A majority of land plants establish symbiotic relationships with mycorrhizal fungi, which play a critical role in terrestrial ecosystems by regulating nutrient and carbon cycles, influencing soil structure, and contributing to ecosystem multifunctionality (Martin and Van Der Heijden, 2024). Approximately 80% of plant N and P are provided by these mutualistic fungi, and the majority of plant species depend on them for growth and survival. An estimated 20,000 fungal species, primarily belonging to the phyla Basidiomycota and Ascomycota, establish ectomycorrhizal (ECM) associations with approximately 6,000 plant species, mostly trees and shrubs (Van Der Heijden et al., 2015). ECM fungi are present in a diverse range of terrestrial ecosystems and are responsible for colonizing 60% of the trees in temperate and boreal forest ecosystems (Baldrian et al., 2023). These tree species, belonging to the Pinaceae, Fagaceae, Betulaceae, Nothofagaceae, Myrtaceae, or Dipterocarpaceae families, play crucial ecological and economic roles in both the northern and southern hemispheres.

During symbiosis development, ECM fungi differentiate the hyphal mantle, ensheathing the rootlets and an intraradical mycelial network, the so-called Hartig net, which penetrates host roots. In numerous ECM associations, an extraradical mycelium permeating the soil environment extends from ECM roots. Mycelial networks facilitate the acquisition of water and nutrients by plants and enhance their resistance to environmental stressors. ECM symbionts secrete extracellular enzymes that degrade soil organic matter (SOM) to facilitate nitrogen acquisition in their hosts (Nicolas et al., 2019). ECM fungi from different independently evolved lineages exhibit varying capacities to degrade SOM and transfer N to their hosts (Nicolas et al., 2019). In boreal and temperate forests, ECM fungi provide 70% of N flux to their hosts (Smith and Read, 2010). Consequently, ECM plays a crucial role in C and N cycles in forest soils. In exchange for soil minerals, 10–20% of photoassimilates are allocated to fungal partners by the host plant. Plant communities allocate 9.07 Gt of atmospheric CO₂ per year to their mycorrhizal symbionts (Hawkins et al., 2023).

The ascomycetous fungus Cenococcum geophilum, previously known as C. graniforme, is a cosmopolitan ECM fungus and one of the most prevalent mutualistic species found in soil fungal communities worldwide (LoBuglio, 1999; Figure 1). It forms mycorrhizal associations with over 200 trees, shrubs, and herbaceous species in boreal, temperate, and subtropical forests as well as in savannas and alpine meadows. As the only known ECM member of the class Dothideomycetes, C. geophilum exhibits several distinctive characteristics that distinguish it from other ECM fungi (LoBuglio, 1999; Obase et al., 2017). As an early colonizer of primary forest succession, C. geophilum contributes significantly to ecosystem stability and development. It is particularly important in nutrient cycling because it facilitates the transfer of nutrients, especially nitrogen (N) and phosphorus (P), from the soil to its host plants (LoBuglio, 1999). Additionally, C. geophilum enhances the drought resistance of its host plants (Coleman et al., 1989), a trait that is becoming increasingly important in the context of a warming world with an increased occurrence of drought events (Zheng et al., 2023). C. geophilum is therefore a compelling model system for research on fungal ecology, evolution, and mycorrhizal symbiosis.

The biological and ecological attributes of C. geophilum have been documented extensively (LoBuglio, 1999; Obase et al., 2017). Recently, genomics has emerged as a crucial tool for investigating the biology, evolution, and ecology of mutualistic symbionts including C. geophilum (Kohler et al., 2015; Peter et al., 2016; Miyauchi et al., 2020; Lebreton et al., 2021). This approach not only provides essential mechanistic insights but also identifies key genetic traits, such as adaptation to drought stress (Li et al., 2023; Zhang et al., 2024), which can be prioritized to select strains for the application of this mycorrhizal symbiont in forestry. This review provides a brief account of the biological and ecological attributes of C. geophilum, followed by a discussion of recent studies that have demonstrated the impact of genomics and related techniques (i.e., DNA metabarcoding, population genomics, and transcriptomics) on our understanding of this enigmatic mycorrhizal fungus. Additionally, it briefly explores the potential applications of C. geophilum in sustainable forestry and ecosystem restoration, highlighting the significance of understanding the functional traits and ecological roles of these ECM fungi in adapting to environmental changes. By consolidating the latest research findings, this review aims to identify knowledge gaps and suggest future research directions for this ubiquitous symbiont to address the global challenges in forestry and environmental sustainability.

The black fungus C. geophilum is distinguished by its septate dematiaceous hyphae, which contain high concentrations of melanin in their cell walls (Figure 1; Fernandez and Koide, 2013). This pigmentation enables mycelia to endure various environmental challenges including UV exposure, dehydration, high temperatures, enzymatic breakdown, antimicrobial agents, and heavy metal exposure (Pal et al., 2013). The resilience of C. geophilum enables it to thrive in challenging environments for several years, where other mycorrhizal fungi may find it difficult to survive (McCormack et al., 2017). Its hyphae show various shapes according to the growth medium and the age of the mycelial colony (Trappe, 1962). Chlamydospore-like structures have been observed in both solid and liquid media (Massicotte et al., 1992). These chlamydospore-like structures are always intercalary and rarely terminal in the mycelia (Mikola, 1948). This structure also exists in the taxonomically related species Glonium spp. (Amano, 1983) and Pseudocenococcum floridanum (Obase et al., 2016).

Cenococcum geophilum can differentiate sclerotium (Figure 1), which is a compact mass of hardened fungal mycelium containing nutrient reserves, including carbohydrates and lipids. The sclerotia constitute an underestimated source of polysaccharides in forest soils, accounting for 3.6% of the total carbohydrates in subalpine forest soils (Murayama and Sugiura, 2021). These melanized sclerotia resist decomposition by soil microorganisms (Fernandez and Koide, 2014) and remain viable for up to 40 years under extreme environmental conditions (Nyamsanjaa et al., 2022). They host specific fungal and bacterial communities (Obase et al., 2014; Narisawa et al., 2021).

Although molecular evidence, such as recombination and diploidy (see below), suggests the presence of unknown sexual stages in the life cycle of C. geophilum, no sexual structures have been observed under laboratory or field conditions (Bourne et al., 2014).

The only ECM fossil related to C. geophilum is Eomelanomyces cenococcoides gen. Spec. nov., discovered in a 52-million-year-old amber specimen from a lignite mine in Gujarat State, India (Beimforde et al., 2011). This amber was produced by representatives of Dipterocarpaceae trees in the early tropical broadleaf forests. The fossil is similar to the extant Cenococcum; however, it is distinguished by high variability in the branching of ECM rootlets and by the regular formation of microsclerotia and chlamydospore-like structures (Beimforde et al., 2011).

The identification of C. geophilum relies on a combination of morphological and molecular techniques, as it shares soil habitats and many physical characteristics with dark septate root endophyte (DSE) fungi such as Piceirhiza bicolorata and Cadophora finlandia (Rosling et al., 2003). DNA metabarcoding surveys have shown that this ECM fungus is a major component of the soil fungal communities in most of the forest ecosystems (Figure 2). It is considered a keystone species essential for maintaining the microbial network structure and stability (Zhu et al., 2024). As an early colonizer in primary successions, C. geophilum significantly contributes to ecosystem stability and development (LoBuglio, 1999). Its rapid establishment in disturbed or newly formed habitats creates favorable conditions for other plant species, thus playing a vital role in ecological succession and ecosystem recovery. Additionally, C. geophilum can collaborate with other bacteria to establish ECM associations under varying climatic conditions. Reis et al. (2021) examined beneficial symbiotic microorganisms, including ECM fungi and mycorrhiza helper bacteria in cork oak (Quercus suber L.) forests. C. geophilum and Bacillus sp. were among the most prevalent interacting microbes. Furthermore, Kataoka et al. (2009) reported that B. subtilis can enhance C. geophilum growth during symbiosis establishment. This mutual support benefits all three partners and could play a crucial role in forest resilience to future climate change.

Cenococcum geophilum is a cosmopolitan ECM fungus and one of the most prevalent species found in soil fungal communities worldwide (Figure 2). It forms ECM or ectendomycorrhizal associations with over 200 trees, shrubs, and herbaceous species in boreal, temperate, and subtropical forests as well as in savannas. In alpine and circumpolar biomes, C. geophilum establishes ectendomycorrhizas or ECM with herbaceous plants such as sedges or shrubs (Obase et al., 2017). Its abundance in tropical ecosystems is relatively low (Tedersoo et al., 2010; Bakray et al., 2024), although high root colonization and genetic diversity have been reported in the dry deciduous forests of Thailand (Phosri et al., 2012). However, C. geophilum ECM is seldom found in African or South American tropical forests (Becerra and Zak, 2011; Bâ et al., 2012). It has also been found at the edges of deserts (Massicotte et al., 1992) and in sandy forests of Picea mongolica (Bao, 2005).

Zheng et al. (2023) employed the MaxEnt model (Phillips et al., 2017) to analyze the historical shifts in geographical distribution patterns of C. geophilum since the Last Glacial Maximum and forecast its future spread under changing climatic conditions. They showed that this geographical distribution is closely associated with climatic factors, particularly temperature and precipitation. Temperature has greater relative importance than precipitation. This is also true for majority of the ECM fungi (Bennett and Classen, 2020). C. geophilum occupied a significantly smaller area during the Last Glacial Maximum and mid-Holocene, primarily concentrated in China’s Qinling–Huaihe Line region and eastern Peninsular Malaysia. As global temperatures continue to rise, the model predicts a northward shift toward a suitable habitat for C. geophilum, resulting in an anticipated increase in suitable areas from 9 to 21%.

Cenococcum geophilum ECM rootlets are abundant in the top 0–5 cm soil layer (Rosling et al., 2003; Genney et al., 2006; Scattolin et al., 2008) but can also be found in much deeper soil layers, such as the mineral layer at a depth of 20 cm (Genney et al., 2006). C. geophilum is a pioneer species because of its propensity to partner with pioneer host trees such as Salix spp., which colonize newly exposed glacier moraines (Trappe, 1988). Moreover, the symbiont is recognized as a “multi-stage” fungus in secondary forest successions, indicating that it forms ECM associations with both seedlings and adult host plants (Visser, 1995; Danielson, 1991). In the volcanic desert of Mount Fuji, C. geophilum is present in both the early and later stages of vegetation development, colonizing young and old pioneer shrubs, such as Salix reinii, and herbaceous species, such as Polygonum cuspidatum (Nara, 2006). Interestingly, the symbiont has been found in old growth forests (Peter, 2003), although it is known to primarily colonize young trees in alpine regions near treelines (Hasselquist et al., 2005). In particular, C. geophilum is associated with seedlings and juvenile trees of Picea engelmannii and Abies lasiocarpa, with colonization rates 20 times greater for juveniles than for seedlings (Hasselquist et al., 2005). These findings suggest that this fungus plays an important role in the early stages of forest succession. However, C. geophilum has not been replaced by late-stage ECM species in older forest stands. The high prevalence of C. geophilum in mature alpine forest ecosystems, which are known for their cold climate, slow litter breakdown, and organic matter buildup in the soil, is believed to be a consequence of the substantial presence of sclerotia (approximately 3,600 kg ha⁻¹) and synchronization of rootlet growth bursts with sclerotia germination in autumn (Vogt et al., 1982). Furthermore, C. geophilum is among the most frequent ECM symbionts following a short fire return interval (Buscardo et al., 2010).

Mineral weathering by C. geophilum can release potassium from potassium aluminosilicate minerals, such as feldspar, nepheline, biotite, muscovite, and illite (Xue et al., 2019). The symbiotic fungus can also break down the mycorrhizal necromass (Fernandez and Koide, 2014; Gray and Kernaghan, 2020), with the initial N and melanin levels strongly influencing the early decay rates and determining the remaining mass after several years.

N addition reduced the prevalence of C. geophilum in the fungal communities of the humus and fine roots. Forsmark et al. (2024) analyzed the organic layer beneath undisturbed litter in a Norway spruce (Picea abies) forest in northern Sweden after two decades of annual N application at low (12.5 kg N ha⁻¹ yr.⁻¹) and high (50 kg N ha⁻¹ y^r − 1) levels. N supplementation decreased C. geophilum abundance, suggesting that decomposition linked to organic N acquisition was suppressed when inorganic forms of N were readily accessible. These community changes were associated with a decreased activity of Mn-peroxidase and peptidase and an increase in the activity of C-acquiring enzymes.

Wen et al. (2022) studied the influence of C. geophilum inoculation on the growth and nutrient uptake of Pinus thunbergii seedlings under salt stress. Their results indicated that mycorrhizal inoculation significantly increased seedling biomass, chlorophyll, and nutrient elements (such as P, N, and K) in shoots and maintained a low Na/K ratio in roots under salt stress, suggesting that inoculation with C. geophilum could assist the host in overcoming salt stress. Geographical isolates of C. geophilum have shown patterns of local adaptation to serpentine soils, with Ni concentrations having a significant effect on fitness-related traits (Gonçalves et al., 2009; Bazzicalupo et al., 2020).

C. geophilum exhibits drought tolerance and is prevalent in water-stressed environments (Pigott, 1982; McCormack et al., 2017). Several surveys of soil fungal communities have demonstrated that the proportions of C. geophilum ECM and extramatrical mycelia increase under water stress conditions and are often higher during summer in natural settings (Pigott, 1982; Querejeta et al., 2009). This tolerance has been verified through in vitro mycelial culture experiments using osmotically adjusted media (Mexal and Reid, 1973; Coleman et al., 1989), cell damage tests following desiccation (Di Pietro et al., 2007), and respiration measurements under water stress (Jany et al., 2003). The level of tolerance varies among geographical isolates (Coleman et al., 1989; Jany et al., 2003). However, the physiological mechanisms responsible for this symbiont’s success under water stress remain largely unknown. Multiple factors likely contribute to this trait, such as the accumulation of compatible osmolytes (e.g., polyols), heat shock proteins, hydrophobic proteins, and melanin in the cell walls. It has also been suggested that drought resistance in C. geophilum may be associated with the increased expression of aquaporin water channels (see below, Peter et al., 2016). Although C. geophilum is widely recognized as a drought-tolerant symbiont, this contention has recently been debated. A study utilizing Pinus seedlings colonized by C. geophilum and subjected to water shortages showed that the drought resistance of mycorrhizal plantlets was not directly correlated with that of C. geophilum isolates cultivated in liquid medium (Zhang et al., 2024). Xie et al. (2024) used inoculated Quercus mongolica and Tilia amurensis to investigate the responses of ECM fungal communities and their exploration types under drought conditions in a pot system. The relative abundance of C. geophilum in both hosts decreased. Nickel et al. (2018) examined ECM fungal community diversity changes in European beech and Norway spruce forests under drought conditions by utilizing retractable roofs to exclude rain for 3 years. The results indicated that the abundance of C. geophilum decreased irrespective of the depth, year, or host.

Laboratory experiments demonstrated that the growth inhibition of several C. geophilum isolates occurred at a temperature of 26°C (Yan et al., 2022); however, this species is capable of forming mycorrhizal associations following exposure to heat stress at approximately 70°C for a brief period or at 5°C above ambient temperature. Nevertheless, combined stress, including drought and heat stress, at a temperature of 5°C above ambient temperature and 50% precipitation can be lethal to C. geophilum (Kipfer et al., 2010; Gehring et al., 2020). Herzog et al. (2013) reported that increased temperature and water shortage can differentially affect the relative ECM abundance and exoenzyme activities of C. geophilum associated with various oak species, specifically Q. robur, Q. petraea, and Q. pubescens.

Furthermore, because of their prevalence as symbionts in arctic and alpine ecosystems, C. geophilum mycelia and ECM are likely to exhibit high tolerance to cold stress. Corbery and Le Tacon (1997) demonstrated that C. geophilum mycelium remained viable even when exposed to a freezing temperature of −80°C for a brief period, exhibiting greater resistance to cold than other ECM fungi. Additionally, studies have indicated that this fungus thrives at temperatures below 1°C (Vogt et al., 1982). This cold stress resistance may be attributed to its high mannitol synthesis rate (Martin et al., 1985) because mannitol is known to shield fungi from severe cryoenvironments (Weinstein et al., 1997).

C. geophilum is recognized as a mycorrhizal generalist species. This symbiont can form ecto-or ectendomycorrhizal associations with a broad host range. Based on the morphology and anatomy of mycorrhizal roots sampled in natural settings, three groups of host plants were identified (Trappe, 1962; LoBuglio, 1999): In Group 1, the hosts include members of the Salicaceae and Betulaceae families (excluding Corylus spp.), as well as ectotrophic genera within the Rosaceae family. The ECM root tips are typically monopodial or occasionally branched, with the mantle covering only the root tips. The Hartig net in these hosts never extends deeper than the third layer of the cortical cells, and intracellular penetration is sparse and limited to occasional cells. In Group 2, C. geophilum associates with Pinus species. The ECM root tips are monopodial, dichotomous, or occasionally irregularly branched. The mantles typically cover all short roots and have thicknesses ranging between 8 and 60 μm. The Hartig net extends inward to the innermost layer of cortical cells, and the cortex experiences strong intracellular infection. The hosts in Group 3 predominantly comprise Fagaceae, including Corylus, and Pinaceae, with the exception of Pinus spp. The root tips of these associations exhibit a range of morphologies, including monopodial, racemose, irregularly branched, long, or short structures. The mantle typically covers a significant portion or all of the short roots, and its thickness ranges from to 8 to 60 μm. The Hartig net extends to the innermost layer of the cortical cells, and intracellular infection is prevalent throughout the cortex.

Additionally, this groups includes many shrubs and herbaceous plants such as Pedicularis capitata (Kohn and Stasovski, 1990), Cistus spp. (Massicotte et al., 2010), Bistorta vivipara (Massicotte et al., 1998), Carex myosuroides (Massicotte et al., 1998), and Rhododendron spp. (Largent et al., 1980; Vohník et al., 2007). Unusual for an ECM symbiont, C. geophilum can also establish ectendomycorrhizal associations with shrubs and herbaceous plants, sharing mycelial networks with woody plants such as oak and Helianthemum bicknellii (Dickie and Reich, 2005), or the Dryas octopetala–Bistorta vivipara–Salix herbacea association (Mühlmann and Peintner, 2008). Symbiosis with herbaceous plants appears to enhance the colonization of woody plants (Dickie and Reich, 2005; Hoeksema et al., 2018). Although there is no evidence of nutrient transfer between herbaceous and woody plants sharing common mycorrhizal networks (CMNs) with C. geophilum, this structure could possibly act as a physical link between roots of herbaceous and woody plants, thereby enhancing C. geophilum colonization in sharing plants. The CMNs may also alter the bacterial communities of the hyphosphere (Vik et al., 2013).

Variations in colonization rates and/or host preferences can be attributed to genetic factors in both partners, as well as environmental factors such as soil organic matter content, total N, and available P (Wurentaoges, 2012). Zhu et al. (2024) reported that leaf photosynthesis and root morphological traits drive the topological structure of plant–fungus association networks involving Cenococcum species. Abundant plants may play a key role as reservoirs of symbiotic fungal diversity and thus contribute to the maintenance of ecosystem functions.

As previously mentioned, C. geophilum is widespread and has historically posed challenges in terms of physiological and phylogenetic classification. Collections of C. geophilum isolates, both locally and globally, have shown remarkable genetic diversity. Genetic studies on C. geophilum have revealed a complex population structure, even at the soil core sample level, with evidence of both local adaptation and limited gene flow between populations (Jany et al., 2002; Douhan and Rizzo, 2005; Matsuda et al., 2015; Obase et al., 2016; Obase et al., 2017; Vélez et al., 2021). They uncovered the presence of multiple hidden clades and distinct phylogenetic groups within C. geophilum, supporting the widely held view that this species represents a highly diverse assemblage of ectomycorrhizal fungi at regional and global levels. The structure of symbiont populations is influenced by several factors, including geographic distance, environmental gradients, and host–plant associations. They are often structured according to environmental conditions such as soil type, moisture level, and temperature. For example, populations from dry nutrient-poor soils tend to be genetically distinct from those in more fertile environments, suggesting a local adaptation to specific ecological niches (Douhan and Rizzo, 2005; Lian et al., 2006). A subtle geographic structure with long-distance disjunction suggests complex alternation of sexual and asexual reproduction over space and time (Obase et al., 2016; Obase et al., 2017). However, gene flow between populations can occur through sclerotia dispersal, leading to a combination of local adaptation and genetic exchange.

The presence of cryptic species within C. geophilum has also been confirmed, with distinct genetic lineages corresponding to different ecological and geographical regions (Obase et al., 2017; Vélez et al., 2021). Obase et al. (2017) resolved seven clades with high bootstrap support among the isolates of Cenococcum derived from different geographical regions across the world using both single-and multi-locus and maximum likelihood (ML) analyses (Figure 3). All Cenococcum clades clustered together with high bootstrap support, whereas Pseudocenococcum floridanum isolates were resolved as a separate group. More recently, Vélez et al. (2021) examined a set of 200+ C. geophilum isolates obtained from the soil beneath Populus trichocarpa along an ~280 mile north–south corridor in the Pacific Northwest, United States. Additionally, they performed global phylogenetic analysis by incorporating 789 isolates with publicly accessible data from the United States, Japan, and Europe. This analysis identified 34 strongly supported clades using ML and Bayesian methods, with some clades exhibiting intra-and intercontinental distributions. These findings strongly indicate divergence within multiple cryptic species.

Furthermore, the genetic diversity and structure of C. geophilum populations were analyzed based on the rDNA ITS2 sequences of 219 ECM root samples collected from 3 plant families (Betulaceae, Fagaceae, and Pinaceae) from 10 forest sites across China (Guo et al., 2021). Analysis of molecular variance (AMOVA) confirmed that genetic differentiation was evident within each geographical population and the population in each host plant family. The Fagaceae population was distinct from the Betulaceae and Pinaceae populations, and the haplotype composition was conspicuously different among the three plant families. These cryptic species may represent locally adapted forms of C. geophilum, which have evolved in response to specific environmental conditions. The genetic diversity of angiosperm-associated C. geophilum populations is higher than that of gymnosperm-associated populations, suggesting that angiosperm and gymnosperm hosts exert different selective pressures on their symbionts (Vélez et al., 2021). Tedersoo et al. (2024) also provided evidence for niche differentiation in tens of cryptic species of Cenococcum, many of which exhibit a preference toward particular partner plant genera.

Currently, it remains uncertain whether C. geophilum constitutes a single, highly diverse global species or whether it comprises numerous cryptic species. Subsequent studies could shed light on these local and worldwide relationships by comparing nuclear and mitochondrial genomes from a wide range of geographical isolates along with population genomics approaches.

Cenococcum geophilum is a highly adaptable ECM fungus that demonstrates significant potential for ecological restoration and environmental remediation through microbial engineering. The symbiont forms a dense network of melanized hyphae around the roots of host plants, creating a protective sheath. This symbiotic association is particularly beneficial in water-limited environments, where C. geophilum helps the host tree maintain hydraulic conductivity and photosynthetic activity under drought stress. Additionally, the fungus has been shown to enhance salt tolerance of host plants, making it valuable for reclaiming saline soils. Finally, its extensive distribution, broad host range, and high stress tolerance make it particularly valuable for addressing desertification and adapting to climate change (Zhai et al., 2023). Through the utilization of genomics and other-omics techniques, we acquired a more comprehensive understanding of the molecular, physiological, and ecological mechanisms underlying the establishment and functioning of C. geophilum ECM under environmental stress. Candidate genes related to adaptation to these environmental stresses can be used to select appropriate strains for the mycorrhizal inoculation of tree seedlings in environments prone to drought or other abiotic stresses. Surveys of soil fungal communities using DNA metabarcoding can be used to predict the environmental conditions under which C. geophilum inoculation is beneficial for forest management and restoration. This enhanced knowledge should be leveraged to develop practical applications, such as mycorrhizal inoculation or microbial engineering, which would enhance ecosystem function and preservation, aid in alleviating climate change impacts, and maintain the sustainability of forest ecosystems.

Furthermore, C. geophilum colonizes herbaceous plants. By forming associations with both woody and non-woody plants, symbionts can contribute to the development of diverse plant communities in challenging environments. Its ability to support multiple plant species can increase soil stability, reduce erosion, and improve nutrient cycling in degraded ecosystems. In arid regions, C. geophilum colonizes both ECM trees and Cistaceae plants. The physical connection of C. geophilum mycelial networks with both tree roots and herbaceous plants could redistribute water from the deeper roots of the tree, retain a portion of the water in the upper soil layers, and facilitate enhanced nutrient acquisition by the host plants. Similarly, the mouse-tail bog sedge (Carex (Kobresia) myosuroides) can be incorporated into tree plantations in northern and alpine regions. In environments contaminated by industrial waste, C. geophilum has shown promising results in the remediation of soils affected by heavy metals and petroleum (Danielson and Visser, 1989). The fungus has also exhibited the capacity to accumulate and sequester various heavy metals, including Pb, Cd, and Zn, in its melanized cell walls (Huang et al., 2014; Azaiez et al., 2018; Shi et al., 2022; Zhang et al., 2023,). This characteristic renders C. geophilum a potential candidate for mycoremediation of polluted soils. Moreover, their association with host plants can enhance phytoremediation efforts by improving plant survival and growth at contaminated sites.

Urban environments often present challenging conditions for plant growth such as soil compaction, elevated temperatures, and air pollution. C. geophilum is frequently the most abundant ECM symbiont found in the roots of urban trees (Garbaye and Churin, 1996; Hui et al., 2017; Van Geel et al., 2018; Olchowik et al., 2021). Its ability to form symbiotic relationships can improve resilience to these stressors, potentially leading to increased tree longevity and enhanced ecosystem services in urban areas.

Several enduring challenges persist in utilizing genomics and other-omics approaches to enhance our understanding of the biology and ecology of C. geophilum, including its evolutionary history, developmental processes, functional aspects, and its resilience to environmental stress. We have identified several critical questions that require further investigation:

The role of C. geophilum in ecosystem resilience is becoming increasingly important in the context of climate change. As extreme weather events and environmental stressors become more frequent, the capacity of this fungus and other mycorrhizal fungi to support plant growth and survival under adverse conditions may be crucial for maintaining ecosystem stability and biodiversity. Furthermore, their potential to enhance carbon sequestration through increased plant growth and soil organic matter accumulation may contribute to climate-change mitigation.