattern of nitrogen (N) use in pure culture. Here, we investigate whether this functional variation is maintained in symbiosis using three ascomycetes from a clade not previously shown to include ericoid mycorrhizal taxa. Vaccinium macrocarpon and Vaccinium vitis-idaea were inoculated with three fungal strains known to form coils in Vaccinium roots, which differed in their patterns of N use in liquid culture. (15)N was used to trace the uptake of -N, -N and glutamine-N into shoots. (15)N transfer differed among the three fungal strains, including two that had identical internal transcribed spacer (ITS) sequences, and was quantitatively related to fungal growth in liquid culture at low carbon availability. These results demonstrate that functional differences among closely related ericoid mycorrhizal fungi are maintained in symbiosis with their hosts, and suggest that N transfer to plant shoots in ericoid mycorrhizas is under fungal control.