Ultrastructure variations in Sphagnum denticulatum ecotypes in response to desiccation stress matter to conservation.

Global warming and peat bogs drying are having a strong negative effect on the survival of endangered peat mosses. Here, we aimed to identify ultrastructural and physiological trait variation during dehydration and rehydration in the (sub-)meristematic cells of buds among clonally propagated individuals of Sphagnum denticulatum in relation to their ecological origin. We cultivated five clones in common garden conditions (CGCs) to exclude a carryover effect and we subsequently water-stressed (-40 MPa) and rehydrated (7 days) them. For the ultrastructure analysis, over 1280 measurements were recorded for 34 traits. Compared with the control, the treatment led to alterations in organelles that appeared to be ecotype- and genotype-dependent and characteristic for desiccation-sensitive mosses. Also, the recovery of chloroplasts, as measured by the initial and maximal fluorescence yield, were incomplete for all studied plants indicating desiccation sensitivity. Terrestrial genotypes possessed better recovery capability than did aquatic genotypes, suggesting an adaptation of the former to tolerate unpredictable terrestrial conditions in time and space. Genotype-specific requirements of water availability in the original environments should be considered before transplanting gametophytes for peatland restoration programs.

Novel insights on the structure and composition of pseudostomata of Sphagnum.

PREMISE OF THE STUDY: The occurrence of stomata on sporophytes of mosses and hornworts is congruent with a single origin in land plants. Although true stomata are absent in early-divergent mosses, Sphagnum has specialized epidermal cells, pseudostomata, that partially separate but do not open to the inside. This research examined two competing hypotheses that explain the origin of pseudostomata: (1) they are modified stomata, or (2) they evolved from epidermal cells independently from stomata.• METHODS: Capsule anatomy and ultrastructure of pseudostomata were studied using light and electron microscopy, including immunolocalization of pectins.• KEY RESULTS: Cell walls in pseudostomata are thin, two-layered, and rich in pectins, similar to young moss stomata, including the presence of cuticle on exterior walls. Outer and ventral walls have a thick cuticle that suggests that initial separation of ventral walls involves cuticle deposition as in true stomata. Further mechanical separation between ventral walls does not form a pore and occurs as the capsule dries.• CONCLUSIONS: As in moss stomata, pseudostomata wall architecture and behavior facilitate capsule dehydration, shape change, and dehiscence, supporting a common function. The divergent structure and fate of pseudostomata may be explained by the retention of Sphagnum sporophytes within protective leaves until nearly mature. Ultrastructural and immunocytological data suggest that pseudostomata are related to stomata but do not conclusively support either hypothesis. Solving the relationship of early land plants is critical to understanding stomatal evolution. Pseudostomata are structurally and anatomically unique, but their relationship to true stomata remains to be determined.

High specificity but contrasting biodiversity of Sphagnum-associated bacterial and plant communities in bog ecosystems independent of the geographical region.

Mosses represent ecological niches that harbor a hitherto largely uncharacterized microbial diversity. To investigate which factors affect the biodiversity of bryophyte-associated bacteria, we analyzed the bacterial communities associated with two moss species, which exhibit different ecological behaviors and importance in bog ecosystems, Sphagnum magellanicum and Sphagnum fallax, from six temperate and boreal bogs in Germany and Norway. Furthermore, their surrounding plant communities were studied. Molecular analysis of bacterial communities was determined by single-strand conformation polymorphism (SSCP) analysis using eubacterial and genus-specific primers for the dominant genera Burkholderia and Serratia as well as by sequence analysis of a Burkholderia 16S rRNA gene clone library. Plant communities were analyzed by monitoring the abundance and composition of bryophyte and vascular plant species, and by determining ecological indicator values. Interestingly, we found a high degree of host specificity for associated bacterial and plant communities of both Sphagnum species independent of the geographical region. Calculation of diversity indices on the basis of SSCP gels showed that the S. fallax-associated communities displayed a statistically significant higher degree of diversity than those associated with S. magellanicum. In contrast, analyses of plant communities of Sphagnum-specific habitats resulted in a higher diversity of S. magellanicum-specific habitats for all six sites. The higher content of nutrients in the S. fallax-associated ecosystems can explain higher diversity of microorganisms.

In vitro decomposition of Sphagnum by some microfungi resembles white rot of wood.

The abilities of some ascomycetes (Myxotrichaceae) from a Sphagnum bog in Alberta to degrade cellulose, phenolics, and Sphagnum tissue were compared with those of two basidiomycetes. Most Myxotrichaceae degraded cellulose and tannic acid, and removed cell-wall components simultaneously from Sphagnum tissues, whereas the basidiomycetes degraded cellulose and insoluble phenolics, and preferentially removed the polyphenolic matrix from Sphagnum cell walls. Mass losses from Sphagnum varied from up to 50% for some ascomycetes to a maximum of 35% for the basidiomycetes. The decomposition of Sphagnum by the Myxotrichaceae was analogous to the white rot of wood and indicates that these fungi have the potential to cause significant mineralization of carbon in bogs.

Ozone effects on the ultrastructure of peatland plants: Sphagnum mosses, Vaccinium oxycoccus, Andromeda polifolia and Eriophorum vaginatum.

BACKGROUND AND AIMS: Ozone effects on peatland vegetation are poorly understood. Since stress responses are often first visible in cell ultrastructure, electron microscopy was used to assess the sensitivity of common peatland plants to elevated ozone concentrations. METHODS: Three moss species (Sphagnum angustifolium, S. magellanicum and S. papillosum), a graminoid (Eriophorum vaginatum) and two dwarf shrubs (Vaccinium oxycoccus and Andromeda polifolia), all growing within an intact canopy on peat monoliths, were exposed to a concentration of 0, 50, 100 or 150 ppb ozone in two separate growth chamber experiments simulating either summer or autumn conditions in central Finland. After a 4- or 5-week-long exposure, samples were photographed in a transmission electron microscope and analysed quantitatively using image processing software. KEY RESULTS: In the chlorophyllose cells of the Sphagnum moss leaves from the capitulum, ozone exposure led to a decrease in chloroplast area and in granum stack thickness and various changes in plastoglobuli and cell wall thickness, depending on the species and the experiment. In E. vaginatum, ozone exposure significantly reduced chloroplast cross-sectional areas and the amount of starch, whereas there were no clear changes in the plastoglobuli. In the dwarf shrubs, ozone induced thickening of the cell wall and an increase in the size of plastoglobuli under summer conditions. In contrast, under autumn conditions the cell wall thickness remained unchanged but ozone exposure led to a transient increase in the chloroplast and starch areas, and in the number and size of plastoglobuli. CONCLUSIONS: Ozone responses in the Sphagnum mosses were comparable to typical ozone stress symptoms of higher plants, and indicated sensitivity especially in S. angustifolium. The responses in the dwarf shrubs suggest stimulation of photosynthesis by low ozone concentrations and ozone sensitivity only under cool autumn conditions.

Distribution of cell wall components in Sphagnum hyaline cells and in liverwort and hornwort elaters.

Spiral secondary walls are found in hyaline cells of Sphagnum, in the elaters of most liverworts, and in elaters of the hornwort Megaceros. Recent studies on these cells suggest that cytoskeletal and ultrastructural processes involved in cell differentiation and secondary wall formation are similar in bryophytes and vascular plant tracheary elements. To examine differences in wall structure, primary and secondary wall constituents of the hyaline cells of Sphagnum novo-zelandicum and elaters of the liverwort Radula buccinifera and the hornwort Megaceros gracilis were analyzed by immunohistochemical and chemical methods. Anti-arabinogalactan-protein antibodies, JIM8 and JIM13, labeled the central fibrillar secondary wall layer of Megaceros elaters and the walls of Sphagnum leaf cells, but did not label the walls of Radula elaters. The CCRC-M7 antibody, which detects an arabinosylated (1-->6)-linked beta-galactan epitope, exclusively labeled hyaline cells in Sphagnum leaves and the secondary walls of Radula elaters. Anti-pectin antibodies, LM5 and JIM5, labeled the primary wall in Megaceros elaters. LM5 also labeled the central layer of the secondary wall but only during formation. In Radula elaters, JIM5 and another anti-pectin antibody, JIM7, labeled the primary wall. The distribution of arabinogalactan-proteins and pectic polysaccharides restricted to specific wall types and stages of development provides evidence for the developmental and functional regulation of cell wall composition in bryophytes. Monosaccharide-linkage analysis of Sphagnum leaf cell walls suggests they contain polysaccharides similar to those of higher plants. The most abundant linkage was 4-Glc, typical of cellulose, but there was also evidence for xyloglucans, 4-linked mannans, 4-linked xylans and rhamnogalacturonan-type polysaccharides.

Sulphur, nitrogen and carbon content of Sphagnum capillifolium and Pseudevernia furfuracea exposed in bags in the Naples urban area.

The accumulation ability of the major elements sulphur, nitrogen and carbon by the moss Sphagnum capillifolium (Ehrh.) Hedw. and the lichen Pseudevernia furfuracea (L.) Zopf exposed in bags in Naples urban area,was investigated. Bags were exposed at the beginning of July 1999 and gathered in two subsequent moments: at the end of the dry season (after 10 weeks of exposure) and during the wet season (after 17 weeks of exposure), to include the effects of rainy conditions. Sulphur and N content of the lichen increased all over the exposure period, while the level of C did not change significantly either after 10 or 17 weeks of exposition. For the moss the S accumulation was limited to the dry period of exposure, whereas N and C content decreased with exposure. Results, in contrast with those obtained in a previous study on trace elements bioaccumulation [Adamo et al., Environmental Pollution, (2003) 122, 91-103], suggest that accumulation of gaseous pollutants is strongly influenced by biomonitor vitality and that lichen bags are a more reliable and effective tool for monitoring S, N and C atmospheric depositions in urban areas compared to moss bags, because of greater lichen resistance to dry and stressing conditions of urban environment.