Empirical testing of cryoconite granulation: Role of cyanobacteria in the formation of key biogenic structure darkening glaciers in polar regions

Cryoconite, the dark sediment on the surface of glaciers, often aggregates into oval or irregular granules serving as biogeochemical factories. They reduce a glacier's albedo, act as biodiversity hotspots by supporting aerobic and anaerobic microbial communities, constitute one of the organic matter (OM) sources on glaciers, and are a feeder for micrometazoans. Although cryoconite granules have multiple roles on glaciers, their formation is poorly understood. Cyanobacteria are ubiquitous and abundant engineers of cryoconite hole ecosystems. This study tested whether cyanobacteria may be responsible for cryoconite granulation as a sole biotic element. Incubation of Greenlandic, Svalbard, and Scandinavian cyanobacteria in different nutrient availabilities and substrata for growth (distilled water alone and water with quartz powder, furnaced cryoconite without OM, or powdered rocks from glacial catchment) revealed that cyanobacteria bind mineral particles into granules. The structures formed in the experiment resembled those commonly observed in natural cryoconite holes: they contained numerous cyanobacterial filaments protruding from aggregated mineral particles. Moreover, all examined strains were confirmed to produce extracellular polymeric substances (EPS), which suggests that cryoconite granulation is most likely due to EPS secretion by gliding cyanobacteria. In the presence of water as the only substrate for growth, cyanobacteria formed mostly carpet-like mats. Our data empirically prove that EPS-producing oscillatorialean cyanobacteria isolated from the diverse community of cryoconite microorganisms can form granules from mineral substrate and that the presence of the mineral substrate increases the probability of the formation of these important and complex biogeochemical microstructures on glaciers.     

Culture Independent Diversity of Bacterial Communities Indigenous to Lower Altitude at Laohugou Glacial Environment

Abstract

High-throughput sequencing approach of the 16S rRNA gene was employed to evaluate the bacterial diversity inhabit in melted water, snow, soil, and rocks samples at the lower altitudes of the Laohugou glacial environment. Bioinformatics tools were used to process millions of Illumina reads for alpha and beta diversities of bacterial communities. The diversity indices such as Chao, Shannon, and Simpson were different in the collected samples and solid samples (soil and rocks) showed higher taxon richness and evenness. Taxonomic diversity was unexpectedly higher and the major portion of sequences was assigned to Proteobacteria, Actinobacteria, and Acidobacteria. Higher variation in community structure was reported at the class level and Alphaproteobacteria was dominant. The solid niches were occupied by a higher number of phyla compared with liquid. The physicochemical variables acted as spatial gradients and associated with the bacterial structural communities of the glacial ecosystem. Findings showed that both Proteobacteria and Actinobacteria in solid samples influenced the bacterial community structure in downstream liquid samples. Interestingly, the metagenomic biomarkers were higher in liquid samples. This study provides precious datasets to understand the bacterial community in a better way under the influence of spatial, physical and environmental factors.     

Loss of small glaciers will diminish beta diversity in Pyrenean streams at two levels of biological organization

Aim Small (< 1 km²) alpine glaciers are likely to disappear in this century, resulting in decreased regional habitat heterogeneity in associated streams. Both heterogeneity within and spatial isolation among glacier‐influenced streams can enhance beta diversity of stream‐dwelling organisms. We measured beta at both community and population‐genetic levels within and among streams currently influenced by small Pyrenean glaciers. We aimed to evaluate whether patterns are analogous between the two levels, to apply various approaches for characterizing beta, and to infer the outcome of future glacier loss on regional biodiversity. Location Four glacier‐fed basins in the Parc National des Pyrénées, France. Methods We classified each of 18 stream reaches across the basins into either high‐, mid‐ or low‐‘glaciality’ (glacial influence) groups according to four physicochemical characteristics. At each reach, we collected macroinvertebrate communities and evaluated mitochondrial DNA haplotypes for 11–13 individuals of Baetis alpinus Pictet. Using taxa/haplotypes as basic units, we evaluated community and population‐genetic beta diversity simultaneously. We measured beta diversity in three major ways: as multivariate (Sørensen's dissimilarity, Jost D) and ‘classical’ (gamma/alpha) variation to compare among glaciality groups, and as turnover along the glaciality gradient within each basin. Results For most approaches at both organizational levels, beta was greatest among high‐glaciality reaches, absolute values of variation of beta in high‐glaciality streams were strikingly similar between levels, and the steepest turnover within basins occurred between high‐ and mid‐glaciality reaches. Therefore, high‐glaciality reaches contained assemblages and populations that were unique both within that stream type (among basins) and compared with other stream types within basins. Main conclusions Parallel beta diversity patterns at population‐genetic and community levels suggested that environmental drivers influence these levels analogously. Extreme conditions (e.g. low temperature, high instability, isolation) in high‐glaciality streams probably enhance beta at both levels. Stream beta diversity is likely to decrease substantially with continued glacial reduction in this system.     

冰川退缩地15种丛藓科植物茎的比较结构学观察

应用石蜡切片和扫描电镜方法对一号冰川退缩地生长的15种丛藓科植物茎的结构及表面微形态特征进行观察,结果表明：该地区的15种丛藓科植物的茎分为具中轴和无中轴两类,其细胞壁均有不同程度的加厚。而具中轴的丛藓科植物的茎又分为表皮、皮部、中轴三部分,茎表皮细胞短,1层,细胞壁大多向外突出,表面粗糙,表面纹饰多为颗粒状;皮部所占面积最大,大部分有内、外皮部的分化,大多数种的细胞壁由外向内逐渐变薄,细胞由小到大整齐排列;中轴所占的面积也不同,其细胞壁多具角隅加厚;而没有中轴分化的种类,其各自细胞壁加厚的程度基本一致。     

冰川退缩地26种丛藓科植物叶中肋细胞结构的研究

该研究应用离析方法,并通过光学显微镜对新疆天山一号冰川退缩地的26种丛藓科植物叶片中肋细胞的形态结构进行比较分析,结果表明:(1)丛藓科植物叶片的中肋细胞的长、宽和细胞壁厚度、纹孔场数目及细胞端尾数目在一定程度上存在着差异,反映出各中肋细胞的功能及导水作用在同属及不同属植物之间存在一定的差异。(2)中肋细胞的端尾多以及细胞壁的波状结构都具有增强细胞间的联系、提高机械固着和支撑作用。(3)不同生境下,中肋细胞侧壁的纹孔场数目能有效控制导水和物质交换的速度。这些特征可能都是冰川地区苔藓植物对恶劣生境的积极响应,具有一定的生态学和分类学意义。     

Egg development and hatching success in alpine chironomids

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Climate warming could increase recruitment success in glacier foreland plants

Background and Aims Glacier foreland plants are highly threatened by global warming. Regeneration from seeds on deglaciated terrain will be crucial for successful migration and survival of these species, and hence a better understanding of the impacts of climate change on seedling recruitment is urgently needed to predict future plant persistence in these environments. This study presents the first field evidence of the impact of climate change on recruitment success of glacier foreland plants.Methods Seeds of eight foreland species were sown on a foreland site at 2500 m a.s.l., and at a site 400 m lower in altitude to simulate a 2·7 °C increase in mean annual temperature. Soil from the site of origin was used to reproduce the natural germination substrate. Recruitment success, temperature and water potential were monitored for 2 years. The response of seed germination to warming was further investigated in the laboratory.Key Results At the glacier foreland site, seedling emergence was low (0 to approx. 40 %) and occurred in summer in all species after seeds had experienced autumn and winter seasons. However, at the warmer site there was a shift from summer to autumn emergence in two species and a significant increase of summer emergence (13–35 % higher) in all species except two. Survival and establishment was possible for 60–75 % of autumn-emerged seedlings and was generally greater under warmer conditions. Early snowmelt in spring caused the main ecological factors enhancing the recruitment success.Conclusions The results suggest that warming will influence the recruitment of glacier foreland species primarily via the extension of the snow-free period in spring, which increases seedling establishment and results in a greater resistance to summer drought and winter extremes. The changes in recruitment success observed here imply that range shifts or changes in abundance are possible in a future warmer climate, but overall success may be dependent on interactions with shifts in other components of the plant community.     

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