Ectomycorrhizal access to organic nitrogen mediates CO2 fertilization response in a dominant temperate tree

Plant–mycorrhizal interactions mediate plant nitrogen (N) limitation and can inform model projections of the duration and strength of the effect of increasing CO2 on plant growth. We present dendrochronological evidence of a positive, but context-dependent fertilization response of Quercus rubra L. to increasing ambient CO2 (iCO2) along a natural soil nutrient gradient in a mature temperate forest. We investigated this heterogeneous response by linking metagenomic measurements of ectomycorrhizal (ECM) fungal N-foraging traits and dendrochronological models of plant uptake of inorganic N and N bound in soil organic matter (N-SOM). N-SOM putatively enhanced tree growth under conditions of low inorganic N availability, soil conditions where ECM fungal communities possessed greater genomic potential to decay SOM and obtain N-SOM. These trees were fertilized by 38 years of iCO2. In contrast, trees occupying inorganic N rich soils hosted ECM fungal communities with reduced SOM decay capacity and exhibited neutral growth responses to iCO2. This study elucidates how the distribution of N-foraging traits among ECM fungal communities govern tree access to N-SOM and subsequent growth responses to iCO2.

A Transcriptomic Approach Provides Insights on the Mycorrhizal Symbiosis of the Mediterranean Orchid Limodorum abortivum in Nature

The study of orchid mycorrhizal interactions is particularly complex because of the peculiar life cycle of these plants and their diverse trophic strategies. Here, transcriptomics has been applied to investigate gene expression in the mycorrhizal roots of Limodorum abortivum, a terrestrial mixotrophic orchid that associates with ectomycorrhizal fungi in the genus Russula. Our results provide new insights into the mechanisms underlying plant–fungus interactions in adult orchids in nature and in particular into the plant responses to the mycorrhizal symbiont(s) in the roots of mixotrophic orchids. Our results indicate that amino acids may represent the main nitrogen source in mycorrhizal roots of L. abortivum, as already suggested for orchid protocorms and other orchid species. The upregulation, in mycorrhizal L. abortivum roots, of some symbiotic molecular marker genes identified in mycorrhizal roots from other orchids as well as in arbuscular mycorrhiza, may mirror a common core of plant genes involved in endomycorrhizal symbioses. Further efforts will be required to understand whether the specificities of orchid mycorrhiza depend on fine-tuned regulation of these common components, or whether specific additional genes are involved.

Specificity of assemblage, not fungal partner species, explains mycorrhizal partnerships of mycoheterotrophic Burmannia plants

Mycoheterotrophic plants (MHPs) growing on arbuscular mycorrhizal fungi (AMF) usually maintain specialized mycorrhizal associations. The level of specificity varies between MHPs, although it remains largely unknown whether interactions with mycorrhizal fungi differ by plant lineage, species, and/or by population. Here, we investigate the mycorrhizal interactions among Burmannia species (Burmanniaceae) with different trophic modes using high-throughput DNA sequencing. We characterized the inter- and intraspecific dynamics of the fungal communities by assessing the composition and diversity of fungi among sites. We found that fully mycoheterotrophic species are more specialized in their fungal associations than chlorophyllous species, and that this specialization possibly results from the gradual loss of some fungal groups. In particular, although many fungal species were shared by different Burmannia species, fully MHP species typically host species-specific fungal assemblages, suggesting that they have a preference for the selected fungi. Although no apparent cophylogenetic relationship was detected between fungi and plants, we observe that evolutionarily closely related plants tend to have a greater proportion of shared or closely related fungal partners. Our findings suggest a host preference and specialization toward fungal assemblages in Burmannia, improving understanding of interactions between MHPs and fungi.

Mycorrhizal Fungi Isolated from Native Terrestrial Orchids from Region of La Araucanía, Southern Chile

Mycorrhizal interactions of orchids are influenced by several environmental conditions. Hence, knowledge of mycorrhizal fungi associated with orchids inhabiting different ecosystems is essential to designing recovery strategies for threatened species. This study analyzes the mycorrhizal associations of terrestrial orchids colonizing grassland and understory in native ecosystems of the region of La Araucanía in southern Chile. Mycorrhizal fungi were isolated from peloton-containing roots and identified based on the sequence of the ITS region. Their capacities for seed germination were also investigated. We detected Tulasnella spp. and Ceratobasidium spp. in the pelotons of the analyzed orchids. Additionally, we showed that some Ceratobasidium isolates effectively induce seed germination to differing degrees, unlike Tulasnella spp., which, in most cases, fail to achieve protocorm growth. This process may underline a critical step in the life cycle of Tulasnella-associated orchids, whereas the Ceratobasidium-associated orchids were less specific for fungi and were effectively germinated with mycorrhizal fungi isolated from adult roots.

Micro-community associated with ectomycorrhizal Russula symbiosis and sporocarp-producing Russula in Fagaceae dominant nature areas in southern China

ABSTRACTRussula griseocarnosa, an ectomycorrhizal (ECM) fungus, is a species of precious wild edible mushrooms with very high market value in southern China. Its yield is affected by many factors including the tree species and environmental conditions such as soil microbiome, humidity. How the microbiome promotes the ECM fungus symbiosis with Fagaceae plants and sporocarp-producing has never been studied. In this study, we collected rhizosphere samples from Fujian province, the microbiota in the root and mycorrhizal rhizosphere were identified by Illumina MiSeq high-throughput sequencing. First, we compared three types of fungal communities: root tips infected with ECM Russula (type 1), tips with Russula sporocarp (type 2) and tips without ECM (type 3). Our results showed that the fungal richness was negatively correlated with Russula. Russula, Tomentella and Lactarius were common in Fagaceae ECM roots. As to the mycorrhizal interactions, Boletus may be considered as an indicator species for sporocarp-producing Russula, and Acremonium, Cladophialophora were associated with Russula symbiosis. Second, we analyzed the fungal and bacterial communities in rhizosphere soils from the corresponding to previously three types (type 1, 2, 3). Dacryobolus and Acidocella may be considered as an indicator species for sporocarp-producing Russula. Fungi Tomentella, Saitozyma, Elaphomyces and bacteria Acidicaldus, Bryobacter, Sorangium and Acidobacterium occurred more frequently in the ECM Russula rhizosphere. Furthermore, the indicators Elaphomyces, Tomentella, Sorangium had a positive correlation with Russula symbiosis by network analyses. Overall, our results suggest a relationship between micro-community and ECM Russula formation and Russula sporocarp, which may provide new strategies for improving Russula symbiosis rate and sporocarp production.