The distribution of epiphytic orchids in Nigeria in relation to each other and to geographic location and climate, type of vegetation and tree species

The epiphytic orchids of 31 sites in Eastern, Midwestern, Western and Northern Nigeria are enumerated. The distribution of these 109 species of orchids is related to geographic location and to the environmental factors: climate, vegetation type, most common tree species. Distribution is further discussed in relation to variation within species. An hypothesis of a former more or less continuous orchid population fragmented by climatic shifts toward dryness, by erosion and land level sinkage, and by change of vegetation brought about by man, is advanced. It is suggested that, with such fragmentation, the orchids are now in a phase of rapid speciation and evolutionary development.     

Many broadly-shared mycobionts characterize mycorrhizal interactions of two coexisting epiphytic orchids in a high elevation tropical forest

Interspecific interactions play an important role in community assembly. A basic ecological question is whether interactions are specialized (one to one) or generalized (many to many). Specialization of interactions should ideally be assessed across several populations because species could be specialists at a particular site but generalists when several sites are considered. Mycorrhizal interactions are fundamental for orchid life and distribution, but their level of specialization is still under debate. To understand the extent to which epiphytic orchids are specialists in their mycorrhizal interactions, we studied the richness and phylogenetic structure of mycobionts across different sites, and the similarity in the mycobiont composition between coexisting orchid species. We sequenced the nrDNA ITS2 region and explored the mycobiont communities associated with two epiphytic orchids, Epidendrum marsupiale and Cyrtochilum pardinum, at two elevations within two sites in Ecuador. We found 108 OTUs belonging to Serendipitaceae (66), Ceratobasidiaceae (22), Atractiellales (11) and Tulasnellaceae (9). Orchids at the highest elevations hosted the highest OTU richness. The two orchid species shared a high percentage of mycobionts between all sites. No phylogenetic structure within orchid mycorrhizal communities was found at any sites or elevations. Our results indicate that the studied orchids are generalists and share a broad group of mycobionts (16 OTUs) with no apparent niche segregation within or between sites.     

Diversity,distribution and host-species associations of epiphytic orchids in Nepal

Associations between epiphytes and their hosts are among the main factors affecting the biodiversity and distribution of epiphytes. While several previous studies explored the association between epiphyte diversity and host characteristics, very little is known about the generality of such associations at larger spatial scales. We aim to explore the associations between diversity and distribution of epiphytic orchids and host characteristics in different localities in Nepal. Epiphytic orchids and their hosts were recorded along the transects in total of 23,539 host individuals. To describe the diversity of orchids in the different localities, a rarefaction function was used. Univariate and multivariate analyses were carried out to explore the associations with locality, host characteristics, and their interactions with locality. In total, we recorded 141 species of orchids growing on 192 host species. The five localities significantly differed in orchid diversity and abundance. The number of orchid individuals per host species significantly increased with increasing number of host individuals. Species richness, abundances, occupancy of orchid species on host species and composition of orchids varied across the localities. Species richness and abundance was significantly higher on hosts in the higher strata and differed between families of host species. Abundance was higher on evergreen hosts. Composition of orchid communities are also associated with host characteristics, such as habit (shrub/tree/climber), bark texture, nature (deciduous/evergreen) and the plant families of host species. This study revealed a high diversity of epiphytic orchids in the localities studied and strong associations between the orchids and their hosts. Future studies looking at the relationships between epiphyte communities and host characteristics need to identify relationships at a wider scale in order to determine whether they are really general rather than site-specific.     

西双版纳片段化石灰岩森林附生兰科植物多样性研究

西双版纳石灰岩地区拥有丰富的兰科植物资源,但近年来随着橡胶树的大面积种植,使得该地区很多石灰岩森林呈片段化。为了解片段化石灰岩森林中附生兰科植物多样性状况以及片段化对附生兰科植物的影响,该研究选取了生境片段化的青岩寨和曼纳览,以及连续生境的绿石林和巴卡新寨等4个样地的29个样方进行多样性调查和对比研究。结果表明:4个石灰岩森林样共记录到附生兰科植物34属76种1 528株(丛)。通过对坡向、坡度、海拔、地形、郁闭度和森林类型等6个环境因子与附生兰科植物丰富度进行CCA分析,发现石灰岩地区附生兰科植物的分布主要受海拔和森林类型2个因素的影响,在海拔较高的青岩寨和巴卡新寨附生兰科植物物种丰富度高于低海拔的绿石林和曼纳览,而片段化对附生兰科植物的物种多样性和多度均无显著影响,这可能与片段化的历史较短有关。虽然目前来看生境片段化对石灰岩地区的附生兰科植物多样性无显著影响,但生境脆弱的石灰岩森林植被的保护对于兰科植物多样性保护则更具重要性。     

Population dynamics of epiphytic orchids in a metapopulation context

Background and Aims

Populations of many epiphytes show a patchy distribution where clusters of plants growing on individual trees are spatially separated and may thus function as metapopulations. Seed dispersal is necessary to (re)colonize unoccupied habitats, and to transfer seeds from high- to low-competition patches. Increasing dispersal distances, however, reduces local fecundity and the probability that seeds will find a safe site outside the original patch. Thus, there is a conflict between seed survival and colonization.

Methods

Populations of three epiphytic orchids were monitored over three years in a Mexican humid montane forest and analysed with spatially averaged and with spatially explicit matrix metapopulation models. In the latter, population dynamics at the scale of the subpopulations (epiphytes on individual host trees) are based on detailed stage-structured observations of transition probabilities and trees are connected by a dispersal function.

Key Results

Population growth rates differed among trees and years. While ignoring these differences, and averaging the population matrices over trees, yields negative population growth, metapopulation models predict stable or growing populations because the trees that support growing subpopulations determine the growth of the metapopulation. Stochastic models which account for the differences among years differed only marginally from deterministic models. Population growth rates were significantly lower, and extinctions of local patches more frequent in models where higher dispersal results in reduced local fecundity compared with hypothetical models where this is not the case. The difference between the two models increased with increasing mean dispersal distance. Though recolonization events increased with dispersal distance, this could not compensate the losses due to reduced local fecundity.

Conclusions

For epiphytes, metapopulation models are useful to capture processes beyond the level of the single host tree, but local processes are equally important to understand epiphyte population dynamics.     

Bacteria associated with the roots of epiphytic orchids

This work is the first to report the isolation and identification of bacteria colonizing the roots of the tropical epiphytic orchids Acampe papillosa (Lindl.) Lindl. and Dendrobium moschatum (Buch.-Ham.) Swartz. and bacteria inhabiting inner layers of the aerial and substrate roots of A. papillosa. We showed by the example of this epiphyte that associative bacteria are present in large amounts on the aerial but not the substrate roots. We isolated and identified bacteria from the substrate roots of D. Moschatum and from its growth substrate (pine bark). The structure of the intercellular matrix of the associative bacteria was studied.Translated from Mikrobiologiya, Vol. 73, No. 6, 2004, pp. 825–831.Original Russian Text Copyright © 2004 by Tsavkelova, Cherdyntseva, Netrusov.     

Bacteria associated with the roots of epiphytic orchids

This work is the first to report the isolation and identification of bacteria colonizing the roots of tropical epiphytic orchids Acampe papillosa (Lindl.) Lindl. and Dendrobium moschatum (Buch.-Ham.) Swartz. and bacteria inhabiting inner layers of the aerial and substrate roots of A. papillosa. We showed by the example of this epiphyte that associative bacteria are present in large amounts on the aerial but not substrate roots. We isolated and identified bacteria from the substrate roots of D. moschatum and from its growth substrate (pine bark). The structure of the intercellular matrix of the associative bacteria was studied.     

Pollination ecology of four epiphytic orchids of New Zealand

BACKGROUND AND AIMS: In New Zealand epiphytic orchids are represented by four genera and eight species. The genera Earina (three species) and Winika (one species) are the most conspicuous and widespread. These are likely to be some of the southernmost distributed genera of epiphytic orchids in the world. METHODS: To identify the pollination strategies that have evolved in these orchids, hand-pollination treatments were done and floral visitors were observed in several wild populations at two areas of southern North Island (approx. 40 degrees S). Pollen:ovule ratio and osmophores were also studied and the total carbohydrate content of the nectar produced by each species was measured. KEY RESULTS: Earina autumnalis and Earina mucronata are self-compatible, whereas Earina aestivalis and Winika cunninghamii appear to be partially self-incompatible. All four orchids are incapable of autonomous selfing and therefore completely dependent on pollinators to set fruits. Floral visitors observed in the genus Earina belong to Diptera, Coleoptera and Hymenoptera and to Diptera and Hymenoptera in W. cunninghamii. CONCLUSIONS: Contrary to many epiphytic orchids in the tropics, the orchid-pollinator relationship in these orchids is unspecialized and flowers are visited by a wide range of insects. Putative pollinators are flies of the families Bibionidae, Calliphoridae, Syrphidae and Tachinidae. All four orchids display anthecological adaptations to a myophilous pollination system such as simple flowers, well-exposed reproductive structures, easily accessed nectar and high pollen : ovule ratios.     

Associative cyanobacteria isolated from the roots of epiphytic orchids

Associative cyanobacteria were isolated from the rhizoplane and velamen of the aerial roots of the epiphytic orchids Acampe papillosa, Phalaenopsis amabilis, and Dendrobium moschatum and from the substrate roots of Acampe papillosa and Dendrobium moschatum. Cyanobacteria were isolated on complete and nitrogen-free variants of BG-11 medium. On all media and in all samples, cyanobacteria of the genus Nostoc predominated. Nostoc, Anabaena, and Calothrix were isolated from the surface of the A. papillosa aerial roots, whereas the isolates from the substrate roots were Nostoc, Oscillatoria, and representatives of the LPP-group (Lyngbia, Phormidium, and Plectonema, incapable of nitrogen fixation). On the D. moschatum substrate roots, Nostoc and LPP-group representatives were also found, as well as Fischerella. On the aerial roots of P. amabilis and D. phalaenopsis grown in a greenhouse simulating the climate of moist tropical forest, cyanobacteria were represented by Nostoc, LPP-group, and Scytonema in the D. phalaenopsis and by Nostoc, Scytonema, Calothrix, Spirulina, Oscillatoria, and the LPP-group in P. amabilis. For D. moschatum, the spectra of cyanobacteria populating the substrate root zhizophane and the substrate (pine bark) were compared. In the parenchyma of the aerial roots of P. amabilis, fungal hyphae and/or their half-degraded remains were detected, which testifies to the presence of mycorrhizal fungi this plant. This phenomenon is attributed to the presence of a sheath formed by cyanobacteria and serving as a substrate for fungi.     

Localization of associative cyanobacteria on the roots of epiphytic orchids

This work is the first study of the localization of phototrophic microorganisms in the rhizoplane and velamen of epiphytic orchids, namely on the aerial and substrate roots of Acampe papillosa and Dendrobium moschatum and on the aerial roots of the Phalaenopsis amabilis and Dendrobium phalaenopsis. The composition of the bacterial community on the plant roots depended on the conditions of plant growth. Under conditions simulating climate of moist tropical forests, the aerial roots proved to be populated with phototrophic microorganisms among which cyanobacteria predominated. Interlaced fungal hyphae and filamentous cyanobacteria formed a sheath on the surface of aerial roots. The nitrogen-fixing capacity of the sheath of aerial roots was studied by the example of P. amabilis.     

The photosynthetic pathway of the roots of twelve epiphytic orchids with CAM leaves

The photosynthetic pathway of the roots (both the white velamentous main portions and the green, nonvelamentous tips) was investigated in twelve taxa (natural species and intergeneric hybrid cultivars) of epiphytic orchids having CAM leaves. All organs contained chlorophyll, and the a/b ratios indicate that the organs, especially the roots, are likely shade-adapted. Stable carbon isotope ratios of the tissues were near −15‰ for all organs, a value typical of obligate (constitutive) CAM plants. Values for root tissues were slightly lower (more negative) than those of the leaves. The presence of CAM in the leaves of these orchids did not ensure that their roots performed CAM photosynthesis. Further work is needed to address the questions raised in this study and to determine if the photosynthetic roots of these taxa are capable of assimilating atmospheric CO₂.     

西双版纳5种附生兰非菌根内生真菌多样性研究

从西双版纳纳板河流域国家级自然保护区的盆距兰Gastrochilus、隔距兰Cleisostoma、毛兰Eria、贝母兰Coelogyne和万代兰Vanda的根、茎、叶分离得到172株非菌根内生真菌,根据ITS1-5.8S-ITS2 rDNA系统发育分析鉴定为盘菌亚门的4纲11目29属,其中炭角菌目、肉座菌目和格孢腔菌目真菌的相对频率最高;Xylaria、Fusarium和Phoma为主要优势属,相对频率分别为23.3%、14.5%和10.5%,它们的组织专化性不同,其中Xylaria在根、茎和叶均有分布,而Fusarium和Phoma都分离自根部。不同组织的内生真菌多样性和种类组成差异明显,根、茎和叶的内生真菌Shannon多样性指数分别为2.4083、1.0312和0.6557,表明根部内生真菌多样性显著高于茎、叶内生真菌多样性,其中根的主要优势内生真菌类群有Fusarium、Xylaria和Phoma,茎的主要优势内生真菌类群有Xylaria、Pestalotiopsis和Colletotrichum,叶的主要优势内生真菌类群有Colletotrichum、Pallidocercospora、Pantospora和Phyllosticta。从附生兰种类来看,盆距兰、隔距兰、毛兰、贝母兰和万代兰内生真菌的Shannon多样性指数分别为2.2689、2.2635、2.0115、1.9197、1.7139,表明盆距兰和隔距兰内生真菌多样性高于毛兰、贝母兰和万代兰。     

Host tree utilization by epiphytic orchids in different land-use intensities in Kathmandu Valley, Nepal

We studied the influence of site conditions on epiphytic orchids under a subtropical climate in the Kathmandu Valley, Nepal. We analysed 96 systematically distributed grid points situated in Kathmandu Valley across a land-use intensity gradient (national park to urbanised city area). Geographical Information System (GIS) and remote sensing were used for classification of land-use types. We identified 23 species of epiphytic orchids, within 13 genera, from 42 different host tree species. Host preference is obvious for some orchid species (e.g., Dendrobium nobile), with certain tree species (e.g., Schima wallichii, Ficus religiosa) hosting more orchid species than others. The orchid Rhynchostylis retusa was the most common species found on many different host tree species across the land-use intensity gradient. Host species and host bark characteristics (e.g., rugosity, pH and exposure to wind) played a vital role for orchid distribution, with lower abundance in areas of higher impact. Under strong human impact (urban city area), F. religiosa was the dominant host tree, with large individual trees (mean diameter in breast height, dbh?=?1.3?m) providing the habitat for considerable populations of R. retusa individuals. In general, epiphytic orchids were found on larger host trees in urban areas than in areas of lower human impact. We found that some hosts are more likely to harbour orchid species, especially native host species. Older larger trees with rougher bark, low pH, exposed to wind and reduced human impact provided better habitats for orchids. We suggest these characteristics should be considered in urban planning to reduce human impact on the associated orchid epiphytic community.     

The use of epiphytic algae to indicate environmental changes

The distribution of an epiphytic alga, shown in earlier studies to be an indicator species, has changed after modification of environmental conditions.     

附生兰科植物根被组织研究概述

植物根被组织是指存在于附生兰科植物、地生兰科植物、一些石蒜科、天南星科、薯蓣科以及百合科植物根部的典型适应性结构特征;成熟根被组织是由1～25层左右死细胞构成的白色鞘,其细胞壁多有螺旋式增厚,呈天鹅绒状或网状、羽毛状结构,具有海绵质地.该组织有六种应用于分类学特征的形态,依据这六种形态可将其分为12种类型;根被组织具有...     

Gas exchange of terrestrial and epiphytic orchids from Brazilian Atlantic Rainforest

Leaf gas exchange of terrestrial and epiphytic orchids from the Atlantic Rainforest in northeast Brazil was investigated under artificial growth conditions. The terrestrial orchids showed higher values of all photosynthetic parameters in comparison to epiphytic ones. There was a close relationship between P _N and g _s for both terrestrial and epiphytic orchids. Taken together, our results demonstrated that the photosynthetic parameters were related to the specific growth habits of the orchids under study.     

Germination niches and seed persistence of tropical epiphytic orchids in an urban landscape

Journal of Plant Research - Urbanisation has contributed to significant biodiversity loss, yet, urban areas can facilitate biodiversity conservation. For instance, there is evidence of urban trees...     

The use of RAPD to characterize Bipolaris sorokiniana isolates

Bipolaris sorokiniana is a phytopathogenic fungus causing diseases of cereal crops such as common root rot, the leaf spot disease, seedling blight, and black point of the grain. Random-amplified polymorphic DNA (RAPD) assay was used to investigate the genetic diversity of 20 isolates collected from different cultivars in wheat-producing regions in Brazil. Seventy primers, with random nucleotide sequences, were tested. Reproducibility to amplify the genomic DNA of isolates was found for 30 of the 70 primers tested, generating between 1 and 17 fragments ranging from 0.35 to 2.0 kb (average size). The degree of similarity between samples was calculated through simple association and the dendrogram was assessed using the unweighted pair group method with arithmetical average. After the RAPD analyses 19 isolates were closely grouped, having a similarity coefficient of >or= 78%. Isolate I017 showed very low similarity coefficients, ranging between 38 and 46%. The RAPD analyses provided important information as to the degree of genetic variability and the relationship between the isolates investigated, revealing polymorphism and establishing electrophoretic profiles useful to characterize the phytopathogen.