[Show abstract][Hide abstract] ABSTRACT: Rapidly decreasing water availability as a consequence of climate change is likely to endanger the range of long-lived tree species. A pressing question is, therefore, whether adaptation to drought exists in important temperate tree species like European beech (Fagus sylvatica L.), a wide-spread, dominant forest tree in Central Europe. Here, five beech stands were selected along a precipitation gradient from moist to dry conditions. Neutral genetic markers revealed strong variation within and little differentiation between the populations. Natural regeneration from these stands was transferred to a common garden and used to investigate the expression of genes for abscisic acid (ABA)-related drought signaling [9-cis-epoxy-dioxygenase (NCED), protein phosphatase 2C (PP2C), early responsive to dehydration (ERD)] and stress protection [ascorbate peroxidase (APX), superoxide dismutase (SOD), aldehyde dehydrogenase (ALDH), glutamine amidotransferase (GAT)] that are involved in drought acclimation. We hypothesized that progenies from dry sites exhibit constitutively higher expression levels of ABA-and stress-related genes and are less drought responsive than progenies from moist sites. Transcript levels and stress responses (leaf area loss, membrane integrity) of well-irrigated and drought-stressed plants were measured during the early, mid-and late growing season. Principal component (PC) analysis ordered the beech progenies according to the mean annual precipitation at tree origin by the transcript levels of SOD, ALDH, GAT and ERD as major loadings along PC1. PC2 separated moist and drought treatments with PP2C levels as important loading. These results suggest that phosphatase-mediated signaling is flexibly acclimated to the current requirements, whereas stress compensatory measures exhibited genotypic variation, apparently underlying climate selection. In contrast to expectation, the drought responses were less pronounced than the progeny-related differences and the transcript levels were constitutively lower in beeches from dry than from moist sites. These results imply that beeches from dry origins may have evolved mechanisms to avoid oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: The nutrient status and physiological responses to drought were investigated in young poplar (Populus x canescens) trees, which were either non-mycorrhizal (NM) or colonized with the ectomycorrhizal fungus Paxillus involutus (EM). Stomatal conductance declined rapidly with limited water availability indicating that Populus x canescens is a strongly water-saving tree species. EM trees showed higher stomatal conductance than NM trees but the magnitude of the effect was very small. Nitrogen uptake was traced by 15N. 15N enrichment was higher in EM root tips than in NM root tips. The 15N enrichment in root tips and in roots was significantly linked with stomatal conductance, whereas the enrichment in leaves was correlated with the enrichment in roots, indicating that N uptake is influenced by photosynthetic processes and that the internal translocation to leaves depends on the concentration in the below-ground tissues. Phosphorus and cations, in particular the main osmolyte potassium K, were enriched leaves of EM plants, but not in roots. Under drought, K and Mg increased in roots regardless the EM status, whereas the foliar concentrations increased only in EM plants. A decline in the leaf water content was prevented by increases in both, cations and soluble sugars. EM also delayed root tip mortality compared with NM plants, thus, suggesting transiently positive effects of EM on poplar performance under drought. Under stronger stress at water potentials of about -1.1 MPa, the transcript levels of stress marker genes (aquaporin PIP2.5, ABA-responsive RD26, ammonium transporter AMT3.1) were increased regardless the mycorrhizal status of the trees.
Environmental and Experimental Botany 12/2014; · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Paxillus involutus strains MAJ and NAU improve ion homeostasis under salt stress although only strain MAJ forms a functional ectomycorrhiza with poplar roots, whereas strain NAU induces defense reactions. The goal of the present study was to determine whether beneficial effects of MAJ and NAU on root nutrient element fluxes are induced during early stages of fungal-root interaction or require long-term co-culture. Salt-induced flux profiles of H+, Na+, K+, and Ca2+ were examined in the salt-sensitive poplar Populus × canescens after inoculation for 10 d and 20 d with the P. involutus strains, MAJ and NAU and after short-term (24 h) and long-term (7 d) salt stress. Inoculation with P. involutus for 10 d and 20 d increased the capacity of P. × canescens roots to retain K+ after short and long-term exposure to NaCl stress (100 mM). P. involutus-inoculated plants reduced the influx of Na+, especially in the NAU-inoculated roots. The salt-elicited Na+ efflux corresponded with an apparent decline of H+ extrusion in NAU-inoculated roots, which was presumably the result of increased Na+/H+ exchange activity across the plasma membrane. After 10 days of fungal inoculation, P. × canescens roots exhibited an enhanced Ca2+ uptake ability upon salt treatments, whereas a prolonged inoculation time of 20 d caused a marked Ca2+ efflux from P. × canescens roots. The P. involutus-elicited Ca2+ enrichment was probably replaced by Na+ at the later stage of fungal colonization. Ca2+ enrichment is known to mediate K+/Na+ homeostasis in poplar roots under salt stress and therefore both NAU- and MAJ-impeded Na+ accumulation compared with non-inoculated roots. NAU provided greater benefit to the inoculated roots to the maintenance of the K+/Na+ homeostasis because of the pronounced Na+ extrusion during the early stage of fungal colonization when the Ca2+ enrichment was greater than in MAJ-inoculated roots. In accordance with flux data, the whole-plant assessment revealed that inoculation with P. involutus attenuated NaCl-induced leaf damage in P. × canescens. Overall, our results support that the formation of a mature ectomycorrhiza is not required for the amelioration of the protection from salinity stress.
Environmental and Experimental Botany 12/2014; 108:99–108. · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ectomycorrhizas (EMs) are mutualistic associations between certain soil fungi and higher plants. EMs can modulate the cellular, physiological and molecular processes of host plants, resulting in altered responses of the colonized plants to heavy metals. Progress in elucidating the role of EMs in modulating heavy metal tolerance of host trees is reviewed. In the last decade, a number of ectomycorrhizal fungal isolates and host plants have been characterized for their tolerance to heavy metals. Additionally, the cellular processes have been investigated with regard to heavy metal uptake, transport, distribution, toxicity and detoxification by ectomycorrhizal fungi and/or host plants. At the cellular level, mechanisms of heavy metal detoxification include (i) binding of heavy metals to cell wall and extracellular exudates, (ii) decreased uptake and/or pumping metal ions out of cytosol, (iii) chelation of metal ions in cytosol, (iv) compartmentation of metals in vacuoles or other subcellular structures, and (v) repair of damaged biomolecules. The efficiency of these protective measures is often increased by EMs, resulting in improved physiological status and rescued growth. While physiological and cellular responses to heavy metals have been well studied, experimental data on the underlying molecular mechanisms, especially those induced by the interaction of ectomycorrhizal fungi and hosts, are scattered. Progress in genome sequencing of EM partners has revealed the importance of metal transporters in mediating tolerance. A better understanding of the molecular mechanisms is essential for effective application of selected fungal isolates and hosts to improve the efficiency of bioremediation on heavy metal polluted sites.
Environmental and Experimental Botany 12/2014; 108:47–62. · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soil microbial community responses to elevated atmospheric CO2 concentrations (eCO2) occur mainly indirectly via CO2-induced plant growth stimulation leading to quantitative as well as qualitative changes in rhizodeposition and plant litter. In order to gain insight into short-term, site-specific effects of eCO2 on the microbial community structure at the plant-soil interface, young beech trees (Fagus sylvatica L.) from two opposing mountainous slopes with contrasting climatic conditions were incubated under ambient (360 ppm) CO2 concentrations in a greenhouse. One week before harvest, half of the trees were incubated for 2 days under eCO2 (1,100 ppm) conditions. Shifts in the microbial community structure in the adhering soil as well as in the root rhizosphere complex (RRC) were investigated via TRFLP and 454 pyrosequencing based on 16S ribosomal RNA (rRNA) genes. Multivariate analysis of the community profiles showed clear changes of microbial community structure between plants grown under ambient and elevated CO2 mainly in RRC. Both TRFLP and 454 pyrosequencing showed a significant decrease in the microbial diversity and evenness as a response of CO2 enrichment. While Alphaproteobacteria dominated by Rhizobiales decreased at eCO2, Betaproteobacteria, mainly Burkholderiales, remained unaffected. In contrast, Gammaproteobacteria and Deltaproteobacteria, predominated by Pseudomonadales and Myxococcales, respectively, increased at eCO2. Members of the order Actinomycetales increased, whereas within the phylum Acidobacteria subgroup Gp1 decreased, and the subgroups Gp4 and Gp6 increased under atmospheric CO2 enrichment. Moreover, Planctomycetes and Firmicutes, mainly members of Bacilli, increased under eCO2. Overall, the effect intensity of eCO2 on soil microbial communities was dependent on the distance to the roots. This effect was consistent for all trees under investigation; a site-specific effect of eCO2 in response to the origin of the trees was not observed.
[Show abstract][Hide abstract] ABSTRACT: The class I KNOX transcription factors SHOOT MERISTEMLESS (STM) and KNAT1 are important regulators of meristem maintenance in shoot apices, with a dual role of promoting cell proliferation and inhibiting differentiation. We examined whether they control stem cell maintenance in the cambium of Arabidopsis hypocotyls, a wood-forming lateral meristem, in a similar fashion as in the shoot apical meristem. Weak loss-of-function alleles of KNAT1 and STM led to reduced formation of xylem fibers - highly differentiated cambial derivatives - whereas cell proliferation in the cambium was only mildly affected. In a knat1;stm double mutant, xylem fiber differentiation was completely abolished, but residual cambial activity was maintained. Expression of early and late markers of xylary cell differentiation was globally reduced in the knat1;stm double mutant. KNAT1 and STM were found to act through transcriptional repression of the meristem boundary genes BLADE-ON-PETIOLE 1 (BOP1) and BOP2 on xylem fiber differentiation. Together, these data indicate that, in the cambium, KNAT1 and STM, contrary to their function in the shoot apical meristem, promote cell differentiation through repression of BOP genes.
Development (Cambridge, England). 11/2014; 141(22):4311-9.
[Show abstract][Hide abstract] ABSTRACT: Phenylcoumaran benzylic ether reductase (PCBER) is one of the most abundant proteins in poplar (Populus spp) xylem, but its biological role has remained obscure. In this work, metabolite profiling of transgenic poplar trees downregulated in PCBER revealed both the in vivo substrate and product of PCBER. Based on mass spectrometry and NMR data, the substrate was identified as a hexosylated 8-5-coupling product between sinapyl alcohol and guaiacylglycerol, and the product was identified as its benzyl-reduced form. This activity was confirmed in vitro using a purified recombinant PCBER expressed in Escherichia coli. Assays performed on 20 synthetic substrate analogs revealed the enzyme specificity. In addition, the xylem of PCBER-downregulated trees accumulated over 2000-fold higher levels of cysteine adducts of monolignol dimers. These compounds could be generated in vitro by simple oxidative coupling assays involving monolignols and cysteine. Altogether, our data suggest that the function of PCBER is to reduce phenylpropanoid dimers in planta to form antioxidants that protect the plant against oxidative damage. In addition to describing the catalytic activity of one of the most abundant enzymes in wood, we provide experimental evidence for the antioxidant role of a phenylpropanoid coupling product in planta.
[Show abstract][Hide abstract] ABSTRACT: Overexpression of bacterial γ-glutamylcysteine synthetase in the cytosol of Populus tremula × P. alba produces higher glutathione (GSH) concentrations in leaves, thereby indicating the potential for cadmium (Cd) phytoremediation. However, the net Cd2+ influx in association with H+/Ca2+, Cd tolerance, and the underlying molecular and physiological mechanisms are uncharacterized in these poplars.We assessed net Cd2+ influx, Cd tolerance and the transcriptional regulation of several genes involved in Cd2+ transport and detoxification in wild-type and transgenic poplars.Poplars exhibited highest net Cd2+ influxes into roots at pH 5.5 and 0.1 mM Ca2+. Transgenics had higher Cd2+ uptake rates and elevated transcript levels of several genes involved in Cd2+ transport and detoxification compared with wild-type poplars. Transgenics exhibited greater Cd accumulation in the aerial parts than wild-type plants in response to Cd2+ exposure. Moreover, transgenic poplars had lower concentrations of O2˙− and H2O2; higher concentrations of total thiols, GSH and oxidized GSH in roots and/or leaves; and stimulated foliar GSH reductase activity compared with wild-type plants.These results indicate that transgenics are more tolerant of 100 μM Cd2+ than wild-type plants, probably due to the GSH-mediated induction of the transcription of genes involved in Cd2+ transport and detoxification.
[Show abstract][Hide abstract] ABSTRACT: Saline and sodic soils that cannot be used for agriculture occur worldwide. Cultivating stress- tolerant trees to obtain biomass from salinised areas has been suggested. Various tree species of economic importance for fruit, fibre and timber production exhibit high salinity tolerance. Little is known about the mechanisms enabling tree crops to cope with high salinity for extended periods. Here, the molecular, physiological and anatomical adjustments underlying salt tolerance in glycophytic and halophytic model tree species, such as Populus euphratica in terrestrial habitats, and mangrove species along coastlines are reviewed. Key mechanisms that have been identified as mediating salt tolerance are discussed at scales from the genetic to the morphological level, including leaf succulence and structural adjustments to wood anatomy. The genetic and transcriptomic bases for physiological salt acclimation are salt sensing and signalling networks that activate target genes; the target genes keep reactive oxygen species under control, maintain the ion balance and restore water status. Evolutionary adaptation includes gene duplication in these pathways. Strategies for and limitations to tree improvement, particularly transgenic approaches for increasing salt tolerance by transforming trees with single and multiple candidate genes, are discussed.
Plant Cell and Environment 08/2014; · 5.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A greenhouse experiment was conducted to study whether exogenous abscisic acid (ABA) mediates the responses of poplars to excess zinc (Zn). Populus × canescens seedlings were treated with either basal or excess Zn levels and either 0 or 10 μM ABA. Excess Zn led to reduced photosynthetic rates, increased Zn accumulation, induced foliar ABA and salicylic acid (SA), decreased foliar gibberellin (GA3 ) and auxin (IAA), elevated root H2 O2 levels, and increased root ratios of glutathione (GSH) to GSSG and foliar ratios of ascorbate (ASC) to dehydroascorbate (DHA) in poplars. While exogenous ABA decreased foliar Zn concentrations with 7-day treatments, it increased levels of endogenous ABA, GA3 and SA in roots, and resulted in highly increased foliar ASC accumulation and ratios of ASC to DHA. The transcript levels of several genes involved in Zn uptake and detoxification, such as yellow stripe-like family protein 2 (YSL2) and plant cadmium resistance protein 2 (PCR2), were enhanced in poplar roots by excess Zn but repressed by exogenous ABA application. These results suggest that exogenous ABA can decrease Zn concentrations in P. × canescens under excess Zn for 7 days, likely by modulating the transcript levels of key genes involved in Zn uptake and detoxification.
Plant Cell and Environment 08/2014; · 5.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the exchange of nitrogen and carbon between ectomycorrhiza and host plant, young beech (Fagus sylvatica) trees from natural regeneration in intact soil cores were labelled for one growing season in a greenhouse with (13)CO2 and (15)NO3 (15)NH4. The specific enrichments of (15)N and (13)C were higher in ectomycorrhizas (EMs) than in any other tissue. The enrichments of (13)C and (15)N were also higher in the fine-root segments directly connected with the EM (mainly second-order roots) than that in bulk fine or coarse roots. A strict, positive correlation was found between the specific (15)N enrichment in EM and the attached second-order roots. This finding indicates that strong N accumulators provide more N to their host than low N accumulators. A significant correlation was also found for the specific (13)C enrichment in EM and the attached second-order roots. However, the specific enrichments for (15)N and (13)C in EM were unrelated showing that under long-term conditions, C and N exchange between host and EMs are uncoupled. These findings suggest that EM-mediated N flux to the plant is not the main control on carbon flux to the fungus, probably because EMs provide many different services to their hosts in addition to N provision in their natural assemblages.
[Show abstract][Hide abstract] ABSTRACT: Verticillium longisporum is a soil-borne vascular pathogen causing economic loss in rape. Using the model plant Arabidopsis this study analyzed metabolic changes upon fungal infection in order to identify possible defense strategies of Brassicaceae against this fungus. Metabolite fingerprinting identified infection-induced metabolites derived from the phenylpropanoid pathway. Targeted analysis confirmed the accumulation of sinapoyl glucosides, coniferin, syringin and lignans in leaves from early stages of infection on. At later stages, the amounts of amino acids increased. To test the contribution of the phenylpropanoid pathway, mutants in the pathway were analyzed. The sinapate-deficient mutant fah1-2 showed stronger infection symptoms than wild-type plants, which is most likely due to the lack of sinapoyl esters. Moreover, the coniferin accumulating transgenic plant UGT72E2-OE was less susceptible. Consistently, sinapoyl glucose, coniferyl alcohol and coniferin inhibited fungal growth and melanization in vitro, whereas sinapyl alcohol and syringin did not. The amount of lignin was not significantly altered supporting the notion that soluble derivatives of the phenylpropanoid pathway contribute to defense. These data show that soluble phenylpropanoids are important for the defense response of Arabidopsis against V. longisporum and that metabolite fingerprinting is a valuable tool to identify infection-relevant metabolic markers.
[Show abstract][Hide abstract] ABSTRACT: 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.
PLoS ONE 01/2014; 9(12):e114672. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Roots of forest trees are associated with various ectomycorrhizal (ECM) fungal species that are involved in nutrient exchange between host plant and the soil compartment. The identification of ECM fungi in small environmental samples is difficult. The present study tested the feasibility of attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy followed by hierarchical cluster analysis (HCA) to discriminate in situ collected ECM fungal species. Root tips colonized by distinct ECM fungal species, i.e., Amanita rubescens, Cenococcum geophilum, Lactarius subdulcis, Russula ochroleuca, and Xerocomus pruinatus were collected in mono-specific beech (Fagus sylvatica) and mixed deciduous forests in different geographic areas to investigate the environmental variability of the ECM FTIR signatures. A clear HCA discrimination was obtained for ECM fungal species independent of individual provenance. Environmental variability neither limited the discrimination between fungal species nor provided sufficient resolution to discern species sub-clusters for different sites. However, the de-convoluted FTIR spectra contained site-related spectral information for fungi with wide nutrient ranges, but not for Lactarius subdulcis, a fungus residing only in the litter layer. Specific markers for distinct ECM were identified in spectral regions associated with carbohydrates (i.e., mannans), lipids, and secondary protein structures. The present results support that FTIR spectroscopy coupled with multivariate analysis is a reliable and fast method to identify ECM fungal species in minute environmental samples. Moreover, our data suggest that the FTIR spectral signatures contain information on physiological and functional traits of ECM fungi.
Frontiers in Plant Science 01/2014; 5:229. · 3.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Populus × euramericana (Pe) displays higher stable carbon isotope composition (δ(13) C) and intrinsic water use efficiency (WUEi ) than P. cathayana (Pc) under unlimited water conditions, rendering us to hypothesize that Pe is better acclimated to water deficiency than Pc. To examine this hypothesis, saplings of Pc and Pe were exposed to drought and subsequently re-watered. Pc and Pe exhibited distinct anatomical, physiological and transcriptional responses in acclimation to drought and re-watering, mainly due to stronger responsiveness of transcriptional regulation of genes encoding plasma membrane intrinsic proteins (PIPs), higher starch accumulation, δ(13) C, stable nitrogen isotope composition (δ(15) N) and WUEi , and lower reactive oxygen species (ROS) accumulation and scavenging in Pe. In acclimation to drought, both poplar genotypes demonstrated altered anatomical properties, declined height growth, differential expression of PIPs, activation of ABA signaling pathway, decreased total soluble sugars and starch, increased δ(13) C, δ(15) N and WUEi , and shifted homeostasis of ROS production and scavenging, and these changes can be recovered upon re-watering. These data indicate that Pe is more tolerant to drought than Pc, and that anatomical, physiological and transcriptional acclimation to drought and re-watering is essential for poplars to survive and grow under projected dry climate scenarios in the future.
Physiologia Plantarum 12/2013; · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Populus euphratica is a salt-tolerant tree species that develops leaf succulence after a prolonged period of salinity stress. In the present study, a putative xyloglucan endotransglucosylase/hydrolase gene (PeXTH) from P. euphratica was isolated and transferred to tobacco plants. PeXTH localized exclusively to the endoplasmic reticulum and cell wall. Plants overexpressing PeXTH were more salt tolerant than wild-type tobacco with respect to root and leaf growth, and survival. The increased capacity for salt tolerance was due mainly to the anatomical and physiological alterations caused by PeXTH overexpression. Compared with the wild type, PeXTH-transgenic plants contained 36% higher water content per unit area and 39% higher ratio of fresh weight to dry weight, a hallmark of leaf succulence. However, the increased water storage in the leaves in PeXTH-transgenic plants was not accompanied by greater leaf thickness but was due to highly packed palisade parenchyma cells and fewer intercellular air spaces between mesophyll cells. In addition to the salt dilution effect in response to NaCl, these anatomical changes increased leaf water-retaining capacity, which lowered the increase of salt concentration in the succulent tissues and mesophyll cells. Moreover, the increased number of mesophyll cells reduced the intercellular air space, which improved carbon economy and resulted in a 47-78% greater net photosynthesis under control and salt treatments (100-150mM NaCl). Taken together, the results indicate that PeXTH overexpression enhanced salt tolerance by the development of succulent leaves in tobacco plants without swelling.
Journal of Experimental Botany 10/2013; · 5.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mycorrhizal fungi have a key role in nitrogen (N) cycling, particularly in boreal and temperate ecosystems. However, the significance of ectomycorrhizal fungal (EMF) diversity for this important ecosystem function is unknown. Here, EMF taxon-specific N uptake was analyzed via (15)N isotope enrichment in complex root-associated assemblages and non-mycorrhizal root tips in controlled experiments. Specific (15)N enrichment in ectomycorrhizas, which represents the N influx and export, as well as the exchange of (15)N with the N pool of the root tip, was dependent on the fungal identity. Light or water deprivation revealed interspecific response diversity for N uptake. Partial taxon-specific N fluxes for ectomycorrhizas were assessed, and the benefits of EMF assemblages for plant N nutrition were estimated. We demonstrated that ectomycorrhizal assemblages provide advantages for inorganic N uptake compared with non-mycorrhizal roots under environmental constraints but not for unstressed plants. These benefits were realized via stress activation of distinct EMF taxa, which suggests significant functional diversity within EMF assemblages. We developed and validated a model that predicts net N flux into the plant based on taxon-specific (15)N enrichment in ectomycorrhizal root tips. These results open a new avenue to characterize the functional traits of EMF taxa in complex communities.