Characterizing root-associated fungal communities and soils of Douglas-fir (Pseudotsuga menziesii) stands that naturally produce Oregon white truffles (Tuber oregonense and Tuber gibbosum)

Seasonal Succession of Fungal Communities in Native Truffle (Tuber indicum) Ecosystems

Truffles are a rare underground fungus and one of the most expensive, and sought-after kitchen ingredients in the world. Microbial ecology plays an important role in the annual growth cycle of truffles, but fungal communities in native truffle ecosystems are still largely unknown, especially for Tuber indicum from China. In this study, the spatial and temporal dynamics of soil physicochemical properties and fungal communities were described associated with four T. indicum-producing plots (TPPs) and one non-truffle-producing plot in four successive growing seasons. A total of 160 biological samples were collected, 80 of which were used for the determination of 10 soil physicochemical indices and 80 for Illumina-based analysis of the fungal microbiome. Soil physicochemical properties and fungal communities exhibited considerable seasonal variation. Ascomycetes, Basidiomycetes, and Mucormycoides dominated. The core microbiome work on the microecological changes in TPPs, and the identified core members contribute to the seasonal succession of communities. The genus Tuber occupies a central position in healthy TPPs. There was a strong correlation between soil physicochemical properties and fungal communities. The genus Tuber showed a positive correlation with Ca, Mg, and total nitrogen, but a negative correlation with total phosphorus and available potassium. This study describes the complex ecological dynamics of soil physicochemical indices and fungal communities occurring during the annual cycle of Tuber indicum, and highlights the succession of core communities in truffle plots, which contribute to better protection of native truffle ecosystems and control of mycorrhizal fungal contamination in artificial truffle plantations in China. IMPORTANCE The spatial and temporal dynamics of soil physicochemical properties and fungal communities associated with four Tuber indicum-producing plots and one non truffle producing plot in four different growing seasons are described. Soil physicochemical properties and fungal communities exhibited considerable seasonal variation. This study examines the complex ecological dynamics of soil physicochemical indices and fungal communities occurring during the annual cycle of Tuber indicum and highlights the succession of core communities in truffle plots, which contributes to better protection of native truffle ecosystems and control of mycorrhizal fungal contamination in artificial truffle plantations in China.

Tuber indicum and T. lijiangense colonization differentially regulates plant physiological responses and mycorrhizosphere bacterial community of Castanopsis rockii seedlings

Black truffles and white truffles are widely studied around the world, but their effects on plant growth and physiological responses, and on the mycorrhizosphere bacterial community of the host plant remain unclear. Here, mycorrhizal colonization of Castanopsis rockii by Tuber indicum (Chinese black truffle) and T. lijiangense (Chinese white truffle), respectively, was induced in a greenhouse study, and their effects on host growth, physiological responses and mycorrhizosphere bacterial communities were compared. The results show that colonization of both Tuber species significantly increased leaf photosynthetic rate, leaf P concentration and mycorrhizosphere acid phosphatase activity, as well as richness of mycorrhizosphere bacterial communities of C. rockii seedlings. However, T. indicum colonization on the one hand significantly decreased tartrate content, bacterial acid phosphatase, phoC gene abundance in the mycorrhizosphere, and peroxidase (POD) activity of ectomycorrhizal root tips, but on the other hand increased mycorrhizosphere pH and superoxide dismutase (SOD) of ectomycorrhizal root tips, compared to T. lijiangense colonization. Moreover, principal coordinate and β-diversity analyses show significant differences in mycorrhizosphere bacterial community composition between T. indicum and T. lijiangese colonized C. rockii seedlings. Finally, the relative abundance of the bacterium Agromyces cerinus significantly correlated to mycorrhizosphere acid phosphatase activity and leaf P concentration, suggesting that this bacterium might play an important role in P mobilization and acquisition. Overall, these results suggest that T. indicum and T. lijiangense differently regulate their host plant's physiological responses and mycorrhizosphere bacterial community.

Arbuscular Mycorrhizal Fungi Mitigate Nitrogen Leaching under Poplar Seedlings

The leaching of soil nitrogen (N) has become one of the most concerning environmental threats to ecosystems. Arbuscular mycorrhizal (AM) fungi have important ecological functions, however, their influence on soil N leaching and the mechanism of action remain unclear. We conducted a two-factor (N application level × AM inoculation) experiment on poplar, and for the first time, comprehensively analyzed the mechanism by which AM fungi influence soil N leaching. The results showed that, under optimum (7.5 mM) and high (20 mM) N levels, the nitrate (NO3−) and ammonium (NH4+) concentrations of leachate in the AM inoculated treatment (+AM) were lower than in the non-inoculated treatment (−AM), with significant reductions of 20.0% and 67.5%, respectively, under high N level, indicating that AM inoculation can reduce soil N leaching and that it is more effective for NH4+. The arbuscular and total colonization rates gradually increased, and the morphology of spores and vesicles changed as the N level increased. Under optimum and high N levels, +AM treatment increased the root N concentration by 11.7% and 50.7%, respectively; the increase was significant (p < 0.05) at the high N level, which was associated with slightly increased transpiration and root activity despite reductions in root surface area and root length. Additionally, the +AM treatment increased soil cation exchange capacity (CEC), soil organic carbon (SOC), and significantly (p < 0.05) increased the proportions of macroaggregates (but without significant change in microaggregates), causing soil total nitrogen (TN) to increase by 7.2% and 4.7% under optimum and high N levels, respectively. As the N levels increased, the relative contributions of AM inoculation on N leaching increased, however, the contributions of plant physiological and soil variables decreased. Among all of the variables, SOC had important contributions to NH4+ and total N in the leachate, while root N concentration had a higher contribution to NO3−. In conclusion, AM fungi can mitigate soil N leaching and lower the risk of environmental pollution via enhancing N interception by the inoculated fungi, increasing N sequestration in plant roots, and by improving soil N retention.

Chinese Black Truffle-Associated Bacterial Communities of Tuber indicum From Different Geographical Regions With Nitrogen Fixing Bioactivity

It is well known that the microbes associated with truffle fruiting bodies play a very important role during the truffle lifecycle. Tuber indicum, commonly called Chinese black truffle, is a species endemic to Eastern Asia and in the genus of Tuber. Here, we reported the bacterial communities of T. indicum from different geographical regions and described the bacterial diversity from three compartments (soil, ectomycorrhizae and ascocarps) of T. indicum using high-throughput sequencing combined tissue culture. The results revealed that Bradyrhizobium was the dominant genus in fruiting bodies of T. indicum from nine geographical sites in China, and the microbes in T. indicum ascocarps were influenced by geological locations and soil characteristics. More specific bacterial taxa were enriched in the fruiting bodies than in the ectomycorrhizae and soil. In addition, 60 cultural bacteria were isolated from T. indicum fruiting bodies (4 families, 24 genera), and Pseudomonas, Alcaligenes faecalis, Microbacterium, and Arthrobacter were dominant. One of 13 strains that have potential nitrogen-fixation activities was further verified by an acetylene reduction assay (ARA). Together, this research provides new and important data for better understanding of the interaction between truffle and associated microbe and the biology of truffle itself.

Ectomycorrhizal fungal communities in high mountain conifer forests in central Mexico and their potential use in the assisted migration of Abies religiosa

Abies religiosa forests in central Mexico are the only overwinter refuge of the monarch butterfly and provide important ecosystem services. These forests have lost 55% of their original area and as a consequence, diversity and biotic interactions in these ecosystems are in risk. The aim of this study was to compare the soil fungal diversity and community structure in the Abies religiosa forests and surrounding Pinus montezumae, Pinus hartwegii, and coniferous mixed forest plant communities to provide data on ecology of mycorrhizal interactions for the assisted migration of A. religiosa. We sampled soil from five coniferous forests, extracted total soil DNA, and sequenced the ITS2 region by Illumina MiSeq. The soil fungi community was integrated by 1746 taxa with a species turnover ranging from 0.280 to 0.461 between sampling sites. In the whole community, the more abundant and frequent species were Russula sp. (aff. olivobrunnea), Mortierella sp.1, and Piloderma sp. (aff. olivacearum). The ectomycorrhizal fungi were the more frequent and abundant functional group. A total of 298 species (84 ectomycorrhizal) was shared in the five conifer forests; these widely distributed species were dominated by Russulaceae and Clavulinaceae. The fungal community composition was significantly influenced by altitude and the lowest species turnover happened between the two A. religiosa forests even though they have different soil types. As Pinus montezumae forests have a higher altitudinal distribution adjacent to A. religiosa and share the largest number of ectomycorrhizal fungi with it, we suggest these forests as a potential habitat for new A. religiosa populations.

A new cinnamic acid derivative from plant-derived endophytic fungus Pyronema sp

Ten secondary metabolites (1-10) including a new 4-hydroxycinnamic acid derivatives, methyl 2-{(E)-2-[4-(formyloxy)phenyl]ethenyl}-4-methyl-3-oxopentanoate (1), and nine known compounds (2-10) were isolated from an EtOAc extract derived from a solid rice medium of endophytic fungal strain Pyronema sp. (A2-1 & D1-2). Their structures were elucidated from NMR and HRMS data. All the compounds were tested for antibacterial activity against Mycobacterium marinum ATCCBAA-535. Compounds 1, 8 and 9 exhibited moderate antibiotic activity with IC₅₀ of 64, 43 and 32 μM, respectively.

First detection of Endogone ectomycorrhizas in natural oak forests

The order Endogonales in Mucoromycotina, an early divergent lineage of fungi, includes ectomycorrhizal (EM) fungi. This order is therefore considered a key taxon for elucidation of the evolution of EM associations. Recent studies have revealed high diversity of EM lineages of Basidiomycota and Ascomycota; however, EM associations of Endogonales and its relatives remain largely unknown. In this study, EM root tips with a unique fungal sheath, with aseptate and highly branched hyphae of variable widths, were identified in Quercus acutissima and Quercus crispula forests in the temperate zone of Japan. The mycobionts were confirmed as Endogone sp., which were placed as a sister clade of Endogone pisiformis, based on phylogenetic analyses of the small and large subunits of the nuclear ribosomal RNA and elongation factor-1α genes. This is the first report of EM of Endogone in natural forests of the Northern Hemisphere and the first finding on Quercus.