A subarctic heath where Hylocomium splendens and Polytrichum commune dominate the bryophyte layer was irradiated with enhanced UV-B radiation, simulating 15% ozone depletion. The extra UV-B radiation was supplied by fluorescent tubes during three growing seasons. H. splendens reacted quicker and to a greater extent to enhanced UV-B radiation than did P. commune. Annual length increment in H. splendens was unaffected in the first year but was suppressed in the subsequent years. In P. commune, annual length increment did not decrease until the third growing season. Dry mass production of H. splendens decreased in segments from all three years. Annual dry mass production in P. commune did not change due to enhanced UV-B. Shoot morphology was measured after the third growing season. In H. splendens, the segment area decreased. Leaf density along P. commune shoots increased, and the shoots became stunted. The UV-B enhancement induced a higher variance in the concentration of UV-B absorbing compounds in H. splendens after the first and the third growing season. In P. commune, the variance remained unaffected, but the concentration was significantly decreased after the third year. Indirect UV-B impacts on intra- and interspecific relations, which may be mediated by changes in shoot growth and morphology, are discussed.

Impacts of enhanced ultraviolet‐b radiation on mosses in a subarctic heath ecosystem

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 δ13C 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.

/pdf/some-like-it-wet-biological-characteristics-underpinning-3ftwor7nso.pdf

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

Increases in solar ultraviolet-B radiation (UV-B; 280–320 nm) reaching the earth have been estimated to continue until 2050s in the boreal and subarctic regions with an abundant peatland cover. Peatlands are significant sinks for carbon dioxide (CO2) and sources for methane (CH4). To assess whether the future increases in UV-B could affect the fluxes of CO2 and CH4 in peatlands via an impact on vegetation, we exposed peatland microcosms to modulated 30% supplementation of erythemally weighted UV-B at an outdoor facility for one growing season. The experimental design included appropriate controls for UV-A and ambient radiation. The UV-B caused a significant reduction in gross photosynthesis, net ecosystem CO2 exchange, and CH4 emission of the peatland microcosms. These changes in the carbon gas cycling can be partly explained by UV-B-induced morphological changes in Eriophorum vaginatum which acts as a conduit for CH4. Leaf cross section and the percentage of CH4-conducting aerenchymatous tissue in E. vaginatum were significantly reduced by UV-B. Methanol-extractable UV-B absorbing compounds decreased under both UV-B and UV-A in Sphagnum angustifolium, and tended to accumulate under UV-B in S. papillosum. Membrane permeability to magnesium (Mg) and calcium (Ca) ions was higher in UV-B exposed S. angustifolium. Amount of chlorophyll and carotenoid pigments was increased by UV-A in S. magellanicum. The observed changes in Sphagnum mosses did not coincide with those in carbon gas fluxes but occurred at the time of the highest UV intensity in the mid summer. Our findings indicate that increasing UV-B may have more substantial effects on gas exchange in peatlands than previously thought.

Elevated UV-B radiation alters fluxes of methane and carbon dioxide in peatland microcosms

Fine structure, carbohydrates and photosynthetic pigments of sugar maize leaves under UV-B radiation

In this review all recent field studies on the effects of UV-B radiation on bryophytes are discussed. In most of the studies fluorescent UV-B tubes are used to expose the vegetation to enhanced levels of UV-B radiation to simulate stratospheric ozone depletion. Other studies use screens to filter the UV-B part of the solar spectrum, thereby comparing ambient levels of UV-B with reduced UV-B levels, or analyse effects of natural variations in UV-B arising from stratospheric ozone depletion. Nearly all studies show that mosses are well adapted to ambient levels of UV-B radiation since UV-B hardly affects growth parameters. In contrast with outdoor studies on higher plants, soluble UV-B absorbing compounds in bryophytes are typically not induced by enhanced levels of UV-B radiation. A few studies have demonstrated that UV-B radiation can influence plant morphology, photosynthetic capacity, photosynthetic pigments or levels of DNA damage. However, there is only a limited number of outdoor studies presented in the literature. More additional, especially long-term, experiments are needed to provide better data for statistical meta-analyses. A mini UV-B supplementation system is described, especially designed to study effects of UV-B radiation at remote field locations under harsh conditions, and which is therefore suited to perform long-term studies in the Arctic or Antarctic. The first results are presented from a long-term UV-B supplementation experiment at Signy Island in the Maritime Antarctic.

Outdoor studies on the effects of solar UV-B on bryophytes: overview and methodology.

Effects of UV-B radiation on fine structure, carbohydrates, and pigments in Polytrichum commune.

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Effects of UV-B radiation on fine structure, carbohydrates, and pigments in Polytrichum commune.