Explore the vast range of titles available.

1. Climate change in the subarctic is expected to influence vegetation composition, specifically bryophyte and lichen communities, thereby modifying litter decomposition rates and carbon (C) dynamics of these systems with possible feedbacks to climate. 2. In a 2-year experiment, we investigated decomposition rates and chemical traits of 27 bryophytes, 17 lichens and 5 vascular plants in litter beds in subarctic Sweden. The majority of the sampled cryptogam species are widespread at higher northern latitudes. 3. Average 2-year litter decomposition rates (exponential mass loss constant k) of lichen (0.44 ± 0.01) and vascular plant (0.56 ± 0.03) species were higher than that of bryophytes (0.11 ± 0.01), while within main cryptogam taxa, species identity was an important determinant of mass loss rates. At cryptogam group level, 2-year litter mass loss of Sphagnum was significantly lower than for non-Sphagnum mosses and liverworts. Within lichens, N₂-fixing versus non-N₂-fixing lichens showed no variation in decomposability. 4. In a subset of the large species set, mass loss differed both among incubation environments (reflecting nutrient-rich and poor birch forest and Sphagnum peatlands, respectively) and species. The pattern of mass loss across incubation environments was not consistent among cryptogam species. N₂-fixing, in contrast to non-N₂-fixing lichens with lower nitrogen (N) levels displayed similar decomposition rates across incubation environments. Mass loss of non-Sphagnum mosses was correlated with initial N irrespective of incubation environment. 5. Litter mass loss of cryptogam taxa could be predicted very well from infrared spectra of the initial chemical composition of the species, by application of Fourier transform infrared using an attenuated total reflectance probe. The initial macronutrient concentrations (N, phosphorus, C and cations) and initial litter pH correlated less well. 6. Synthesis. We showed comprehensively that decomposition rates of bryophytes are generally lower than those of lichens and vascular plants. Among bryophyte or lichen species there is also great variation in litter decomposability which depends strongly on species-specific chemistry. Our data will help predict changing land surface feedback to C cycles and climate in cold biomes by understanding long-term climate effects on litter decomposability through shifting vegetation composition.

The diversity and spatial pattern of the bacterial community hosted by the shrub-like reindeer lichen Cladonia arbuscula were investigated by general DNA staining and FISH, coupled with confocal laser scanning microscopy (CLSM). Using an optimized protocol for FISH using cryosections of small lichen fragments, we found about 6 x 10⁷ bacteria g⁻¹ of C. arbuscula. Approximately 86% of acridine orange-stained cells were also stained by the universal FISH probe EUB338. Using group-specific FISH probes, we detected a dominance of Alphaproteobacteria (more than 60% of all bacteria), while the abundance of Actinobacteria and Betaproteobacteria was much lower (<10%). Firmicutes were rarely detected, and no Gammaproteobacteria were present. Bacterial cells of different taxonomic groups are embedded in a biofilm-like, continuous layer on the internal surface of the C. arbuscula podetia, mainly occurring in small colonies of a few to a few hundred cells. The other parts of the lichen showed a lower bacterial colonization. α-proteobacterial 16S rRNA genes were amplified using total DNA extracts from C. arbuscula and separated by single-strand conformation polymorphism (SSCP). Sequencing of excised bands revealed the dominance of Acetobacteraceae.

Biological nitrogen fixation (BNF) is the major nitrogen (N) input in many terrestrial ecosystems, yet we know little about the mechanisms and feedbacks that control this process in natural ecosystems. We here examine BNF in four taxonomically and ecologically different groups over the course of forest ecosystem development. At nine sites along the Franz Josef soil chronosequence (South Westland, New Zealand) that range in age from 7 to 120 000 yr old, we quantified BNF from the symbiotic plant Coriaria arborea, cyanolichens (primarily Pseudocyphellaria spp.), bryophytes (many species), and heterotrophic bacteria in leaf litter. We specifically examined whether these groups could act as \"nitrostats\" at the ecosystem level, turning BNF on when N is scarce (early in primary succession) and off when N is plentiful (later in succession and retrogression). Coriaria was abundant and actively fixing (∼11 kg N·ha⁻¹·yr⁻¹) in the youngest and most N-poor site (7 yr old), consistent with nitrostat dynamics. Coriaria maintained high BNF rates independent of soil N availability, however, until it was excluded from the community after a single generation. We infer that Coriaria is an obligate N fixer and that the nitrostat feedback is mechanistically governed by species replacement at the community level, rather than down-regulation of BNF at the physiological scale. Biological nitrogen fixation inputs from lichens (means of 0-2 kg N·ha⁻¹·yr⁻¹), bryophytes (0.7-10 kg N·ha⁻¹·yr⁻¹), and litter (1-2 kg N·ha⁻¹·yr⁻¹) were driven primarily by changes in density, which peaked at intermediate-aged sites (and increased with soil N availability) for both lichens and bryophytes, and grew monotonically with soil age (but did not change with soil N) for litter. This non-nitrostatic link between soil N availability and lichen/bryophyte BNF likely stems from increased tree biomass in more fertile sites, which increases epiphytic moisture conditions and habitable surface area. This apparent positive feedback could produce N-rich conditions.

1. The stress-gradient hypothesis (SGH) predicts that the frequency of facilitative and competitive interactions will vary inversely across abiotic stress gradients, with facilitation being more common when abiotic stress is high. The effect of competition intensity on species richness is generally thought to be negative, but tests along true stress gradients are lacking. This body of research has primarily focused on vascular plants and could be well informed by broadening to other communities. 2. We report the first regional-scale test of the SGH using biological soil crusts dominated by mosses and lichens, a key multi-functional community of arid and semi-arid ecosystems worldwide. We examined the intensity of facilitative or competitive interactions at the level of the community and among species pairs along an aridity gradient. Along this gradient we also examined the relationship between competition intensity and species richness. 3. All evidence strongly suggested that negative species interactions are prevalent in this study system and much more common than expected by chance. At the community scale, we found that abiotic stress associated with aridity was positively related to and explained 6-56% of the variance in indicators of facilitation or competition, dependent on the index and algorithm used. Despite this intriguing contradiction of the SGH at the whole community scale, we found scant dependency of species-level interactions upon abiotic stress. However, the sign and intensity of these interactions proved to be species-specific. We also found that the relationship between competition and species richness, usually negatively affected by competition, was positively related to richness at low abiotic stress, and negatively related to richness at high abiotic stress. 4. Synthesis. We propose that the response of species interactions to stress gradients may partially depend upon the particular modes of facilitation and competition, in addition to type of stressor and life-history strategies of species involved. We also hypothesize that because stress can act as a filter, a greater number of species interactions are possible under low stress conditions. We believe that this may render intransitivity dominant over niche segregation and expansion, potentially resulting in positive effects of competition on species richness in low stress situations.

Dispersal is a process critical for the dynamics and persistence of metapopulations, but it is difficult to quantify. It has been suggested that the old-forest lichen Lobaria pulmonaria is limited by insufficient dispersal ability. We analyzed 240 DNA extracts derived from snow samples by a L. pulmonaria-specific real-time PCR (polymerase chain reaction) assay of the ITS (internal transcribed spacer) region allowing for the discrimination among propagules originating from a single, isolated source tree or propagules originating from other locations. Samples that were detected as positives by real-time PCR were additionally genotyped for five L. pulmonaria microsatellite loci. Both molecular approaches demonstrated substantial dispersal from other than local sources. In a landscape approach, we additionally analyzed 240 snow samples with real-time PCR of ITS and detected propagules not only in forests where L. pulmonaria was present, but also in large unforested pasture areas and in forest patches where L. pulmonaria was not found. Monitoring of soredia of L. pulmonaria transplanted to maple bark after two vegetation periods showed high variance in growth among forest stands, but no significant differences among different transplantation treatments. Hence, it is probably not dispersal limitation that hinders colonization in the old-forest lichen L. pulmonaria, but ecological constraints at the stand level that can result in establishment limitation. Our study exemplifies that care has to be taken to adequately separate the effects of dispersal limitation from a limitation of establishment.

Our two main goals are first to evaluate the resilience of the boreal forest according to latitude across the closed-crown forest zone using the post-disturbance distribution and cover of lichen woodlands and closed-crown forests as a metric, and second to identify the disturbance factors responsible for the regeneration and degradation of the closed-crown forest according to latitude since the 1950s. The study area extends between 70°00' and 72°00' W and throughout the closed-crown forest zone, from its southern limit near 47°30' N to its northern limit at the contact with the lichen woodland zone at around 52°40' N. Recent (1972-2002) and old (1954-1956) aerial photos were used to map the distribution of lichen woodlands across the closed-crown forest zone. Forest disturbances such as fire, spruce budworm (Choristoneura fumiferana (Clemens)) outbreak, and logging were recorded on each set of aerial photos. Each lichen woodland and stand disturbance was validated by air-borne surveys and digitized using GIS software. Over the last 50 years, the area occupied by lichen woodlands has increased according to latitude; that is, 9% of the area that was occupied by closed-crown forests has shifted to lichen woodlands. Although logging activities have been concentrated in the same areas during the last 50 years, the area covered by logging has increased significantly. Outbreaks by the spruce budworm occurred predominantly in the southern (47°30' N to 48°30' N) and central (48°53' N to 50°42' N) parts of the study area, where balsam fir stands are extensive. In the northern part of the study area (51°-52°40' N), extensive fires affected the distribution and cover of closed-crown forests and lichen woodlands. Over the last 50 years, the area occupied by closed-crown forests has decreased dramatically, and the ecological conditions that allow closed-crown forests to establish and develop are currently less prevalent. Fire is by far the main disturbance, reducing the ability of natural closed-crown forests to self-regenerate whatever the latitude. Given the current biogeographical shift from dense to open forests, the northern part of the closed-crown forest zone is in a process of dramatic change towards the dominance of northern woodlands.

• In tropical lowland forests, corticolous crustose green algal lichens are abundant and highly diverse. This may be related to adaptation to prevailing microenvironmental conditions including, for example, high precipitation and low light intensities. • In the understory of a tropical lowland rain forest in French Guiana, we studied the morphology of crustose green algal lichens and measured gas exchange and chlorophyll a fluorescence. • We found that (i) periods of thallus suprasaturation with water were reduced by the presence of water-repelling surface structures of mycobiont hyphae at the thallus surface and the medulla; (ii) photosynthesis was adapted to the low light intensities present in the understory; and (iii) photosynthesis was rapidly activated in fluctuating light. • The combination of these three mechanisms enables corticolous lichens to implement specific morphological and physiological strategies, which may favour growth in the limiting understory habitat of tropical lowland rain forests.

Aim: We reconstructed the phylogeny of the lichen genus Nephroma (Peltigerales) to assess the relationships of species endemic to Macaronesia. We estimated dates of divergences to test the hypothesis that the species arose in Macaronesia (neo-endemism) versus the oceanic archipelagos serving as refugia for formerly widespread taxa (palaeo-endemism). Location: Cosmopolitan with a special focus on the archipelagos of the Azores, Madeira and the Canary Islands. Methods: DNA sequences were obtained from 18 species for three loci and analysed using maximum parsimony, maximum likelihood and Bayesian inferences. Divergence dates were estimated for the internal transcribed spacer (ITS)-based phylogeny using a relaxed molecular clock. Reconstruction of the ancestral geographical range was conducted using the Bayesian 50% majority rule consensus tree under a parsimony method. Results: The backbone phylogenetic tree was fully supported, with Nephroma plumbeum as sister to all other species. Four strongly supported clades were detected: the Nephroma helveticum, the N. bellum, the N. laevigatum and the N. parile clades. The latter two share a common ancestor and each includes a widespread Holarctic species (N. laevigatum and N. parile, respectively) and all species endemic to Macaronesia. The data suggest a neo-endemic origin of Macaronesian taxa, a recent range expansion from Macaronesia of both widespread species, a range expansion limited to the Mediteranean Basin and south-western Europe for another taxon, and a long dispersal event that resulted in a speciation event in the western parts of North America. Main conclusions: The Macaronesian endemic species belong to two sister clades and originated from a most recent common ancestor (MRCA) shared with one widely distributed taxon, either N. parile or N. laevigatum. Estimates of the mean divergence dates suggest that the endemics originated in the archipelagos after the rise of the volcanic islands, along with the ancestor to the now widespread species, which probably expanded their range beyond Macaronesia via long-distance dispersal. This study provides the first phylogenetic evidence of Macaronesian neo-endemism in lichenized fungi and provides support for the hypothesis that oceanic islands may serve as a source for the colonization of continents. However, further data are needed to properly assess the alternative hypothesis, namely colonization from western North America.

The paper presents Absconditella fossarum, a species new to Poland, found on sands in the Noteć river valley and A. sphagnorum from the new stands found on peated shore of pure, forest lakes in the Tuchola Forest (Bory Tucholskie) region.