Vascular Plants Facilitated Bryophytes in a Grassland Experiment

In grassland communities vascular plants and bryophytes form two distinct layers. In order to understand the factors responsible for plant community structure, more information about interactions between these plant groups is needed. Often negative correlations between vascular plant and bryophyte covers have been reported, suggesting competition. Here we tested experimentally whether different grassland vascular plant species (Trifolium pratense, Festuca pratensis, Prunella vulgaris) had different influences on the cover of two bryophyte species (Rhytidiadelphus squarrosus, Brachythecium rutabulum). In a two-year garden pot experiment one bryophyte species and one vascular plant species were planted per pot. Bryophytes were planted at a constant density, vascular plants in four densities. The cover of both bryophyte species increased with increasing vascular plant cover, showing the facilitative effect of vascular plants through creating better microclimate, e.g., optimising temperature. Bryophyte responses to vascular plant species were species-specific. Festuca had significantly positive effects on both bryophyte species in the second year, and Trifolium on Brachythecium in both years, whereas Prunella had no significant effect on bryophytes. The facilitative effect of vascular plants was stronger at the second experimental year. In summary, the biotic effects between bryophytes and grassland vascular plants are species-specific and positive interactions are prevailing at low vascular plant densities.     

金川泥炭地两个尺度下苔藓植物间及其与维管植物间的种间关系分析

在金川泥炭地设置1m×1m和25 cm ×25 cm两个尺度的大、小样方进行植被调查,并利用方差比率法、x2检验、Pearson相关分析和Spearman秩相关分析方法,定量分析了9种苔藓植物和30种主要维管植物间的种间关系.偏叶泥炭藓、大泥炭藓和尖叶泥炭藓3种优势苔藓植物彼此呈显著负关联,占领着各自不同的生境;该3种优势苔藓植物同伴生苔藓及维管植物主要呈正相关,形成独特的群落,据此划分出4个生态种组.Spearman秩相关分析表明,大样方741个种对中,正联结种对数占49.53％,明显大于小样方666个种对中的41.14％.样方大小对分析植物个体大小差异悬殊的泥炭地植物群落的种间联结的影响巨大.苔藓与维管植物间以及苔藓植物间的种间联结甚至种间关系应在大、小样方中分别探讨更合适.     

Litter Decomposition Rates of Biocrust-Forming Lichens Are Similar to Those of Vascular Plants and Are Affected by Warming

Ecosystems - Despite the high relevance of communities dominated by lichens, mosses and cyanobacteria living on the soil surface (biocrusts) for ecosystem functioning in drylands, no study to date...     

Occurrence of Gibberellins in Vascular Plants, Fungi, and Bacteria

The occurrence of GA1 to GA126 in vascular plants, fungi, and bacteria is listed. The data are discussed with reference to criteria for identification and to the frequency of occurrence of GAs in vascular plants.     

Vegetation and flora associated with localized snow accumulation at Mount Field West,Tasmania

The vegetation associated with a snow patch at Mt Field in Tasmania is described and mapped. Seven distinct vegetation types were found to be related directly to topography and hence to the patterns of snow accumulation, snow melt and soil drainage. The fjaeldmark found where snow lies longest is unusual for Tasmania and may be the product of past climatic events and a peculiar parent material. At the generic level there exists a high similarity with the snow patch flora of the Australian Alps.     

Bryophytes and heavy metals: a literature review

The literature on heavy metals in bryophytes is reviewed, including mechanisms of metal uptake, retention, toxicity and tolerance. Interspecies differences in particular are discussed, including the development of extreme tolerance encountered in certain taxa. The use of bryophytes in monitoring heavy metal deposition is considered and comparisons are made with direct deposition measurements.     

C4 Plants in the Vegetation of Tibet,China: Their Natural Occurrence and Altitude Distribution Pattern

Floristic composition, life forms for C₄ species, and the pattern of altitude distribution were studied on Tibetan Plateau. 79 species, in 7 families and 46 genera, were identified with C₄ photosynthesis. 95 % of these C₄ species belong to Gramineae (51 species), Cyperaceae (14 species), and Chenopodiaceae (10 species), indicating that C₄ plants mainly occur in very few families (7 of 204) on the Tibetan Plateau. High altitude distribution for all the Chenopodiaceae C₄ species (> 3 000 m above sea level) suggests that plants of this kind have large tolerance to cold, dryness, and strong ultraviolet radiation. Most Gramineae and Cyperaceae C₄ species occurrences are consistent with extensive distribution of steppes and meadows in the vast flat of the central Plateau (1 000–3 000 m a.s.l.). Relatively high amount of hemicryptophyte form plants (44 %) in the region indicates that the vegetation, especially grassland, meadows, and steppe, are in good condition. There is a strong relationship between numbers of C₄ species and altitude in the Tibetan Plateau. Occurrence of C₄ species is significantly less in both high and low altitude plateaux in Tibet. Altitude distribution pattern for C₄ species in the region is not only consistent with the altitude and climate, but also with the vegetation types in altitude gradient.     

Bioassays and Field Studies for Allelopathy in Terrestrial Plants: Progress and Problems

Bioassays are an integral part of allelopathy research. The unsuitability of laboratory bioassays to explain field situations is discussed previously. In this article, we discuss progress in bioassay experimental design and several unresolved problems associated with research on allelopathy. The objectives of this article are to discuss problems related to (1) collection of allelopathic material for bioassay, (2) allelochemical quantification in bioassays, (3) selection of concentration of allelochemicals in bioassay, (4) selection of appropriate control, (5) interaction between allelochemicals and other substances, and (6) in situ allelochemical bioassays. We concluded that new experimental designs for in situ bioassay are needed that can account for the large number of confounding factors in a complex field environment, and can be linked to physiological monitoring of target species and biochemical monitoring of the growth medium. Referee: Dr. Stella Elakovich, Dept. of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 390406-5043     

Circular Vessels and the Control of Vascular Differentiation in Plants

The occurrence of vessels in the form of rings is used as a critical example for a hypothesis about the control of the pattern of cells in vascular tissues. These vessels, rare in intact plants, are common in the basal or root side of tissues close to transverse wounds of bean seedlings, radish storage tissues, and other plant material. Their formation is promoted, as are normal vascular tissues, by developing parts of the shoot or by a source of the hormone auxin. They are also found in grafts where cells of opposite polarities are close together, and in cut plants where vascular induction occurs from the direction of the roots and is therefore opposite to the original polarity of the tissue. Circular vessels are found, therefore, where the flux of auxin and possibly other signals controlling vascular differentiation is expected to follow a circular route. They show that differentiation is a response of individual cells to the flux rather than the gradient or concentration of the hormonal signals and suggest a hormonal interpretation of differences between apical and basal callus growth.     

Technic in the Study of Vascular Systems in Plants

Methods have been improvised for studying the morphology of rosaceous fruits. One method is to dissect the buds and to immerse over night in 20% HCl; then in 5% NaOCl until bleached; after dehydrating, clearing and mounting in cedar oil, they are examined in dark field or with intense reflected light. Another method is to place the living stems, bearing buds, in a 0.01% aqueous solution of Niagara sky blue, forcing infiltration of the dye by means of pressure obtained in an ordinary pressure cooker thru the use of a bicycle pump; the buds are then dehydrated and embedded by ordinary methods. A series of photographs, if desired, may be taken of the cut surfaces of such a stained bud, after each section has been removed from the block.     

Technic in the Study of Vascular Systems in Plants

Methods have been improvised for studying the morphology of rosaceous fruits. One method is to dissect the buds and to immerse over night in 20% HCl; then in 5% NaOCl until bleached; after dehydrating, clearing and mounting in cedar oil, they are examined in dark field or with intense reflected light. Another method is to place the living stems, bearing buds, in a 0.01% aqueous solution of Niagara sky blue, forcing infiltration of the dye by means of pressure obtained in an ordinary pressure cooker thru the use of a bicycle pump; the buds are then dehydrated and embedded by ordinary methods. A series of photographs, if desired, may be taken of the cut surfaces of such a stained bud, after each section has been removed from the block.     

Vegetation of a snow bed at Godhavn, West Greenland

The vegetation of a snow bed has been described by a pin-point method and a modified Raunkiær frequency analysis. The thawing of the snow has been followed and some soil properties have been investigated. It is concluded that the composition of the vegetation in the snow bed is influenced mainly by the duration of the growth period, but locally the density and the species composition are determined by the downward flow of the melt water.     

长江三角洲地区水生维管植物的多样性

根据野外调查及相关资料,分析了长江三角洲地区水生植物区系的种类组成、地理成分以及濒危现状.该区现有水生维管植物39科90属185种,其生活型以挺水植物为主(占64.32％),主要分布于田边沟渠、农田以及池塘等不同水体.属、种等级的地理成分分析结果表明:其区系性质主要为温带性质.根据水生植物的濒危现状,参照世界自然保护联盟(IUCN)红色名录的等级和标准(3.1版本),将该区的植物分为9大类,其中地区性灭绝1种,极危种3种,濒危种8种,易危种10种,并简要讨论了该区水生植物受威胁的主要原因.     

香港长洲岛野生植物物种多样性与植被的研究

长洲岛共有野生维管植物237种,隶属于73科184属.植被类型以次生常绿阔叶林为主,其次为灌丛群落.植物区系以热带亚热带植物地理成分占优势,热带性质明显.该岛的植物区系与邻近岛屿植物区系具有极大的相似性,在香港植物区系组成中占有一定地位.由于人为活动和外来植物的影响,其植物多样性及植被的保护应引起注意.     

Lichens: a promising source of antibiotic and anticancer drugs

Lichens are symbiotic associations between fungi and a photosynthetic alga and/or cyanobacteria. Lichenized fungi have been found to produce a wide array of secondary metabolites, most of which are unique to the lichenized condition. These secondary metabolites have shown an impressive range of biological activities including antibiotics, antifungal, anti-HIV, anticancer, anti-protozoan, etc. This review focuses primarily on the antibiotic and anticancer properties of lichen secondary chemicals. We have reviewed various publications related to antibiotic and anticancer drug therapies emphasizing results about specific lichens and/or lichen compounds, which microbes or cancer cells were involved and the main findings of each study. We found that crude lichen extracts and various isolated lichen compounds often demonstrate significant inhibitory activity against various pathogenic bacteria and cancer cell lines at very low concentrations. There were no studies examining the specific mechanism of action against pathogenic bacteria; however, we did find a limited number of studies where the mechanism of action against cancer cell lines had been explored. The molecular mechanism of cell death by lichen compounds includes cell cycle arrest, apoptosis, necrosis, and inhibition of angiogenesis. Although lichens are a reservoir for various biologically active compounds, only a limited number have been tested for their biological significance. There is clearly an urgent need for expanding research in this area of study, including in depth studies of those compounds which have shown promising results as well as a strong focus on identifying specific mechanisms of action and extensive clinical trials using the most promising lichen based drug therapies followed by large scale production of the best of those compounds.