Asymmetric Interaction Between Two Mycorrhizal Fungal Guilds and Consequences for the Establishment of Their Host Plants

Arbuscular mycorrhiza (AM) and ectomycorrhiza (EcM) are the most abundant and widespread types of mycorrhizal symbiosis, but there is little and sometimes conflicting information regarding the interaction between AM fungi (AMF) and EcM fungi (EcMF) in soils. Their competition for resources can be particularly relevant in successional ecosystems, which usually present a transition from AM-forming herbaceous vegetation to EcM-forming woody species. The aims of this study were to describe the interaction between mycorrhizal fungal communities associated with AM and EcM hosts naturally coexisting during primary succession on spoil banks and to evaluate how this interaction affects growth and mycorrhizal colonization of seedlings of both species. We conducted a greenhouse microcosm experiment with Betula pendula and Hieracium caespitosum as EcM and AM hosts, respectively. They were cultivated in three-compartment rhizoboxes. Two lateral compartments contained different combinations of both host plants as sources of fungal mycelia colonizing the middle compartment, where fungal biomass, diversity, and community composition as well as the growth of each host plant species' seedlings were analyzed. The study's main finding was an asymmetric outcome of the interaction between the two plant species: while H. caespitosum and associated AMF reduced the abundance of EcMF in soil, modified the composition of EcMF communities, and also tended to decrease growth and mycorrhizal colonization of B. pendula seedlings, the EcM host did not have such effects on AM plants and associated AMF. In the context of primary succession, these findings suggest that ruderal AM hosts could hinder the development of EcM tree seedlings, thus slowing the transition from AM-dominated to EcM-dominated vegetation in early successional stages.

The first record of the genus Geopora (Pezizales) for Uzbekistan

The first record of Geopora arenicola for Uzbekistan is reported from Nuratau Nature Reserve. The genus Geopora is also recorded for the first time in Uzbekistan. Ascocarps of the fungus at first are usually spherical, completely immersed in soil, later they emerge at the ground surface and open at the top. Mature apothecia have a central opening with torn edges and whitish to grayish hymenium surface. A description, distribution data, images of apothecia and micromorphological characters of the fungus are provided.

Glacier retreat in the High Arctic: opportunity or threat for ectomycorrhizal diversity?

Climate change causes Arctic glaciers to retreat faster, exposing new areas for colonization. Several pioneer plants likely to colonize recent deglaciated, nutrient-poor areas depend on fungal partners for successful establishment. Little is known about general patterns or characteristics of facilitating fungal pioneers and how they vary with regional climate in the Arctic. The High Arctic Archipelago Svalbard represents an excellent study system to address these questions, as glaciers cover ∼60% of the land surface and recent estimations suggest at least 7% reduction of glacier area since 1960s. Roots of two ectomycorrhizal (ECM) plants (Salix polaris and Bistorta vivipara) were sampled in eight glacier forelands. Associated ECM fungi were assessed using DNA metabarcoding. About 25% of the diversity was unknown at family level, indicating presence of undescribed species. Seven genera dominated based on richness and abundance, but their relative importance varied with local factors. The genus Geopora showed surprisingly high richness and abundance, particularly in dry, nutrient-poor forelands. Such forelands will diminish along with increasing temperature and precipitation, and faster succession. Our results support a taxonomical shift in pioneer ECM diversity with climate change, and we are likely to lose unknown fungal diversity, without knowing their identity or ecological importance.

Legacy effects of tree mortality mediated by ectomycorrhizal fungal communities

Successive droughts have resulted in extensive tree mortality in the southwestern United States. Recovery of these areas is dependent on the survival and recruitment of young trees. For trees that rely on ectomycorrhizal fungi (EMF) for survival and growth, changes in soil fungal communities following tree mortality could negatively affect seedling establishment. We used tree-focused and stand-scale measurements to examine the impact of pinyon pine mortality on the performance of surviving juvenile trees and the potential for mutualism limitation of seedling establishment via altered EMF communities. Mature pinyon mortality did not affect the survival of juvenile pinyons, but increased their growth. At both tree and stand scales, high pinyon mortality had no effect on the abundance of EMF inocula, but led to altered EMF community composition including increased abundance of Geopora and reduced abundance of Tuber. Seedling biomass was strongly positively associated with Tuber abundance, suggesting that reductions in this genus with pinyon mortality could have negative consequences for establishing seedlings. These findings suggest that whereas mature pinyon mortality led to competitive release for established juvenile pinyons, changes in EMF community composition with mortality could limit successful seedling establishment and growth in high-mortality sites.

Wild boars as spore dispersal agents of ectomycorrhizal fungi: consequences for community composition at different habitat types

The success of dispersal events depend on the organism's ability to reach and establish in a new habitat. In symbiotic organisms, establishment also depends on the presence of their symbiont partner in the new habitat. For instance, the establishment of obligate ectomycorrhizal (EM) trees outside the forest is largely limited by the presence of EM fungi in soil. Wild boars (Sus scrofa) are important dispersal agents of EM fungal spores, particularly in the moderately dry Mediterranean region. The aim of this study was to explore how EM fungal spores dispersed by wild boars influence the EM fungal community associated with the roots of Pinus halepensis seedlings at different habitat types. Using a greenhouse bioassay, we grew pine seedlings in two soil types: old-field and forest soils mixed with either natural or autoclaved wild boar feces. In both soils, we observed a community dominated by a few EM fungal species. Geopora (85 %) and Suillus (68 %) species dominated the forest and old-field soils, respectively. The addition of natural wild boar feces increased the abundance of Tuber species in both EM fungal communities. However, this effect was more pronounced in pots with old-field soil, leading to a more even community, equally dominated by both Tuber and Suillus species. In forest soil, Geopora maintained dominance, but decreased in abundance (67 %), due to the addition of Tuber species. Our findings indicate that wild boar feces can be an important source for EM inoculum, especially in habitats poor in EM fungi such as old-fields.

Convergence in mycorrhizal fungal communities due to drought, plant competition, parasitism, and susceptibility to herbivory: consequences for fungi and host plants

Plants and mycorrhizal fungi influence each other's abundance, diversity, and distribution. How other biotic interactions affect the mycorrhizal symbiosis is less well understood. Likewise, we know little about the effects of climate change on the fungal component of the symbiosis or its function. We synthesized our long-term studies on the influence of plant parasites, insect herbivores, competing trees, and drought on the ectomycorrhizal fungal communities associated with a foundation tree species of the southwestern United States, pinyon pine (Pinus edulis), and described how these changes feed back to affect host plant performance. We found that drought and all three of the biotic interactions studied resulted in similar shifts in ectomycorrhizal fungal community composition, demonstrating a convergence of the community towards dominance by a few closely related fungal taxa. Ectomycorrhizal fungi responded similarly to each of these stressors resulting in a predictable trajectory of community disassembly, consistent with ecological theory. Although we predicted that the fungal communities associated with trees stressed by drought, herbivory, competition, and parasitism would be poor mutualists, we found the opposite pattern in field studies. Our results suggest that climate change and the increased importance of herbivores, competitors, and parasites that can be associated with it, may ultimately lead to reductions in ectomycorrhizal fungal diversity, but that the remaining fungal community may be beneficial to host trees under the current climate and the warmer, drier climate predicted for the future.