Germination, survival and growth of three vascular plants on biological soil crusts from a Mexican tropical desert

Information about the effects of biological soil crusts (BSC) on germination, seedling survival and growth of vascular plants is controversial because they can have positive, neutral or negative effects. This controversy may be because most studies conducted until now have just analysed one or two recruitment stages independently. To understand the BSC effects on vascular plants, it is necessary to consider each stage of the recruitment process and synthesise all this information. The goal of this study was twofold. First, we analyse germination, seedling survival and growth of three vascular plants (Agave marmorata, Prosopis laevigata and Neobuxbaumia tetetzo) on BSC (cyanobacteria and mixed crust) from a tropical desert region of south-central México. Second, we synthesise the information to determine the total effect of BSC on plant species performance. We conducted experiments under controlled conditions to evaluate the proportion of germinated seeds, proportion of surviving seedlings and seedling dry weight in BSC and bare soil. Results showed that BSC have different effects on germination, seedling survival and growth of plant species. Plant species performance was qualitatively higher on BSC than bare soil. The highest performance of A. marmorata and P. laevigata was observed on cyanobacteria and mixed crusts, respectively. The highest performance of N. tetetzo was on both crust types.     

Characterization of yeast groupings in the phyllosphere of <Emphasis Type="Italic">Sphagnum</Emphasis> mosses

Significant differences were revealed in the taxonomic structure of the epiphytic yeast communities formed on Sphagnum mosses and on the leaves of vascular plants. On mosses, low abundance of red yeasts was found (the most typical epiphytes on vascular plant leaves), along with a relatively high content and diversity of nonpigmented dimorphic basidiomycetes related to the order Leucosporidiales. The species composition of epiphytic yeasts from mosses is different from that of both forest and meadow grasses and of the parts of vascular plants submerged in the turf. The specific composition of the Sphagnum mosses yeast community is probably determined by the biochemical characteristics of this environment, rather than by the hydrothermal regime in the turf.     

一号冰川地区四种藓类植物的解剖学研究

运用石蜡切片技术和扫描电镜方法,对一号冰川地区生长的4种藓类植物茎、叶的内部结构及叶表皮角质层褶皱、疣和中肋等进行观察,结果表明：红扭口藓(Barbula asperifolia Mitt.)茎横切面呈多棱形;叶背、腹面角质层厚,粗疣不分叉,但顶端朝细胞凹陷处倾斜;叶背面细胞壁凹陷深,象张开的气孔,粗疣也藏在其中,中肋突出明显。丛叶扭藓(Tortella humilis (Hedw.) Jenn.)茎横切面呈椭圆形;叶背、腹面中上部均密被鹿角状粗疣,这些分叉的粗疣,从凹陷的细胞壁处成束突起,顶端向下弯曲成钩状,在叶的下部疣状突起则逐渐减少至无,中肋较宽。异叶提灯藓(Mnium heterophyllum (Hook.)Schwagr.)茎横切面呈五棱形;叶细胞一层,呈不规则多边形,细胞壁凹陷使叶片呈网状;中肋红色。大灰藓(Hypnum plumaeforme Wils.)茎的横切面呈圆形;叶背、腹面均密被疣状突起,且差异不大,粗疣顶部均倒向孔口呈遮盖状;中肋短而弱。     

Influence of environmental conditions, bacterial activity and viability on the viral component in 10 Antarctic lakes

The influence of biotic and environmental variables on the abundance of virus-like particles (VLP) and lysogeny was investigated by examining 10 Antarctic lakes in the Vestfold Hills, Antarctica, in the Austral Spring. Abundances of viruses and bacteria and bacterial metabolic activity were estimated using SYBR Gold (Molecular Probes), Baclight (Molecular Probes) and 6-carboxy fluorescein diacetate (6CFDA). Total bacterial abundances among the lakes ranged between 0.12 and 0.47 x 10(9) cells L(-1). The proportion of intact bacteria (SYTO 9-stained cells) ranged from 13.5% to 83.5% of the total while active (6CFDA-stained) bacteria ranged from 33% to 116%. Lysogeny, as determined with Mitomycin C, was only detected in one of the lakes surveyed, indicating that viral replication was occurring predominantly via the lytic cycle. Principal component analysis and confirmatory correlation analysis of individual variables showed that high abundances of VLP occurred in lakes of high conductivity with high concentrations of soluble reactive phosphorus and dissolved organic carbon. These lakes supported high concentrations of chlorophyll a, intact bacteria, rates of bacterial production and virus to bacteria ratios. Thus, it was suggested that viral abundance in the Antarctic lakes was determined by the trophic status of the lake and the resultant abundance of intact bacterial hosts.     

Novel clades of chromodomain-containing Gypsy LTR retrotransposons from mosses (Bryophyta)

Retrotransposons are the major component of plant genomes. Chromodomain-containing Gypsy long terminal repeat (LTR) retrotransposons are widely distributed in eukaryotes. Four distinct clades of chromodomain-containing Gypsy retroelements are known from the vascular plants: Reina, CRM, Galadriel and Tekay. At the same time, almost nothing is known about the repertoire of LTR retrotransposons in bryophyte genomes. We have combined a search of chromodomain-containing Gypsy retroelements in Physcomitrella genomic sequences and an experimental investigation of diverse moss species. The computer-based mining of the chromodomain-containing LTR retrotransposons allowed us to describe four different elements from Physcomitrella. Four novel clades were identified that are evolutionarily distinct from the chromodomain-containing Gypsy LTR retrotransposons of other plants.     

Epiphytic ferns and bryophytes of Tasmanian tree‐ferns: A comparison of diversity and composition between two host species

Abstract Ferns, bryophytes and lichens are the most diverse groups of plants in wet forests in south‐eastern Australia. However, management of this diversity is limited by a lack of ecological knowledge of these groups and the difficulty in identifying species for non‐experts. These problems may be alleviated by the identification and characterization of suitable proxies for this diversity. Epiphytic substrates are potential proxies. To evaluate the significance of some epiphytic substrates, fern and bryophyte assemblages on a common tree‐fern species, Dicksonia antarctica (soft tree‐fern), were compared with those on a rare species, Cyathea cunninghamii (slender tree‐fern), in eastern Tasmania, Australia. A total of 97 fern and bryophyte species were recorded on D. antarctica from 120 trunks at 10 sites, and 64 species on C. cunninghamii from 39 trunks at four of these sites. The trunks of C. cunninghamii generally supported fewer species than D. antarctica, but two mosses (particularly Hymenodon pilifer) and one liverwort showed significant associations with this host. Several other bryophytes and epiphytic ferns showed an affinity for the trunks of D. antarctica. Species assemblages differed significantly between both sites and hosts, and the differences between hosts varied significantly among sites. The exceptionally high epiphytic diversity associated with D. antarctica suggests that it plays an important ecological role in Tasmanian forests. Evidently C. cunninghamii also supports a diverse suite of epiphytes, including at least one specialist species.     

Phytogeography of Hong Kong bryophytes

Aim Hong Kong is in a biogeographically interesting location on the northern margins of the Asian tropics. This paper analyzes the phytogeography of Hong Kong's bryophyte flora for the first time. Location Hong Kong lies on the South China coast, 22°9′–22°37′ N, 113°52′–114°30′ E. It is one of the most densely populated places in the world, but because of the rugged topography only 20% of the total land area of 1100 km² is urbanized. Although 130 km south of the Tropic of Cancer, it has a subtropical climate with distinct hot, humid and cool, dry seasons. Methods The analysis is based on a new and relatively complete inventory of Hong Kong's bryoflora. Each taxon was assigned to a phytogeographical pattern on the basis of its present worldwide distribution. Krober's percentage similarity was employed to evaluate the floristic affinities between different regions. Results The bryophyte flora consists of at least 360 species and twelve infraspecific taxa in 159 genera and seventy families, of which four taxa are locally endemic. The largest families are Lejeuneaceae (fifty‐one taxa), Fissidentaceae (28), Hypnaceae (21), Dicranaceae (20), Calymperaceae (18), and Sematophyllaceae (15). The largest genera are Fissidens (28), Cololejeunea (17), Lejeunea (10), Syrrhopodon (9), Frullania (8), and Macromitrium (8). Fourteen phytogeographical patterns are recognized. The East Asian pattern is the commonest (seventy‐three taxa, 19.6%), followed by Asian–Australian–Oceanian (45, 12.1%) and Temperate (44, 11.8%). Overall, a third of taxa have tropical distributions. The bryofloras of eleven regions were compared with that of Hong Kong. The most similar regions are Hainan Province, Taiwan Province, and Japan. Mosses and liverworts show very similar phytogeographical distributions. Main conclusions (1) The Hong Kong bryoflora is best described as northern marginal tropical, with a strong Eastern Asian and Temperate influence; (2) the region of closest phytogeographical affinity for which information is available is Hainan; (3) in comparison with vascular plants, vertebrates and those invertebrate groups for which there is information, the bryoflora has a relatively low proportion of tropical taxa; (4) the bryoflora of Hong Kong appears to be exceptionally rich for its small area.     

The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer

SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000.
2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell⁻¹ day⁻¹ in Lake Fryxell and 0.36–11.76 bacteria cell⁻¹ day⁻¹ in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell⁻¹ h⁻¹ in Lake Fryxell and 0.074 to 1.08 pg C cell⁻¹ h⁻¹ in Lake Hoare.
3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12–21% of the community carbon budget in November and 1–28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration.
4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth.     

长白山地表藓类分布格局与环境因子的关系

对长白山自然保护区41个样地中的42种主要地表藓类分布与6种重要环境因子间的关系进行了定量研究。应用双向指标种分析法（TWINSPAN）发现调查的41个样地可分成4个样地组,42种地面藓 类可分成4种藓类群,应用除趋势典范对应分析（DCCA）的研究结果表明,海拨高度、土壤含砂量、土壤酸度、林冠层郁闭度、土壤含水量是5个影响42种地表藓类分布格局的主要环境因子,在DCCA排序图上,显示出藓类群与样地类型良好的对应性,藓类群1－4分别在落叶松（Larix olgensis）沼泽地、高山苔原、暗针叶林、亚高山岳松（Betula ernanni）林和岳松－落叶松林中占优势。     

Molecular variation and speciation in Antitrichia curtipendula s.l. (Leucodontaceae, Bryophyta)

Molecular variation in Antitrichia curtipendula (Hedw.) Brid. s.l. was studied based on the nuclear internal transcribed spacer (ITS) and the chloroplast markers trn L- trn F and rpl 16, and analysed by neighbour joining (for ITS; recombination present), maximum parsimony (chloroplast markers) and TCS (haplotype network). Old World plus E North American populations belong to a different lineage than those of W North America. These are molecularly well differentiated and are treated as A. curtipendula and A. gigantea (Sull. & Lesq.) Kindb. Two distinct groups of Old World haplotypes are separated by one 'missing' haplotype and are interpreted as cryptic species. Tropical African populations share one ITS deletion and form a lineage within one of the cryptic species. Molecular variation within A. gigantea , within each of the two cryptic Old World plus E North American (except tropical African) haplotype groups, and among tropical African populations are of similar magnitude, suggesting that analogous mechanisms and similar time spans explain the found variation. Events related to Pleistocene climatic oscillations are suggested as having caused this differentiation within each group, whereas the African lineage was probably split off before this. Identical tRNA-Gly sequences were found in 33 specimens; new primers were designed for rpl 16 and ITS 1+2.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 341–354.