蓝莓根系复合共生体及其根区土壤中AM真菌调查

蓝莓Vaccinium uliginosum是欧石南菌根（ericoid mycorrhiza,ERM）真菌典型的寄主植物,但同时也可与丛枝菌根（arbuscular mycorrhiza,AM）真菌和深色有隔内生真菌（dark septate endophytes,DSE）共生形成复合共生体。本研究旨在调查和评价不同栽培体制下蓝莓成年树花果期根系共生体发育状况及其根区土壤中AM真菌资源分布状况,以期为优质蓝莓栽培管理提供理论依据和技术基础。从青岛佳沃蓝莓基地采集暖棚、冷棚和露地3种方式栽培的9-10年生‘蓝丰’、‘奥尼尔’和‘公爵’蓝莓的根系及根区土样,观察测定根系共生体着生数量、根区土壤中AM真菌孢子数量和菌种组成。结果表明,所有栽培方式下供试品种蓝莓根系均形成ERM、AM和DSE结构及其复合共生体;其中,AM着生数量最多,其次是ERM,DSE侵染率最低;复合共生体中则呈现ERM+AM>ERM+DSE>ERM+AM+DSE;蓝莓复合共生体着生数量、AM真菌侵染率、丛枝着生率及孢子数量等不同种植方式下呈现暖棚>冷棚>露地,不同品种呈现‘蓝丰’>‘公爵’>‘奥尼尔’,而ERM和DSE侵染率也呈现上述变化趋势。依据AM真菌形态特征,供分离鉴定获得5属11种AM真菌,以暖棚栽培条件下分离获得的AM真菌数量最多,‘蓝丰’根区土壤中分布的AM真菌属种最多。暖棚内成年树花果期蓝莓根系共生体发育健全,AM真菌种类和孢子数量较多,可能有利于提高蓝莓的产量、改善果实品质和抗逆性。     

Impact of soil stockpiling on ericoid mycorrhizal colonization and growth of velvetleaf blueberry (Vaccinium myrtilloides) and Labrador tea (Ledum groenlandicum)

Soil stockpiling is a common practice prior to the reclamation of surface mines. In this study, velvetleaf blueberry and Labrador tea plants were grown from seed in fresh soil, stockpiled soil (1 year), and autoclaved stockpiled soil (1 year) obtained from the Canadian boreal forest. After 7 months of growth, the root colonization intensity with ericoid mycorrhizal (ERM) fungi in both plants growing in stockpiled soil was lower compared to plants growing in the fresh soil. The diversity of ERM fungal species in roots also decreased due to soil stockpiling and Pezoloma ericae was absent from the plants growing in stockpiled soil. Changes in the ERM root colonization in plants growing in stockpiled soil were accompanied by decreases in root and shoot dry weights. Leaf chlorophyll, nitrogen, and phosphorus concentrations of velvetleaf blueberry were higher in fresh soil compared to 1‐year stockpiled soil. Plants grown in the autoclaved stockpiled soil became colonized by the thermotolerant ERM fungus Leohumicola verrucosa and showed higher root and shoot biomass compared to the nonautoclaved stockpiled soil. The results point to the importance of ERM fungi for growth of ericaceous plants, even under favorable environmental conditions and adequate fertilization, and suggest that reduced ERM colonization intensity and ERM fungal diversity in roots likely contributed to the negative effects of soil stockpiling on growth of velvetleaf blueberry and Labrador tea.     

Enzymatic activities and stable isotope patterns of ectomycorrhizal fungi in relation to phylogeny and exploration types in an afrotropical rain forest

? Ectomycorrhizal (ECM) fungi obtain both mineral and simple organic nutrients from soil and transport these to plant roots. Natural abundance of stable isotopes ((15) N and (13) C) in fruit bodies and potential enzymatic activities of ECM root tips provide insights into mineral nutrition of these mutualistic partners. ? By combining rDNA sequence analysis with enzymatic and stable isotope assays of root tips, we hypothesized that phylogenetic affinities of ECM fungi are more important than ECM exploration type, soil horizon and host plant in explaining the differences in mineral nutrition of trees in an African lowland rainforest. ? Ectomycorrhizal fungal species belonging to extraradical mycelium-rich morphotypes generally displayed the strongest potential activities of degradation enzymes, except for laccase. The signature of (15) N was determined by the ECM fungal lineage, but not by the exploration type. ? Potential enzymatic activities of root tips were unrelated to (15) N signature of ECM root tip. The lack of correlation suggests that these methods address different aspects in plant nutrient uptake. Stable isotope analysis of root tips could provide an additional indirect assessment of fungal and plant nutrition that enables enhancement of taxonomic coverage and control for soil depth and internal nitrogen cycling in fungal tissues.     

Organic nutrient uptake by mycorrhizal fungi enhances ecosystem carbon storage: a model-based assessment

Understanding the factors that drive soil carbon (C) accumulation is of fundamental importance given their potential to mitigate climate change. Much research has focused on the relationship between plant traits and C sequestration, but no studies to date have quantitatively considered traits of their mycorrhizal symbionts. Here, we use a modelling approach to assess the contribution of an important mycorrhizal fungal trait, organic nutrient uptake, to soil C accumulation. We show that organic nutrient uptake can significantly increase soil C storage, and that it has a greater effect under nutrient-limited conditions. The main mechanism behind this was an increase in plant C fixation and subsequent increased C inputs to soil through mycorrhizal fungi. Reduced decomposition due to increased nutrient limitation of saprotrophs also played a role. Our results indicate that direct uptake of nutrients from organic pools by mycorrhizal fungi could have a significant effect on ecosystem C cycling and storage.     

Extraradical mycelium of the arbuscular mycorrhizal fungus Glomus lamellosum can take up,accumulate and translocate radiocaesium under root-organ culture conditions

Radiocaesium enters the food chain when plants absorb it from soil, in a process that is strongly dependent on soil properties and plant and microbial species. Among the microbial species, arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the root cortex of many plants and develop an extraradical mycelial (ERM) network that ramifies in the soil. Despite the well-known involvement of this ERM network in mineral nutrition and uptake of some heavy metals, only limited data are available on its role in radiocaesium transport in plants. We used root-organ culture to demonstrate that the ERM of the AM fungus Glomus lamellosum can take up, possibly accumulate and unambiguously translocate radiocaesium from a 137Cs-labelled synthetic root-free compartment to a root compartment and within the roots. The accumulation of 137Cs by hyphae in the root-free compartment may be explained by sequestration in the hyphae or by a bottleneck effect resulting from a limited number of hyphae crossing the partition between the two compartments. Uptake and translocation resulted from the incorporation of 137Cs into the fungal hyphae, as no 137Cs was detected in mycorrhizal roots treated with formaldehyde. The importance of the translocation process was indicated by the correlation between 137Cs measured in the roots and the total hyphal length connecting the roots with the labelled compartment. 137Cs may be translocated via a tubular vacuolar system or by cytoplasmic streaming per se.     

A widespread plant-fungal-bacterial symbiosis promotes plant biodiversity,plant nutrition and seedling recruitment

Highly diverse microbial assemblages colonize plant roots. It is still poorly understood whether different members of this root microbiome act synergistically by supplying different services (for example, different limiting nutrients) to plants and plant communities. In order to test this, we manipulated the presence of two widespread plant root symbionts, arbuscular mycorrhizal fungi and nitrogen-fixing rhizobia bacteria in model grassland communities established in axenic microcosms. Here, we demonstrate that both symbionts complement each other resulting in increased plant diversity, enhanced seedling recruitment and improved nutrient acquisition compared with a single symbiont situation. Legume seedlings obtained up to 15-fold higher productivity if they formed an association with both symbionts, opposed to productivity they reached with only one symbiont. Our results reveal the importance of functional diversity of symbionts and demonstrate that different members of the root microbiome can complement each other in acquiring different limiting nutrients and in driving important ecosystem functions.     

Diversity and host preference of fungi co-inhabiting Cenococcum mycorrhizae

Diverse fungal assemblages colonize the fine feeder roots of woody plants, including mycorrhizal fungi, fungal root endophytes and soil saprotrophs. The fungi co-inhabiting Cenococcum geophilum ectomycorrhizae (ECM) of Abies balsamea, Betula papyrifera and Picea glauca were studied at two boreal forest sites in Eastern Canada by direct PCR of ITS rDNA. 50 non-Cenococcum fungal sequence types were detected, including several potentially mycorrhizal species as well as fungal root endophytes. Non-melanized ascomycetes dominated, in contrast to the dark septate endophytes (DSE) reported in most culture dependent studies. The results demonstrate significant differences in root associated fungal assemblages among the host species studied. Fungal diversity was also host dependent, with P. glauca roots supporting a more diverse community than A. balsamea. Differences in root associated fungal communities may well influence ecological interactions among host plant species.     

Recent 14C-labelled assimilate allocation to Scots pine seedling root and mycorrhizosphere compartments developed on reconstructed podzol humus,E- and B- mineral horizons

In northern boreal forests, podzolic soils prevail that comprise of a distinct upper organic humus/mor (O) horizon that is supported by underlying eluvial (E) and illuvial (B) mineral horizons. The dominant tree species, Scots pine (Pinus sylvestris L.), is known to be highly dependent on root symbiosis with ectomycorrhizal fungi that develop in constituent podzol horizons for growth in these nutrient limited soils. The aim of this microcosm-based study was a quantification of photosynthetically fixed ¹⁴C allocation, following standard pulse-feeding of 7-month-old Scots pine seedling shoots, to respective root and mycorrhizosphere compartments that developed in the reconstructed podzol (O, E and B) profile. Biomass of roots and mycorrhizas decreased with increasing soil depth but no soil origin, control forest vs. clear-cut area, related differences were observed. Similarly, no major soil origin- or podzol horizon-related differences in categorised ectomycorrhizal morphotypes and number of mycorrhizas, in relation to pooled root and mycorrhiza biomass, were detected. However, the total recovery of ¹⁴C-label was significantly higher in clear-cut soil microcosms compared to control counterparts. A significant finding was equivalent ¹⁴C-carbon allocation to roots and ectomycorrhizas in all three major, organic and mineral, podzol profile horizons studied. These carbon allocation data provide additional support for direct (or indirect) roles of roots and symbiotic mycorrhizal fungi in mineral weathering and biodegradation of organic ligands that are central for plant acquisition of growth limiting nutrients and the podzolization process in boreal forest ecosystems.     

Transport processes at the plant-fungus interface in mycorrhizal associations: physiological studies

The roots of most plants form symbiotic associations with mycorrhizal fungi. The net flux of nutrients, particularly phosphorus (P), from the soil into the plant is greater in mycorrhizal than in comparable non-mycorrhizal plants. However despite the widespread occurrence of mycorrhizal associations the processes controlling the transfer of solutes between the symbionts are poorly understood. To understand the mechanisms regulating the transfer of solutes information about conditions at the interface between plant and fungus is needed.Measurements of apoplastic and intracellular electrical potential difference in leek roots colonised by mycorrhizal fungi and estimates of cytosolic pH in fungal hyphae are presented. These and the implications for plant/fungal mineral nutrition in vesicular-arbuscular mycorrhizas are discussed.     

Thoughts on the processes that maintain local species diversity of ectomycorrhizal fungi

Ectomycorrhizal fungi exhibit high diversity even in small monoculture forests. Roughly 20 to 35 species typically occupy such sites. Explanations for this diversity can be based on resource partitioning, disturbance, competition, or interaction with other organisms. Mycorrhizal fungi compete for two general classes of resources: host-derived carbon and soil or detritus derived mineral nutrients. Both types of resources are arrayed in space (e.g., soil depth, distance from tree) and time (e.g., season, host successional series). Some species seem to be partitioned in space and time at these scales, but the question of how widespread these patterns are remains largely unanswered. Mineral resources are distributed in discrete substrates in soil, litter, and within other soil microorganisms; the biochemical diversity exhibited by fungi may translate into differences in access to these resources among species. Small-scale natural disturbances that sever roots, mix soil horizons and litter layers, or change local pH and nutrient availability, are likely to create additional habitats for ectomycorrhizal fungi. Evidence from fruiting patterns and differences in colonization strategies suggest that such disturbances may be important for establishment of some species. Competitive replacement networks among species have the theoretical potential to increase diversity. The frequency of species replacements, observed co-infections of ectomycorrhizal fungi on single host roots, and high rates of rootlet turn-over all suggest that competition is important, but whether it plays a creative role in maintaining diversity remains to be demonstrated. Other organisms could be important in the maintenance of diversity, if they effect competition among mycorrhizal fungi. Bacteria and soil invertebrates are the most likely groups for such interactions. Technological advances in root observation and PCR methods for indentification of mycorrhizae make many of these theories testable.     

Wood-decay fungi in fine living roots of conifer seedlings

The mycorrhizal basidiomycetes are known to have multiple, independent evolutionary origins from saprotrophic ancestors. To date, a number of studies have revealed functional resemblance of mycorrhizal fungi to free-living saprotrophs, but information on the ability of saprotrophic fungi to perform as mycorrhizal symbionts is scarce. Here, the objective was to investigate the ability of three wood-decay fungi, Phlebiopsis gigantea, Phlebia centrifuga and Hypholoma fasciculare, to colonize fine roots of conifer seedlings. For each fungus, mycorrhizal syntheses were attempted with Picea abies and Pinus sylvestris. After 24 wk, isolation of fungi and direct sequencing of fungal internal transcribed spacer (ITS) rDNA were carried out from healthy-looking surface-sterilized root tips that yielded both pure cultures and ITS sequences of each inoculated strain. Mycelial mantle of P. gigantea was frequently formed on root tips of P. abies, and microscopical examination has shown the presence of intercellular hyphae inside the roots. The results provide evidence of the ability of certain wood-decay fungi to colonise fine roots of tree seedlings.     

The foliar endophytic fungal community composition in Cirsium arvense is affected by mycorrhizal colonization and soil nutrient content

Foliar fungal endophytes are ubiquitous, but understudied symbionts of most plant species; relatively little is known about the factors affecting their occurrence, diversity and abundance. We tested the effects of soil nutrient content and arbuscular mycorrhizal (AM) colonization on the occurrence of foliar endophytic fungi in Cirsium arvense in two field studies. In the first study, we assessed relationships between soil moisture, organic matter, carbon and nitrogen content and plant water, nitrogen and carbon content and AM colonization and the occurrence of foliar endophytic fungal species. In the second study, we manipulated soil nutrient content and AM colonization of potted seedlings and identified differences in endophytic fungal species composition of the leaves and stems. The results reveal that endophytes can occur either more or less frequently, depending on soil nutrient and plant water content and AM colonization. We propose that these patterns were the result of differences in fungal growth responses to nutrient availability in the leaves, which can be affected by resources obtained from the soil or symbiotic fungi in the roots.     

Subcellular Nutrient Element Localization and Enrichment in Ecto- and Arbuscular Mycorrhizas of Field-Grown Beech and Ash Trees Indicate Functional Differences

Mycorrhizas are the chief organ for plant mineral nutrient acquisition. In temperate, mixed forests, ash roots (Fraxinus excelsior) are colonized by arbuscular mycorrhizal fungi (AM) and beech roots (Fagus sylvatica) by ectomycorrhizal fungi (EcM). Knowledge on the functions of different mycorrhizal species that coexist in the same environment is scarce. The concentrations of nutrient elements in plant and fungal cells can inform on nutrient accessibility and interspecific differences of mycorrhizal life forms. Here, we hypothesized that mycorrhizal fungal species exhibit interspecific differences in mineral nutrient concentrations and that the differences correlate with the mineral nutrient concentrations of their associated root cells. Abundant mycorrhizal fungal species of mature beech and ash trees in a long-term undisturbed forest ecosystem were the EcM Lactarius subdulcis, Clavulina cristata and Cenococcum geophilum and the AM Glomus sp. Mineral nutrient subcellular localization and quantities of the mycorrhizas were analysed after non-aqueous sample preparation by electron dispersive X-ray transmission electron microscopy. Cenococcum geophilum contained the highest sulphur, Clavulina cristata the highest calcium levels, and Glomus, in which cations and P were generally high, exhibited the highest potassium levels. Lactarius subdulcis-associated root cells contained the highest phosphorus levels. The root cell concentrations of K, Mg and P were unrelated to those of the associated fungal structures, whereas S and Ca showed significant correlations between fungal and plant concentrations of those elements. Our results support profound interspecific differences for mineral nutrient acquisition among mycorrhizas formed by different fungal taxa. The lack of correlation between some plant and fungal nutrient element concentrations may reflect different retention of mineral nutrients in the fungal part of the symbiosis. High mineral concentrations, especially of potassium, in Glomus sp. suggest that the well-known influence of tree species on chemical soil properties may be related to their mycorrhizal associates.     

Nutrient demand and fungal access to resources control the carbon allocation to the symbiotic partners in tripartite interactions of Medicago truncatula

Legumes form tripartite interactions with arbuscular mycorrhizal fungi and rhizobia, and both root symbionts exchange nutrients against carbon from their host. The carbon costs of these interactions are substantial, but our current understanding of how the host controls its carbon allocation to individual root symbionts is limited. We examined nutrient uptake and carbon allocation in tripartite interactions of Medicago truncatula under different nutrient supply conditions, and when the fungal partner had access to nitrogen, and followed the gene expression of several plant transporters of the Sucrose Uptake Transporter (SUT) and Sugars Will Eventually be Exported Transporter (SWEET) family. Tripartite interactions led to synergistic growth responses and stimulated the phosphate and nitrogen uptake of the plant. Plant nutrient demand but also fungal access to nutrients played an important role for the carbon transport to different root symbionts, and the plant allocated more carbon to rhizobia under nitrogen demand, but more carbon to the fungal partner when nitrogen was available. These changes in carbon allocation were consistent with changes in the SUT and SWEET expression. Our study provides important insights into how the host plant controls its carbon allocation under different nutrient supply conditions and changes its carbon allocation to different root symbionts to maximize its symbiotic benefits.     

Diversity and community structure of ectomycorrhizal fungi in a wooded meadow

Wooded meadows are seminatural plant communities that support high diversity of various taxa. Due to changes in land use, wooded meadows have severely declined during the last century. The dominant trees in wooded meadows acquire mineral nutrients via ectomycorrhizal fungi. Using anatomotyping and sequencing of root tips, interpolation and extrapolation methods, we studied the diversity and community structure of ectomycorrhizal fungi in two soil horizons of both managed and forested parts of a wooded meadow in Estonia. Species of Thelephoraceae, Sebacinaceae and the genus Inocybe dominated the whole ectomycorrhizal fungal community of 172 observed species. Forested and managed parts of the wooded meadow harboured different communities of ectomycorrhizal fungi, whereas soil horizon had a negligible effect on the fungal community composition. Diverse soil conditions and host trees likely support the high richness of ectomycorrhizal fungi in the wooded meadow ecosystem. Direct sequencing integrated with interpolation and extrapolation methods are promising to identify the fungi at the species level and to compare species richness between communities of ectomycorrhizal fungi.     

Context dependence in foraging behaviour of Achillea millefolium

Context-dependent foraging behaviour is acknowledged and well documented for a diversity of animals and conditions. The contextual determinants of plant foraging behaviour, however, are poorly understood. Plant roots encounter patchy distributions of nutrients and soil fungi. Both of these features affect root form and function, but how they interact to affect foraging behaviour is unknown. We extend the use of the marginal value theorem to make predictions about the foraging behaviour of roots, and test our predictions by manipulating soil resource distribution and inoculation by soil fungi. We measured plant movement as both distance roots travelled and time taken to grow through nutrient patches of varied quality. To do this, we grew Achillea millefolium in the centers of modified pots with a high-nutrient patch and a low-nutrient patch on either side of the plant (heterogeneous) or patch-free conditions (homogeneous). Fungal inoculation, but not resource distribution, altered the time it took roots to reach nutrient patches. When in nutrient patches, root growth decreased relative to homogeneous soils. However, this change in foraging behaviour was not contingent upon patch quality or fungal inoculation. Root system breadth was larger in homogeneous than in heterogeneous soils, until measures were influenced by pot edges. Overall, we find that root foraging behaviour is modified by resource heterogeneity but not fungal inoculation. We find support for predictions of the marginal value theorem that organisms travel faster through low-quality than through high-quality environments, with the caveat that roots respond to nutrient patches per se rather than the quality of those patches.     

Co-existing grass species have distinctive arbuscular mycorrhizal communities

Arbuscular mycorrhizal (AM) fungi are biotrophic symbionts colonizing the majority of land plants, and are of major importance in plant nutrient supply. Their diversity is suggested to be an important determinant of plant community structure, but the influence of host-plant and environmental factors on AM fungal community in plant roots is poorly documented. Using the terminal restriction fragment length polymorphism (T-RFLP) strategy, the diversity of AM fungi was assessed in 89 roots of three grass species (Agrostis capillaris, Festuca rubra, Poa pratensis) that co-occurred in the same plots of a field experiment. The impact of different soil amendments (nitrogen, lime, nitrogen and lime) and insecticide application on AM fungal community was also studied. The level of diversity found in AM fungal communities using the T-RFLP strategy was consistent with previous studies based on clone libraries. Our results clearly confirm that an AM fungal host-plant preference exists, even between different grass species. AM communities colonizing A. capillaris were statistically different from the others (P < 0.05). Although grass species evenness changed in amended soils, AM fungal community composition in roots of a given grass species remained stable. Conversely, in plots where insecticide was applied, we found higher AM fungal diversity and, in F. rubra roots, a statistically different AM fungal community.     

Root fungal symbionts interact with mammalian herbivory, soil nutrient availability and specific habitat conditions

Herbivory, competition and soil fertility interactively shape plant communities and exhibit an important role in modifying conditions for host-dependent fungal symbionts. However, field studies on the combined impacts of natural herbivory, competition and soil fertility on root fungal symbionts are rare. We asked how mammalian herbivory, fertilization, liming and plant–plant competition affect the root colonization of arbuscular mycorrhizal fungi (AMF) and dark septate endophytic (DSE) fungi of the dicot herb, Solidago virgaurea. The 2-year full-factorial experiment was conducted in two contrasting habitats: non-acidic and acidic mountain tundra. We found that herbivory increased arbuscular colonization (i.e. the site of resource exchange) at fertile non-acidic sites, where vegetation was rich in species having AMF symbionts, whereas at infertile acidic sites, where plants having AMF symbiont are scarce, the response was the opposite. Herbivory of the host plant negatively affected DSE hyphal and sclerotial colonization in unfertilized plots, possibly due to reduced carbon flow from the host plant while there was no effect of herbivory in fertilized plots. DSE colonization was highest in unfertilized exclosures where soil nutrient concentrations were also lowest. Liming had a negative effect on DSE hyphal colonization, and its effect also interacted with herbivory and the habitat. Biomass removal of the neighboring plants did not affect the root colonization percent of either arbuscules or DSE. Our results show that the impacts of aboveground mammalian herbivory, soil nutrient availability and specific habitat conditions on belowground root fungal symbionts are highly dependent on each other. Arbuscule response to herbivory appeared to be regulated by specific habitat conditions possibly caused by differences in the AMF availability in the soil while DSE response was associated with availability of host-derived carbon. Our result of the relationship between herbivory and soil nutrients suggests an important role of DSE in ecosystem processes.     

Arbuscular mycorrhizal adaptation,spore germination,root colonization,and host plant growth and mineral acquisition at low pH

Arbuscular mycorrhizal (AM) fungi colonize plant roots and often enhance host plant growth and mineral acquisition, particularly for plants grown under low nutrient and mineral stress conditions. Information about AM fungi and mycorrhizal ( +AM) host plant responses at low pH ( < 5) is limited. Acaulospora are widely reported in acid soil, and Gigaspora sp. appear to be more common in acid soils than Glomus sp. Spores of some AM fungi are more tolerant to acid conditions and high Al than others; t Acaulospora sp., Gigaspora sp., and Glomus manihotis are particularly tolerant. Root colonization is generally less in low than in high pH soils. Percentage root colonization is generally not related to dry matter (DM) produced. Maximum enhancement of plant growth in acid soil varies with AM fungal isolate and soil pH, indicating adaptation of AM isolates to edaphic conditions. Acquisition of many mineral nutrients other than P and Zn is enhanced by +AM plants in acid soil, and the minerals whose concentration is enhanced are those commonly deficient in acid soils (Ca, Mg, and K). Some AM fungal isolates are effective in overcoming soil acidity factors, especially Al toxicity, that restrict plant growth at low pH.     

Arbuscular mycorrhizal colonization of giant sequoia (Sequoiadendron giganteum) in response to restoration practices

Interactions with soil microbiota determine the success of restoring plants to their native habitats. The goal of our study was to understand the effects of restoration practices on interactions of giant sequoia Sequoiadendron giganteum with arbuscular mycorrhizal (AM) fungi (Glomeromycota). Natural regeneration of Sequoiadendron is threatened by the absence of severe fires that create forest canopy gaps. Generating artificial canopy gaps offers an alternative tool for giant sequoia restoration. We investigated the effect of regeneration practices, including (i) sapling location within gaps, (ii) gap size and (iii) soil substrate, on AM fungal colonization of giant sequoia sapling roots in a native giant sequoia grove of the Sierra Nevada, California. We found that the extent of AM fungal root colonization was positively correlated with sapling height and light availability, which were related to the location of the sapling within the gap and the gap size. While colonization frequency by arbuscules in saplings on ash substrate was higher relative to saplings in mineral soil, the total AM fungal root colonization was similar between the substrates. A negative correlation between root colonization by Glomeromycota and non-AM fungal species indicated antagonistic interactions between different classes of root-associated fungi. Using DNA genotyping, we identified six AM fungal taxa representing genera Glomus and Ambispora present in Sequoiadendron roots. Overall, we found that AM fungal colonization of giant sequoia roots was associated with availability of plant-assimilated carbon to the fungus rather than with the AM fungal supply of mineral nutrients to the roots. We conclude that restoration practices affecting light availability and carbon assimilation alter feedbacks between sapling growth and activity of AM fungi in the roots.