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Soil organic matter (SOM) originates from various sources such as foliar litter, roots and microbial (e.g. fungal) components. The relative sources contribution represents one of the key unknowns in SOM dynamics. Our study aimed to explore whether stable isotope ratios of non-exchangeable hydrogen (Hn) bound to organic matter can be used to differentiate SOM sources, since natural 2Hn abundance can strongly differ between root and foliar tissues. We also investigated if long-term irrigation with 2H-depleted water in a pine forest can be used to track Hn incorporation into organic matter inputs and eventually in the soil pools.In a 17-year-long irrigation experiment in a dry pine forest, we assessed variations in natural abundance of 2Hn, 13C, and 15N in SOM sources (foliar litter, fine roots, fungal mycelia), decomposing litter, soil (organic layers and uppermost 5 cm-mineral soil) and particle-size fractions. We then applied a Bayesian mixing model (including δ2Hn,δ13C, and δ15N) to estimate the relative sources contribution to SOM.Natural 2Hn abundance was significantly higher in roots vs. foliar litter (up to +39‰), and in fungal mycelia vs. roots (up to +41‰). Results from Bayesian mixing model suggest that foliar litter contributed to approximately 68 ± 10% of SOM in organic layers and in coarse particulate organic matter (POM). Foliar litter and roots contributed similarly to upper 2 cm of mineral soil (46 ± 11%), while 2-5 cm of mineral soil were largely derived from roots (61 ± 13%). Fungal mycelia contributed to 18 ± 8% of mineral-associated organic matter (MOM), while only to 1-2% of coarse and fine POM. Bayesian mixing models provided only a general indication of the sources contribution to SOM, also considering that isotopic signatures shifted during decomposition. Measurements of isotope signatures in microbial necromass might allow a more accurate assessment of the different SOM sources contribution.The δ2Hn depletion of soil water under irrigation was paralleled by a comparable decrease in δ2Hn of roots (~12‰). In comparison, the natural 2Hn abundance in fresh needles and foliar litter decreased less strongly (~ 7‰ and 4‰, respectively), likely due to photosynthetic adjustments that may have counterbalanced the irrigation water 2H-depletion. Similar to soil water 2H-depletion, δ2Hn values in coarse POM were 11‰ lower in irrigated vs. dry plots, suggesting that nearly all organic Hn turned over or exchanged with soil water in less than two decades. In contrast, δ2Hn values in fine POM and MOM decreased only by 3‰ under irrigation, which indicate that these fractions comprise slower cycling Hn pools.Our study showed that the natural 2Hn abundance represents a promising tool to differentiate among SOM sources. While 13C and 15N did not clearly separate between roots and foliar litter, Hn isotopic signatures allowed a good discrimination between SOM sources. In addition, long-term irrigation can provide a potential in situ 2H-labelling of SOM, which may help to examine organic Hn turnover rates across SOM pools.

Ectomycorrhizal (ECM) fungi associated with plants constitute one of the most successful symbiotic interactions in forest ecosystems. ECM support trophic exchanges with host plants and are important factors for the survival and stress resilience of trees. However, ECM clades often harbour morpho-species and cryptic lineages, with weak morphological differentiation. How this relates to intraspecific genome variability and ecological functioning is poorly known. Here, we analysed 16 European isolates of the ascomycete Cenococcum geophilum, an extremely ubiquitous forest symbiotic fungus with no known sexual or asexual spore-forming structures but with a massively enlarged genome. We carried out whole-genome sequencing to identify single-nucleotide polymorphisms. We found no geographic structure at the European scale but divergent lineages within sampling sites. Evidence for recombination was restricted to specific cryptic lineages. Lineage differentiation was supported by extensive copy-number variation. Finally, we confirmed heterothallism with a single MAT1 idiomorph per genome. Synteny analyses of the MAT1 locus revealed substantial rearrangements and a pseudogene of the opposite MAT1 idiomorph. Our study provides the first evidence for substantial genome-wide structural variation, lineage-specific recombination and low continent-wide genetic differentiation in C. geophilum. Our study provides a foundation for targeted analyses of intra-specific functional variation in this major symbiosis.

Funder: Forest Science and Technology Centre of Catalonia (CTFC), BLACKDYNAMITE, Funder: Swiss Federal Institute for Forest, Snow and Landscape Research WSL, BLACKDYNAMITE, DITREC, Burgundy truffles are heterothallic ascomycetes that grow in symbiosis with trees. Despite their esteemed belowground fruitbodies, the species' complex lifecycle is still not fully understood. Here, we present the genetic patterns in three natural Burgundy truffle populations based on genotyped fruitbodies, ascospore extracts and ectomycorrhizal root tips using microsatellites and the mating-type locus. Distinct genetic structures with high relatedness in close vicinity were found for females (forming the fruitbodies) and males (fertilizing partner as inferred from ascospore extracts), with high genotypic diversity and annual turnover of males, suggesting that ephemeral male mating partners are germinating ascospores from decaying fruitbodies. The presence of hermaphrodites and the interannual persistence of a few males suggest that persistent mycelia may sporadically also act as males. Only female or hermaphroditic individuals were detected on root tips. At one site, fruitbodies grew in a fairy ring formed by a large female individual that showed an outward growth rate of 30 cm per year, with the mycelium decaying within the ring and being fertilized by over 50 male individuals. While fairy ring structures have never been shown for truffles, the genetics of Burgundy truffle populations support a similar reproductive biology as those of other highly prized truffles.

Drought alters carbon (C) allocation within trees, thereby impairing tree growth. Recovery of root and leaf functioning and prioritized C supply to sink tissues after drought may compensate for drought -induced reduction of assimilation and growth. It remains unclear if C allocation to sink tissues during and following drought is controlled by altered sink metabolic activities or by the availability of new assimilates. Understanding such mechanisms is required to predict forests' resilience to a changing climate. We investigated the impact of drought and drought release on C allocation in a 100-y-old Scots pine forest. We applied (CO2)-C-13 pulse labeling to naturally dry control and long-term irrigated trees and tracked the fate of the label in aboveand belowground C pools and fluxes. Allocation of new assimilates belowground was ca. 53% lower under nonirrigated conditions. A short rainfall event, which led to a temporary increase in the soil water content (SWC) in the topsoil, strongly increased the amounts of C transported belowground in the nonirrigated plots to values comparable to those in the irrigated plots. This switch in allocation patterns was congruent with a tipping point at around 15% SWC in the response of the respiratory activity of soil microbes. These results indicate that the metabolic sink activity in the rhizosphere and its modulation by soil moisture can drive C allocation within adult trees and ecosystems. Even a subtle increase in soil moisture can lead to a rapid recovery of belowground functions that in turn affects the direction of C transport in trees.

Long generation times have been suggested to hamper rapid genetic adaptation of organisms to changing environmental conditions. We examined if environmental memory of the parental Scots pines (Pinus sylvestris L.) drive offspring survival and growth. We used seeds from trees growing under naturally dry conditions (control), irrigated trees (irrigated from 2003 to 2016), and formerly irrigated trees (“irrigation stop”; irrigated from 2003–2013; control condition since 2014). We performed two experiments, one under controlled greenhouse conditions and one at the experimental field site. In the greenhouse, the offspring from control trees exposed regularly to drought were more tolerant to hot–drought conditions than the offspring from irrigated trees and showed lower mortality even though there was no genetic difference. However, under optimal conditions (high water supply and full sunlight), these offspring showed lower growth and were outperformed by the offspring of the irrigated trees. This different offspring growth, with the offspring of the “irrigation‐stop” trees showing intermediate responses, points to the important role of transgenerational memory for the long‐term acclimation of trees. Such memory effects, however, may be overridden by climatic extremes during germination and early growth stages such as the European 2018 mega‐drought that impacted our field experiment., Environmental conditions (natural dry vs. irrigated) experienced by the mother trees of Pinus sylvestris significantly influenced the offspring's growth and survival, indicating that transgenerational environmental memory can shape trees' acclimation potential over the midterm to the long term.

Rapid human-induced environmental changes like climate warming represent a challenge for forest ecosystems. Due to their biological complexity and the long generation time of their keystone tree species, genetic adaptation in these ecosystems might not be fast enough to keep track with conditions changing at such a fast pace. The study of adaptation to environmental change and its genetic mechanisms is therefore key for ensuring a sustainable support and management of forests. The 4-day conference of the European Research Group EvolTree (https://www.evoltree.eu) on the topic of “Genomics and Adaptation in Forest Ecosystems” brought together over 130 scientists to present and discuss the latest developments and findings in forest evolutionary research. Genomic studies in forest trees have long been hampered by the lack of high-quality genomics resources and affordable genotyping methods. This has dramatically changed in the last few years; the conference impressively showed how such tools are now being applied to study past demography, adaptation and interactions with associated organisms. Moreover, genomic studies are now finally also entering the world of conservation and forest management, for example by measuring the value or cost of interspecific hybridization and introgression, assessing the vulnerability of species and populations to future change, or accurately delineating evolutionary significant units. The newly launched conference series of EvolTree will hopefully play a key role in the exchange and synthesis of such important investigations.

SummaryEctomycorrhizal (ECM) fungi associated with plants constitute one of the most successful symbiotic interactions in forest ecosystems. ECM support trophic exchanges with host plants and are important factors for the survival and stress resilience of trees. However, ECM clades often harbour morpho-species and cryptic lineages, with weak morphological differentiation. How this relates to intraspecific genome variability and ecological functioning is poorly known. Here, we analysed 16 European isolates of the ascomycete Cenococcum geophilum, an extremely ubiquitous forest symbiotic fungus with no known sexual or asexual spore forming structures but with a massively enlarged genome. We carried out whole-genome sequencing to identify single-nucleotide polymorphisms. We found no geographic structure at the European scale but divergent lineages within sampling sites. Evidence for recombination was restricted to specific cryptic lineages. Lineage differentiation was supported by extensive copy-number variation. Finally, we confirmed heterothallism with a single MAT1 idiomorph per genome. Synteny analyses of the MAT1 locus revealed substantial rearrangements and a pseudogene of the opposite MAT1 idiomorph. Our study provides the first evidence for substantial genome-wide structural variation, lineage-specific recombination and low continent-wide genetic differentiation in C. geophilum. Our study provides a foundation for targeted analyses of intra-specific functional variation in this major symbiosis.Originality-Significance StatementWe provide the first report on the genetic structure and copy-number variation of the globally ubiquitous and key forest symbiotic fungus Cenococcum geophilum using whole-genome sequencing data. We found divergent lineages within sampling sites, while closely related lineages appear over large geographic distances on a continental scale. Even though no sexual spore forming structures have been reported to date, we provide evidence of recombination in a specific lineage suggesting mating activity. Our findings help explain the high genetic diversity occurring within populations and their resilience to changing and adverse environmental conditions. Furthermore, we identify a single MAT1 idiomorph per genome, confirming heterothallism, and discover that major genomic rearrangements are found in their flanking regions based on chromosomal synteny analysis. Intriguingly, a pseudogene of the opposite functional idiomorph has been characterised in each genome, suggesting a common homothallic ancestor to the species. As Cenococcum geophilum is a pivotal mycorrhizal associate of a broad range of trees and shrubs providing nutrition and water supply to their hosts, we highlight and discuss the potential role of the large genome-wide structural variations in environmental selection.

Despite being one of the most expensive gourmet foods, it remains unclear if the iconic White Truffle ( Tuber magnatum Pico; hereinafter WT) accumulates radioactivity at harmful levels comparable to other fungal species. Here, we measure the active radiocaesium-137 concentration ( 137 Cs) in ten hypogeous WT fruitbodies from southern Hungary, and the soils in which they were growing. All WTs reveal non-significant 137 Cs values, thus providing an ‘all clear’ for WT hunters in the species' northernmost habitats, where corresponding soil samples occasionally exhibit slight 137 Cs concentrations. Our results are particularly relevant in the light of a rapidly increasing global demand for WTs and their subsequent trading extent and price inflation, because up to 600 kg of fresh fruitbodies are harvested each year in southern Hungary. Moreover, some of Europe's forest ecosystems, in which mushroom picking is common practise, are still contaminated with 137 Cs from the Chernobyl fallout more than 30 years ago, posing a serious threat to human health.

Despite its status as a highly-prized and coveted fungi in gastronomy, many aspects of the subterranean life cycle of the Burgundy truffle (Tuber aestivum) are still unknown, because in situ observations of the formation and maturation of truffle fruitbodies remain difficult. Here, we adopted a suite of archaeological fine-scale excavating techniques to provide unique spatiotemporal snapshots of Burgundy truffle growth at three sites in southern Germany. We also recorded the relative position, fresh weight, maturity level and genotype composition of all excavated fruitbodies. Varying by a factor of thousand, the fresh weight of 73 truffle ranged from 0.1 to 103.2 g, with individual maturity levels likely representing different life cycle stages from completely unripe to fully ripe and even decaying. While only a slightly positive relationship between fruitbody weight and maturity level was found, our results suggest that genetically distinct specimens can exhibit different life cycle stages at the same period of time and under the same environmental conditions. We therefore argue that truffles are likely able to grow, mature and ripe simultaneously between early summer and late winter of the following year. Our case study should encourage further eco-archaeological truffle excavations under different biogeographic settings and at different seasons of the year to gain deeper insights into the fungi's subterranean ecology. The expected cross-disciplinary findings will help truffle hunters and farmers to improve their harvest practices and management strategies.

• Changes in above- and below-ground ectomycorrhizal species composition are reported following nitrogen addition for 2 yr to a subalpine spruce (Picea abies) stand. • The macrofungal sporocarp production was recorded before and during N addition. Belowground ectomycorrhizal diversity was measured by PCR-RFLP analysis of the internal transcribed spacer (ITS) region of rDNA extracted from single mycorrhizal root tips before, and after 1 and 2 yr of fertilization. • Sporocarp surveys showed that diversity of the ectomycorrhizal community was drastically reduced following 1 yr of N addition, whereas the saprobic fungal community was not affected. The impact on belowground ectomycorrhizal diversity was less pronounced with no change either in the number of ectomycorrhizal taxa or in Simpson's index of diversity. However, a change in belowground species composition 2 years after N addition was observed with significant changes in abundances of single species. • Species which produced large sporocarps accounted for 25% of all sampled root tips. At least 44% of all ectomycorrhizas were formed by species belonging to the Thelephoraceae and Corticiaceae, taxa which produce inconspicuous sporocarps. • Addition of N caused a shift in ectomycorrhizal abundance from species forming large sporocarps to species with no or resupinate sporocarps.

Mit dem Tod von Laura Sheleen (1925–2021) hat uns eine ausergewohnliche Padagogin fur Korper, Tanz und Bewegung verlassen. Sie war zugleich eine Pionierin der Korpertherapie (Moscovici 1989) und Begrunderin einer ganz eigenen Methode, die auf Theatertechniken, Bewegung und Psychodrama basiert: Mythodrama. Ihre Erfahrungen mit diesem Weg beschreibt Laura in ihrem Buch „Maske und Individuation“ (Sheleen 1987). Ihre Tanzrituale und ihre Korperarbeit in Raum und Zeit wurden unter der Bezeichnung Expression?/?Impression Corporelle (Moscovici 1989, 187–214) bekannt. [...

The success of tree recruitment in Mediterranean Quercus ilex forests is threatened by the increasing intensity, duration and frequency of drought periods. Seedling germination and growth are modulated by complex interactions between abiotic (microhabitat conditions) and biotic factors (mycorrhiza association) that may mitigate the impacts of climate change on tree recruitment. To better understand and anticipate these effects, we conducted a germination experiment in a long-term precipitation reduction (PR) field experiment where we monitored seedling establishment and survival, micro-environmental conditions and ectomycorrhizal (ECM) colonization by different mycelia exploration types during the first year of seedling growth. We hypothesized that (i) the PR treatment decreases seedling survival relative to the control with ambient conditions, (ii) the underlying mechanisms for seedling survival are better understood with detailed information of microhabitat water and light availability irrespective of the PR treatment, (iii) the PR treatment will favour the development of ECM exploration types with drought-resistance traits such as differentiated rhizomorphs. Contrary to our first hypothesis, seedling survival was lower in control plots with overall higher soil moisture. Micro-site light and soil moisture conditions were better predictors of seedling survival and growth than the plot-level PR treatment, confirming our second hypothesis. Furthermore, in line with our third hypothesis, we found that ECM with longer extramatrical mycelia were more abundant in the PR treatment plots and were positively correlated to survival, which suggests a potential role of this ECM exploration type in seedling survival and recruitment. Although summer drought was the main cause of seedling mortality, our study indicates that drier conditions in spring can increase seedling survival, presumably through a synergistic effect of drought adapted ECM species and less favourable conditions for root pathogens.

Although Tuber aestivum is widely distributed across Europe, little is known about its biology and ecology. We assess the vegetation composition of wild T. aestivum sites and use this information to characterise suitable habitats in Fagus sylvatica , Carpinus betulus and Ostrya carpinifolia (FCO) forests. Plant species composition at 16 naturally colonised T. aestivum sites in southwestern Germany and Switzerland was compared with that of 232 reference sites in Swiss FCO forest communities. The vegetation composition of truffle sites exhibits a high proportion of herb and shrub species that are indicators of a warm and dry climate, alkaline soil, and open tree canopy and thus typically occur in thermophilous FCO communities on calcareous bedrock. We conclude that T. aestivum is associated with a set of key species in addition to known host species. Based on their floristic composition, we identified FCO forest communities with high and low suitability for T. aestivum .

Climate warming and elevated CO2 can modify nutrient cycling mediated by enzymes in soils, especially in cold-limited ecosystems with a low availability of nutrients and a high temperature sensitivity of decomposition and mineralization. We estimated responses of soil extracellular enzyme activities (EEAs) to 6 years of soil warming and 9 years of CO2 enrichment at an Alpine treeline site. EEAs were measured in the litter (L), fermentation (F) and humified (H) horizons under Larix decidua and Pinus uncinata trees. Soil warming indirectly affected EEAs through altered soil moisture, fine root biomass, and C:N ratio of the organic horizons. Warming increased β-glucosidase and β-xylosidase activities in the F horizon but led to reduced laccase activity in the L horizon, probably caused by drying of the litter horizon associated with the treatment. In the H horizon, previous CO2 enrichment altered the activity of leucine amino peptidase, N-acetylglucosaminidase, and phosphatase. No interactive effects between warming and CO2 enrichment were detected. Warming affected the temperature sensitivity of β-xylosidase but not of the other enzymes. Altered EEAs after six years of soil warming indicate a sustained stimulation of carbon, nitrogen and nutrient cycling under climatic warming at the alpine treeline.

Although it is logical to think that mycorrhizal mushroom production should be somehow related to the growth of the trees from which the fungi obtain carbohydrates, little is known about how mushroom yield patterns are related to tree performance. In this study, we delved into the understanding of the relationships between aboveground fungal productivity, tree radial growth patterns and climatic conditions across three latitudinally different bioclimatic regions encompassing Mediterranean, temperate and boreal forest ecosystems in Europe. For this purpose, we used a large assemblage of long-term data of weekly or biweekly mushroom yield monitoring in Spain, Switzerland and Finland. We analysed the relationships between annual mushroom yield (considering both biomass and number of sporocarps per unit area), tree ring features (tree ring, earlywood and latewood widths), and meteorological conditions (i.e. precipitation and temperature of summer and autumn) from different study sites and forest ecosystems, using both standard and partial correlations. Moreover, we fitted predictive models to estimate mushroom yield from mycorrhizal and saprotrophic fungal guilds based on climatic and dendrochronological variables. Significant synchronies between mushroom yield and climatic and dendrochronological variables were mostly found in drier Mediterranean sites, while few or no significant correlations were found in the boreal and temperate regions. We observed positive correlations between latewood growth and mycorrhizal mushroom biomass only in some Mediterranean sites, this relationship being mainly mediated by summer and autumn precipitation. Under more water-limited conditions, both the seasonal wood production and the mushroom yield are more sensitive to precipitation events, resulting in higher synchrony between both variables. This comparative study across diverse European forest biomes and types provides new insights into the relationship between mushroom productivity, tree growth and weather conditions.

Truffle fungi are well known for their enticing aromas partially emitted by microbes colonizing truffle fruiting bodies. The identity and diversity of these microbes remain poorly investigated, because few studies have determined truffle-associated bacterial communities while considering only a small number of fruiting bodies. Hence, the factors driving the assembly of truffle microbiomes are yet to be elucidated. Here we investigated the bacterial community structure of more than 50 fruiting bodies of the black truffle Tuber aestivum in one French and one Swiss orchard using 16S rRNA gene amplicon high-throughput sequencing. Bacterial communities from truffles collected in both orchards shared their main dominant taxa: while 60% of fruiting bodies were dominated by α-Proteobacteria, in some cases the β-Proteobacteria or the Sphingobacteriia classes were the most abundant, suggesting that specific factors (i.e., truffle maturation and soil properties) shape differently truffle-associated microbiomes. We further attempted to assess the influence in truffle microbiome variation of factors related to collection season, truffle mating type, degree of maturation, and location within the truffle orchards. These factors had differential effects between the two truffle orchards, with season being the strongest predictor of community variation in the French orchard, and spatial location in the Swiss one. Surprisingly, genotype and fruiting body maturation did not have a significant effect on microbial community composition. In summary, our results show, regardless of the geographical location considered, the existence of heterogeneous bacterial communities within T. aestivum fruiting bodies that are dominated by three bacterial classes. They also indicate that factors shaping microbial communities within truffle fruiting bodies differ across local conditions.

International audience; Most of the edible forest mushrooms are mycorrhizal and depend on carbohydrates produced by the associated trees. Fruiting patterns of these fungi are not yet fully understood since climatic factors alone do not completely explain mushroom occurrence.* The objective of this study was to retrospectively find out if changing tree growth following an increment thinning has influenced the diversity patterns and productivity of associated forest mushrooms in the fungus reserve La Chanéaz, Switzerland. * The results reveal a clear temporal relationship between the thinning, the growth reaction of trees and the reaction of the fungal community, especially for the ectomycorrhizal species. The tree-ring width of the formerly suppressed beech trees and the fruit body number increased after thinning, leading to a significantly positive correlation between fruit body numbers and tree-ring width.* Fruit body production was influenced by previous annual tree growth, the best accordance was found between fruit body production and the tree-ring width two years previously.* The results support the hypothesis that ectomycorrhizal fruit body production must be linked with the growth of the associated host trees. Moreover, the findings indicate the importance of including mycorrhizal fungi as important players when discussing a tree as a carbon source or sink.; La plupart des champignons comestibles des forêts sont mycorhiziens et dépendent des hydrates de carbone produits par les arbres associés. Le processus de fructification de ces champignons n'est pas encore totalement connu. À eux seuls, les facteurs climatiques ne sont pas en mesure d'expliquer l'apparition d'années pauvres ou riches en champignons.* Cette étude a pour but de vérifier, d'une manière rétrospective, si la modification de la croissance des arbres, induite par une mise en lumière suite à une éclaircie, influence la diversité et la productivité des champignons dans la réserve mycologique de La Chanéaz en Suisse.* Les résultats montrent une relation temporelle nette entre l'éclaircie, la réaction de croissance des arbres et la réaction des communautés de champignons, spécialement pour les espèces ectomycorhiziennes. Nous avons observé une augmentation tant de la largeur des cernes des hêtres autrefois dominés que du nombre de carpophores, conduisant à une corrélation positive entre les deux variables.* La production de carpophores était influencée par la croissance annuelle précédente des arbres. La meilleure concordance a été trouvée entre la production de carpophores et la largeur des cernes deux ans auparavant.* Les résultats sont en accord avec l'hypothèse que la production de carpophores des champignons mycorrhiziens est liée à la croissance des arbres associés. En outre, les résultats montrent qu'il est essentiel de tenir compte du rôle important des champignons mycorhiziens lorsqu'on débat de l'arbre en tant que source ou puits de carbone.

Increased CO2 emissions and global warming may alter the composition of fungal communities through the removal of temperature limitation in the plant–soil system, faster nitrogen (N) cycling and changes in the carbon (C) allocation of host plants to the rhizosphere. At a Swiss treeline featuring Larix decidua and Pinus uncinata, the effects of multiple years of CO2 enrichment and experimental soil warming on the fungal community composition in the organic horizons were analysed using 454-pyrosequencing of ITS2 amplicons. Sporocarp production and colonization of ectomycorrhizal root tips were investigated in parallel. Fungal community composition was significantly altered by soil warming, whereas CO2 enrichment had little effect. Tree species influenced fungal community composition and the magnitude of the warming responses. The abundance of ectomycorrhizal fungal taxa was positively correlated with N availability, and ectomycorrhizal taxa specialized for conditions of high N availability proliferated with warming, corresponding to considerable increases in inorganic N in warmed soils. Traits related to N utilization are important in determining the responses of ectomycorrhizal fungi to warming in N-poor cold ecosystems. Shifts in the overall fungal community composition in response to higher temperatures may alter fungal-driven processes with potential feedbacks on ecosystem N cycling and C storage at the alpine treeline.

International audience; Despite an increasing demand for Burgundy truffles (Tuber aestivum), gaps remain in our understanding of the fungus’ overall lifecycle and ecology. Here, we compile evidence from three independent surveys in Hungary and Switzerland. First, we measured the weight and maturity of 2,656 T. aestivum fruit bodies from a three-day harvest in August 2014 in a highly productive orchard in Hungary. All specimens ranging between 2 and 755 g were almost evenly distributed through five maturation classes. Then, we measured the weight and maturity of another 4,795 T. aestivum fruit bodies harvested on four occasions between June and October 2015 in the same truffière. Again, different maturation stages occurred at varying fruit body size and during the entire fruiting season. Finally, the predominantly unrelated weight and maturity of 81 T. aestivum fruit bodies from four fruiting seasons between 2010 and 2013 in Switzerland confirmed the Hungarian results. The spatiotemporal coexistence of 7,532 small-ripe and large-unripe T. aestivum, which accumulate to ~182 kg, differs from species-specific associations between the size and ripeness that have been reported for other mushrooms. Although size-independent truffle maturation stages may possibly relate to the perpetual belowground environment, the role of mycelial connectivity, soil property, microclimatology, as well as other abiotic factors and a combination thereof, is still unclear. Despite its massive sample size and proof of concept, this study, together with existing literature, suggests consideration of a wider ecological and biogeographical range, as well as the complex symbiotic fungus-host interaction, to further illuminate the hidden development of belowground truffle fruit bodies.

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Sclerotinia cirsii-spinosissimi Senn-Irlet sp. nov. ��� MycoBank 516616, Plate 1-3. Apothecia solitaria, discus acetabuliformis, 5-12 mm diam, stipitatus, hymenio brunneo, stipes cylindraceus, colore simile disco, 5���20 �� 0.8���1.5 mm. Asci cylindracei, ��� (120���)130���170 �� 7���9 ��m, octospori, poro jodo caerulescenti. Ascosporae uniseriatae, hyalinae, elipsoideae, inaequilaterales, ��� 9.5���11.8 �� 4.7���6.6 ��m. Microconidia 2���4 ��m diam., globosae, in sporodochiis in hymenio vel in vitro. Sclerotia tuberoidea, 4���8 �� 1.5���4 mm, extus nigra, intus albida. Habitat in bracteas Cirsii spinosissimi in regio alpina, Helvetia. Holotypus: Senn-Irlet 96/32, Uri, Attinghausen, 31 Augusto 1996, in herbario Z-ZT conservatur. Etymology ��� Refers to the species name of the plant host. Apothecia arising singly or rarely in pairs or in triplet from a true sclerotium, embedded in fallen old, last-year bracts of Cirsium spinosissimum lying on the soil (Plate 1a); receptacle 5���12 mm diam., 2���4 mm high, cupulate or discoid with a central depression; hymenium ochraceous to burnt Sienna, smooth; stipe cylindrical, often flexuous, 5���20 �� 0.8���1.5 mm, tapering towards base, concolorous or paler than hymenium, glabrous to felted under hand lens. Asci arising from croziers, cylindric���clavate, (*) 140���180 �� 9��� 10.5 ��m, (���) (120���) 130���140 �� 7���9 ��m, with a tapering, blunt���end base, regularly 8���spored, all spores of about equal size, apex truncated-rounded,apical pore MLZ+ blue, IKI blueish, deep blue in MLZ after KOH (Plate 2d). Ascospores (*) 11.3���15.3 (17) �� 5.7���7.1 ��m (fresh in H2O), Q = 1.6���2.4, mean Q = 2.04, (���) (8) 9.5���11.8 (14.5) �� 4.7���6.6 ��m, Q = 1.5���2.2 (in Congo red and 5% KOH) mean Q = 1.85, (���) uniseriate, young in ascus biseriate, hyaline, unicellular, ellipsoid and slightly inequilateral, eguttulate, with two (to four?) nuclei, content (���) cyanophilous (in Cotton blue), IKI wall hyaline, content yellow. Microconidial state with microconidia globose, hyaline, 2��� 4 ��m diam., produced from phialides in sporodochia (Plate 1f), superficial in hymenium of older apothecia from germinating ascospores, especially towards margin. Paraphyses filiform, septate, simple or sparsely branched, hyaline, in upper part 3���4 ��m wide, fresh with large pale brown guttules in the upper cells, without gelatinous covering, even in living state. Subhymenium 45���60 ��m, of densely septate, prismatic cells, brown-walled, reddish brown. Medullary excipulum of loosely interwoven, filiform, 2���5 ��m wide, colourless hyphae, forming a textura intricata, 40���250 ��m thick, without crystals, no blueing in IKI. Ectal excipulum 50���150 ��m, 3��� 5 cells thick, of pale brown angular to prismatic cells, 20���35 �� 10��� 16 ��m in size, orientated perpendicularly to apothecial surface. No gelatinous matrix observed. Stipe composed of a medullary excipulum forming a textura porrecta, composed of thin-walled, elongated, 5���8 ��m wide, hyaline cells, and an ectal excipulum, 8���20 ��m thick, of 2���3 rows of elongated, light brown, thin-walled cells, forming a textura angularis, outermost cells often with short outgrowths. Both textures arranged parallel to the stipe axis. Pigment brownish, membranaceous, in subhymenium, and outer cells of the stipe, intracellular in paraphyses. Stroma an irregular tuberoid sclerotium (Plate 1b), globose to cylindrical, constricted and often furrowed, variable in shape, 4���8 �� 1.5���4 mm, with scrobiculate, black outer rind and white inner context, developing within fallen, straw-like involucral bracts of Cirsium spinosissimum, but never incorporating remnants of plant material. Sclerotial rind two to four cells wide, of dark brown-walled, angular to prismatic cells, outermost cells heavily melanized, carbonaceous; uppermost cells pale brown, cells compact,(���) 12���20 �� 6��� 10 ��m, forming a textura angularis to textura oblita, sclerotial medulla of interwoven, hyaline hyphae, 4���6 ��m wide, forming a textura oblita-intricata, walls gelatinized, without apparent remnants of host tissue. Ascospores germinate readily on PDA and MA, mycelium whitish, adhering to the agar surface, after 4���6 weeks applanate sclerotia are produced regularly spread over the whole surface of the petridish on PDA (Plate 1c), half to three quarter immerged, irreguarly spread and larger (up to 12 �� 7 mm) on MA. 18 days after inoculation scattered flocculose tufts produced small globular sporodochia, with conidia born on phialides on aerial mycelium, phialides with no obvious collarettes,conidia globose to slightly ovate, 2.5���4 ��m in diam., with one internal guttule. The ITS sequences of the five isolates of Sclerotinia cirsii-spinosissimi collected from different locations in Switzerland were identical. Parsimony analysis revealed 44 of the 514 characters to be parsimony informative.The analysis yielded 530 most parsimonious trees (MPTs) which were reduced to 48 after reweighting (cf. HOLST- JENSEN et al., 1998). S. cirsii-spinosissimi was consistently placed in a cluster with S. borealis, which was supported by the strict consensus tree and a bootstrap value of 64% (Fig. 6). In 32 of the 48 MPTs, S. nivalis clustered with S. glacialis (52% bootstrap). Substratum ��� Sclerotinia cirsii-spinosissimi, always on Cirsium spinosissimum. Distribution ��� Europe, Alps. Specimens examined. SWITZERLAND ��� Uri, Attinghausen-Geissberg, 1740 m alt., 31 August 1996, B. Senn-Irlet & R. M��rner (ZT, holotype, BSI 96/32, culture isolate, NCBI GQ848548); Spirigen-Kinzigpass, 2070 m alt., 19 August 2001, B. Senn-Irlet & R. M��rner (ZT, BSI 01/194); ��� Bern, Guttannen-Oberaar, 2330 m alt., 30 August 1994, B. Senn-Irlet (ZT, BSI 94/43); 15 August 1995, H.U. Aeberhard & B. Senn-Irlet (ZT, BSI 95/150, culture isolate, Sclerotinia spec 2 sensu HOLST- JENSEN et al., 1997), 8 August 1998, H.U. Aeberhard (ZT, 024.98), 2 September 2004 (ZT, BSI 04/130, NCBI EU330398), 17 August 2010, B. Senn-Irlet (ZT, BSI 10/63), 22 August 2010, H. Woltsche (ZT, BSI 10/93); ��� Graub��nden, Bivio, near Leg Grevasalvas, 2460 m alt., B. Senn-Irlet (ZT, BSI 03/80, NCBI EU330399); ��� Ticino, Bedretto, Ponte di Paltano, 1840 m alt., 20 August 2002, H.Woltsche & B. Senn-Irlet (ZT, BSI 02/79); ��� Valais,Val d���Anniviers, Moiry, 21 August 2010, B. Senn-Irlet (ZT, BSI 10/83). Sclerotinia nivalis Saito: JAPAN ��� Hokkaido, Makubedtsu-cho, on Arctium lappa, 15 May 1982, I. Saito (HAK, Holotype, 24055, NCBI EU 330400). Habitat and ecology Sclerotinia cirsii-spinosissimi was exclusively found in association with Cirsium spinosissimum, a widespread, abundant forb of the lower alpine zone of the Alps, forming clones (URBANSKA, 1992) on pastures and near rivulets, especially at nutrient rich sites with forb vegetation and in scree vegetation, often at places indirectly favoured by cattle. The apothecia were always found on the involucral bracts from the almost intact, fallen inflorescenses from the previous year below the forb plant, profiting thus from a favourable humid microclimate.The accompanying macromycetes found were Peziza granularis Donadini, Ombrophila spec., Scutellinia spec., Tarzetta cu- Plate 1 ��� Sclerotinia cirsii-spinosissimi a) Fresh fruit-bodies from holotype (coll. BSI 96/32); b) Sclerotia (coll. 024.98); c) Sclerotia on PDA in culture after 2 months (isolate from BSI 96/32); d) Ectal excipulum, fresh in water (coll. BSI 10/93); e) Ascospores, fresh in water (coll. BSI 10/63); f) Microconidia in hymenium, in water (coll. BSI 10/83); g) Paraphyses in water (coll. BSI 10/83); h) Ascus apex in Lugol (coll. BSI 10/93). Bars = 10 ��m, 1 cm in a), b) and c). pularis (L.) Svrček, and Hemimycena ochrogaleata (J. Favre) M.M. Moser. Involucral bracts of Cirsium spinosissimum lying beyond the forb plant on open grassland are often infected by Crocicreas calathicola (Rehm) S.E. Carpenter, a saprotrophic ascomycete with orange coloured apothecia. Sclerotinia cirsii-spinosissimi and Crocicreas calathicola were never found together suggesting that microclimatic conditions were required for germination and establishment, and humid conditions favoured Sclerotinia. A necrotrophic life-form is suggested as no signs of reduced plant growth or flowering has been observed., Published as part of Beatrice Senn-Irlet & Martina Peter, 2016, Sclerotinia cirsii-spinosissimi, a new species from the Alps, pp. 235-240 in Ascomycete. org 8 (5) on pages 236-238, DOI: 10.5281/zenodo.1040189, {"references":["HOLST- JENSEN A., VAAGE M. & SCHUMACHER T. 1998. - An approximation to the phylogeny of Sclerotinia and related genera. Nordic Journal of Botany, 18: 705 - 719","HOLST- JENSEN A., KOHN L. M. & SCHUMACHER T. 1997. - Nuclear rDNA phylogeny of Sclerotiniaceae. Mycologia, 89: 885 - 899.","URBANSKA K. M. 1992. - Populationsbiologie der Pflanzen. Stuttgart, UTB."]}

Climate projections predict higher precipitation variability with more frequent dry extremes(1). CO2 assimilation of forests decreases during drought, either by stomatal closure(2) or by direct environmental control of sink tissue activities(3). Ultimately, drought effects on forests depend on the ability of forests to recover, but the mechanisms controlling ecosystem resilience are uncertain(4). Here, we have investigated the effects of drought and drought release on the carbon balances in beech trees by combining CO2 flux measurements, metabolomics and (13)CO2 pulse labelling. During drought, net photosynthesis (AN), soil respiration (RS) and the allocation of recent assimilates below ground were reduced. Carbohydrates accumulated in metabolically resting roots but not in leaves, indicating sink control of the tree carbon balance. After drought release, RS recovered faster than AN and CO2 fluxes exceeded those in continuously watered trees for months. This stimulation was related to greater assimilate allocation to and metabolization in the rhizosphere. These findings show that trees prioritize the investment of assimilates below ground, probably to regain root functions after drought. We propose that root restoration plays a key role in ecosystem resilience to drought, in that the increased sink activity controls the recovery of carbon balances.

SPE Pôle IPM UB; International audience; Tuber species are ectomycorrhizal ascomycetes establishing relationships with different host trees and forming hypogeous fruiting bodies known as truffles. Among Tuber species, Tuber aestivum Vittad. has a wide distributional range being found naturally all over Europe. Here, we performed large-scale population genetic analyses in T. aestivum to (i) investigate its genetic diversity at the European scale, (ii) characterize its genetic structure and test for the presence of ecotypes and (iii) shed light into its demographic history. To reach these goals, 230 ascocarps from different populations were genotyped using 15 polymorphic simple sequence repeat markers. We identified 181 multilocus genotypes and four genetic groups which did not show a clear geographical separation; although, one of them was present exclusively in Southeast France, Italy and Spain. Fixation index values between pairs of genetic groups were generally high and ranged from 0.29 to 0.45. A significant deficit of heterozygosity indicated a population expansion instead of a recent population bottleneck, suggesting that T. aestivum is not endangered in Europe, not even in Mediterranean regions. Our study based on a large-scale population genetic analysis suggests that genetically distinct populations and likely ecotypes within T. aestivum are present. In turn, this study paves the way to future investigations aimed at addressing the biological and/or ecological factors that have concurred in shaping the population genetic structure of this species. Present results should also have implications for the truffle market since defining genetic markers are now possible at least for some specific T. aestivum genetic groups.

Community genetics in the time of next generation molecular technologies

Tuber aestivum (Vittadini, Monographia tuberacearum, 1831) is an ectomycorrhizal fungus that establishes a symbiosis with various host tree species, such as oak, beech, and hazel. The mycorrhizas of T. aestivum show a characteristic tangled hairy feature, due to the presence of many curled, interwoven cystidia. Morphological features of the ascocarps include a black peridium and a white-ochre to dark-brown gleba color, depending on the maturity. In 1887, Chatin separated T. aestivum into two distinct species through a novel description of Tuber uncinatum on the basis of morphological characteristics. Recent phylogenetic analyses suggest that existing morphological differences between T. uncinatum and T. aestivum do not reflect two different species and support the use of T. aestivum as the only scientific name. With a distribution throughout Europe and as far east as the Caucasian regions, T. aestivum shows ecological polymorphism, with different maturity periods and a broad range of ecological preferences depending on the geographical location.

Although the Burgundy truffle (Tuber aestivum) is an ectomycorrhizal fungus of important economic value, its subterranean life cycle and population biology are still poorly understood. Here, we determine mating type and simple sequence repeat (SSR) maternal genotypes of mapped fruiting bodies to assess their genetic structure within two naturally colonized forest sites in southern Germany. Forty-one genotypes were identified from 112 fruiting bodies. According to their mating types, the maternal genotypes were aggregated only in one population. Genotypic diversity of individuals that mostly were small and occurred in 1 out of 2 years of sampling was high. Although these results suggested a ruderal colonization strategy, some genets spread several hundred meters. This result indicates that, besides sexual spore dispersal, vegetative growth or spreading by mycelial propagules contributes to dissemination. In one site, fewer individuals with a tendency to expand genets belonging to only one genetic group were observed. In the second site, numerous small individuals were found and were grouped into two clearly differentiated genetic groups that were spatially intermingled. Forest characteristics and disturbances are possible reasons for the observed genetic patterns. Our findings contribute to a better understanding of the biology of one of the most widespread and commercially important truffle species. This knowledge is critical for establishing and maintaining sustainable long-term truffle cultivations.

The present study aimed to elucidate the influence of drought and elevated temperature on relative abundance and functioning of the ectomycorrhizal fungus Cenococcum geophilum on three oak species differing in adaptation to a warm and dry climate. The experiment QUERCO comprised three Quercus species (Q. robur, Q. petraea, Q. pubescens) grown for 3 years under four treatments: elevated air temperature, drought, a combination of the two, and control. Fine root samples were analysed for relative abundance and potential extracellular enzyme activities of ectomycorrhizae of C. geophilum, a fungal species known to be drought resistant. The relative abundance of C. geophilum on the roots of the oak species was significantly increased by temperature, decreased by drought, but unchanged in the combined treatment compared to the control. Although the extent of treatment effects differed among oak species, no significant influence of tree species on relative abundance of C. geophilum was detected. Exoenzyme activities of C. geophilum on Q. robur and Q. petraea (but not Q. pubescens) significantly increased in the combined treatment, but for all oak species were reduced under drought and air warming alone compared to the control. There was a significant negative correlation between abundance of C. geophilum and its leucine aminopeptidase activity. As this enzyme is not frequent among ectomycorrhizal fungi, this emphasises the functional importance of C. geophilum in the ectomycorrhizal community. Our results indicate that increased temperature and drought will influence the relative abundance and enzyme activity of C. geophilum. However, both the Quercus species and C. geophilum tolerated warming and strong drought.

To elucidate the genetic bases of mycorrhizal lifestyle evolution, we sequenced new fungal genomes, including 13 ectomycorrhizal (ECM), orchid (ORM) and ericoid (ERM) species, and five saprotrophs, which we analyzed along with other fungal genomes. Ectomycorrhizal fungi have a reduced complement of genes encoding plant cell wall–degrading enzymes (PCWDEs), as compared to their ancestral wood decayers. Nevertheless, they have retained a unique array of PCWDEs, thus suggesting that they possess diverse abilities to decompose lignocellulose. Similar functional categories of nonorthologous genes are induced in symbiosis. Of induced genes, 7–38% are orphan genes, including genes that encode secreted effector-like proteins. Convergent evolution of the mycorrhizal habit in fungi occurred via the repeated evolution of a ‘symbiosis toolkit’, with reduced numbers of PCWDEs and lineage-specific suites of mycorrhiza-induced genes. This material is based on work conducted by the US Department of Energy Joint Genome Institute, a DOE Office of Science User Facility, supported under contract no. DE-AC02-05CH11231. This work was also supported by the Laboratory of Excellence ARBRE (ANR-11-LABX-0002-01), the Genomic Science Program (Plant-Microbe Interactions project) funded by the US Department of Energy, Office of Science, Biological and Environmental Research (contract DE-AC05-00OR22725), the Lorraine Region Council (to F.M.), US National Science Foundation grants DEB-1208719 and DEB-0933081 (both to D.S.H. and DEB-1021606 (to A.P.)), the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (DFG FTZ 118) and the German Science Foundation (DFG, grant BU941/20-1) (to F.B.) and the Swedish Research Council (to A. Tunlid). This work was partly supported by the Laboratory of Excellence TULIP (ANR-10-LABX-41 and ANR-11-IDEX-0002-02). F.M. would like to acknowledge M.A. Selosse and B. Lindahl for helpful discussions.

International audience; The focus of this work is on the nitrogen starvation stress responses operating in a plant symbiotic fungus. A cDNA array profiling analysis was conducted on N-limited mycelia of the mycorrhizal ascomycete Tuber borchii. Fifty-one unique transcripts, out of 2062 redundant arrayed cDNAs, were differentially expressed by at least 1.5-fold in response to N deprivation. Only two N assimilation components—a nitrate transporter and a high-affinity ammonium transporter—were found among differentially expressed genes. All the other N status responsive genes code for as yet unidentified hypothetical proteins or components not directly involved in N assimilation or metabolism, especially carbohydrate binding proteins and oligosaccharide as well as lipid modifying enzymes. A subset of cDNA array data were confirmed and extended by Northern blot analysis, which showed that most of the latter components respond not only to nitrogen, but also to carbon source depletion.

Forest fungi not only have important functions within the forest ecosystem, but picking their fruit bodies is also a popular past time, as well as a source of income in many developing and developed countries. The expansion of commercial harvesting in many parts of the world has led to widespread concern about overharvesting and possible damage to fungal resources. In 1975, we started a field research project to investigate the effects of mushroom picking on fruit body occurrence. The three treatments applied were the harvesting techniques picking and cutting, and the concomitant trampling of the forest floor. The results reveal that, contrary to expectations, long-term and systematic harvesting reduces neither the future yields of fruit bodies nor the species richness of wild forest fungi, irrespective of whether the harvesting technique was picking or cutting. Forest floor trampling does, however, reduce fruit body numbers, but our data show no evidence that trampling damaged the soil mycelia in the studied time period.

Summary • In an effort to discover genes that are expressed in the ectomycorrhizal basidiomycetes Laccaria bicolor and Pisolithus microcarpus, and in P. microcarpus/Eucalyptus globulus ectomycorrhizas, we have sequenced 1519 and 1681 expressed sequence tags (ESTs) from L. bicolor and P. microcarpus cDNA libraries. • Contig analysis resulted in 905 and 806 tentative consensus sequences (unique transcripts) in L. bicolor and P. microcarpus, respectively. For 36% of the ESTs, significant similarities to sequences in databases were detected. The most abundant transcripts showed no similarity to previously identified genes. Sequence redundancy analysis between different developmental stages indicated that several genes were differentially expressed in free-living mycelium and symbiotic tissues of P. microcarpus. • Based on sequence similarity, 11% of L. bicolor unique transcripts were also detected in P. microcarpus. Similarly, L. bicolor and P. microcarpus shared only a low proportion of common transcripts with other basidiomycetous fungi, such as Pleurotus ostreatus and Agaricus bisporus. Such a low proportion of shared transcripts between basidiomycetes suggests, on the one hand, that the variability of expressed transcripts in different fungi and fungal tissues is considerably high. On the other hand, it might reflect the low number of GenBank entries of basidiomycetous origin and stresses the necessity of an additional sequencing effort. • The present ESTs provide a valuable resource for future research on the development and functioning of ectomycorrhizas.

Sporocarps of Arcangeliella borziana, a hypogeous russuloid fungus, were found in a subalpine spruce forest in the Swiss Alps. We identified the ectomycorrhizas formed by this species using the ITS-PCR-RFLP method and described them in terms of morphological, anatomical, and molecular features. Phylogenetic placement of A. borziana was studied by comparing nucleotide sequences of the mitochondrial large subunit rRNA gene and the ITS region of nuclear rRNA, respectively, with existing sequence databases, and by comparing the ITS-RFLP pattern with a reference library of approx. 180 mainly basidiomycetous fungi. Sequence analysis of the mitochondrial large subunit rRNA gene confirmed the affiliation of A. borziana to the Russulaceae. Sequence as well as RFLP pattern comparison of the ITS region revealed a close affinity of this species to Lactarius sect. Russularia. This is in accordance with morphological and anatomical studies of the ectomycorrhizas, which share many features with ectomycorrhizas of Lactarius sect. Russularia.