Ectomycorrhizal Seedlings Research Articles

Coccoloba uvifera L. associated with Scleroderma Bermudense Coker: a pantropical ectomycorrhizal symbiosis used in restoring of degraded coastal sand dunes.

Coccoloba uvifera L. (Polygonacaeae), named also seagrape, is an ectomycorrhizal (ECM) Caribbean beach tree, introduced pantropically for stabilizing coastal soils and producing edible fruits. This review covers the pantropical distribution and micropropagation of seagrape as well as genetic diversity, functional traits and use of ECM symbioses in response to salinity, both in its native regions and areas where it has been introduced. The ECM fungal diversity associated with seagrape was found to be relatively low in its region of origin, with Scleroderma bermudense Coker being the predominant fungal species. In regions of introduction, seagrape predominantly associated with Scleroderma species, whereas S. bermudense was exclusively identified in Réunion and Senegal. The introduction of S. bermudense is likely through spores adhering to the seed coats of seagrape, suggesting a vertical transmission of ECM colonization in seagrape by S. bermudense. This ECM fungus demonstrated its capacity to enhance salt tolerance in seagrape seedlings by reducing Na concentration and increasing K and Ca levels, consequently promoting higher K/Na and Ca/Na ratios in the tissues of ECM seedlings vs. non-ECM plants in nursery conditions. Moreover, the ECM symbiosis positively influenced growth, photosynthetic and transpiration rates, chlorophyll fluorescence and content, stomatal conductance, intercellular CO2, and water status, which improved the performance of ECM seagrape exposed to salt stress in planting conditions. The standardization of seagrape micropropagation emerges as a crucial tool for propagating homogeneous plant material in nursery and planting conditions. This review also explores the use of the ECM symbiosis between seagrape and S. bermudense as a strategy for restoring degraded coastal ecosystems in the Caribbean, Indian Ocean, and West African regions.

Mycorrhizal associations of temperate forest seedlings mediate rhizodeposition, but not soil carbon storage, under elevated nitrogen availability.

Tree-mycorrhizal associations are associated with patterns in nitrogen (N) availability and soil organic matter storage; however, we still lack a mechanistic understanding of what tree and fungal traits drive these patterns and how they will respond to global changes in soil N availability. To address this knowledge gap, we investigated how arbuscular mycorrhizal (AM)- and ectomycorrhizal (EcM)-associated seedlings alter rhizodeposition in response to increased seedling inorganic N acquisition. We grew four species each of EcM and AM seedlings from forests of the eastern United States in a continuously 13C-labeled atmosphere within an environmentally controlled chamber and subjected to three levels of 15N-labeled fertilizer. We traced seedling 15N uptake from, and 13C-labeled inputs (net rhizodeposition) into, root-excluded or -included soil over a 5-month growing season. N uptake by seedlings was positively related to rhizodeposition for EcM- but not AM-associated seedlings in root-included soils. Despite this contrast in rhizodeposition, there was no difference in soil C storage between mycorrhizal types over the course of the experiment. Instead root-inclusive soils lost C, while root-exclusive soils gained C. Our findings suggest that mycorrhizal associations mediate tree belowground C investment in response to inorganic N availability, but these differences do not affect C storage. Continued soil warming and N deposition under global change will increase soil inorganic N availability and our seedling results indicate this could lead to greater belowground C investment by EcM-associated trees. This potential for less efficient N uptake by EcM-trees could contribute to AM-tree success and a shift toward more AM-dominated temperate forests.

Different phosphorus preferences among arbuscular and ectomycorrhizal trees in a subtropical forest

Phosphorus (P) is one of the most limiting elements for efficient plant growth and regeneration, coexisting plants are found to be able to partition soil P components through different types of mycorrhizal symbiosis. However, previous evidences were mostly based on artificial addition of different forms of P chemicals, there is still a lack of observational and experimental verifications on how tree species respond to soil P heterogeneity in natural soils. Herein, we conducted a field survey to investigate how spatial distribution of tree species with different types of mycorrhizal associations are related with soil P compositions. We found that arbuscular mycorrhizal (AM) trees tend to distribute in soils rich in inorganic P, while ectomycorrhizal (ECM) trees distribute in habitats with low inorganic P. We further established a shade-house experiment to evaluate how P availability of field soils affects seedling performance of AM and ECM trees. Biomass of AM seedlings was highest when grew in soil with the medium level of inorganic P, while ECM seedlings grown best in soil with the lowest inorganic P level. Seedling survival and mycorrhizal colonisation rates decreased, while specific root length and specific area of seedling roots increased, with increasing inorganic P concentrations. Using field soil with natural composition of P-forms and spatial heterogeneity, our findings confirmed the hypothesis that AM trees prefer inorganic P while ECM trees are able to utilise organic P in a more realistic setting, which regulated spatial distributions and promoted coexistence of subtropical tree species at local scale.

Arbuscular mycorrhizal and ectomycorrhizal plants together shape seedling diversity in a subtropical forest

IntroductionBurgeoning mycorrhizal research has focused on identifying the various diverse mycorrhizal strategies of forest communities. Mounting evidence suggests that mycorrhizae play important roles in regulating forest community structure and composition. However, research into the manifestation of this influence in the seedling stage is lacking, especially in small-scale plots.MethodsOur research utilized structural equation models parameterized using data from a subtropical monsoon broad-leaved evergreen forest situated in Yunnan Province, China.ResultsWe noted that seedlings included plants that utilized both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. More seedling plots with the relatively higher species diversity were the product of the mixed mycorrhizal strategy, meaning the coexistence of AM and EM seedlings in a small-scale plot rather than the dominance of one type of strategies. These mixed communities were primarily found on slopes and mountain ridges. The abundance of AM or EM trees indirectly affected seedling diversity by influencing the abundance of different mycorrhizal seedlings. In this case, the diversity of the mixed mycorrhizal community was also restricted by the level of leaf thickness in the community, followed by abiotic factors such as elevation, convexity, soil pH and soil available phosphorus.DiscussionThe effect of leaf thickness on mycorrhizal seedling abundance reflected the importance of water conditions in shaping seedling communities. The effect of convexity on seedling diversity also reflected the limitation of seedling communities by the distribution of humidity and heat conditions during topographic change. The results suggested that it is crucial to preserve seedling diversity via the mixed mycorrhizal strategy of communities in the subtropical forest.

Modification of Density Dependence and Habitat Filtering on Seedling Survival of Different Mycorrhizal-Type Tree Species in Temperate Forests

Conspecific negative density dependence (CNDD) and habitat filtering are critical to seedling survival. However, the relative importance of the two processes in affecting survival of seedlings with different types of mycorrhizae remains unclear. In this study, the effects of CNDD and habitat filtering on the survival of tree seedlings with different mycorrhizal types were investigated at different successional stages of a temperate forest in the Changbai Mountain Natural Reserve, Northeast China. Conspecific negative density dependence and habitat filtering significantly affected seedling survival. In the early successional stage, the interactions between conspecific neighbor tree density and light availability and soil properties significantly negatively affected survival of all species and arbuscular mycorrhizal (AM) seedlings in the community, but not that of ectomycorrhizal (EcM) seedlings, and the CNDD effect was stronger on AM seedlings than on EcM seedlings. In the mid-successional stage, CNDD effects were stronger on EcM seedlings. Therefore, different types of mycorrhizal seedlings responded differently to CNDD and habitat filtering mechanisms during community succession, and thus, tree mycorrhizal association could determine the effects of CNDD and habitat filtering on seedling survival in temperate forests.

Phosphorus Addition Reduces Seedling Growth and Survival for the Arbuscular Mycorrhizal Tree Cinnamomum camphora (Lauraceae) and Ectomycorrhizal Tree Castanopsis sclerophylla (Fagaceae) in Fragmented Forests in Eastern China.

Global changes in nutrient deposition rates and habitat fragmentation are likely to have profound effects on plant communities, particularly in the nutrient-limited systems of the tropics and subtropics. However, it remains unclear how increased phosphorus (P) supply affects seedling growth in P-deficient subtropical fragmented forests. To explore this, we applied P to 11 islands in a subtropical Chinese archipelago and examined the results in combination with a contemporary greenhouse experiment to test the influence of P addition on seedling growth and survival. We measured the growth (i.e., base area) and mortality rate of seedlings for one arbuscular mycorrhizal (AM) and one ectomycorrhizal (EcM) tree species separately and calculated their relative growth rate and mortality when compared with P addition and control treatment on each island. We also measured three functional traits and the biomass of seedlings in the greenhouse experiment. Results showed that P addition significantly increased the mortality of AM and EcM seedlings and reduced the growth rate of EcM seedlings. The relative growth rate of AM seedlings, but not EcM seedlings, significantly decreased as the island area decreased, suggesting that P addition could promote the relative growth rate of AM seedlings on larger islands. The greenhouse experiment showed that P addition could reduce the specific root length of AM and EcM seedlings and reduce the aboveground and total biomass of seedlings, indicating that P addition may affect the resource acquisition of seedlings, thereby affecting their survival and growth. Our study reveals the synergistic influence of habitat fragmentation and P deposition, which may affect the regeneration of forest communities and biodiversity maintenance in fragmented habitats.

The Nurse Plant Acacia spirorbis Enriches Ectomycorrhizal Community Composition of a Target Species: Tristaniopsis calobuxus

We investigated the suitability of Acacia spirorbis Labill., a tropical ectomycorrhizal (ECM) tree, as a nurse plant to improve the growth of Tristaniopsis calobuxus Brongn. & Gris seedlings for the restoration of nickel mines in New Caledonia. Rehabilitation of nickel mines in New Caledonia is a major concern. In such harsh soil conditions, ectomycorrhizal (ECM) symbiosis is important for tree growth, survival, and resistance. To improve ecological restoration in New Caledonia, new technical itineraries have undergone experimentation using ECM as a plant nurse, allowing ECM saplings to rapidly acquire a wide range of ECM fungi. We transplanted ECM seedlings of Tristaniopsis calobuxus from the nursery to bare ferralitic soils harbouring some scattered 12-year-old Acacia spirorbis to be used as ECM nurse plants. Using molecular characterisation of ITS rDNA, we characterised ECM fungal communities of A. spirorbis and of T. calobuxus saplings at transplanting time and 13 months later. We observed changes in the composition of fungal communities of T. calobuxus with an increase in diversity, notably the appearance of operational taxonomic units (OTUs) affiliated with /russula, /boletus and /pisolithus-scleroderma and a decrease in ubiquitous nursery order such as /sebacina. We also observed a higher number of shared OTUs between T. calobuxus and A. spirorbis. The vicinity of A. spirorbis enabled diversification and adaptation of the T. calobuxus ECM fungal community. These results led us to recommend A. spirorbis as a good nurse tree candidate in the framework of ecological restoration of mine sites.

Growth responses of ectomycorrhizal and arbuscular mycorrhizal seedlings to low soil nitrogen availability in a tropical montane forest

Abstract Differences in nutrient acquisition pathways between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi are associated with greater soil organic matter accumulation and reduced inorganic nitrogen (N) availability in EM‐dominated forests. These plant–soil feedbacks are expected to influence seedling recruitment and the maintenance of diversity. Montane forests of Central America are characterized by a mosaic of AM and EM dominance. We used a seedling transplant and soil manipulation experiment on Volcán Barú, Panama, to evaluate whether patches of oak (EM‐dominated) forest and mixed (AM‐dominated) forest affect seedling growth. We predicted that (a) plant–soil feedbacks would result in lower soil inorganic N availability in oak than in mixed forests, (b) consequently AM seedlings would grow more slowly and have lower foliar N concentrations in oak forest and (c) dependence of EM seedlings on organic N uptake via mycorrhiza would mean that inorganic N addition would increase seedling performance for AM but not EM (i.e. oak) seedlings. As soil organic matter accumulation may affect seedling performance beyond altering nutrient supply, we also tested whether organic matter removal differentially affected AM and EM seedlings. Nitrogen availability was six times lower and the soil organic layer three times deeper in oak‐dominated stands compared to mixed stands. Foliar N was lower for AM seedlings growing in oak than in mixed forest, but did not differ for oak seedlings and was increased only marginally by N addition for both AM and EM seedlings growing in both AM and EM forests. Seedling growth did not respond to N addition or organic matter removal. However, AM seedlings generally grew slower in oak forest compared with AM forest, consistent with lower foliar N concentration and low‐light availability. These results suggest that changes in soil nitrogen availability have a limited effect on seedling growth. In the neotropics, EM tree communities occur at high elevation. Future upslope migration of trees may result in AM‐dominated tree communities encountering unfavourable soil conditions generated by EM‐dominated canopies. While longer term experiments are needed, our results suggest that AM seedlings may not be able to tolerate conditions associated with EM forest. A free Plain Language Summary can be found within the Supporting Information of this article.

Growth and physiological responses of ectomycorrhizal Coccoloba uvifera (L.) L. seedlings to salt stress

We studied the effect of the ectomycorrhizal (ECM) fungus Scleroderma bermudense on growth, photosynthesis and transpiration rates, chlorophyll fluorescence and content, K/Na and Ca/Na homeostasis, and water status of two provenances of Coccoloba uvifera L. (named also seagrape) seedlings exposed to four levels of salinity (0.0, 54.7, 164.1 and 273.5 mM NaCl equivalent to 0.02, 5, 15 and 25 dS m−1, respectively). The results indicated that S. bermudense improved the salt tolerance in seagrape seedlings. There were no differences in terms of growth performance, nutritional and physiological functions between the two ECM seagrape provenances in response to salt stress. The reduction of the Na concentration and the increase of K and Ca favored a higher K/Na and Ca/Na ratio, respectively, in the tissues of the ECM seedlings. Furthermore, the beneficial effects of ECM symbiosis on the photosynthetic and transpiration rates, chlorophyll fluorescence and content, stomatal conductance and water status resulted in the improved growth performance of the seagrape provenances exposed to salt stress. From an ecological point of view, seagrape in symbiosis with S. bermudense may be used in the development of ornamental plantings and coastal windbreaks along beaches and roadsides in Cuba.

Ectomycorrhizal fungi enhance the tolerance of phytotoxicity and cadmium accumulation in oak (Quercus acutissima Carruth.) seedlings: modulation of growth properties and the antioxidant defense responses.

Ectomycorrhizal fungi (EMF), which form symbiotic ectomycorrhiza with tree roots, mediate heavy metal tolerance of host plants. To investigate the roles of EMF in the growth, modulation of oxidative stress, and cadmium (Cd) accumulation and translocation in Quercus acutissima seedlings, ectomycorrhizal seedlings inoculated with Suillus luteus were treated with different Cd concentrations (0.1, and 5 mg kg-1) for 14 days. EMF accelerated seedling growth and Cd accumulation in roots under the highest Cd concentration of 5 mg kg-1. Catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities increased in the leaves of ectomycorrhizal seedlings under the highest Cd concentration. Superoxide dismutase (SOD) trended to increase under both Cd concentrations. Although reduced glutathione (GSH) increased after inoculation of EMF under both Cd concentrations, the release of malondialdehyde increased in the leaves and roots under the highest Cd concentration, indicating that the defense role of EMF in Q. acutissima depends on the Cd concentration. These results indicate that EMF mitigate Cd stress by promoting plant growth and nutrient uptake while modulating the antioxidant system to reduce oxidative stress.

Spore germination and ectomycorrhizae formation of Tricholoma matsutake on pine root systems with previously established ectomycorrhizae from a dikaryotic mycelial isolate of T. matsutake.

In vitro ectomycorrhizal synthesis of Tricholoma matsutake with host plants has been widely conducted to elucidate fungal symbiotic properties for future cultivation practices. Here, we report on the importance of basidiospore inocula for this fungus to provide ectomycorrhizal seedlings in vitro. Ectomycorrhizal pine seedlings synthesized in vitro with cultured mycelium of T. matsutake (isolate #45 or #84) in a 250-mL culture vessel (soil volume) were transplanted to a large 1-L culture vessel. Fresh basidiospores of this fungus were aseptically inoculated on the ectomycorrhizal root system. The ectomycorrhizal seedlings in the 1-L vessel were grown for 9 months, and some plants were further grown for 6 more months under non-aseptic conditions in 4.1-L jars. The ectomycorrhizal seedlings previously inoculated with isolate #84 in the 1-L vessel showed significant ectomycorrhizal biomass (mycorrhizal root length) after spore inoculation. The ectomycorrhizal seedlings in the 4.1-L vessel showed large shiro structures (> 10 cm in diameter). PCR amplification of intergenic spacer 1 of the rRNA gene and long terminal repeat retroelement of T. matsutake in ectomycorrhizal root tips in both the 1-L vessels and 4.1-L jars revealed the presence of amplicons of the previously inoculated culture isolate of T. matsutake and the new genet(s) that established via germination of the inoculated basidiospores. This is the first report that inoculated basidiospores of T. matsutake germinated and colonized the host root to generate ectomycorrhizae in vitro.

Soil fungal networks moderate density-dependent survival and growth of seedlings.

Pathogenic and mutualistic fungi have contrasting effects on seedling establishment, but it remains unclear whether density-dependent survival and growth are regulated by access to different types of mycorrhizal fungal networks supported by neighbouring adult trees. Here, we conducted an extensive field survey to test how mycorrhizal and pathogenic fungal colonization of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) seedlings in a subtropical forest respond to density of neighbouring adult trees. In addition, we undertook a hyphal exclusion experiment to explicitly test the role of soil fungal networks in driving density-dependent effects on seedling growth and survival. Conspecific adult density was a strong predictor for the relative abundance of putative pathogens, which was greater in roots of AM than of ECM seedlings, while mycorrhizal fungal abundance and colonization were not consistently affected by conspecific adult density. Both ECM and AM fungal networks counteracted conspecific density-dependent mortality, but ECM fungi were more effective at weakening the negative effects of high seedling density than AM fungi. Our findings reveal a critical role of common fungal networks in mitigating negative density-dependent effects of pathogenic fungi on seedling establishment, which provides mechanistic insights into how soil fungal diversity shapes plant community structure in subtropical forests.

Effects of Ectomycorrhizal Fungi and Heavy Metals (Pb, Zn, and Cd) on Growth and Mineral Nutrition of Pinus halepensis Seedlings in North Africa.

The pollution of soils by heavy metals resulting from mining activities is one of the major environmental problems in North Africa. Mycorrhizoremediation using mycorrhizal fungi and adapted plant species is emerging as one of the most innovative methods to remediate heavy metal pollution. This study aims to assess the growth and the nutritional status of ectomycorrhizal Pinus halepensis seedlings subjected to high concentrations of Pb, Zn, and Cd for possible integration in the restoration of heavy metals contaminated sites. Ectomycorrhizal and non-ectomycorrhizal P. halepensis seedlings were grown in uncontaminated (control) and contaminated soils for 12 months. Growth, mineral nutrition, and heavy metal content were assessed. Results showed that ectomycorrhizae significantly improved shoot and roots dry masses of P. halepensis seedlings, as well as nitrogen shoot content. The absorption of Pb, Zn, and Cd was much higher in the roots than in the shoots, and significantly more pronounced in ectomycorrhizal seedlings—especially for Zn and Cd. The presence of ectomycorrhizae significantly reduced the translocation factor of Zn and Cd and bioaccumulation factor of Pb and Cd, which enhanced the phytostabilizing potential of P. halepensis seedlings. These results support the use of ectomycorrhizal P. halepensis in the remediation of heavy metal contaminated sites.

Effects of imidazole-4-carboxamide and 2-azahypoxanthine on the growth and ectomycorrhizal colonization of Pinus densiflora seedlings inoculated with Tricholoma matsutake

Imidazole-4-carboxamide (ICA) and 2-azahypoxanthine (AHX) obtained from Lepista sordida inhibit and promote the growth of herbaceous plants, respectively. In this study, we examined the effects of these compounds on the growth and ectomycorrhizal (EM) colonization of Pinus densiflora seedlings inoculated with Tricholoma matsutake that forms EM associations with pines. The EM colonization by T . matsutake was observed on the root systems of P . densiflora seedlings treated with and without ICA and AHX. The growth of both non-EM and EM P . densiflora seedlings was inhibited by ICA, regardless of the EM colonization. In contrast, AHX promoted the growth of non-EM P . densiflora seedlings, but not of EM seedlings, suggesting that EM colonization interferes with the effect of AHX on P . densiflora growth. • Imidazole-4-carboxamide (ICA) and 2-azahypoxanthine (AHX) are bioactive compounds. • Tricholoma matsutake – Pinus densiflora ectomycorrhizal (EM) seedlings were tested. • Growth of both non-EM and EM P. densiflora seedlings was inhibited by ICA. • Growth of non-EM P. densiflora was promoted by AHX; EM seedlings were unaffected. • EM colonization interfered with the growth promotion of AHX on P. densiflora.

A Cr(VI)-tolerant strain, Pisolithus sp1, with a high accumulation capacity of Cr in mycelium and highly efficient assisting Pinus thunbergii for phytoremediation

Ectomycorrhizal (ECM) fungi can improve the growth of pine trees and enhance their tolerance to heavy metal stress, and may also be useful during the afforestation and phytoremediation of polluted regions with pine trees. Hebeloma vinosophyllum (Cr(VI)-sensitive strain) and Pisolithus sp1 ((Cr(VI)-tolerant strain) were selected through liquid culture experiment, and were used in symbiosis with Japanese black pine (Pinus thunbergii) in pot experiments, to determine their potential for improving phytoremediation of Cr(VI)-contaminated soils. Our results indicated that Pisolithus sp1 also had a significantly higher accumulation of Cr than H. vinosophyllum in mycelium under the same Cr(VI) treatments in liquid culture experiment. The tolerance index of Pisolithus sp1 ECM seedlings’ shoots and roots to Cr(VI) were significantly higher than that of H. vinosophyllum ECM and non-ectomycorrhizal (NM) seedlings while the total accumulated Cr per seedling in Pisolithus sp1 ECM seedlings were 1.50–1.96 and 2.83–27.75 fold higher that of H. vinosophyllum ECM and NM seedlings, respectively, within 0–800 mg kg−1 Cr(VI) treatments in pot experiments. In addition, the significant differences ratios of photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration between Pisolithus sp1 ECM and NM seedlings were significantly higher than those between H. vinosophyllum ECM and NM seedlings under 400 and 800 mg kg−1 Cr(VI) treatments. Compared with the control (no plant), and planting NM or H. vinosophyllum ECM seedlings, the planting of Pisolithus sp1 ECM seedlings significantly reduced the percentage content of exchangeable Cr in the soil.

Soil propagule bank of ectomycorrhizal fungi associated with Masson pine (Pinus massoniana) grown in a manganese mine wasteland.

Ectomycorrhizal (ECM) fungal propagule bank could facilitate the regeneration and plantation of seedlings in disturbed area. In this study, Masson pine (Pinus massoniana) seedlings were used to bait the ECM fungal propagule bank buried in the soils collected from a manganese (Mn) mine wasteland and a non-polluted area in China. After 6-month growth, we found the seedlings grown in the Mn mine soil (Mn:3200 mg kg-1) did not display any toxicity symptoms. Based on morphotyping and ITS-PCR sequencing, we identified a total of 16 ECM fungal OTUs (operative taxonomic units) at 97% similarity threshold, among which 11 OTUs were recovered in the Mn mine soils and 14 in the non-polluted soil. Two soil types shared 9 OTUs and both of them were dominated by a Tylospora sp. Based on those soil propagule banks in Masson pine forests reported in previous, we speculated that some Atheliaceae species may be preferred in the soil propagule bank of some pine species, such as Masson pine. In addition, NMDS ordination displayed geographical position effects on soil propagule banks in five Masson pine forest from three sites at regional scale. In conclusion, Masson pine ECM seedlings could grow well in the Mn wasteland as a suitable tree species used for reforestation application in Mn mineland, in addition, Mn pollution did not alter the dominant ECM fungal species in the soil propagule banks.

Ectomycorrhizal fungi reduce the light compensation point and promote carbon fixation of Pinus thunbergii seedlings to adapt to shade environments

We examined the effects of three ectomycorrhizal (ECM) symbionts on the growth and photosynthesis capacity of Japanese black pine (Pinus thunbergii) seedlings and estimated physiological and photosynthetic parameters such as the light compensation point (LCP), biomass, and phosphorus (Pi) concentration of P. thunbergii seedlings. Through this investigation, we documented a new role of ectomycorrhizal (ECM) fungi: enhancement of the survival and competitiveness of P. thunbergii seedlings under low-light condition by reducing the LCP of seedlings. At a CO2 concentration of 400 ppm, the LCP of seedlings with ECM inoculations was 40–70 μmol photons m−2 s−1, significantly lower than that of non-mycorrhizal (NM) seedlings (200 μmol photons m−2 s−1). In addition, photosynthetic carbon fixation (Pn) increased with light intensity and CO2 level, and the Pn of ECM seedlings was significantly higher than that of NM seedlings; Pisolithus sp. (Pt)- and Laccaria amethystea (La)-mycorrhizal seedlings had significantly lower Pn than Cenococcum geophilum (Cg)-mycorrhizal seedlings. However, La-mycorrhizal seedlings exhibited the highest fresh weight, relative water content (RWC), and the lowest LCP in the mycorrhizal group. Concomitantly, ECM seedlings showed significantly increased chlorophyll content of needles and higher Pi concentrations compared to NM seedlings. Overall, ECM symbionts promoted growth and photosynthesis while reducing the LCP of P. thunbergii seedlings. These findings indicate that ECM fungi can enhance the survival and competitiveness of host seedlings under low light.

Experimental evidence that mycorrhizal nitrogen strategies affect soil carbon.

Most land plants acquire nitrogen (N) through associations with arbuscular (AM) and ectomycorrhizal (ECM) fungi, but these symbionts employ contrasting strategies for N acquisition, which may lead to different stocks of soil carbon (C). We experimentally test this hypothesis with a mesocosm system where AM and ECM tree seedling roots, or their hyphae only, could access mineral soils with 13 C- and 15 N-enriched organic matter. We quantified loss of soil C and N, plant uptake of N and new inputs of plant C to soil. We found that AM, but not ECM, seedlings reduced soil C relative to controls. Soil C loss was greater in the presence of roots relative to hyphae only for both AM and ECM seedlings, but was correlated with plant N uptake for AM seedlings only. While new plant C inputs stimulated soil C loss in both symbioses, we detected plant C inputs more frequently and measured higher rates of decomposer activity in soils colonized by AM relative to ECM seedlings. Our study experimentally demonstrates how mycorrhizal strategies for N can affect soil C and C:N, even at the scale of an individual plant. Such effects may contribute to broad patterns in soil C across terrestrial ecosystems.

Transfer to forest nurseries significantly affects mycorrhizal community composition of Asteropeia mcphersonii wildings.

Mycorrhizal symbiosis is extremely important for tree growth, survival and resistance after transplantation particularly in Madagascar where deforestation is a major concern. The importance of mycorrhizal symbiosis is further increased when soil conditions at the planting site are limiting. To identify technical itineraries capable of improving ecological restoration in Madagascar, we needed to obtain native ectomycorrhizal (ECM) saplings with a wide diversity of ECM fungi. To this end, we transplanted ECM seedlings from the wild (wildlings) to a nursery. Using molecular characterisation of internal transcribed spacer (ITS) rDNA, we tested the effect of transplanting Asteropeia mcphersonii wildlings on ECM communities after 8months of growth in the nursery. With or without the addition of soil from the site where the seedlings were sampled to the nursery substrate, we observed a dramatic change in the composition of fungal communities with a decrease in the ECM infection rate, a tremendous increase in the abundance of an operational taxonomic unit (OTU) taxonomically close to the order Trechisporales and the disappearance of all OTUs of Boletales. Transplanting to the nursery and/or to nursery conditions was shown to be incompatible with the survival and even less with the development in the nursery of most ECM fungi naturally associated with A. mcphersonii wildings.

Pathway and sink activity for photosynthate translocation in Pisolithus extraradical mycelium of ectomycorrhizal Pinus thunbergii seedlings.

The purpose of this study was to identify the pathway and sink activity of photosynthate translocation in the extraradical mycelium (ERM) of a Pisolithus isolate. We labelled ectomycorrhizal (ECM) Pinus thunbergii seedlings with (14)CO2 and followed (14)C distribution within the ERM by autoradiography. (14)C photosynthate translocation in the ERM resulted in (14)C distribution in rhizomorphs throughout the ERM, with (14)C accumulation at the front. When most radial mycelial connections between ECM root tips and the ERM front were cut, the whole allocation of (14)C photosynthates to the ERM was reduced. However, the overall pattern of (14)C distribution in the ERM was maintained even in regions immediately above and below the cut, with no local (14)C depletion or accumulation. We inferred from this result that every portion in the ERM has a significant sink activity and a definite sink capacity for photosynthates and that photosynthates detour the cut and reach throughout the ERM by translocation in every direction. Next, we prepared paired ECM seedlings, ERMs of which had been connected with each other by hyphal fusion, alongside, labelled the left seedling with (14)CO2, and shaded none, one or both of them. (14)C photosynthates were acropetally and basipetally translocated from the left ERM to ECM root tips of the right seedling through rhizomorphs in the left and right ERMs, respectively. With the left seedling illuminated, (14)C translocation from the left to the right ERM increased by shading the right seedling. This result suggests that reduced photosynthate transfer from the host to its ERM increased sink activity of the ERM.