Impact of changes in natural ultraviolet radiation on pigment composition, physiological and morphological characteristics of the Antarctic moss, Grimmia antarctici

The impact of ambient ultraviolet (UV)-B radiation on the endemic bryophyte, Grimmia antarctici, was studied over 14 months in East Antarctica. Over recent decades, Antarctic plants have been exposed to the largest relative increase in UV-B exposure as a result of ozone depletion. We investigated the effect of reduced UV and visible radiation on the pigment concentrations, surface reflectance and physiological and morphological parameters of this moss. Plexiglass screens were used to provide both reduced UV levels (77%) and a 50% decrease in total radiation. The screen combinations were used to separate UV photoprotective from visible photoprotective strategies, because these bryophytes are growing in relatively high light environments compared with many mosses. G. antarctici was affected negatively by ambient levels of UV radiation. Chlorophyll content was significantly lower in plants grown under near-ambient UV, while the relative proportions of photoprotective carotenoids, especially beta-carotene and zeaxanthin, increased. However, no evidence for the accumulation of UV-B-absorbing pigments in response to UV radiation was observed. Although photosynthetic rates were not affected, there was evidence of UV effects on morphology. Plants that were shaded showed fewer treatment responses and these were similar to the natural variation observed between moss growing on exposed microtopographical ridges and in more sheltered valleys within the turf. Given that other Antarctic bryophytes possess UV-B-absorbing pigments which should offer better protection under ambient UV-B radiation, these findings suggest that G. antarctici may be disadvantaged in some settings under a climate with continuing high levels of springtime UV-B radiation.

Desiccation tolerance of three moss species from continental Antarctica

Tolerance of desiccation was examined in three species of moss, Grimmia antarctici Card., Ceratodon purpureus (Hedw.) Brid. and Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb. collected from two sites of contrasting water availability in the Windmill Islands, continental Antarctica. Physiological tolerance to desiccation was measured using chlorophyll fluorescence in plugs of moss during natural drying in the laboratory. Differences in relative water content, rate of drying and the response of photosynthesis to desiccation were observed among the three species and between sites. Of the three species studied, G. antarctici showed the lowest capacity to sustain photosynthetic processes during desiccation, B. pseudotriquetrum had an intermediate response and showed the greatest plasticity and C. purpureus showed the greatest capacity to sustain photosynthesis during desiccation. These results fit well with the known distribution of the three species with G. antarctici being limited to relatively wet sites, C. purpureus being common in the driest sites and B. pseudotriquetrum showing a wide distribution between these two extremes. Levels of soluble carbohydrates were also measured in these samples following desiccation and these indicate the presence of stachyose, an oligosaccharide known to be important in desiccation tolerance in seeds, in B. pseudotriquetrum. Both gross morphology and carbohydrate content are likely to contribute to differences in desiccation tolerance of the moss species. These results indicate that if the Casey region continues to dry out, as a result of local geological uplifting or global climate change, we would expect to see not only reductions in the moss community but also changes in community composition. G. antarctici is likely to become more limited in distribution as C. purpureus and B. pseudotriquetrum expand into drying areas.

Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function

In this study the variations in surface reflectance properties and pigment concentrations of Antarctic moss over species, sites, microtopography and with water content were investigated. It was found that species had significantly different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm), but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in the visible region and in the characteristics of the red edge over different sites. Reflectance parameters, such as the photochemical reflectance index (PRI) and cold hard band were useful discriminators of site, microtopographic position and water content. The PRI was correlated both with the concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, F-v/F-m, measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and position of the red-edge as well as the PRI, and may be responsible for observed differences in reflectance properties for different species and sites. All moss showed sustained high levels of photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing continual high levels of photochemical stress.

Some like it wet - biological characteristics underpinning tolerance of extreme water stress events in Antarctic bryophytes

Antarctic bryophyte communities presently tolerate physiological extremes in water availability, surviving both desiccation and submergence events. We investigated the relative ability of three Antarctic moss species to tolerate physiological extremes in water availability and identified physiological, morphological, and biochemical characteristics that assist species performance under such conditions. Tolerance of desiccation and submergence was investigated using chlorophyll fluorescence during a series of field- and laboratory-based water stress events. Turf water retention and degree of natural habitat submergence were determined from gametophyte shoot size and density, and delta C-13 signatures, respectively. Finally, compounds likely to assist membrane structure and function during desiccation events (fatty acids and soluble carbohydrates) were determined. The results of this study show significant differences in the performance of the three study species under contrasting water stress events. The results indicate that the three study species occupy distinctly different ecological niches with respect to water relations, and provide a physiological explanation for present species distributions. The poor tolerance of submergence seen in Ceratodon purpureus helps explain its restriction to drier sites and conversely, the low tolerance of desiccation and high tolerance of submergence displayed by the endemic Grimmia antarctici is consistent with its restriction to wet habitats. Finally the flexible response observed for Bryum pseudotriquetrum is consistent with its co-occurrence with the other two species across the bryophyte habitat spectrum. The likely effects of future climate change induced shifts in water availability are discussed with respect to future community dynamics.

Phylogenetic study of the Grimmia Hedw. (Grimmiales, Bryopsida) based on a combination of morphological and molecular characters

Résumé Les mousses sont la plus ancienne lignée de plantes terrestres et leur longue évolution a été accompagnée par des tendances à la simplification des caractères morphologiques. Ce phénomène a quelque peu compliqué les reconstructions phylogénétiques basées sur la morphologie. Les analyses génétiques ont permis de donner de nouvelles informations dans le cadre des analyses phylogénétiques et une réévaluation de certains caractères morphologiques. La plupart des études combinant les données morphologiques et moléculaires ne concernent que des niveaux systématiques élevés comme l'ordre ou la famille et très peu considèrent le niveau du genre. La présente étude tend à tester les relations phylogénétiques du genre Grimmia à l'aide d'une combinaison de caractères morphologiques et moléculaires. Les 40 espèces de Grimmia utilisées dans la première partie de cette étude représentent la majorité des espèces trouvées en Eurasie, un des centres de diversification du genre. Lors de l'analyse morphologique, 52 caractères morphologiques/anatomiques (33 du gamétophyte et 19 du sporophyte) ont été numérisés. Malgré le peu de support statistique des arbres, la topologie des arbres est stable. Les Grimmia, comme décrit précédemment, sont paraphylétiques. Trois clades, correspondant respectivement aux sous-genres Rhabdogrimmia Limpr, Litoneuron I.Hagen et Gasterogrimmia Schimp. sont présents, tandis que le restant des taxons appartenant aux Grimmia forment un groupe non-résolu et indistinct des autres Grimmiaceae. Les séquences chloroplastiques trnL-trnF et rps4 combinés à la morphologie ont été ensuite utilisés pour reconstruire la phylogénie des Grimmia. Les arbres obtenus soutiennent la monophylie des Grimmiaceae tandis que les Grimmia, sont paraphylétiques. Deux clades principaux correspondant aux "Rhabdogrimmia" et aux "Grimmia" se détachent. Seules les espèces de "Rhabdogrimmia" produisent des gemmules foliaires (reproduction asexuée). Dans une étude considèrant 91 séquences trrIL-trnF les espèces appartenant aux "Rhabdogrimrnia" (reproduction asexuée essentiellement) ont des variabilités intraspécifique très faible et interspécifique relativement élevée tandis que les "Grimmia" possèdent la tendance inverse (plus de reproduction sexuée). Summary The mosses are a very old land plant lineage and their long evolutionary history has been accompanied by a trend of morphological character simplifications. This phenomenon has somewhat complicated morphological based phylogenetic reconstructions. Genetic analyses have provided new insights for phylogenetic studies, and have allowed morphological data to be re¬evaluated. Most of the studies combining morphological and molecular data have concerned the higher systematic levels of order and family and only have few considered the genus. The present study aims to test the phylogenetic relationships of the genus Grimmia using a combination of morphological and molecular characters. The 40 chosen Grimmia species represent the majority of those found in Eurasia, one diversification centers of the genus. For the morphological analysis, 52 morphological/anatomical characters (33 gametophyte and 19 sporophyte characters) were numerized. Although the internal statistical support was relatively low, the tree topologies were stable. Grimmia as currently defined was found to be paraphyletic. Three subclades, corresponding to the subgenera Rhabdogrimmia Limpr., Litoneuron I.Hagen, and Gasterogrimmia Schimp. were observed in the trees, while the reminder of the Grimmia species formed an unresolved group indistinct from other Grimmiaceae. Chloroplast (trnL-trnF and rps4) DNA sequences combined with morphology were used to reconstruct the phylogeny of Grimmia. The resulting trees supported the monophyly of Grimmiaceae and that the genus Grimmia, as currently defined, as paraphyletic. Two main clades were resolved corresponding to "Rhabdogrimmia" and "Grimmia". The species belonging to "Rhabdogrimmia" produce foliar-gemmae (asexual reproduction). In a study using 91 sequences of trnL-trnF,"Rhabdogrimmia" species (mainly asexual reproduction) have very low intraspecific variability and high interspecific variability whereas the "Grimmia" species possess the inverse tendency.

Hemispherium ab aeqvinoctiali linea, ad circulum poli arctici : hemispherium ab aeqvinoctiali linea, ad circulum poli antarctici

Julkaisussa: Speculum orbis terrae. Vol I

How to describe species richness patterns for bryophyte conservation?

A large amount of data for inconspicuous taxa is stored in natural history collections; however, this information is often neglected for biodiversity patterns studies. Here, we evaluate the performance of direct interpolation of museum collections data, equivalent to the traditional approach used in bryophyte conservation planning, and stacked species distribution models (S-SDMs) to produce reliable reconstructions of species richness patterns, given that differences between these methods have been insufficiently evaluated for inconspicuous taxa. Our objective was to contrast if species distribution models produce better inferences of diversity richness than simply selecting areas with the higher species numbers. As model species, we selected Iberian species of the genus Grimmia (Bryophyta), and we used four well-collected areas to compare and validate the following models: 1) four Maxent richness models, each generated without the data from one of the four areas, and a reference model created using all of the data and 2) four richness models obtained through direct spatial interpolation, each generated without the data from one area, and a reference model created with all of the data. The correlations between the partial and reference Maxent models were higher in all cases (0.45 to 0.99), whereas the correlations between the spatial interpolation models were negative and weak (-0.3 to -0.06). Our results demonstrate for the first time that S-SDMs offer a useful tool for identifying detailed richness patterns for inconspicuous taxa such as bryophytes and improving incomplete distributions by assessing the potential richness of under-surveyed areas, filling major gaps in the available data. In addition, the proposed strategy would enhance the value of the vast number of specimens housed in biological collections.

Strong quenching of chlorophyll fluorescence in the desiccated state in three poikilohydric and homoiochlorophyllous moss species indicates photo-oxidative protection on highly light-exposed rocks of a tropical inselberg

The three poikilophydric and homoiochlorophyllous moss species Campylopus savannarum (C. Muell.) Mitt., Racocarpus fontinaloides (C. Muell.) Par. and Ptychomitrium vaginatum Besch. grow on sun-exposed rocks of a tropical inselberg in Brazil subject to regular drying and wetting cycles. Effective photo-oxidative protection in the light-adapted desiccated state in all three species is achieved by a reduction of ground chlorophyll fluorescence, F, to almost zero. Upon rewatering, the kinetics of the recovery of F in air dry cushions to higher values is very fast in the first 5min, but more than 80min are needed until an equilibrium is reached gradually. The kinetics were not different between the three species. The three moss species, have a distinct niche occupation and form a characteristic zonation around soil vegetation islands on the rock outcrops, where C. savannarum and R. fontinaloides form an inner and outer belt, respectively, around vegetation islands and P vaginatum occurs as small isolated cushions on bare rock. However, they were not distinguished by the reduction of F in the dry state and the rewetting recovery kinetics and only slightly different in their photosynthetic capacity. Stable isotope ratios (delta C-13, delta N-15) indicate that liquid films of water limiting diffusion of CO2 are important in determining carbon acquisition and suggest that limitation of CO2 fixation by water films must be more pronounced over time in P vaginatum than in the latter species. This is determined by both the micro site occupied and the form of the moss cushions. (c) 2007 Elsevier GmbH. All rights reserved.

Plant frequency and cover abundance at three sites on Disko Island in 1967/1970 and 2009

We report on a revisit in 2009 to sites where vegetation was recorded in 1967 and 1970 on Disko Island, West Greenland. Re-sampling of the same clones of the grass Phleum alpinum after 39 years showed complete stability in biometrics but dramatic earlier onset of various phenological stages that were not related to changes in population density. In a fell-field community, there was a net species loss, but in a herb-slope community, species losses balanced those that were gained. The type of species establishing and increasing in frequency and/or cover abundance at the fell-field site, particularly prostrate dwarf shrubs, indicates a possible start of a shift towards a heath, rather than a fell-field community. At the herb-slope site, those species that established or increased markedly in frequency and/or cover abundance indicate a change to drier conditions. This is confirmed both by the decrease in abundance of Alchemilla glomerulans and Epilobium hornemanii, and the drying of a nearby pond. The causes of these changes are unknown, although mean annual temperature has risen since 1984.

Table 2: Evaporation from individual shoots of antarctic mosses

Experimental observations on pathways of water movement are discussed in relation to anatomical and micromorphological features of five moss species from Signy Island, South Orkney Islands. Significant internal uptake of water was recorded only in the mesic species Polytrichum alpinum (internal=>60% of total) and Bartramia patens (internal=c.30% of total), in experiments in which uptake by cut shoots was compared in individuals with the external pathway blocked, and others with both external and internal pathways open. Internal uptake maintained shoot water content close to full turgor in P. alpinun and at 30% of full tugor in B. patens, whereas water content fell to 12-15% dry wt. in the lithophytes Andreaea gainii and Schistidium antarctici and in the mesic/hydric species Drepanocladus uncinatus, with the external pathway blocked. Where both pathways were open water uptake from below maintained water content at or above full turgor in shoots of all five species. External water uptake by capillarity occurred most rapidly in the lithophytes, and was slower in initially air-dry than in hydrated shoots of the other species. The spreading limbs of leaves in B. patens and P. alpinum are water-repellent, as are the bright green leaves in the apical 1-2 mm of dry shoots of the lithophytes. A central strand of hydroids is well-developed only in B. patens and P. alpinum. These two species have deposits of surface wax on parts of the leaves, and surface wax also occurs on the green apical leaves in some specimens of S. antarcticum and other lithophytes from Signy Island.

Plant species, biomass and environmental characteristics of relevés along the North America Arctic bioclimate gradient

Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small patterned-ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonalpatterned-ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-ground complexes with the largest thermal differential between the patterned-ground features and the surrounding vegetation exhibited the clearest patterned-ground morphologies.