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Large-scale studies that examine the responses of ectomycorrhizal fungi across biogeographic gradients are necessary to assess their role in mediating current and predicted future alterations in forest ecosystem processes. We assessed the extent of environmental filtering on interior Douglas-fir ( var. (Beissn.) Franco) ectomycorrhizal fungal communities across regional gradients in precipitation, temperature, and soil fertility in interior Douglas-fir dominated forests of western Canada. We also examined relationships between fine-root traits and mycorrhizal fungal exploration types by combining root and fungal trait measurements with next-generation sequencing. Temperature, precipitation, and soil C:N ratio affected fungal community dissimilarity and exploration type abundance but had no effect on α-diversity. Fungi with rhizomorphs (e.g., sp.) or proteolytic abilities (e.g., sp.) dominated communities in warmer and less fertile environments. Ascomycetes (e.g., ) or shorter distance explorers, which potentially cost the plant less C, were favored in colder/drier climates where soils were richer in total nitrogen. Environmental filtering of ectomycorrhizal fungal communities is potentially related to co-evolutionary history between Douglas-fir populations and fungal symbionts, suggesting success of interior Douglas-fir as climate changes may be dependent on maintaining strong associations with local communities of mycorrhizal fungi. No evidence for a link between root and fungal resource foraging strategies was found at the regional scale. This lack of evidence further supports the need for a mycorrhizal symbiosis framework that is independent of root trait frameworks, to aid in understanding belowground plant uptake strategies across environments.

Boreal forest soils store a major proportion of the global terrestrial carbon (C) and below‐ground inputs contribute as much as above‐ground plant litter to the total C stored in the soil. A better understanding of the dynamics and drivers of root‐associated fungal communities is essential to predict long‐term soil C storage and climate feedbacks in northern ecosystems. We used 454‐pyrosequencing to identify fungal communities across fine‐scaled soil profiles in a 5000 yr fire‐driven boreal forest chronosequence, with the aim of pinpointing shifts in fungal community composition that may underlie variation in below‐ground C sequestration. In early successional‐stage forests, higher abundance of cord‐forming ectomycorrhizal fungi (such as Cortinarius and Suillus species) was linked to rapid turnover of mycelial biomass and necromass, efficient nitrogen (N) mobilization and low C sequestration. In late successional‐stage forests, cord formers declined, while ericoid mycorrhizal ascomycetes continued to dominate, potentially facilitating long‐term humus build‐up through production of melanized hyphae that resist decomposition. Our results suggest that cord‐forming ectomycorrhizal fungi and ericoid mycorrhizal fungi play opposing roles in below‐ground C storage. We postulate that, by affecting turnover and decomposition of fungal tissues, mycorrhizal fungal identity and growth form are critical determinants of C and N sequestration in boreal forests.

AimSoil microbial legacy is a potentially important regulator of the associations of plants and mycorrhizal fungi. However, our understanding of how plant performance and root-associated fungi react to distinct soil microbial legacies during subalpine forest succession remains unclear.MethodsA pot experiment of two coniferous (Picea asperata Mast. and Abies fargesii var. faxoniana (Rehder & E. H. Wilson) Tang S. Liu) tree seedlings, using sterilized soil inoculated with the soil microbial legacy of herbs, shrubs, and trees, was conducted in a greenhouse. Plant biomass, root morphological traits (total root length, root surface area, and the number of root tips), the percentage of ectomycorrhizal (EcM) root colonization, root-associated fungal communities, and soil inorganic nitrogen content were measured.ResultsBoth coniferous seedling performance and EcM colonization were facilitated when grown in the soil microbial legacies of shrubs and trees rather than herbs. Correspondingly, soil microbial legacy favored root-associated EcM Ascomycetes and EcM fungi with ‘short-distance’ exploration type. The soil microbial legacies of trees induced a greater relative abundance of Wilcoxina, while those of herbs and shrubs resulted in greater abundances of Trichophaea, Geopora, and Hebeloma (belonging to ‘short-distance’ exploration type). Notably, the relative abundances of ‘short-distance’ explorers were positively correlated with root biomass.ConclusionsSoil microbial legacy may affect tree seedling establishment and modify plant performance across successional stages by regulating the colonization, composition, and exploration type of root-associated fungi.

There is growing evidence of the importance of extramatrical mycelium (EMM) of mycorrhizal fungi in carbon (C) cycling in ecosystems. However, our understanding has until recently been mainly based on laboratory experiments, and knowledge of such basic parameters as variations in mycelial production, standing biomass and turnover as well as the regulatory mechanisms behind such variations in forest soils is limited. Presently, the production of EMM by ectomycorrhizal (EM) fungi has been estimated at similar to 140 different forest sites to be up to several hundreds of kg per ha per year, but the published data are biased towards Picea abies in Scandinavia. Little is known about the standing biomass and turnover of EMM in other systems, and its influence on the C stored or lost from soils. Here, focussing on ectomycorrhizas, we discuss the factors that regulate the production and turnover of EMM and its role in soil C dynamics, identifying important gaps in this knowledge. C availability seems to be the key factor determining EMM production and possibly its standing biomass in forests but direct effects of mineral nutrient availability on the EMM can be important. There is great uncertainty about the rate of turnover of EMM. There is increasing evidence that residues of EM fungi play a major role in the formation of stable N and C in SOM, which highlights the need to include mycorrhizal effects in models of global soil C stores.

Ectomycorrhizal (EcM) and saprotrophic fungi interact in the breakdown of organic matter, but the mechanisms underlying the EcM role on organic matter decomposition are not totally clear. We hypothesized that the ecological relations between EcM and saprotroph fungi are modulated by resources availability and accessibility, determining decomposition rates. We manipulated the amount of leaf litter inputs (No-Litter, Control Litter, Doubled Litter) on Trenched (root exclusion) and Non-Trenched plots (with roots) in a temperate deciduous forest of EcM-associated trees. Resultant shifts in soil fungal communities were determined by phospholipid fatty acids and DNA sequencing after 3 years, and CO 2 fluxes were measured throughout this period. Different levels of leaf litter inputs generated a gradient of organic substrate availability and accessibility, altering the composition and ecological relations between EcM and saprotroph fungal communities. EcM fungi dominated at low levels of fresh organic substrates and lower organic matter quality, where short-distances exploration types seem to be better competitors, whereas saprotrophs and longer exploration types of EcM fungi tended to dominate at high levels of leaf litter inputs, where labile organic substrates were easily accessible. We were, however, not able to detect unequivocal signs of competition between these fungal groups for common resources. These results point to the relevance of substrate quality and availability as key factors determining the role of EcM and saprotroph fungi on litter and soil organic matter decay and represent a path forward on the capacity of organic matter decomposition of different exploration types of EcM fungi.

Intrinsic soil properties have been shown to mediate the effects of ectomycorrhizal (ECM) fungi and their associated trees on soil organic matter (SOM) and nitrogen (N) cycling, but variation in the contribution of fungal communities to ECM effects across different forests remains uncertain. To investigate the potential role of fungal communities in driving observed variation in ECM effects, we characterized fungal community composition and function using DNA sequence variability of the ITS2 region of the fungal rRNA operon and measured chemical properties of forest floor leaf litter, soil organic horizon, and soil mineral horizons (0–5cm, 15–20 cm depth) beneath ECM-associated Oreomunnea mexicana focal trees. We sampled beneath focal trees in arbuscular mycorrhizal (AM)- and ECM-dominated stands within four adjacent watersheds that differed in underlying soil pH and fertility. We found that overall fungal community composition and the ratio of ECM to saprotrophic fungi differed between AM- and ECM-dominated stands in the lowest pH and fertility watershed but were similar between stand mycorrhizal types in the highest pH and fertility watershed. Patterns in fungal community composition and function aligned with patterns in N isotopic composition of forest floor leaf litter and mineral soil, which could reflect greater ECM transfer of N to the trees and greater contribution of hyphal biomass to SOM in the lowest pH and fertility watershed. Overall, our results suggest the potential for watershed-scale variation in soil pH and fertility to mediate fungal community contributions to variation in ECM effects on biogeochemical syndromes.

This study investigates the effects of forest aging on ectomycorrhizal (EcM) fungal community and foraging behavior and their interactions with plant–soil attributes. We explored EcM fungal communities and hyphal exploration types via rDNA sequencing and investigated their associations with plant–soil traits by comparing younger (~120 years) and older (~250 years) temperate forest stands in Northeast China. The results revealed increases in the EcM fungal richness and abundance with forest aging, paralleled by plant–soil feedback shifting from explorative to conservative nutrient use strategies. In the younger stands, Tomentella species were prevalent and showed positive correlations with nutrient availability in both the soil and leaves, alongside rapid increases in woody productivity. However, the older stands were marked by the dominance of the genera Inocybe, Hymenogaster, and Otidea which were significantly and positively correlated with soil nutrient contents and plant structural attributes such as the community-weighted mean height and standing biomass. Notably, the ratios of longer-to-shorter distance EcM fungal exploration types tended to decrease along with forest aging. Our findings underscore the integral role of EcM fungi in the aging processes of temperate forests, highlighting the EcM symbiont-mediated mechanisms adapting to nutrient scarcity and promoting sustainability in plant–soil consortia.

Ectomycorrhizal (EM) fungal taxonomic, phylogenetic, and trait diversity (exploration types) were analyzed in beech and conifer forests along a north-to-south gradient in three biogeographic regions in Germany. The taxonomic community structures of the ectomycorrhizal assemblages in top soil were influenced by stand density and forest type, by biogeographic environmental factors (soil physical properties, temperature, and precipitation), and by nitrogen forms (amino acids, ammonium, and nitrate). While α-diversity did not differ between forest types, β-diversity increased, leading to higher γ-diversity on the landscape level when both forest types were present. The highest taxonomic diversity of EM was found in forests in cool, moist climate on clay and silty soils and the lowest in the forests in warm, dry climate on sandy soils. In the region with higher taxonomic diversity, phylogenetic clustering was found, but not trait clustering. In the warm region, trait clustering occurred despite neutral phylogenetic effects. These results suggest that different forest types and favorable environmental conditions in forests promote high EM species richness in top soil presumably with both high functional diversity and phylogenetic redundancy, while stressful environmental conditions lead to lower species richness and functional redundancy.

Morphological plasticity (MP) is an essential strategy for plants in nutrient acquisition, disturbance alleviation, and community coexistence during environmental and climatic changes. However, to date, there has been little research concerning the MP for alpine–subalpine forests on the Qinghai–Tibet plateau. These forests are representative of the ectomycorrhizal (ECM) type, and morphological traits of these ECM roots, such as root tip lengths, diameters, and their adherent hyphal lengths and exploration types, have rarely been studied in the context of nutrient and environmental gradients. In this study, we examined the morphological traits of ECM roots for faxon fir (Abies fargesii var. faxoniana), which dominated in subalpine forests across nine elevations on the Eastern Qinghai–Tibet plateau. By quantifying ca. 90,000 root tips, the hyphal lengths of ectomycorrhizal extraradical mycelium (EEM, i.e., short- and long-distance exploration types) reached up to 1.1 × 106 cm/m3 in soil, which decreased significantly due to gradually increasing altitude. In contrast, the variability of ECM root traits (diameter, length, and superficial area) was highly conserved along the altitudinal gradients, yet the root tip lengths were positively associated with soil protease enzyme activity. The increase in diameter and length of ECM root tips was climate-independent yet significantly associated with increasing root N concentration. In the studied forests, a long-distance exploration type of ECM hyphae was controlled by precipitation (p < 0.05), whereas the short-distance one was controlled by precipitation and temperature simultaneously. The EEM lengths of short- and long-distance exploration types were associated with high C concentration and low N concentration in host tree root tissues. Our findings demonstrated that MP expression in nutrient-foraging strategies for the dominant coniferous trees facilitates the adaptation to changing environments by specialized hyphal structures. In conclusion, ECM root tips and hyphal structures are two dimensions of functional traits linked to root N concentration in opposite ways, and their MP collectively ensures the temporal stability and resistance of subalpine forests on the Qinghai–Tibet plateau. These results provide new insights into ECM morphological traits and their adaptation in changing environments, which is valuable for understanding responses of subalpine forests to climate change.

Summary Phenology‐induced changes in carbon assimilation by trees may affect carbon stored in fine roots and as a consequence, alter carbon allocated to ectomycorrhizal fungi. Two competing models exist to explain carbon mobilization by ectomycorrhizal fungi. Under the ‘saprotrophy model’, decreased allocation of carbon may induce saprotrophic behaviour in ectomycorrhizal fungi, resulting in the decomposition of organic matter to mobilize carbon. Alternatively, under the ‘nutrient acquisition model’, decomposition may instead be driven by the acquisition of nutrients locked within soil organic matter compounds, with carbon mobilization a secondary process. We tested whether phenology‐induced shifts in carbon reserves of fine roots of aspen (Populus tremuloides) affect potential activity of four carbon‐compound degrading enzymes, β‐glucuronidase, β‐glucosidase, N‐acetylglucosaminidase and laccase, by ectomycorrhizal fungi. Ectomycorrhizal roots from mature aspen were collected across eight stands in north‐eastern Alberta, Canada, and analysed during tree dormancy, leaf flush, full leaf expansion and leaf abscission. We predicted potential extracellular enzyme activity to be highest when root carbon reserves were lowest, should host phenology induce saprotrophism. Further, we anticipated enzyme activity to be mediated by invertase, a plant‐derived enzyme which makes carbon available to fungal symbionts in the plant–fungus interface. Root carbon reserves were positively correlated with invertase, suggesting phenology may affect carbon allocation to ectomycorrhizal fungi. However, of the four enzymes, host phenology had the largest effect on β‐glucuronidase, but activity of this enzyme was not correlated with root carbon reserves or invertase. Low‐biomass ectomycorrhizas had greater potential laccase activity than high‐biomass ectomycorrhizas, highlighting discrete functional traits in fungi for litter decomposition. Our results suggest that the decomposition of organic matter may be driven by foraging by fungi for nutrients locked within organic compounds rather than for mobilizing carbon. Furthermore, the potential ability to degrade lignin was more common in low‐biomass ectomycorrhizas when compared to high‐biomass ectomycorrhizas. A Lay Summary is available for this article. Lay Summary