Untangling above‐ and belowground mycorrhizal fungal networks in tropical orchids

Orchids typically depend on fungi for establishment from seeds, forming mycorrhizal associations with basidiomycete fungal partners in the polyphyletic group rhizoctonia from early stages of germination, sometimes with very high specificity. This has raised important questions about the roles of plant and fungal phylogenetics, and their habitat preferences, in controlling which fungi associate with which plants. In this issue of Molecular Ecology, Martos et al. (2012) report the largest network analysis to date for orchids and their mycorrhizal fungi, sampling a total of over 450 plants from nearly half the 150 tropical orchid species on Reunion Island, encompassing its main terrestrial and epiphytic orchid genera. The authors found a total of 95 operational taxonomic units of mycorrhizal fungi and investigated the architecture and nestedness of their bipartite networks with 73 orchid species. The most striking finding was a major ecological barrier between above‐ and belowground mycorrhizal fungal networks, despite both epiphytic and terrestrial orchids often associating with closely related taxa across all three major lineages of rhizoctonia fungi. The fungal partnerships of the epiphytes and terrestrial species involved a diversity of fungal taxa in a modular network architecture, with only about one in ten mycorrhizal fungi partnering orchids in both groups. In contrast, plant and fungal phylogenetics had weak or no effects on the network. This highlights the power of recently developed ecological network analyses to give new insights into controls on plant–fungal symbioses and raises exciting new hypotheses about the differences in properties and functioning of mycorrhiza in epiphytic and terrestrial orchids.     

Phylogeny of Caragana (Fabaceae) based on DNA sequence data from rbcL, trnS–trnG, and ITS

Phylogenetic relationships of 48 species of Caragana (Fabaceae: tribe Hedysareae) and one representative each of Astragalus, Calophaca, Halimodendron, and Hedysarum are estimated from DNA sequences of the rbcL gene, trnS–trnG intron and spacer, and ITS region. At least one representative of all five sections and 12 series within Caragana are included. Analyses yielded strongly supported clades corresponding to sections Caragana, Bracteolatae, and Frutescentes. The species of section Jubatae are distributed among three strongly supported clades, i.e., one with the species of section Bracteolatae, another with two species of section Spinosae, and a third as sister to section Frutescentes. All but the last of these six clades are corroborated by at least one unambiguously traced morphological character. The placement of the other four species of section Spinosae are not well supported and lack unambiguous morphological synapomorphies, and the samples of Calophaca and Halimodendron nest within Caragana with weak support.     

Invasion of a Habitat-Forming Seaweed: Effects on Associated Biota

Fucus evanescens is a brown alga of arctic origin that has invaded European coasts. The epiphytic community of F. evanescens in southern Sweden was compared with that of the native Fucus vesiculosus, to examine to what extent an invading seaweed can modify local biodiversity. F. evanescens was much less fouled than F. vesiculosus, supporting both less biomass and fewer species of epiphytes. Multivariate analysis of the most common epiphyte taxa showed that the epiphytic community composition of F. evanescens was not entirely separated from that of F. vesiculosus, but host species contributed significantly to explain the variation in community composition. The biomass of free-living invertebrates was also lower on F. evanescens, although the pattern differed between taxonomic groups. While the biomass of amphipods was lower on F. evanescens, there was no significant difference in biomass of isopods or gastropods between the Fucus species. The good correlation between biomass of epiphytes and free-living animals suggests that the epiphytes play an important role in providing a suitable habitat for many species of free-living epifauna. The study shows that the invasion of F. evanescens affects the environmental conditions for many species associated with the Fucus community but that the direct effect on biodiversity is probably low.     

Post-pollination hybridization barriers in <Emphasis Type="Italic">Nicotiana</Emphasis> section <Emphasis Type="Italic">Alatae</Emphasis>

Nicotiana section Alatae contains eight species with variable flower sizes and morphologies. Section members readily hybridize in the glasshouse, but no hybrids have been observed in natural sympatric and parapatric populations. To investigate interspecific crossing relationships with respect to mechanisms preventing hybridization, all members of section Alatae were intercrossed in a complete diallel. We found positive correlation between the pistil length of the pollen donor and interspecific seed set relative to the conspecific cross. Pollen tube growth rate and pollen donor pistil length were positively correlated as well. Furthermore, pollen from short-pistil members of section Alatae could only grow a maximum distance proportional to, but greater than, their own pistil lengths. Our results show that pollen tube growth capacity (i.e., rate and distance), provides a hybridization barrier in long-pistil species × short-pistil species crosses. We also found another hybridization barrier not specifically related to pollen tube growth capacity in short-pistil species × long-pistil species. Taken together, these barriers can generally be described by a ‘pistil-length mismatch’ rule; in section Alatae, pollen has the most success fertilizing ovules from species with pistil lengths similar to their own. This rule could contribute to hybridization barriers in Section Alatae because the species display dramatically different pistil lengths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of Habitat and Climate Variables on Arbuscular Mycorrhizal Fungus Community Distribution,as Revealed by a Case Study of Facultative Plant Epiphytism under Semiarid Conditions

In semiarid Mediterranean ecosystems, epiphytic plant species are practically absent, and only some species of palm trees can support epiphytes growing in their lower crown area, such as Phoenix dactylifera L. (date palm). In this study, we focused on Sonchus tenerrimus L. plants growing as facultative epiphytes in P. dactylifera and its terrestrial forms growing in adjacent soils. Our aim was to determine the possible presence of arbuscular mycorrhizal fungi (AMF) in these peculiar habitats and to relate AMF communities with climatic variations. We investigated the AMF community composition of epiphytic and terrestrial S. tenerrimus plants along a temperature and precipitation gradient across 12 localities. Epiphytic roots were colonized by AMF, as determined by microscopic observation; all of the epiphytic and terrestrial samples analyzed showed AMF sequences from taxa belonging to the phylum Glomeromycota, which were grouped in 30 AMF operational taxonomic units. The AMF community composition was clearly different between epiphytic and terrestrial root samples, and this could be attributable to dispersal constraints and/or the contrasting environmental and ecophysiological conditions prevailing in each habitat. Across sites, the richness and diversity of terrestrial AMF communities was positively correlated with rainfall amount during the most recent growing season. In contrast, there was no significant correlation between climate variables and AMF richness and diversity for epiphytic AMF communities, which suggests that the composition of AMF communities in epiphytic habitats appears to be largely determined by the availability and dispersion of fungal propagules from adjacent terrestrial habitats.     

亚热带森林附生植物叶片气孔特征及其可塑性对光照变化的响应

附生植物是热带亚热带森林生态系统中物种多样性极高且极其脆弱敏感的生物类群之一。光照被认为是促进附生植物由陆生类群演化而来并决定其生长和分布的关键因素。然而,由于接近林冠和规范性采样的限制,附生植物与光照的关系仍亟待阐述。为揭示附生植物对光强变化的响应和适应策略,该研究以亚热带常绿阔叶林6种附生植物(林冠层木本:鼠李叶花楸、毛棉杜鹃;林冠层草本:狭瓣贝母兰、毛唇独蒜兰;树干区草本:点花黄精、距药姜)为对象,对其在4个光处理梯度下生长的叶片气孔特征及其可塑性进行了对比分析。结果表明:(1) 2种附生小乔木的气孔面积(SA)、气孔密度(SD)、潜在气孔导度指数(PCI)和表皮细胞密度(ECD)均对光强改变显著响应。2种附生兰科植物的SA最大,而SD最小;附生乔木叶片SD和ECD的光响应趋势与陆生植物更相似,而附生草本则出现种间差异。(2) 6种附生植物的气孔、表皮细胞特性及其表型可塑性,在草本-木本、常绿-落叶植物、林冠-树干区之间,均无明显差别。(3)附生植物气孔特性和表皮细胞平均可塑性指数均低于陆生植物。综上结果表明,亚热带常绿阔叶林中附生植物对于光环境变化的适应性相对较弱。不同的附生植物可以通过不同程度地增加叶片SD和ECD来适应高光强生境,并通过对SD和SA的双重调节以增大潜在光合能力从而应对低光胁迫。     

Liparis tsii: a new species of Orchidaceae (tribe-Malaxideae) from Guangdong,China with its phylogenetic position

Liparis tsii, a new orchid from Guangdong, China, is described and illustrated. It is compared with its closest allies: L. sasakii Hayata, L. nanlingensis H.Z. Tian & F.W. Xing, L. krameri Franch. & Sav., L. reckoniana T.C. Hsu and L. brunnea Ormerod belonging to section Liparis. Further phylogenetic study based on combined molecular data from nrITS and plastid trnL-F ascertained its phylogenetic position as L. tsii being sister to L. sasakii and L. nanlingensis. A key to identification with the allied species is provided.     

Pollination by fungus gnats (Diptera: Mycetophilidae) and self-recognition sites in Tolmiea menziesii (Saxifragaceae)

Coleeae (Bignoniaceae) are a tribe almost entirely restricted to Madagascar. Coleeae have previously been placed in neotropical Crescentieae due to species with indehiscent fruits, a character otherwise unusual in Bignoniaceae. A phylogeny based on three chloroplast regions (ndhF, trnT-L spacer, trnL-F spacer) identifies a monophyletic Coleeae that is endemic to Madagascar and surrounding islands of the Indian Ocean (Seychelles, Comores and Mascarenes). African Kigelia is not a member of Coleeae, rather it is more closely related to a subset of African and Southeast Asian species of Tecomeae. The molecular phylogeny indicates that indehiscent fruit have arisen repeatedly in Bignoniaceae: in Coleeae, Kigelia and Crescentieae. The characteristic fleshy fruits of species of Coleeae likely arose autochthonously in Madagascar. Within Coleeae Colea and Ophiocolea are sisters, Phyllarthron is sister to Colea + Ophiocolea, and Rhodocolea is sister to the rest of the tribe.     

Diverse non-mycorrhizal fungal endophytes inhabiting an epiphytic,medicinal orchid (<Emphasis Type="Italic">Dendrobium nobile</Emphasis>): estimation and characterization

Although the terrestrial and temperate orchids–fungal biology have been largely explored, knowledge of tropical epiphytic orchids–fungus relationships, especially on the ecological roles imparted by non-mycorrhizal fungal endophytes, is less known. Exploitation of the endophytic fungal mycobiota residing in epiphytic orchid plants may be of great importance to further elucidate the fungal ecology in this special habitat as well as developing new approaches for orchid conversations. The composition of fungal endophytes associated with leaves, stems and roots of an epiphytic orchid (Dendrobium nobile), a famous Chinese traditional medicinal plant, was investigated. Microscopic imaging, culture-dependant method and molecular phylogeny were used to estimate their entity and diversity. Totally, there were 172 isolates, at least 14 fungal genera and 33 different morphospecies recovered from 288 samples. Ascomycetes, coelomycetes and hyphomycetes were three major fungal groups. There were higher overall colonization and isolation rates of endophytic fungi from leaves than from other tissues. Guignardia mangiferae was the dominant fungal species within leaves; while the endophytic Xylariaceae were frequently observed in all plant tissues; Colletotrichum, Phomopsis and Fusarium were also frequently observed. Phylogenetic analysis based on ITS gene revealed the high diversity of Xylariacea fungi and relatively diverse of non-Xylariacea fungi. Some potentially promising beneficial fungi such as Clonostachys rosea and Trichoderma chlorosporum were found in roots. This is the first report concerning above-ground and below-ground endophytic fungi community of an epiphytic medicinal orchid, suggesting the ubiquitous distribution of non-mycorrhizal fungal endophytes in orchid plants together with heterogeneity and tissue specificity of the endophyte assemblage. Possible physiological functions played by these fungal endophytes and their potential applications are also discussed briefly. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A comparative study of endophytic and epiphytic fungal association with leaf of <Emphasis Type="Italic">Eucalyptus citriodora</Emphasis> Hook., and their antimicrobial activity

Eucalyptus citriodora Hook, is frequently cultivated tree in India for its wood and medicinal usages. The endophytic and epiphytic fungi were estimated from healthy leaves of E. citriodora growing in the premise of Banaras Hindu University, Varanasi, India. A total of 33 fungal species were isolated from leaf segments. Of 33 taxa, 20 were recorded as endophytes, while 22 as epiphytes. Nine, out of 33 species were found to be common in leaf tissues and surfaces (Alternaria alternata, Aspergillus fumigatus, A. terreus, Cladosporium cladosporioides, Drechslera rostrata, Humicola grisea, Nigrospora oryzae, Penicillium cristata, and Pestalotia sp.). Out of 478 fungal isolates, 279 were epiphytic while only 199 were endophytic. Most isolates were anamorphic filamentous fungi which often don’t produce sexual spores. The Sorensen’s index of similarity between endophytes and epiphytes (leaf surface colonizers) was found to be at 0.300. Diversity index of fungal species was higher in endophytes than epiphytes. The frequency of colonization differs greatly in both myco-populations. Cladosporium cladosporioides (26%) was dominant species on leaf surfaces while Botrytis cinerea (10.5%) was dominant in leaf tissues. Out of 16 endophytic isolates evaluated for antagonistic test, 8 (50%) gave the antagonistic activity against variety of fungi representing pathogens to both humans and plants.     

Phylogeny,Species Richness,and Ecological Specialization in Cyperaceae Tribe Cariceae

Cyperaceae tribe Cariceae is characterized by both species richness and habitat diversity, making it an ideal system to study ecological specialization and niche differentiation. We present a phylogenetic hypothesis for the tribe based on nuclear and chloroplast DNA sequence comparisons (ETS-1f, ITS, trnL intron, trnL-trnF intergenic spacer) for 140 representative species from five continents, and use this hypothesis to suggest patterns of both niche conservatism and niche differentiation, particularly within the large subgenus Carex. We identify a new major clade, comprising forest species of East Asian Carex section Siderostictae (subgenus Carex) as sister to the rest of tribe Cariceae. Within Carex subgenus Carex, species tolerant of water-saturated habitats occur in only a few, apparently derived groups, with varying species richness. Clades of predominantly wetland species tend to have broad geographic distribution, often with sister species on different continents, suggesting recent dispersal. In contrast, species within several clades are predominantly forest specialists with distinct Asian and North American lineages. Niche segregation along environmental gradients, such as soil moisture or acidity, is quite common among closely related wetland species, but more difficult to demonstrate within upland forest groups. More complete sampling of species within both wetland and forest groups, combined with comparable sampling of environmental preferences and testing against null models, will be needed for more rigorous exploration of the observed patterns.     

A phylogenetic analysis of <Emphasis Type="Italic">Leucothoe</Emphasis> s.l. (Ericaceae; tribe Gaultherieae) based on phenotypic characters

Phylogenetic relationships within the genus Leucothoe s.l. (including all eight species) and related taxa of the Gaultherieae, Andromedeae, and Vaccinieae were investigated by a cladistic analysis based on phenotypic (external morphology, anatomy, chromosome number, and secondary chemistry) characters. The parsimony analysis resulted in two most parsimonious trees, both very similar, which show Leucothoe s.l. to be polyphyletic, with its species distributed among three distinct clades. Our results indicate that L. racemosa and L. recurva form a strongly supported clade, which is sister to Chamaedaphne calyculata, and these three species are probably the sister-group of the wintergreen clade (consisting of Gaultheria and Diplycosia). Leucothoe axillaris, L. fontanesiana, L. davisiae, L. griffithiana, and L. keiskei, consistently form a monophyletic group corresponding to Leucothoe s.s., which is probably sister to the remaining members of the tribe Gaultherieae. Leucothoe grayana, the final species traditionally placed in the genus, belongs to neither of these clades and may be sister to Andromeda. Phenotypic characters provide no support for the monophyly of Leucothoe, instead suggesting that it is polyphyletic, in agreement with preliminary DNA-based analyses. Thus, we redefine the genus Leucothoe, placing its species into three genera: 1) Eubotrys (the E. racemosa + E. recurva clade), 2) Leucothoe s.s. (the L. axillaris + L. fontanesiana + L. davisiae + L. griffithiana + L. keiskei clade), and 3) Eubotryoides (containing only E. grayana).     

Vesicular-arbuscular mycorrhizal fungi,particularly Glomus tenue,in Venezuelan bromeliad epiphytes

The mycorrhizal status of water-impounding tank bromeliad epiphytes from three locales differing in altitude and moisture regime within Venezuelan cloud forest was examined. Species of vesicular-arbuscular mycorrhizal (VAM) fungi found in arboreal soils were compared to VAM fungi found in terrestrial soils. Sixteen of the 19 epiphytes examined for the presence of VAM fungi had roots with infection stages; 14 of these specimens showed growth of the fine endophyte Glomus tenue. Fine endophyte was the only VAM fungus found associated with epiphytes in the driest locale studied, while coarse VAM fungi (Gigaspora and Scutellospora spp.) were found at sampling locales receiving more moisture. Root infection was usually composed of intercellular hyphae and peletons; few arbuscules were observed. However, abundant extracellular hyphae were often observed tangled about roots in arboreal soil. It is concluded that epiphytic bromeliads probably benefit, at least periodically, from VAM fungi scavenging for sporadically available nutrients in arboreal soils. Glomus tenue may be particularly important as a colonizing VAM fungus in drier sites of Venezuelan cloud forest. The species composition of VAM fungi in arboreal soils was different to that of terrestrial soils sampled directly under epiphytic bromeliad perches, suggesting that VAM fungi species associated with bromeliads are dispersed to their hosts by vagile animal vectors.     

Comparative phylogeography of two closely related <Emphasis Type="Italic">Viola</Emphasis> species occurring in contrasting habitats in the Japanese archipelago

Similar distribution ranges shared by closely related plant species may have been shaped through different migration histories if those species have differing habitat preference. To test this hypothesis, phylogeographical patterns and population genetic structures were compared between two sister Viola species: Viola eizanensis preferring woodland and V. chaerophylloides var. sieboldiana preferring grassland, both being native to the Japanese Archipelago. Amplified fragment length polymorphism (AFLP) was used for phylogenetic reconstruction, together with Bayesian ancestry analysis, AMOVA, analysis of genetic diversity statistics, and analysis of the relative contribution of each population to total diversity. The results indicated that V. eizanensis had two distinct lineages occurring in the western and eastern part of Japan, but such lineages are not distinct in V. chaerophylloides var. sieboldiana. Both species exhibited the low genetic diversity and high between-population differentiation typical of selfing plants. In V. chaerophylloides var. sieboldiana, one particular population made a significantly higher contribution to the total heterozygosity (H _T), whereas in V. eizanensis, no population was identified as making a particularly higher contribution to H _T. These findings suggest that V. eizanensis had been isolated in two large glacial refugia, whereas populations of V. chaerophylloides var. sieboldiana were restricted to a single small refuge. Different light requirements between these two closely related species probably caused these differing responses to climatic change during the last ice age. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Temporal dynamics of algal epiphytes on Leathesia marina and Colpomenia sinuosa macrothalli (Phaeophyceae)

This is the first study on the temporal dynamics of the epiphyte communities of Leathesia marina and Colpomenia sinuosa, in terms of richness, diversity and abundance, and their relationships between the hosts and the environmental factors. A total of 31 epiphyte taxa were recorded, with the two hosts sharing 64.5% of the epiphytic species found. The red algal epiphytic group had the highest abundance on both hosts and the diatoms presented the highest species richness. The epiphyte species on L. marina showed a progressive increase in abundance during the warm seasons that was related to the end of the macroscopic life stage of the host. They also showed a greater specific richness on L. marina than on C. sinuosa, but a lower diversity and evenness, and a clear dominance of the species Urospora penicilliformis and Erythrotrichia carnea. Low abundance of epiphytes was found on C. sinuosa, without temporal variation, but high diversity and evenness and without any dominant species. In addition, a clear zonation was observed on this host, where epiphytic abundance decreased on the lateral and upper part of the thallus.     

Molecular phylogeny of genus Vigna subgenus Ceratotropis based on rDNA ITS and atpB-rbcL intergenic spacer of cpDNA sequences

The genetic diversity and phylogenetic relationships among species in the genus Vigna subgenus Ceratotropis were investigated using sequence data from the ribosomal DNA ITS and atpB-rbcL intergenic spacer of chloroplast DNA regions. While both sets of sequences were of similar lengths about 700bp the rDNA-ITS was more informative than atpB-rbcL having 170% more polymorphic sites and five times as many parsimony-informative sites. The atpB-rbcL spacer may be appropriate for analysis of taxa above the species level in the genus Vigna. Results of analyzing rDNA-ITS revealed, with low level of statistical bias, separation of the subgenus into three groups that correspond to the three sections Aconitifoliae, Angulares, and Ceratotropis. The ancestral section is Aconitifoliae based on comparison with the outgroup species cowpea, Vigna unguiculata. The V. minima complex, V. minima, V. riukiuensis, and V. nakashimae, has a distinct evolutionary path within section Angulares. Other species in section Angulares are very closely related except V. trinervia. Vigna trinervia has an intermediate position between sections. Sequence data suggests one genome donor to V. reflexo-pilosa came from a lineage within section Angulares close to V. exilis, V. hirtella, and V. umbellata. Data presented supports the view that section Angulares is the most recently diversified section in the subgenus, as inferred by short terminal branch lengths among the species of this section.     

Phylogeny of Carpinus and subfamily Coryloideae (Betulaceae) based on chloroplast and nuclear ribosomal sequence data

Phylogenetic studies were conducted for Carpinus and the subfamily Coryloideae (Betulaceae) using sequences of the chloroplast matK gene, the trnL-trnF region (trnL intron, and trnL [UAA] 3' exon-trnF [GAA] intergenic spacer) and the psbA-trnH intergenic spacer, and the nuclear ribosomal ITS regions. The combined analyses of the three chloroplast regions suggest that Coryloideae is monophyletic; Ostryopsis is sister to the Carpinus - Ostrya clade; Corylus is monophyletic and sister to the Ostrya - Carpinus - Ostryopsis clade; Ostrya is paraphyletic; and within Carpinus, species of sect. Carpinus from eastern Asia form a monophyletic group, whereas the positions of C. betulus from Europe and C. caroliniana from eastern North America are unresolved within the Carpinus clade. The cpDNA tree generated in this study is largely congruent with the previously published ITS results, but the ITS tree places Carpinus sect. Distegocarpus as sister to the Ostrya - Carpinus sect. Carpinus clade. Future work is needed to examine the relationships within the Ostrya - Carpinus clade, evaluate the generic status of Ostrya, and test the phylogenetic position of Ostryopsis.