Dr. Martina Peter

Aim: This study aims to (1) test whether mapped soil properties can improve the performance of species distribution models (SDMs) for 162 terricolous macrofungi at a regional level, (2) identify relevant soil predictors for macrofungal regional distribution and (3) quantify the relative importance of soil properties as compared to climate and topography in explaining macrofungal regional distribution.
Location: The forested area (~ 12,000 km²) in Switzerland.
Taxon: Terricolous Macrofungi.
Methods: We collected occurrences (presence-only) for 162 species of terricolous macrofungi, including 111 ectomycorrhizal and 51 saprotrophic species, from the SwissFungi database. We used soil property maps, generated through digital soil mapping at a 25 m resolution, to enhance macrofungal SDMs. For each species, we selected two climate, two topography and two soil predictors by an automated variable selection procedure. We built SDMs with randomised soil properties for performance comparison. We quantified the importance of soil properties based on permutation and variance partitioning. Finally, we projected the SDMs for three representative species at 25 m resolution with and without soil properties to assess the role of soil properties in shaping their biogeographical distributions.
Results: Soil properties significantly improved the median performance of the SDMs across the 162 species. Ectomycorrhizal fungi showed a significantly greater improvement than saprotrophic fungi. On average, our models were able to explain two-thirds of the variance in macrofungal distribution, of which 11% could be independently explained by soil properties. Air temperature and topographic slope were identified as additional important factors controlling macrofungal distribution. Evident changes in geographical distribution were observed for the three representative species after adding soil properties.
Main conclusions: High-resolution digital soil maps significantly improve the predictive accuracy of macrofungal regional distribution. They should therefore be taken into account when modelling the geographical distribution of macrofungi.

Ectomycorrhizal symbiosis supports tree growth and is crucial for nutrient cycling and temperate and boreal ecosystems functioning. The establishment of functional ectomycorrhiza (ECM) first requires the association of compatible partners. However, host and fungal genetic determinants governing mycorrhizal compatibility are unknown. To identify such factors in poplar and its fungal associates, we mined existing and de novo tree and fungal transcriptional datasets. We identified co-expressed genes enabling ECM symbiosis at early and mature stages of the interaction. These sets of genes can be divided into general fungal-sensing and ECM-specific components. We highlight the importance of fungal modulation of plant JA-related defenses and the regulation of secretory pathways for ECM compatibility, including upregulation of key fungal small secreted proteins, the downregulation of plant secreted peroxidases, and the downregulation of plant cell wall remodeling proteins concomitantly with the upregulation of fungal glycosyl hydrolases acting on pectin. Not only gene regulation, but also its temporal scale and dynamics seem to play a crucial role for mycorrhizal compatibility. The expression profile of the host Common Symbiosis Pathway and nutrient transporters was also studied, revealing constitutive levels of expression and moderate upregulation in compatible ECM interactions. Overall, these results underscore the importance of novel biological functions during the establishment of ECM symbiosis, help us gain insights into the molecular events determining mycorrhiza compatibility, and serve as a data-rich transcriptomic resource to open new research questions in the field.

Qua o là sta amo ün tal eroe plain fideltà sün seis post, cun büst sfrattamà, e stenda il bratsch our da spelm e grava, sco üna sgür pronta pel cumbat, o ch'el sta ingramüschà sco ün vegliet cha la burasca da la vita ha fat sgobar sün sias crotschas.

Vegetation changes in a warming Arctic may affect plant-associated soil microbial communities with possible consequences for the biogeochemical cycling of carbon (C) and nitrogen (N). In a sub-arctic tundra heath, we factorially removed plant species with ecto- and ericoid mycorrhizal associations. After two years, we explored how mycorrhizal type-specific plant removal influences microbial communities, soil and microbial C and N pools, and extracellular enzymatic activities. Removal of ecto- and ericoid mycorrhizal plants did not change the soil fungal or bacterial community composition or their extracellular enzyme activities. However, ericoid plant removal decreased microbial C:N ratio, suggesting a stoichiometric effect decoupled from microbial community composition. In other words, microbial communities appear to show initial plasticity in response to major changes in tundra vegetation. This highlights the importance of longer-term perspectives when investigating the effects of vegetation changes on biogeochemical processes in Arctic ecosystems.

Wie alle Bäume unserer Wälder bildet die Fichte eine Lebensgemeinschaft mit einer Vielzahl von unterirdischen Helfern, den Mykorrhizapilzen. Mehr als 50 verschiedene Mykorrhizapilzarten kommen in reinen Fichtenbeständen vor mit vielfältigen Funktionen in der Wasser- und Nährstoffversorgung ihrer Baumpartnerin, die ihnen dafür Zucker als Energiequelle liefert. Hohe Stickstoffeinträge und Trockenheit reduzieren diese Vielfalt, was die Gefahr einer verminderten Stresstoleranz der Fichte birgt.

The ectomycorrhizal fungi Tuber melanosporum Vittad. and Tuber aestivum Vittad. produce highly valuable truffles, but little is known about the soil fungal communities associated with these truffle species in places where they co-occur. Here, we compared soil fungal communities present in wild and planted truffle sites, in which T. melanosporum and T. aestivum coexist, in Mediterranean and temperate regions over three sampling seasons spanning from 2018 to 2019. We showed that soil fungal community composition and ectomycorrhizal species composition are driven by habitat type rather than climate regions. Also, we observed the influence of soil pH, organic matter content and C:N ratio structuring total and ectomycorrhizal fungal assemblages. Soil fungal communities in wild sites revealed more compositional variability than those of plantations. Greater soil fungal diversity was found in temperate compared to Mediterranean sites when considering all fungal guilds. Ectomycorrhizal diversity was significantly higher in wild sites compared to plantations. Greater mould abundance at wild sites than those on plantation was observed while tree species and seasonal effects were not significant predictors in fungal community structure. Our results suggested a strong influence of both ecosystem age and management on the fungal taxa composition in truffle habitats.

Ectomycorrhizal (ECM) fungi serve key functions in forest ecosystems by supplying water and nutrients to tree hosts, yet mutualistic plant–fungi interactions are jeopardised by environmental alterations. Here, we discuss the great potential and current limitations of landscape genomics in investigating signatures of local adaptation in natural populations of ECM fungi.

The contribution from foliage, roots, and fungi to soil organic matter (SOM) represents a key unknown in SOM dynamics. Since stable hydrogen isotope ratios (δ²H_n) can greatly differ among these sources, we explored δ²H_n to elucidate sources contribution to SOM. Moreover, we assessed whether addition of ²H-depleted water - providing ²H-signal that gets incorporated into organic matter - allows tracing of new organic H and thus assessing SOM turnover.
In a 17-year-long irrigation experiment in a dry pine forest, we measured δ²H_n and stable carbon and nitrogen isotope ratios (δ¹³C, δ¹⁵N) in SOM sources, bulk SOM and particle-size fractions. Relative source contribution to SOM was estimated by Bayesian mixing models including all three isotopes.
The δ²H_n increased from foliar litter (-153‰) to fine roots (-118‰) and fungal mycelia (-81‰). Mixing models indicated that foliar litter dominated organic layers (69 ± 15%) and coarse particulate organic matter (POM) at 0-5 cm (65 ± 12%). In contrast, roots dominated fine POM at 2-5 cm (58 ± 12%). Fungal mycelia contributed only to 1-5% of coarse and fine POM, but to 5-25% of mineral associated organic matter (MOM) at 0-5 cm.
The soil water ²H-depletion with irrigation (-76‰ vs -68‰ at 0-10 cm) was paralleled by lower δ²H_n in coarse POM of irrigated vs dry plots (-122‰ vs -111‰ at 0-5 cm), indicating organic H turnover of less than 17 years. In contrast, δ²H_n in fine POM and MOM decreased only by 3‰ with irrigation, implying mean residence times of approximately 30 years.
While δ¹³C and δ¹⁵N differed by a maximum of 1‰ between plant sources, δ²H_n were 30-39‰ higher in roots than foliar litter, thus improving SOM sources differentiation. Long-term ²H-labelling by irrigation indicated higher organic H turnover in coarse vs fine soil fractions, offering a novel tool to identify SOM cycling and microbial H incorporation into SOM pools.

Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from aboveground tree traits (e.g., tree-ring width, needle length, and crown transparency) compared to belowground tree traits (e.g., fine-root biomass). The altered aboveground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem-level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees, which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree- and ecosystem-level responses were pervasive across a number of traits on long-term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions.

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.

Meist gut versteckt im Boden lebt eine Vielzahl von Helfern an den Wurzeln unserer Waldbäume. Es sind die Mykorrhizapilze. Sie durchdringen den Boden, vernetzen die Bäume, liefern ihnen Nährstoffe und Wasser und erhalten im Austausch dafür Zucker. Es ist eine enge Lebensgemeinschaft, die beiden Partnern, Baum wie Pilz, dient und ohne die beide wohl nicht überlebensfähig wären.

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.