Culturable root endophyte communities are shaped by both warming and plant host identity in the Rocky Mountains, USA

Shifts in Structure and Assembly Processes of Root Endophytic Community Caused by Climate Warming and Precipitation Increase in Alpine Grassland

Climate change poses great challenges to the survival of plants. Plant endophytes play important roles in improving plant adaptability. However, our knowledge of the effects of climate change on endophytic community structures is limited. Relying on a field experimental platform simulating climate warming, precipitation increases, and their combination in an alpine grassland, the root endophytic bacterial community structures and assembly processes of three coexisting plant species (Elymus nutans, Kobresia humilis, and Melissilus ruthenicus) were measured. The results indicated that Proteobacteria was the dominant phylum, with a relative abundance ranging from 50% to 80%, followed by Actinobacteria and Bacteroidetes. Bacterial diversity decreased significantly under the combined treatment for all three plant species, with the largest reduction observed in E. nutans. The climate manipulation treatments had a minimal effect on the endophytic bacterial community structures. The relative abundance of Burkholderiaceae increased significantly under the combined treatment for the three plant species. Moreover, the endophytic community assembly processes changed from stochastic dominated under control plots to deterministic dominated under the combined plots for E. nutans, while this shift was reversed for M. ruthenicus. The root endophytic bacterial community was affected by the soil's available nitrogen and stoichiometric ratio. These results revealed that the sensitivity of endophyte community structures to climate change varies with host plant species, which has implications for plant fitness differences.

"Mini-community" simulation revealed the differences of endophytic fungal communities between the above- and below-ground tissues of Ephedra sinica Stapf

The microecology of endophytic fungi in special habitats, such as the interior of different tissues from a medicinal plant, and its effects on the formation of metabolites with different biological activities are of great importance. However, the factors affecting fungal community formation are unclear. This study is the first to utilize "mini-community" remodeling to understand the above phenomena. First, high-throughput sequencing technology was applied to explore the community composition and diversity of endophytic fungi in the above-ground tissues (Ea) and below-ground tissues (Eb) of Ephedra sinica. Second, fungi were obtained through culture-dependent technology and used for "mini-community" remodeling in vitro. Then, the effects of environmental factors, partner fungi, and plant tissue fluid (internal environment) on endophytic fungal community formation were discussed. Results showed that environmental factors played a decisive role in the selection of endophytic fungi, that is, in Ea and Eb, 93.8% and 25.3% of endophytic fungi were halophilic, respectively, and 10.6% and 60.2% fungi were sensitive to high temperature (33 °C), respectively. Meanwhile, pH had little effect on fungal communities. The internal environment of the plant host further promoted the formation of endophytic fungal communities.

Characterization of root-associated fungi and reduced plant growth in soils from a New Mexico uranium mine

Characterizing the diverse, root-associated fungi in mine wastes can accelerate the development of bioremediation strategies to stabilize heavy metals. Ascomycota fungi are well known for their mutualistic associations with plant roots and, separately, for roles in the accumulation of toxic compounds from the environment, such as heavy metals. We sampled soils and cultured root-associated fungi from blue grama grass (Bouteloua gracilis) collected from lands with a history of uranium (U) mining and contrasted against communities in nearby, off-mine sites. Plant root-associated fungal communities from mine sites were lower in taxonomic richness and diversity than root fungi from paired, off-mine sites. We assessed potential functional consequences of unique mine-associated soil microbial communities using plant bioassays, which revealed that plants grown in mine soils in the greenhouse had significantly lower germination, survival, and less total biomass than plants grown in off-mine soils but did not alter allocation patterns to roots versus shoots. We identified candidate culturable root-associated Ascomycota taxa for bioremediation and increased understanding of the biological impacts of heavy metals on microbial communities and plant growth.

Grass species identity shapes communities of root and leaf fungi more than elevation

Fungal symbionts can buffer plants from environmental extremes and may affect host capacities to acclimate, adapt, or redistribute under environmental change; however, the distributions of fungal symbionts along abiotic gradients are poorly described. Fungal mutualists should be the most beneficial in abiotically stressful environments, and the structure of networks of plant-fungal interactions likely shift along gradients, even when fungal community composition does not track environmental stress. We sampled 634 unique combinations of fungal endophytes and mycorrhizal fungi, grass species identities, and sampling locations from 66 sites across six replicate altitudinal gradients in the western Colorado Rocky Mountains. The diversity and composition of leaf endophytic, root endophytic, and arbuscular mycorrhizal (AM) fungal guilds and the overall abundance of fungal functional groups (pathogens, saprotrophs, mutualists) tracked grass host identity more closely than elevation. Network structures of root endophytes become more nested and less specialized at higher elevations, but network structures of other fungal guilds did not vary with elevation. Overall, grass species identity had overriding influence on the diversity and composition of above- and belowground fungal endophytes and AM fungi, despite large environmental variation. Therefore, in our system climate change may rarely directly affect fungal symbionts. Instead, fungal symbiont distributions will most likely track the range dynamics of host grasses.

Mycena citrinomarginata is associated with roots of the perennial grass Festuca roemeri in Pacific Northwest prairies

Prairies in the Pacific Northwest are dominated by perennial bunchgrasses. A Mycena in the citrinomarginata complex was observed to tightly co-occur with bunchgrasses at several prairie study sites. Mapping and spatial statistics showed that it was strongly and significantly associated with Festuca roemeri tussocks. We further found that this fungus is attached to F. roemeri roots (17/17 examined) and both specific primers and next-generation DNA sequencing established that the fungus is in the roots, suggesting that M. citrinomarginata may be endophytic or biotrophic in some contexts, and not simply saprotrophic. These results combined with a literature review indicate that Mycena species are often found as endophytes in grass roots. Given the importance of grasses and grasslands for humans, this ecological association deserves further study.