ALBERT

Description: Questions Has the observed decline in the willow Salix caprea L., one of the most common colonizers of post-mining sites in Central Europe, contributed to changes in the rest of the plant community on post-mining sites? How does S. caprea modify its understorey? How is the understorey vegetation affected by above-ground and below-ground competition with S. caprea ? Location Heaps after coal mining near Sokolov, Czech Republic (50°14′21″ N, 12°40′45″ E). Methods The effects of above-ground and below-ground competition with the willow S. caprea on its understorey plant community were studied in un-reclaimed post-mining sites. Below-ground competition was evaluated by comparing (1) frames inserted into the soil that excluded woody roots (frame treatment), (2) frames that initially excluded woody root growth but then allowed regrowth of the roots (open-frame treatment), and (3) undisturbed soil (no-frame treatment). These treatments were combined with S. caprea thinning to assess the effect of above-ground competition. Results Three years after the start of the experiment, above-ground competition from S. caprea (as modified by thinning of the S. caprea canopy) had not affected understorey biomass or species number, but had affected species composition. In contrast, below-ground competition significantly affected both the above-ground and below-ground biomass of the understorey. The above-ground biomass of the understorey was larger in the frame treatment (which excluded woody roots) than in the other two treatments. The below-ground biomass of the understorey was larger in the frame than in the open-frame treatment. Unlike above-ground competition (light availability), below-ground competition did not affect understorey species composition. Conclusions Our results suggest that S. caprea is an important component during plant succession on post-mining sites because it considerably modifies its understorey plant community. Below-ground competition is a major reason for the low cover and biomass of the herbaceous understorey in S. caprea stands on post-mining sites. We experimentally manipulated with aboveground and belowground competition of willow Salix caprea L., one of the most common colonizers of post mining sites in Central Europe, with its understory plant community. We found that biomass of understory is limited mainly by belowground competition, while species composition of understory community is driven mainly by aboveground competition for light.

Description: Arctic ecosystems are characterized by a wide range of soil moisture conditions and thermal regimes and contribute differently to the net methane (CH 4 ) budget. Yet, it is unclear how climate change will affect the capacity of those systems to act as a net source or sink of CH 4 . Here, we present results of in situ CH 4 flux measurements made during the growing season 2014 on Disko Island (west Greenland) and quantify the contribution of contrasting soil and landscape types to the net CH 4 budget and responses to summer warming. We compared gas flux measurements from a bare soil and a dry heath, at ambient conditions and increased air temperature, using open-top chambers (OTCs). Throughout the growing season, bare soil consumed 0.22 ± 0.03 g CH 4 -C m −2 (8.1 ± 1.2 g CO 2 -eq m −2 ) at ambient conditions, while the dry heath consumed 0.10 ± 0.02 g CH 4 -C m −2 (3.9 ± 0.6 g CO 2 -eq m −2 ). These uptake rates were subsequently scaled to the entire study area of 0.15 km 2 , a landscape also consisting of wetlands with a seasonally integrated methane release of 0.10 ± 0.01 g CH 4 -C m −2 (3.7 ± 1.2 g CO 2 -eq m −2 ). The result was a net landscape sink of 12.71 kg CH 4 -C (0.48 tonne CO 2 -eq) during the growing season. A nonsignificant trend was noticed in seasonal CH 4 uptake rates with experimental warming, corresponding to a 2% reduction at the bare soil, and 33% increase at the dry heath. This was due to the indirect effect of OTCs on soil moisture, which exerted the main control on CH 4 fluxes. Overall, the net landscape sink of CH 4 tended to increase by 20% with OTCs. Bare and dry tundra ecosystems should be considered in the net CH 4 budget of the Arctic due to their potential role in counterbalancing CH 4 emissions from wetlands – not the least when taking the future climatic scenarios of the Arctic into account.

Description: Krüger, L. C., Paus, A., Svendsen, J. I. & Bjune, A. E. 2011: Lateglacial vegetation and palaeoenvironment in W Norway, with new pollen data from the Sunnmøre region. Boreas , 10.1111/j.1502-3885.2011.00213.x. ISSN 0300-9483. Two sediment sequences from Sunnmøre, northern W Norway, were pollen-analytically studied to reconstruct the Lateglacial vegetation history and climate. The coastal Dimnamyra was deglaciated around 15.3 ka BP, whereas Løkjingsmyra, further inland, became ice-free around 14 ka BP. The pioneer vegetation dominated by snow-bed communities was gradually replaced by grassland and sparse heath vegetation. A pronounced peak in Poaceae around 12.9 ka BP may reflect warmer and/or drier conditions. The Younger Dryas (YD) cooling phase shows increasing snow-bed vegetation and the local establishment of Artemisia norvegica . A subsequent vegetation closure from grassland to heath signals the Holocene warming. Birch forests were established 500–600 years after the YD–Holocene transition. This development follows the pattern of the Sunnmøre region, which is clearly different from the Empetrum dominance in the Lateglacial interstadial further south in W Norway. The Lateglacial oscillations GI-1d (Older Dryas) and GI-1b (Gerzensee) are hardly traceable in the north, in contrast to southern W Norway. The southern vegetation was probably closer to an ecotone and more susceptible to climate changes.

Description: Many Arctic regions are currently experiencing substantial summer and winter climate changes. Litter decomposition is a fundamental component of ecosystem carbon and nutrient cycles, with fungi being among the primary decomposers. To assess the impacts of seasonal climatic changes on litter fungal communities and their functioning, Betula glandulosa leaf litter was surface-incubated in two adjacent Low Arctic sites with contrasting soil moisture regimes: dry shrub heath and wet sedge tundra at Disko Island, Greenland. At both sites, we investigated the impacts of factorial combinations of enhanced summer warming (using open top chambers; OTCs) and deepened snow (using snow fences) on surface litter mass loss, chemistry and fungal decomposer communities after approximately one year. Enhanced summer warming significantly restricted litter mass loss by 32% in the dry and 17% in the wet site. Litter moisture content was significantly reduced by summer warming in the dry, but not in the wet site. Likewise, fungal total abundance and diversity were reduced by OTC warming at the dry site, while comparatively modest warming effects were observed in the wet site. These results suggest that increased evapotranspiration in the OTC plots lowered litter moisture content to the point where fungal decomposition activities became inhibited. In contrast, snow addition enhanced fungal abundance in both sites but did not significantly affect litter mass loss rates. Across sites, control plots only shared 15% of their fungal phylotypes, suggesting strong local controls on fungal decomposer community composition. Nevertheless, fungal community functioning (litter decomposition) was negatively affected by warming in both sites. We conclude that although buried soil organic matter decomposition is widely expected to increase with future summer warming, surface litter decay and nutrient turnover rates in both xeric and relatively moist tundra are likely to be significantly restricted by the evaporative drying associated with warmer air temperatures. This article is protected by copyright. All rights reserved.

Description: The Arctic is warming which may potentially affect substrate availability, organic matter decomposition, plant growth, and plant species composition. This may lead to changes in the exchange of methane (CH 4 ) and carbon dioxide (CO 2 ) between the soil system and the atmosphere. Yet, the correlations among substrate availability, CH 4 production, and net emissions of CH 4 have been scarcely studied in arctic wetlands. Presently, the impact of increasing temperatures on CH 4 exchange is uncertain as the two existing reports on field warming in arctic wetlands present opposite results. We here report results on how summer warming and shrub removal affect soil water substrate (acetate, formate, oxalate, and dissolved organic carbon (DOC)) concentrations as well as dissolved CH 4 and CH 4 emissions in a fen at Disko Island (West Greenland). The peak in dissolved CH 4 followed the peak in acetate concentration, and appeared after the peak in CH 4 emissions, which indicates a lack of correlation between CH 4 production and emissions. The peak in CH 4 emissions coincided with maximum gross ecosystem production (GEP) suggesting that CH 4 emissions are closely linked to photosynthesis. This was supported by an experiment with removal of the sedge Carex aquatilis ssp. stans which contributed with up to 77% of the CH 4 emitted from the ecosystem. By contrast, shrub removal and summer warming did not significantly affect CH 4 emissions, possibly due to the treatments impacting CH 4 production more than emissions. This implies that such wetlands may be less sensitive to moderate warming and changes in shrub cover than previously assumed.

Description: Pisione is a scaleless group of small scale worms inhabiting sandy bottoms in shallow marine waters. This group was once considered rare, but now 45 described species can be characterized, among others, by their paired, segmental copulatory organs (one to multiple external pairs), which display a complexity of various accessory structures. The evolutionary significance of these unique organs was suggested in the late 1960s, but has been heavily debated since the late 1990s and remains controversial. In the present paper, we study the internal relationships within Pisione, employing combined phylogenetic analyses of both molecular and morphological data from 16 terminals of Pisione, as well as two terminals of Pisionidens, and eight additional scale worms as outgroups. Our taxon sampling covers all geographical areas where the genus has been reported, as well as most of their morphological and copulatory variability, including representatives of the “africana,” “remota,” “crassa,” and “papuensis” groups, established previously by Yamanishi. We hereby provide a first insight into the relationships of the genus, testing previously proposed hypotheses on the evolutionary significance of male copulatory structures within Pisione , while attempting to understand patterns of distribution. The phylogenetic analyses using maximum likelihood and Bayesian methods consistently recovered two large clades spanning the East Atlantic (including the Mediterranean) and the Indo-Pacific–West Atlantic, respectively. Character optimization on our trees revealed a high degree of homoplasy in both non-reproductive and sexual characters of Pisione, with buccal acicula found to be the sole apomorphy among the morphological features assessed herein, with none defining the biogeographical subclades within. Overall, our comparative analyses highlight the high degree of morphological variation in this widely distributed genus, rejecting previous assertions of an increasing number and complexity of copulatory structures across the genus. Pisione is a scaleless group of small scale worms inhabiting sandy bottoms in shallow marine waters. The phylogenetic analyses consistently recovered two large clades spanning the East Atlantic (including the Mediterranean) and the Indo-Pacific–West Atlantic, respectively. Our comparative analyses highlight the high degree of morphological plasticity in this widely distributed genus, rejecting previous assumptions of an increasing number and complexity of copulatory structures across the genus.