Rapid temporal changes in root colonization by arbuscular mycorrhizal fungi and fine root endophytes, not dark septate endophytes, track plant activity and environment in an alpine ecosystem.

Fungal root endophytes play an important role in plant nutrition, helping plants acquire nutrients in exchange for photosynthates. We sought to characterize the progression of root colonization by arbuscular mycorrhizal fungi (AMF), dark septate endophytes (DSE), and fine root endophytes (FRE) over an alpine growing season, and to understand the role of the host plant and environment in driving colonization levels. We sampled four forbs on a regular schedule from June 26th-September 11th from a moist meadow (3535 m a.s.l) on Niwot Ridge, Rocky Mountain Front Range, CO, USA. We quantified the degree of root colonization by storage structures, exchange structures, and hyphae of all three groups of fungi. AMF and FRE percent colonization fluctuated significantly over time, while DSE did not. All AMF structures changed over time, and the degree of change in vesicles differed by plant species. FRE hyphae, AMF arbuscules and AMF vesicles peaked late in the season as plants produced seeds. AMF hyphae levels started high, decreased, and then increased within 20 days, highlighting the dynamic nature of plant-fungal interactions. Overall, our results show that AMF and FRE, not DSE, root colonization rapidly changes over the course of a growing season and these changes are driven by plant phenology and seasonal changes in the environment.

Disentangling identity of species of the genus Taphrina parasitizing herbaceous Rosaceae, with proposal of Taphrina gei-montani sp. nov.

Five strains (CCY 058-007-001T, CCY 058-007-002, CCY 058-007-003, CCY 058-007-004 and CCY 058-007-005) of a novel parasitic yeast belonging to the genus Taphrina were isolated from leaf tissues of Geum montanum L. (Rosaceae), collected from the Vysoké Tatry Mountains, Slovakia. Genetic analyses revealed that these isolates differ by 15 unique substitutions in the ITS region and by six substitutions in the rns gene from all other species of the genus Taphrina analysed hitherto. The novel strains are also distinguished from all other species of the genus Taphrina by their morphology, biochemical properties and ecology. These strains represent a novel species, for which the name Taphrina gei-montani sp. nov. is proposed. The type strain is CCY 058-007-001T (=CBS 14159=BU001). The MycoBank number is MB815677. The present study also demonstrates that two distinct species of the genus Taphrina parasitize the herbaceous Rosaceae: Taphrina gei-montani sp. nov. on Geum montanum and Taphrina tormentillae on Potentilla species.

Rhizobium gei sp. nov., a bacterial endophyte of Geum aleppicum.

A bacterial strain, designated as ZFJT-2T, was isolated from the stem of Geum aleppicum Jacq. collected from Taibai Mountain in Shaanxi Province, north-west China. Cells of strain ZFJT-2T were Gram-stain-negative, strictly aerobic, rod-shaped and motile by means of a single polar flagellum. The major fatty acids were summed feature 8 (comprising C18 : 1ω7c and/or C18 : 1ω6c), C16 : 0, 11-methyl C18 : 1ω7c and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c), and the DNA G+C content was 58.3 mol% (HPLC). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain ZFJT-2T was a member of the genus Rhizobium and was most closely related to Rhizobium giardinii KACC 10720T (98.6 % similarity) and Rhizobium herbae CCBAU 83011T (98.5 %). The low levels of sequence similarity found between the atpD, recA and glnII gene sequences of strain ZFJT-2T and those of recognized species of the genus Rhizobium (no more than 94.4, 87.2 and 89.5 %, respectively) indicated that it may represent a separate species of the genus Rhizobium. The DNA-DNA relatedness values for strain ZFJT-2T with respect to R. giardinii KACC 10720T and R. herbae CCBAU 83011T were 17.6 and 41.9 %, respectively. On the basis of phenotypic, phylogenetic and genotypic data, strain ZFJT-2T is considered to represent a novel species of the genus Rhizobium, for which the name Rhizobium gei sp. nov. is proposed. The type strain is ZFJT-2T (=CCTCC AB 2013015T=KCTC 32301T=LMG 27603T).

Sphingomonas gei sp. nov., isolated from roots of Geum aleppicum.

A yellow-pigmented bacterium, designated strain ZFGT-11(T), was isolated from roots of Geum aleppicum Jacq. collected from Taibai Mountain in Shaanxi Province, north-west China, and was subjected to a taxonomic study by using a polyphasic approach. Cells of strain ZFGT-11(T) were Gram-stain-negative, strictly aerobic rods that were surrounded by a thick capsule and were motile by means of a single polar flagellum. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain ZFGT-11(T) was a member of the genus Sphingomonas and was closely related to Sphingomonas naasensis KACC 16534(T) (97.6% similarity), Sphingomonas kyeonggiense JCM 18825(T) (96.8%), Sphingomonas asaccharolytica IFO 15499(T) (96.7%) and Sphingomonas leidyi DSM 4733(T) (96.6%). The predominant respiratory quinone was ubiquinone-10 (Q-10) and the major cellular fatty acids were summed feature 8 (comprising C(18 : 1)ω7c and/or C(18 : 1)ω6c), C(17 : 1)ω6c, C(14 : 0) 2-OH, C(16 : 0) and C(15 : 0) 2-OH. The major polyamine of strain ZFGT-11(T) was sym-homospermidine. Phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine, sphingoglycolipid, two unidentified aminoglycolipids, two unidentified phospholipids and two unidentified lipids were detected in the polar lipid profile. The DNA G+C content was 66.8 mol%. DNA-DNA relatedness for strain ZFGT-11(T) with respect to its closest phylogenetic relative S. naasensis KACC 16534(T) was 26.2±4.8% (mean±SD). On the basis of data from the present polyphasic taxonomic study, strain ZFGT-11(T) is considered to represent a novel species of the genus Sphingomonas , for which the name Sphingomonas gei sp. nov. is proposed. The type strain is ZFGT-11(T) ( = CCTCC AB 2013306(T) = KCTC 32449(T) = LMG 27608(T)).

Nitrogen deposition alters plant-fungal relationships: linking belowground dynamics to aboveground vegetation change.

Nitrogen (N) deposition rates are increasing globally due to anthropogenic activities. Plant community responses to N are often attributed to altered competitive interactions between plants, but may also be a result of microbial responses to N, particularly root-associated fungi (RAF), which are known to affect plant fitness. In response to N, Deschampsia cespitosa, a codominant plant in the alpine tundra at Niwot Ridge (CO), increases in abundance, while Geum rossii, its principal competitor, declines. Importantly, G. rossii declines with N even in the absence of its competitor. We examined whether contrasting host responses to N are associated with altered plant-fungal symbioses, and whether the effects of N are distinct from effects of altered plant competition on RAF, using 454 pyrosequencing. Host RAF communities were distinct (only 9.4% of OTUs overlapped). N increased RAF diversity in G. rossii, but decreased it in D. cespitosa. D. cespitosa RAF communities were more responsive to N than G. rossii RAF communities, perhaps indicating a flexible microbial community aids host adaptation to nutrient enrichment. Effects of removing D. cespitosa were distinct from effects of N on G. rossii RAF, and D. cespitosa presence reversed RAF diversity response to N. The most dominant G. rossii RAF order, Helotiales, was the most affected by N, declining from 83% to 60% of sequences, perhaps indicating a loss of mutualists under N enrichment. These results highlight the potential importance of belowground microbial dynamics in plant responses to N deposition.

Asticcacaulis endophyticus sp. nov., a prosthecate bacterium isolated from the root of Geum aleppicum.

A strictly aerobic, light-yellow-coloured, stalked bacterium, designated strain ZFGT-14(T), was isolated from the root of Geum aleppicum Jacq. collected from Taibai Mountain in Shaanxi province, north-west China, and was subjected to a taxonomic study using a polyphasic approach. This novel isolate grew at 7-33 °C (optimum 25-28 °C) and pH 6.0-10.0 (optimum pH 7.0-8.0). Flexirubin-type pigments were not produced. Cells were Gram-stain-negative, rod-shaped and motile with a single polar flagellum. The predominant respiratory quinone was Q-10. The major cellular fatty acids were summed feature 8 (comprising C18 : 1ω7c/C18 : 1ω6c), C16 : 0, C19 : 0 cyclo ω8c and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c) and the major polar lipids were phosphatidylglycerol and glycolipids. The DNA G+C content was 57.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain ZFGT-14(T) was most closely related to the genus Asticcacaulis and had low sequence similarity (95.0-95.9 %) with all species with validly published names within the genus Asticcacaulis. Based on the phenotypic, phylogenetic and genotypic data, strain ZFGT-14(T) is considered to represent a novel species of the genus Asticcacaulis, for which the name Asticcacaulis endophyticus sp. nov. is proposed. The type strain is ZFGT-14(T) ( = CCTCC AB 2013012(T) = KCTC 32296(T) = LMG 27605(T)).

Pseudoxanthomonas gei sp. nov., a novel endophytic bacterium isolated from the stem of Geum aleppicum.

A Gram stain-negative, strictly aerobic, rod-shaped, non-motile and deep-yellow-coloured bacterial strain, designated ZFJR-3(T), was isolated from the stem of Geum aleppicum Jacq. collected from Taibai Mountain in Shaanxi Province, north-west China, and characterized by using a polyphasic approach. The novel isolate grew optimally at 25-28 °C and in the absence of NaCl. Flexirubin-type pigments were produced. The predominant respiratory quinone was ubiquinone-8 (Q-8) and the major cellular fatty acids were iso-C15:0 (29.2 %), iso-C16:0 (18.5 %), summed feature 9 (comprising iso-C17:1 ω9c and/or C16:0 10-methyl; 8.8 %), C16:1 ω7c alcohol (8.8 %), iso-C11:0 3-OH (6.9 %) and iso-C11:0 (6.8 %). The DNA G+C content was 66.1 mol %. The only polyamine was spermidine and the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain ZFJR-3(T) belongs to the genus Pseudoxanthomonas and was most closely related to Pseudoxanthomonas yeongjuensis KCTC 22757(T) (16S rRNA gene sequence similarity, 99.0 %) and Pseudoxanthomonas sacheonensis KCTC 22080(T) (98.0 %). The levels of 16S rRNA gene sequence similarity with respect to other Pseudoxanthomonas species with validly published names were less than 96.5 %. DNA-DNA relatedness values for strain ZFJR-3(T) with respect to its closely related neighbours P. yeongjuensis KCTC 22757(T) and P. sacheonensis KCTC 22080(T) were 48.7 and 36.3 %, respectively. Based on the phenotypic, phylogenetic and genotypic data, strain ZFJR-3(T) is considered to represent a novel species of the genus Pseudoxanthomonas, for which the name Pseudoxanthomonas gei sp. nov. is proposed. The type strain is ZFJR-3(T) (=CCTCC AB 2013020(T) =KCTC 32298(T)).

Slight dependence of temperate-forest herbaceous plants, Geum urbanum and Senecio ovatus, on arbuscular mycorrhizal fungi (AMF) enables them to colonise soils with a low level of AMF abundance.

While numerous studies have revealed that arbuscular mycorrhizal fungi (AMF) enhance plant performance, the influence of these symbionts on temperate-forest herbaceous species in relation to soil physical and chemical properties has been left largely unexplored. Therefore, two perennial herbs, Geum urbanum (Rosaceae) and Senecio ovatus (Asteraceae), were examined in a laboratory pot experiment to determine whether AMF influenced their growth, photosynthetic performance index, and N and P contents in biomass. The treatments, involving three widespread AMF species, were prepared in the soils of two habitats colonised by both plants, namely beech and riparian forests, as follows: (1) control-soils without AMF, (2) Claroideoglomus claroideum, (3) Funneliformis geosporus, and (4) Funneliformis mosseae. Neither shoot mass nor photosynthetic performance index of G. urbanum and S. ovatus was enhanced by AMF. Senecio ovatus root mass was increased compared to control only by F. geosporus. Inconsistent effects were observed in N and P contents in shoots and roots of both species. The direction and magnitude of these responses were dependent on the fungal species and soil type. Although the plant species belong to families whose representatives are usually regularly colonised by and highly responsive to AMF, our study indicates that AMF had only a slight impact on the performance of G. urbanum and S. ovatus at the early stages of their development. The plants being slightly dependent on AMF are thus adapted to colonise temperate-forest soils with a low level of availability of AMF propagules.

Novel weapons: invasive plant suppresses fungal mutualists in America but not in its native Europe.

Why some invasive plant species transmogrify from weak competitors at home to strong competitors abroad remains one of the most elusive questions in ecology. Some evidence suggests that disproportionately high densities of some invaders are due to the release of biochemicals that are novel, and therefore harmful, to naive organisms in their new range. So far, such evidence has been restricted to the direct phytotoxic effects of plants on other plants. Here we found that one of North America's most aggressive invaders of undisturbed forest understories, Alliaria petiolata (garlic mustard) and a plant that inhibits mycorrhizal fungal mutualists of North American native plants, has far stronger inhibitory effects on mycorrhizas in invaded North American soils than on mycorrhizas in European soils where A. petiolata is native. This antifungal effect appears to be due to specific flavonoid fractions in A. petiolata extracts. Furthermore, we found that suppression of North American mycorrhizal fungi by A. petiolata corresponds with severe inhibition of North American plant species that rely on these fungi, whereas congeneric European plants are weakly affected. These results indicate that phytochemicals, benign to resistant mycorrhizal symbionts in the home range, may be lethal to naïve native mutualists in the introduced range and indirectly suppress the plants that rely on them.