Factors associated with seedling establishment on logs of different fungal decay types-A seed-sowing experiment.

Wood decay fungi alter the abiotic and biotic properties of deadwood, which are important as nurse logs for seedling regeneration. However, the relationship between fungal decay type and seedling performance has not been evaluated experimentally. In this study, we examined the germination, growth, and survival of six arbuscular mycorrhizal (AM) and six ectomycorrhizal (ECM) tree species on three substrates (pine logs with brown and white rot and soil) by conducting seed-sowing experiments in a mixed forest dominated by Pinus densiflora and Quercus serrata. Analysis using ribosomal DNA internal transcribed spacer 1 (rDNA ITS1) sequencing revealed that the fungal community was significantly different across three substrates. The richness of operational taxonomic units (OTUs) of AM and ECM fungi was the largest on brown rot logs and soil, respectively. The substrate significantly affected the seedling performance when comparing wood decay types, but these were not consistent across the mycorrhizal status of the seedlings. Nevertheless, seedlings of some AM trees showed better growth and enhanced mycorrhizal colonization on brown rot logs than on white rot logs. The wood decay type influenced fungal communities in the logs and the performance of some seedling species partly by different mycorrhizal colonization rates. However, the effect was seedling species dependent and showed no apparent difference between AM and ECM trees.

[Effects of mycorrhizal types on herbaceous species richness in forest ecosystem]. / èŒæ ¹ç±»åž‹å¯¹æ£®æž—è‰æœ¬æ¤ç‰©ç¾¤è½ç‰©ç§ä¸°å¯Œåº¦çš„å½±å“.

Species richness plays an important role in ecosystem stability and health. Mycorrhizal type is an important factor affecting ecological processes. How mycorrhizal types affect understory herb species richness and their responses to environmental changes remain largely unknown. We investigated the effects of mycorrhizal types on species richness and their responses to environmental change in understory herbaceous communities based on data of three mycorrhizal types of dominated trees (including 1604 arbuscular mycorrhiza (AM) trees, 4654 ectomycorrhiza (ECM) trees, and 5568 AM+ECM trees) and environmental factors in America. The results showed significant differences in species richness of herbaceous plant communities among different mycorrhizal types. Forests with higher dominance of AM plants tended to have higher herbaceous plant richness, supporting the mycorrhizal mediation hypothesis. The impacts of environmental factors (latitude, temperature, precipitation, nitrogen deposition, and soil characteristics) on species richness of herbaceous plant communities depended on mycorrhizal type of forests. The species richness of understory herbs in AM, ECM, and AM+ECM forests was mostly affected by nitrogen deposition, temperature, and soil pH, with the relative importance of 42.3%, 41.1% and 48.7%, respectively. Mycorrhizal types of dominant trees played a vital role in regulating the species richness of understory herbs and influenced their responses to environmental changes.

Influence of tree mycorrhizal type, tree species identity, and diversity on forest root-associated mycobiomes.

Understanding the complex interactions between trees and fungi is crucial for forest ecosystem management, yet the influence of tree mycorrhizal types, species identity, and diversity on tree-tree interactions and their root-associated fungal communities remains poorly understood. Our study addresses this gap by investigating root-associated fungal communities of different arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) tree species pairs (TSPs) in a subtropical tree diversity experiment, spanning monospecific, two-species, and multi-species mixtures, utilizing Illumina sequencing of the ITS2 region. The study reveals that tree mycorrhizal type significantly impacts the alpha diversity of root-associated fungi in monospecific stands. Meanwhile, tree species identity's influence is modulated by overall tree diversity. Tree-related variables and spatial distance emerged as major drivers of variations in fungal community composition. Notably, in multi-species mixtures, compositional differences between root fungal communities of AM and EcM trees diminish, indicating a convergence of fungal communities irrespective of mycorrhizal type. Interestingly, dual mycorrhizal fungal communities were observed in these multi-species mixtures. This research underscores the pivotal role of mycorrhizal partnerships and the interplay of biotic and abiotic factors in shaping root fungal communities, particularly in varied tree diversity settings, and its implications for effective forest management and biodiversity conservation.

Herbarium specimens reveal that mycorrhizal type does not mediate declining temperate tree nitrogen status over a century of environmental change.

Rising atmospheric carbon dioxide concentrations (CO2 ) and atmospheric nitrogen (N) deposition have contrasting effects on ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) symbioses, potentially mediating forest responses to environmental change. In this study, we evaluated the cumulative effects of historical environmental change on N concentrations and δ15 N values in AM plants, EM plants, EM fungi, and saprotrophic fungi using herbarium specimens collected in Minnesota, USA from 1871 to 2016. To better understand mycorrhizal mediation of foliar δ15 N, we also analyzed a subset of previously published foliar δ15 N values from across the United States to parse the effects of N deposition and CO2 rise. Over the last century in Minnesota, N concentrations declined among all groups except saprotrophic fungi. δ15 N also declined among all groups of plants and fungi; however, foliar δ15 N declined less in EM plants than in AM plants. In the analysis of previously published foliar δ15 N values, this slope difference between EM and AM plants was better explained by nitrogen deposition than by CO2 rise. Mycorrhizal type did not explain trajectories of plant N concentrations. Instead, plants and EM fungi exhibited similar declines in N concentrations, consistent with declining forest N status despite moderate levels of N deposition.

Plant species identity and mycorrhizal type explain the root-associated fungal pathogen community assembly of seedlings based on functional traits in a subtropical forest.

Introduction: As a crucial factor in determining ecosystem functioning, interaction between plants and soil-borne fungal pathogens deserves considerable attention. However, little attention has been paid into the determinants of root-associated fungal pathogens in subtropical seedlings, especially the influence of different mycorrhizal plants. Methods: Using high-throughput sequencing techniques, we analyzed the root-associated fungal pathogen community for 19 subtropical forest species, including 10 ectomycorrhizal plants and 9 arbuscular mycorrhizal plants. We identified the roles of different factors in determining the root-associated fungal pathogen community. Further, we identified the community assembly process at species and mycorrhizal level and managed to reveal the drivers underlying the community assembly. Results: We found that plant species identity, plant habitat, and plant mycorrhizal type accounted for the variations in fungal pathogen community composition, with species identity and mycorrhizal type showing dominant effects. The relative importance of different community assembly processes, mainly, homogeneous selection and drift, varied with plant species identity. Interestingly, functional traits associated with acquisitive resource-use strategy tended to promote the relative importance of homogeneous selection, while traits associated with conservative resource-use strategy showed converse effect. Drift showed the opposite relationships with functional traits compared with homogeneous selection. Notably, the relative importance of different community assembly processes was not structured by plant phylogeny. Drift was stronger in the pathogen community for ectomycorrhizal plants with more conservative traits, suggesting the predominant role of stochastic gain and loss in the community assembly. Discussion: Our work demonstrates the determinants of root-associated fungal pathogens, addressing the important roles of plant species identity and plant mycorrhizal type. Furthermore, we explored the community assembly mechanisms of root-associated pathogens and stressed the determinant roles of functional traits, especially leaf phosphorus content (LP), root nitrogen content (RN) and root tissue density (RTD), at species and mycorrhizal type levels, offering new perspectives on the microbial dynamics underlying ecosystem functioning.

Environmental modulation of plant mycorrhizal traits in the global flora.

Mycorrhizal symbioses are known to strongly influence plant performance, structure plant communities and shape ecosystem dynamics. Plant mycorrhizal traits, such as those characterising mycorrhizal type (arbuscular (AM), ecto-, ericoid or orchid mycorrhiza) and status (obligately (OM), facultatively (FM) or non-mycorrhizal) offer valuable insight into plant belowground functionality. Here, we compile available plant mycorrhizal trait information and global occurrence data ( ∼ 100 million records) for 11,770 vascular plant species. Using a plant phylogenetic mega-tree and high-resolution climatic and edaphic data layers, we assess phylogenetic and environmental correlates of plant mycorrhizal traits. We find that plant mycorrhizal type is more phylogenetically conserved than plant mycorrhizal status, while environmental variables (both climatic and edaphic; notably soil texture) explain more variation in mycorrhizal status, especially FM. The previously underestimated role of environmental conditions has far-reaching implications for our understanding of ecosystem functioning under changing climatic and soil conditions.

Peat loss collocates with a threshold in plant-mycorrhizal associations in drained peatlands encroached by trees.

Drainage-induced encroachment by trees may have major effects on the carbon balance of northern peatlands, and responses of microbial communities are likely to play a central mechanistic role. We profiled the soil fungal community and estimated its genetic potential for the decay of lignin and phenolics (class II peroxidase potential) along peatland drainage gradients stretching from interior locations (undrained, open) to ditched locations (drained, forested). Mycorrhizal fungi dominated the community across the gradients. When moving towards ditches, the dominant type of mycorrhizal association abruptly shifted from ericoid mycorrhiza to ectomycorrhiza at c. 120 m from the ditches. This distance corresponded with increased peat loss, from which more than half may be attributed to oxidation. The ectomycorrhizal genus Cortinarius dominated at the drained end of the gradients and its relatively higher genetic potential to produce class II peroxidases (together with Mycena) was positively associated with peat humification and negatively with carbon-to-nitrogen ratio. Our study is consistent with a plant-soil feedback mechanism, driven by a shift in the mycorrhizal type of vegetation, that potentially mediates changes in aerobic decomposition during postdrainage succession. Such feedback may have long-term legacy effects upon postdrainage restoration efforts and implication for tree encroachment onto carbon-rich soils globally.

Functional Potential of Soil Microbial Communities and Their Subcommunities Varies with Tree Mycorrhizal Type and Tree Diversity.

Soil microbial communities play crucial roles in the earth's biogeochemical cycles. Yet, their genomic potential for nutrient cycling in association with tree mycorrhizal type and tree-tree interactions remained unclear, especially in diverse tree communities. Here, we studied the genomic potential of soil fungi and bacteria with arbuscular (AM) and ectomycorrhizal (EcM) conspecific tree species pairs (TSPs) at three tree diversity levels in a subtropical tree diversity experiment (BEF-China). The soil fungi and bacteria of the TSPs' interaction zone were characterized by amplicon sequencing, and their subcommunities were determined using a microbial interkingdom co-occurrence network approach. Their potential genomic functions were predicted with regard to the three major nutrients carbon (C), nitrogen (N), and phosphorus (P) and their combinations. We found the microbial subcommunities that were significantly responding to different soil characteristics. The tree mycorrhizal type significantly influenced the functional composition of these co-occurring subcommunities in monospecific stands and two-tree-species mixtures but not in mixtures with more than three tree species (here multi-tree-species mixtures). Differentiation of subcommunities was driven by differentially abundant taxa producing different sets of nutrient cycling enzymes across the tree diversity levels, predominantly enzymes of the P (n = 11 and 16) cycles, followed by the N (n = 9) and C (n = 9) cycles, in monospecific stands and two-tree-species mixtures, respectively. Fungi of the Agaricomycetes, Sordariomycetes, Eurotiomycetes, and Leotiomycetes and bacteria of the Verrucomicrobia, Acidobacteria, Alphaproteobacteria, and Actinobacteria were the major differential contributors (48% to 62%) to the nutrient cycling functional abundances of soil microbial communities across tree diversity levels. Our study demonstrated the versatility and significance of microbial subcommunities in different soil nutrient cycling processes of forest ecosystems. IMPORTANCE Loss of multifunctional microbial communities can negatively affect ecosystem services, especially forest soil nutrient cycling. Therefore, exploration of the genomic potential of soil microbial communities, particularly their constituting subcommunities and taxa for nutrient cycling, is vital to get an in-depth mechanistic understanding for better management of forest soil ecosystems. This study revealed soil microbes with rich nutrient cycling potential, organized in subcommunities that are functionally resilient and abundant. Such microbial communities mainly found in multi-tree-species mixtures associated with different mycorrhizal partners can foster soil microbiome stability. A stable and functionally rich soil microbiome is involved in the cycling of nutrients, such as carbon, nitrogen, and phosphorus, and their combinations could have positive effects on ecosystem functioning, including increased forest productivity. The new findings could be highly relevant for afforestation and reforestation regimes, notably in the face of growing deforestation and global warming scenarios.

Species of fast bulk-soil nutrient cycling have lower rhizosphere effects: A nutrient spectrum of rhizosphere effects.

Tree roots not only acquire readily-usable soil nutrients but also affect microbial decomposition and manipulate nutrient availability in their surrounding soils, that is, rhizosphere effects (REs). Thus, REs challenge the basic understanding of how plants adapt to the environment and co-exist with other species. Yet, how REs vary among species in response to species-specific bulk soil nutrient cycling is not well-known. Here, we studied how plant-controlled microbial decomposition activities in rhizosphere soils respond to those in their corresponding bulk soils and whether these relations depend on species-specific nutrient cycling in the bulk soils. We targeted 55 woody species of different clades and mycorrhizal types in three contrasting biomes, namely a temperate forest, a subtropical forest, and a tropical forest. We found that microbial decomposition activities in rhizosphere soils responded linearly to those in their corresponding bulk soils at the species level. Thereafter, we found that REs (parameters in rhizosphere soils minus those in corresponding bulk soils) of microbial decomposition activities had negative linear correlations with microbial decomposition activities in corresponding bulk soils. A multiple factor analysis revealed that soil organic carbon, total nitrogen, and soil water content favored bulk soil decomposition activities in all three biomes, showing that the magnitude of REs varied along a fast-slow nutrient cycling spectrum in bulk soils. The species of fast nutrient cycling in their bulk soils tended to have smaller or even negative REs. Therefore, woody plants commonly utilize both positive and negative REs as a nutrient-acquisition strategy. Based on the trade-offs between REs and other nutrient-acquisition strategies, we proposed a push and pull conceptual model which can bring plant nutrient-acquisition cost and plant carbon economics spectrum together in the future. This model will facilitate not only the carbon and nutrient cycling but also the mechanisms of species co-existence in forest ecosystems.

Mycorrhizal type of woody plants influences understory species richness in British broadleaved woodlands.

Mature temperate woodlands are commonly dominated by ectomycorrhizal trees, whereas understory plants predominantly form arbuscular mycorrhizal associations. Due to differences in plant-fungus compatibility between canopy and ground layer vegetation the 'mycorrhizal mediation hypothesis' predicts that herbaceous plant establishment may be limited by a lack of suitable mycorrhizal fungal inoculum. We examined plant species data for 103 woodlands across Great Britain recorded in 1971 and in 2000 to test whether herbaceous plant species richness was related to the proportion of arbuscular mycorrhizal woody plants. We compared the effect of mycorrhizal type with other important drivers of woodland plant species richness. We found a positive effect of the relative abundance of arbuscular mycorrhizal woody plants on herbaceous plant species richness. The size of the observed effect was smaller than that of pH. Moreover, the effect persisted over time, despite many woodlands undergoing marked successional change and increased understorey shading. This work supports the mycorrhizal mediation hypothesis in British woodlands and suggests that increased abundance of arbuscular mycorrhizal woody plants is associated with greater understory plant species richness.

Interspecific differences in the responses of root phosphatase activities and morphology to nitrogen and phosphorus fertilization in Bornean tropical rain forests.

Soil organic phosphorus (P) compounds can be the main P source for plants in P-limited tropical rainforests. Phosphorus occurs in diverse chemical forms, including monoester P, diester P, and phytate, which require enzymatic hydrolysis by phosphatase into inorganic P before assimilation by plants. The interactions between plant interspecific differences in organic P acquisition strategies via phosphatase activities with root morphological traits would lead to P resource partitioning, but they have not been rigorously evaluated. We measured the activities of three classes of phosphatases (phosphomonoesterase, PME; phosphodiesterase, PDE; and phytase, PhT), specific root length (SRL), root diameter, and root tissue density in mature tree species with different mycorrhizal associations (ectomycorrhizal [ECM] or arbuscular mycorrhizal [AM]) and different successional status (climax or pioneer species) in Sabah, Malaysia. We studied nitrogen (N)- and P-fertilized plots to evaluate the acquisition strategies for organic P under P-limited conditions 7 years after fertilization was initiated. P fertilization reduced the PME activity in all studied species and reduced PhT and PDE activities more in climax species than in the two pioneer species, irrespective of the mycorrhizal type. PDE activity increased in some climax species after N fertilization, suggesting that these species allocate excess N to the synthesis of PDE. Moreover, PME and PhT activities, but not PDE activity, correlated positively with SRL. We suggest that climax species tend to be more strongly dependent on recalcitrant organic P (i.e., phytate and/or diester P) than pioneer species, regardless of the mycorrhizal type. We also suggest that trees in which root PME or PhT activity is enhanced can increase their SRL to acquire P efficiently. Resource partitioning of soil organic P would occur among species through differences in their phosphatase activities, which plays potentially ecologically important role in reducing the competition among coexisting tree species in lowland tropical rainforests.

A Database on Mycorrhizal Traits of Chinese Medicinal Plants.

The mycorrhizal traits of plants have been widely reported based on different scales or plant functional groups. To better utilize mycorrhizae to improve the cultivation yield and active ingredient accumulation of medicinal plants, a database of medicinal plant mycorrhizal characteristics is needed. A database on mycorrhizal traits including mycorrhizal type or status of Chinese medicinal plant species was assembled. In this study, the mycorrhizal type or status of a total of 3,230 medicinal plants was presented. Among them, the mycorrhizal traits of 1,321 species were ascertained. These medicinal plants had three mycorrhizal statuses, both single mycorrhiza (SM) and multi-mycorrhiza (MM) contained four mycorrhizal types. The majority of medicinal plants were obligatorily symbiotic with mycorrhizal fungi with 926 (70.10%) species. The most widespread mycorrhizal type is AM, which is associated with 842 medicinal plant species (90.93% of mycorrhiza has an obligatorily symbiotic relationship with Chinese medicinal plants). Another broadly studied mycorrhizal type is ECM, which is associated with 15 medicinal plant species. This study is the first exclusive database on mycorrhizal traits of medicinal plants, which provides both mycorrhizal type and status. This database provides valuable resources for identifying the mycorrhizal information of medicinal plants and enriching the theory of mycorrhizal traits, which will greatly benefit the production or management of medicinal plants.

[Relationships between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies in subtropical young plantations]. / äºšçƒ­å¸¦å¹¼æž—æ ‘æœ¨åŠŸèƒ½æ€§çŠ¶ä¸Žå¶ç‰‡æ°®ç£·é‡å¸æ”¶çŽ‡çš„å ³ç³».

We examined the relationship between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies across 29 species in 3-year-old pure plantations in subtropical China. The results showed that the average nitrogen (NRE) and phosphorus (PRE) resorption efficiencies in 29 young plantations were 50.5% and 57.3%, respectively. The average NRE of 22 arbuscular mycorrhizal (AM) tree species was 52.7%, significantly higher than that of the seven ectomycorrhizal (EM) tree species (45.1%). NRE was positively correlated with fine root tissue density across the 29 tree species. PRE was positively correlated with root diameter in the seven EM tree species. Functional traits of 22 AM tree species were not associated with NRE and PRE. Among all of the 29 tree species, mycorrhizal type, specific leaf area, fine root tissue density, leaf thickness, and the interaction effects of mycorrhizal type with leaf thickness explained 27% variation in NRE. Specific root length, fine root carbon content, fine root carbon to nitrogen ratio, mycorrhizal type, leaf carbon content, and the interaction effects of mycorrhizal type with leaf carbon content explained 35% variation in PRE. Root functional trait of subtropical species could predict nitrogen and phosphorus resorption efficiencies. The model with multiple functional traits could better reveal the relative importance of different biological factors on nutrient resorption efficiency.

Tree growth response to soil nutrients and neighborhood crowding varies between mycorrhizal types in an old-growth temperate forest.

Forest dynamics are shaped by both abiotic and biotic factors. Trees associating with different types of mycorrhizal fungi differ in nutrient use and dominate in contrasting environments, but it remains unclear whether they exhibit differential growth responses to local abiotic and biotic gradients where they co-occur. We used 9-year tree census data in a 25-ha old-growth temperate forest in Northeast China to examine differences in tree growth response to soil nutrients and neighborhood crowding between tree species associating with arbuscular mycorrhizal (AM), ectomycorrhizal (EM), and dual-mycorrhizal (AEM) fungi. In addition, we tested the role of individual-level vs species-level leaf traits in capturing differences in tree growth response to soil nutrients and neighborhood crowding across mycorrhizal types. Across 25 species, soil nutrients decreased AM tree growth, while neighborhood crowding reduced both AM and EM tree growth, and neither soil nor neighbors impacted AEM tree growth. Across mycorrhizal types, individual-level traits were stronger predictors of tree growth than species-level traits. However, most traits poorly mediated tree growth response to soil nutrients and neighborhood crowding. Our findings indicate that mycorrhizal types strongly shape differences in tree growth response to local soil and crowding gradients, and suggest that including plant-mycorrhizae associations in future work offers great potential to improve our understanding of forest dynamics.

A tipping point in carbon storage when forest expands into tundra is related to mycorrhizal recycling of nitrogen.

Tundra ecosystems are global belowground sinks for atmospheric CO2 . Ongoing warming-induced encroachment by shrubs and trees risks turning this sink into a CO2 source, resulting in a positive feedback on climate warming. To advance mechanistic understanding of how shifts in mycorrhizal types affect long-term carbon (C) and nitrogen (N) stocks, we studied small-scale soil depth profiles of fungal communities and C-N dynamics across a subarctic-alpine forest-heath vegetation gradient. Belowground organic stocks decreased abruptly at the transition from heath to forest, linked to the presence of certain tree-associated ectomycorrhizal fungi that contribute to decomposition when mining N from organic matter. In contrast, ericoid mycorrhizal plants and fungi were associated with organic matter accumulation and slow decomposition. If climatic controls on arctic-alpine forest lines are relaxed, increased decomposition will likely outbalance increased plant productivity, decreasing the overall C sink capacity of displaced tundra.

Compatible Mycorrhizal Types Contribute to a Better Design for Mixed Eucalyptus Plantations.

Mixed-species forest plantation is a sound option to facilitate ecological restoration, plant diversity and ecosystem functions. Compatible species combinations are conducive to reconstruct plant communities that can persist at a low cost without further management and even develop into natural forest communities. However, our understanding of how the compatibility of mycorrhizal types mediates species coexistence is still limited, especially in a novel agroforestry system. Here, we assessed the effects of mycorrhizal association type on the survival and growth of native woody species in mixed-species Eucalyptus plantations. To uncover how mycorrhizal type regulates plant-soil feedbacks, we first conducted a pot experiments by treating distinct mycorrhizal plants with soil microbes from their own or other mycorrhizal types. We then compared the growth response of arbuscular mycorrhizal plants and ectomycorrhizal plants to different soil microbial compositions associated with Eucalyptus plants. We found that the type of mycorrhizal association had a significant impact on the survival and growth of native tree species in the Eucalyptus plantations. The strength and direction of the plant-soil feedbacks of focal tree species depended on mycorrhizal type. Non-mycorrhizal plants had consistent negative feedbacks with the highest survival in the Eucalyptus plantations, whereas nitrogen-fixing plants had consistent positive feedbacks and the lowest survival. Arbuscular mycorrhizal and ectomycorrhizal plants performed varied feedback responses to soil microbes from distinct mycorrhizal plant species. Non-mycorrhizal plants grew better with Eucalyptus soil microbes while nitrogen-fixing plants grew worse with their own conspecific soil microbes. Different soil microbial compositions of Eucalyptus consistently increased the aboveground growth of arbuscular mycorrhizal plants, but the non-mycorrhizal microbial composition of the Eucalyptus soil resulted in greater belowground growth of ectomycorrhizal plants. Overall, Eucalyptus plants induced an unfavorable soil community, impeding coexistence with other mycorrhizal plants. Our study provides consistent observational and experimental evidence that mycorrhizal-mediated plant-microbial feedback on species coexistence among woody species. These findings are with important implications to optimize the species combinations for better design of mixed forest plantations.

Plastic responses of fine root morphology and architecture traits to nitrogen addition in ectomycorrhizal and arbuscular mycorrhizal tree species in an evergreen broadleaved forest.

We measured the morphology traits (specific root length, specific root surface area, root tissue density, average root diameter) and architecture traits (root fork, root fork ratio, increase rate of root length, root tip density, root fork density) of fine roots in two mycorrhiza tree species, Castanopsis faberi (ectomycorrhizal) and Schima superba (arbuscular mycorrhizal), in an evergreen broadleaved forest in the middle subtropical zone. Root bags method was used in an in situ nitrogen deposition experiment. The aim of this study was to reveal the differences in the plastic responses of fine root morphology and architecture traits to nitrogen deposition between the different mycorrhizal trees. The plastic responses of specific root length, specific root surface area and root fork to nitrogen addition decreased from the first-order root to the fourth-order root, while root tissue density showed an opposite pattern. Such a result indicated a trade-off between nutrient acquisition and resource maintenance of different fine root orders. Different mycorrhizal tree species adopted diffe-rent adaptation strategies to the variations of soil nitrogen availability. C. faberi adopted an opportuni-stic strategy, which relied on fine root to improve nutrient absorption efficiency, enhanced the capacity of space expansion and in-situ nutrient absorption to focus on rapid nutrient absorption strategy. S. superba did not change fine root morphological traits through the trade-off between nutrient absorption efficiency and root construction cost, but relied more on the complementarity between mycorrhizal fungi and fine root architecture traits for nutrient acquisition. The differences in the cost of maintaining and constructing fine root C between different mycorrhizal trees led to fine root adopting the most suitable nutrient capture strategy.

Aboveground herbivores drive stronger plant species-specific feedback than belowground fungi to regulate tree community assembly.

Ectomycorrhizal (EcM) tree species often become more dominant than arbuscular mycorrhizal (AM) tree species in temperate forests, but they generally coexist. Theory predicts that ecological feedback mediated by aboveground herbivory and/or belowground microbes could explain these dominance/coexistence patterns. An experimental test of how aboveground/belowground organisms associated with AM/EcM trees mediate ecological feedbacks has been lacking at the community-level. By establishing AM and EcM tree sapling assemblages in mesocosms and then introducing seedlings of each type in a reciprocal planting experiment, we compared seedling performance under varying sapling species (conspecifics, heterospecifics within the same and different mycorrhizal types), using traits that reflect either aboveground herbivory-mediated feedback or belowground fungal-mediated feedback or both. When examining seedling traits that reflect aboveground herbivory-mediated feedbacks (i.e., foliar damage), AM plants tended to experience less foliar damage and EcM plants more damage under conspecific versus heterospecific saplings within the same mycorrhizal types, and aboveground herbivory-mediated feedback was species-specific rather than mycorrhizal type-specific. Conversely, when examining traits that reflect belowground fungal-mediated feedbacks, both AM and EcM plant species often exhibited mycorrhizal type-specific feedbacks (e.g., greater aboveground biomass under the same versus different mycorrhizal-type saplings) rather than species-specific feedbacks. Furthermore, tree species affected by herbivory-mediated feedback were less affected by belowground feedback, indicating that the relative importance of the feedbacks varied among plant species. Analysis of plant-associated organisms verified that the feedback outcomes corresponded with species accumulation of belowground fungi (but not of aboveground herbivores). Thus, aboveground herbivores drive stronger plant species-specific feedback than belowground fungi to regulate temperate tree diversity.

Variation in hyphal production rather than turnover regulates standing fungal biomass in temperate hardwood forests.

Soil fungi link above- and belowground carbon (C) fluxes through their interactions with plants and contribute to C and nutrient dynamics through the production, turnover, and activity of fungal hyphae. Despite their importance to ecosystem processes, estimates of hyphal production and turnover rates are relatively uncommon, especially in temperate hardwood forests. We sequentially harvested hyphal ingrowth bags to quantify the rates of Dikarya (Ascomycota and Basidiomycota) hyphal production and turnover in three hardwood forests in the Midwestern United States, where plots differed in their abundance of arbuscular (AM)- vs. ectomycorrhizal (ECM)-associated trees. Hyphal production rates increased linearly with the percentage of ECM trees and annual production rates were 66% higher in ECM- than AM-dominated plots. Hyphal turnover rates did not differ across the mycorrhizal gradient (plots varying in their abundance of AM vs. ECM trees), suggesting that the greater fungal biomass in ECM-dominated plots relates to greater fungal production rather than slower fungal turnover. Differences in hyphal production across the gradient aligned with distinctly different fungal communities and activities. As ECM trees increased in dominance, fungi inside ingrowth bags produced more extracellular enzymes involved in degrading nitrogen (N)-bearing relative to C-bearing compounds, suggesting greater fungal (and possibly plant) N demand in ECM-dominated soils. Collectively, our results demonstrate that shifts in temperate tree species composition that result in changes in the dominant type of mycorrhizal association may have strong impacts on Dikarya hyphal production, fungal community composition and extracellular enzyme activity, with important consequences for soil C and N cycling.