2,271 research outputs found
An ecophysiological study on the moss hydrogoniuh fontanum from the Asir mountains, Saudi Arabia
No full textThe thesis describes a study on the ecophysiology of the moss Hydrogonium fontanum (C. Mail.) Jaeg., the dominant plant at a waterfall in Saudi Arabia. The influence of environmental variables and water stress on the growth, stress metabolite accumulation and phosphatase activities of the moss was studied in laboratory axenic culture along with observations and experiments conducted in the field. The variables chosen for growth experiments were light flux, flooding, nutrient concentrations and water stress. For phosphatase activities, the influence of temperature, pH, ions, water stress were studied. Differences were found in phosphatase activities for rhlzoids, protonema and leafy shoots of the moss and, therefore, the phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities of these fractions were also investigated. H. fontanum was originally collected from the tufa-depositing waterfall (Water chemistry - 44 mg 1(^-1) Na, 44 mg 1(^-1) Ca). High Na and Ca had significant positive effect on yield of the protonema under the laboratory conditions. Low light intensity (10 µmol photon m(^-2) s(^-1)) decreased the yield, but high light intensity (90 µmol photon m(^-2) s(^-1)) increased the yield of the protonema. The moss showed no response to water stress in respect to praline accumulation. Protein content decreased significantly over 48 h with increase in water stress. The Influence of water stress was greater in terms of dry weight and chlorophyll content changes in protonema than in leafy shoots. The protonema was capable of using various organic P substrates as sources of phosphorus and showed both PMEase and PDEase activities. PMEase and PDEase activities were detectable in all moss fractions (rhizoids, protonema, leafy shoots). Laboratory grown material showed higher activities than field grown material. Rhizoids produced the highest PMEase and PDEase activities among the moss fractions. Some leafy shoots collected from the field had low phosphorus content with high phosphatase activities, while others had high phosphorus content with low phosphatase activities. Changes in phosphatase activities in batch culture were studied in relation to growth rate. PMEase activity was first evident when cellular P was 1.15% with low activity (0.117 µmol pNP mg d. wt(^-1) h(^-1)) and PDEase appeared 4 days later when cellular P was 0.54%. The activities increased up to day 12 after which the activities maintained this level. The optimum temperatures, measured over a period of 1 h, for PMEase and PDEase activities were 60 ºC and 65 ºC with pH optima of 5.5-6.0 and 6.4-6.8, respectively. Of the six ions tested, Ca, Zn and P had significant inhibitory effects on the activities at the highest concentration used (10 mM).Drying the moss decreases PMEase and PDEase activities by about 23% and 21% (5-d) and 3.7 and 2,8 times (3 months), respectively. Water stress (PEG treatment) also reduced significantly the activities of PMEase and PDEase with a greater effect on the activity of the latter. A brief comparison in PMEase activity using two different substrates p- nitrophenyl phosphate (pNPP) and 4-methylumbelliferyl phosphate (4-MUP) was made to investigate the pH optima and time course. PMEase activity measured using 250 µM 4-MUP was about 60% of that measured using the same concentration of pNPP
Checklist of the mosses of sub-Saharan Africa
No full text2939 moss taxa are listed for sub-Saharan Africa and adjacent islands, with distribution by country. Each distribution record is supported by a literature reference. The following new combinations are made: Calyptrochaeta cristata (Hedw.) O’Shea, Groutiella elimbata (Thér) O’Shea, Meiothecium undulatum (Ren. & Card.) O’Shea, Orthodontium ruwenzorensis (Thér. & Nav.) O’Shea, Pohlia lacouturei (Thér.) O’Shea, Sematophyllum corticolum (Aongstr.) O’Shea, Sematophyllum dixonii (Thér.) O’Shea, Sematophyllum nanopyxis (Geh.) O’Shea, Sematophyllum rigescens (Card.) O’Shea, and Thamnobryum malgachum (Card.) O’Shea
Photosynthetic responses of three common mosses from continental Antarctica
No full textPredicting the effects of climate change on Antarctic terrestrial vegetation requires a better knowledge of the ecophysiology of common moss species. In this paper we provide a comprehensive matrix for photosynthesis and major environmental parameters for three dominant Antarctic moss species (Bryum subrotundifolium, B. pseudotriquetrum and Ceratodon purpureus). Using locations in southern Victoria Land, (Granite Harbour, 77°S) and northern Victoria Land (Cape Hallett, 72°S) we determined the responses of net photosynthesis and dark respiration to thallus water content, thallus temperature, photosynthetic photon flux densities and CO2 concentration over several summer seasons. The studies also included microclimate recordings at all sites where the research was carried out in field laboratories. Plant temperature was influenced predominantly by the water regime at the site with dry mosses being warmer. Optimal temperatures for net photosynthesis were 13.7°C, 12.0°C and 6.6°C for B. subrotundifolium, B. pseudotriquetrum and C. purpureus, respectively and fall within the known range for Antarctic mosses. Maximal net photosynthesis at 10°C ranked as B. subrotundifolium > B. pseudotriquetrum > C. purpureus. Net photosynthesis was strongly depressed at subzero temperatures but was substantial at 0°C. Net photosynthesis of the mosses was not saturated by light at optimal water content and thallus temperature. Response of net photosynthesis to increase in water content was as expected for mosses although B. subrotundifolium showed a large depression (60%) at the highest hydrations. Net photosynthesis of both B. subrotundifolium and B. pseudotriquetrum showed a large response to increase in CO2 concentration and this rose with increase in temperature; saturation was not reached for B. pseudotriquetrum at 20°C. There was a high level of variability for species at the same sites in different years and between different locations. This was substantial enough to make prediction of the effects of climate change very difficult at the moment
The feeding ecology of certain larvae in the genus tipula (Tipulidae, Diptera), with special reference to their utilisation of Bryophytes
No full textBryophytes are rarely used as a food source by any animal species, but the genus Tipula (Diptera, Tipulidae) contains some of the few insect species able to feed, and complete their life-cycle, on bryophytes. Vegetation particle volumes ingested by larvae of eleven Tipula species increased only marginally between instars and not to the extent expected from the rate of growth of body mass. Early and late instars within a species frequently ingested similar sized particles. The overall efficiency of digestion of vegetation particles was low and similar between the four instars of each of the eleven species. Generally, the only method by which later larval instars can obtain a higher proportion of nutrients is by feeding on a larger number of smaller vegetation particles and not by ingesting large particles. In feeding choice experiments, Tipula confusa preferred moss species from woodland habitats, whereas Tipula subnodicornis did not show an overall preference for either woodland or moorland moss species. Tipula subnodicornis also showed a less extensive hierachical preference/avoidance than Tipula confusa for the ten moss species investigated. The moss species Campylopus paradoxus and Sphagnum papillosum accumulated Pb(^2+) ions and Zn(^2+) ions to high concentrations. There was some evidence that Tipula subnodicornis larvae were deterred from feeding on these mosses with high levels of introduced heavy metal ions. Tipula montana was able to thrive and complete its life-cycle in Britain at lower altitudes than had been previously thought. Individuals of this species show a combination of one-year and two-year life-cycles at Waskerley Common. The feeding methods employed by Tipula species can explain why some of them have remained as consumers of bryophytes
The contribution of symptoms of post-traumatic stress disorder (PTSD), health anxiety and intolerance of uncertainty to distress in Ménière's disease
No full textThis study assessed whether symptoms of post-traumatic stress disorder (PTSD), health anxiety, and intolerance of uncertainty were associated with distress in members of the Ménière's Society (n = 800), and compared the extent of anxiety, depression, intolerance of uncertainty and health anxiety with a healthy control group (n = 484). PTSD symptoms were associated with anxiety, depression, and handicap. Health anxiety was associated with anxiety and depression. Intolerance of uncertainty was directly associated with anxiety; its association with depression and handicap was mediated by PTSD symptoms. The Ménière's group reported more anxiety, depression, and health anxiety than the control group, but were not more intolerant of uncertainty. More than half of the Ménière's group reported experiencing partial or full PTSD symptoms. As PTSD, health anxiety and intolerance of uncertainty are modifiable with psychological treatment, we advise that clinicians should screen patients with Ménière's disease who are particularly distressed
From Canon Road, 900 ft. above river, S.E. to Upper Falls (109 ft. high), Yellowstone Park, U.S.A.
No full textFrom Canon Road, 900 ft. above river, S.E. to Upper Falls (109 ft. high), Yellowstone Park, U.S.A
New and noteworthy records and new synonyms in pottiaceous mosses : mostly from SE Asia
No full textNew country records and range extensions for several pottiaceous mosses, mostly from S.E. Asia, are reported. Thirteen new synonyms are proposed
Victimised Actors and Despotic Directors: Clichés of Theatre at Stake in Beckett's 'Catastophe'
No full textThe essay focuses on 'Catastrophe', one of the last plays Beckett wrote, which the author sees as almost the culmination of his idea of the theatre. This 1982 play is the epitome of the demanding performance Beckett's theatre requires from the actors and of the great freedom and power paradoxically it gives them. By undermining, with a great sense of irony, himself and his working method, but even more radically the directorial function itself, in this play, Beckett, the celebrated 'tyrant-director' reveals the sole concrete reality of the production: that it is the realm of the actor
A comparative case study of coordination mechanisms in Design and Build BIM-based projects in the Netherlands
No full textBIM implementation can affect the project coordination mechanisms in unexpected ways, even in widely-applied project procurement structures. Apart from the chosen procurement approach, the BIM technology and the distribution of roles in the project team influence and shape the project coordination. This paper aims to explore the emerging coordination structures and processes from BIM implementation in design-build procurement. An exploratory comparative case study has been undertaken. The findings included two main coordination mechanisms: a centralized and decentralized structure and a hierarchical ver-sus participative decision-making processes. These two patterns subsequently open a debate about the rela-tions between BIM implementation and business models in AEC and particularly the emergence of specialized all-around BIM firms versus BIM-knowledgeable engineering firms.Accepted Author ManuscriptDesign & Construction Managemen
Controls on carbon and energy exchange by a black spruce–moss ecosystem: Testing the mathematical model Ecosys with data from the BOREAS Experiment
No full textStomatal limitations to mass and energy exchange over boreal black spruce forests may be caused by low needle N concentrations that limit CO(2) fixation rates. These low concentrations may be caused by low N uptake rates from cold boreal soils with high soil C:N ratios and by low N deposition rates from boreal atmospheres. A mathematical model of terrestrial ecosystems ecosys was used to examine the likelihood that slow N cycling could account for the low rates of mass and energy exchange measured over a 115-year old boreal spruce/moss forest as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). In the model, net N mineralization was slowed by the high C:N ratios measured in tile forest floor and by high lignin contents in spruce litterfall. Slow mineralization caused low N uptake rates and hence high C:N ratios in spruce and moss leaves that reduced specific activities and areal densities of rubisco and chlorophyll. Consequent low CO(2) fixation rates caused low stomatal conductances and transpiration rates which in turn caused high soil water contents. Wet soils, in conjunction with large accumulations of surface detritus generated by slow litter mineralization, caused low soil temperatures that further slowed mineralization rates. Model outputs for ecosystem N status were corroborated by low needle N concentrations (< 10 mg g(-1)), stomatal conductances (< 0.05 mol m(-2) s(-1)) and CO(2) fixation rates (< 6 <mu>mol m(-2) s(-1)), and by high canopy Bowen ratios (1.5-2.0) and low canopy net CO(2) exchange(-1)) measured over the black spruce/moss forest at the BORES site. rates (< 10 <mu>mol m(-1) s Modeled C accumulation rates of 60 (wood) + 10 (soil) = 70 g C m(-2) yr(-1) were consistent with estimates from aggregated CO(2) fluxes measured over the spruce canopy and from allometric equations developed for black spruce in Canadian boreal forests. Model projections under IS92a climate change indicate that rates of wood C accumulation would rise and those of soil C accumulation would decline from those under current climate. Because these rates are N-limited, they would be raised by increases in atmospheric N deposition
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