Patterns and Potential Drivers of Dramatic Changes in Tibetan Lakes, 1972–2010

Most glaciers in the Himalayas and the Tibetan Plateau are retreating, and glacier melt has been emphasized as the dominant driver for recent lake expansions on the Tibetan Plateau. By investigating detailed changes in lake extents and levels across the Tibetan Plateau from Landsat/ICESat data, we found a pattern of dramatic lake changes from 1970 to 2010 (especially after 2000) with a southwest-northeast transition from shrinking, to stable, to rapidly expanding. This pattern is in distinct contrast to the spatial characteristics of glacier retreat, suggesting limited influence of glacier melt on lake dynamics. The plateau-wide pattern of lake change is related to precipitation variation and consistent with the pattern of permafrost degradation induced by rising temperature. More than 79% of lakes we observed on the central-northern plateau (with continuous permafrost) are rapidly expanding, even without glacial contributions, while lakes fed by retreating glaciers in southern regions (with isolated permafrost) are relatively stable or shrinking. Our study shows the limited role of glacier melt and highlights the potentially important contribution of permafrost degradation in predicting future water availability in this region, where understanding these processes is of critical importance to drinking water, agriculture, and hydropower supply of densely populated areas in South and East Asia.     

三极冰川冰尘微生物及其介导的碳氮生物地球化学循环研究进展

冰尘是散落在冰川表面由矿物质、有机质和微生物组成的聚合体,其主要来源包括远源输送来的细粉尘和气溶胶组分、局地源的粗冰碛物及来自周围生态系统的土壤和植物碎屑等。冰尘对太阳辐射具有较强的吸收作用,可降低冰面反照率、促进冰川融化。冰尘也是迄今为止生物多样性最高的冰川表面微生物栖息地,生活着细菌、真菌、藻类等。冰尘微生物是冰川表面地球化学循环的主要驱动者,微生物分解转化冰尘内有机质,降低冰川表面反照率影响冰川物质平衡。基于冰尘的重要性,本文综述了南极、北极、青藏高原第三极冰川冰尘的物理和化学特征及其影响因素,冰尘微生物群落组成及其介导的碳氮生物地球化学循环过程,并展望了冰尘微生物研究的前景。     

A distinctive fungal community inhabiting cryoconite holes on glaciers in Svalbard

Cryoconite holes on glacier surfaces are ice-cold hot spots of microbial diversity and activity but still little is known about their fungal inhabitants. We provide the first report of distinctive fungal communities in cryoconite debris from three valley glaciers at Kongsfjorden, Svalbard. Multivariate analysis of terminal-restriction fragment length polymorphism (T-RFLP) profiles of rRNA ITS amplicons revealed that quite distinct fungal communities were found in cryoconite holes compared with soils from adjacent moraine and tundra sites, and that communities on glaciers with contrasting ice-surface hydrology also differed. Most of the fungi cultured from cryoconite sediment were basidiomycetous yeasts or filamentous Ascomycota (Helotiales/Pleosporales). The latter included aeroaquatic fungi, such as Articulospora and Varicosporium, implying a role for these important freshwater decomposers in the carbon dynamics of cryoconite holes. Matching of the dominant peaks from T-RFLP analysis to predicted peaks of cultured isolates confirmed the abundance of these aeroaquatic fungi but also revealed that most of the dominant T-RFLP peaks did not match any cultured isolates. Considering the prevalence and endangerment of glacial environments worldwide, these findings would suggest that their potential as reservoirs of fungal diversity should not be overlooked.     

Fate of glacier surface snow-originating bacteria in the glacier-fed hydrologic continuums

Glaciers represent important biomes of Earth and are recognized as key species pools for downstream aquatic environments. Worldwide, rapidly receding glaciers are driving shifts in hydrology, species distributions and threatening microbial diversity in glacier-fed aquatic ecosystems. However, the impact of glacier surface snow-originating taxa on the microbial diversity in downstream aquatic environments has been little explored. To elucidate the contribution of glacier surface snow-originating taxa to bacterial diversity in downstream aquatic environments, we collected samples from glacier surface snows, downstream streams and lakes along three glacier-fed hydrologic continuums on the Tibetan Plateau. Our results showed that glacier stream acts as recipients and vectors of bacteria originating from the glacier environments. The contributions of glacier surface snow-originating taxa to downstream bacterial communities decrease from the streams to lakes, which was consistently observed in three geographically separated glacier-fed ecosystems. Our results also revealed that some rare snow-originating bacteria can thrive along the hydrologic continuums and become dominant in downstream habitats. Finally, our results indicated that the dispersal patterns of bacterial communities are largely determined by mass effects and increasingly subjected to local sorting of species along the glacier-fed hydrologic continuums. Collectively, this study provides insights into the fate of bacterial assemblages in glacier surface snow following snow melt and how bacterial communities in aquatic environments are affected by the influx of glacier snow-originating bacteria.     

Possible interactions between bacterial diversity,microbial activity and supraglacial hydrology of cryoconite holes in Svalbard

The diversity of highly active bacterial communities in cryoconite holes on three Arctic glaciers in Svalbard was investigated using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA locus. Construction and sequencing of clone libraries allowed several members of these communities to be identified, with Proteobacteria being the dominant one, followed by Cyanobacteria and Bacteroidetes. T-RFLP data revealed significantly different communities in holes on the (cold) valley glacier Austre Brøggerbreen relative to two adjacent (polythermal) valley glaciers, Midtre Lovénbreen and Vestre Brøggerbreen. These population compositions correlate with differences in organic matter content, temperature and the metabolic activity of microbial communities concerned. No within-glacier spatial patterns were observed in the communities identified over the 2-year period and with the 1 km-spaced sampling. We infer that surface hydrology is an important factor in the development of cryoconite bacterial communities.     

High microbial activity on glaciers: importance to the global carbon cycle

Cryoconite holes, which can cover 0.1–10% of the surface area of glaciers, are small, water-filled depressions (typically <1 m in diameter and usually <0.5 m deep) that form on the surface of glaciers when solar-heated inorganic and organic debris melts into the ice. Recent studies show that cryoconites are colonized by a diverse range of microorganisms, including viruses, bacteria and algae. Whether microbial communities on the surface of glaciers are actively influencing biogeochemical cycles or are just present in a dormant state has been a matter of debate for long time. Here, we report primary production and community respiration of cryoconite holes upon glaciers in Svalbard, Greenland and the European Alps. Microbial activity in cryoconite holes is high despite maximum temperatures seldom exceeding 0.1 °C. In situ primary production and respiration in cryoconites during the summer is often comparable with that found in soils in warmer and nutrient richer regions. Considering only glacier areas outside Antarctica and a conservative average cryoconite distribution on glacial surfaces, we found that on a global basis cryoconite holes have the potential to fix as much as 64 Gg of carbon per year (i.e. 98 Gg of photosynthesis minus 34 Gg of community respiration). Most lakes and rivers are generally considered as heterotrophic systems, but our results suggest that glaciers, which contain 75% of the freshwater of the planet, are largely autotrophic systems.     

Microbial biodiversity in glacier-fed streams

While glaciers become increasingly recognised as a habitat for diverse and active microbial communities, effects of their climate change-induced retreat on the microbial ecology of glacier-fed streams remain elusive. Understanding the effect of climate change on microorganisms in these ecosystems is crucial given that microbial biofilms control numerous stream ecosystem processes with potential implications for downstream biodiversity and biogeochemistry. Here, using a space-for-time substitution approach across 26 Alpine glaciers, we show how microbial community composition and diversity, based on 454-pyrosequencing of the 16S rRNA gene, in biofilms of glacier-fed streams may change as glaciers recede. Variations in streamwater geochemistry correlated with biofilm community composition, even at the phylum level. The most dominant phyla detected in glacial habitats were Proteobacteria, Bacteroidetes, Actinobacteria and Cyanobacteria/chloroplasts. Microorganisms from ice had the lowest α diversity and contributed marginally to biofilm and streamwater community composition. Rather, streamwater apparently collected microorganisms from various glacial and non-glacial sources forming the upstream metacommunity, thereby achieving the highest α diversity. Biofilms in the glacier-fed streams had intermediate α diversity and species sorting by local environmental conditions likely shaped their community composition. α diversity of streamwater and biofilm communities decreased with elevation, possibly reflecting less diverse sources of microorganisms upstream in the catchment. In contrast, β diversity of biofilms decreased with increasing streamwater temperature, suggesting that glacier retreat may contribute to the homogenisation of microbial communities among glacier-fed streams.     

Fukushima Nuclear Accident Recorded in Tibetan Plateau Snow Pits

The β radioactivity of snow-pit samples collected in the spring of 2011 on four Tibetan Plateau glaciers demonstrate a remarkable peak in each snow pit profile, with peaks about ten to tens of times higher than background levels. The timing of these peaks suggests that the high radioactivity resulted from the Fukushima nuclear accident that occurred on March 11, 2011 in eastern Japan. Fallout monitoring studies demonstrate that this radioactive material was transported by the westerlies across the middle latitudes of the Northern Hemisphere. The depth of the peak β radioactivity in each snow pit compared with observational precipitation records, suggests that the radioactive fallout reached the Tibetan Plateau and was deposited on glacier surfaces in late March 2011, or approximately 20 days after the nuclear accident. The radioactive fallout existed in the atmosphere over the Tibetan Plateau for about one month.     

Response of Glacier and Lake Dynamics in Four Inland Basins to Climate Change at the Transition Zone between the Karakorum And Himalayas

Inland glacier and lake dynamics on the Tibetan Plateau (TP) and its surroundings over recent decades are good indicators of climate change and have a significant impact on the local water supply and ecosystem. The glacier and lake changes in Karakoram are quite different from those of the Himalayas. The mechanisms of the complex and regionally heterogeneous behavior of the glacier and lake changes between the Karakorum and Himalayas are poorly understood. Based on satellite images and meteorological data of Shiquanhe, Hetian, and Yutian stations, we demonstrate that the overall retreat of glaciers and increase of lake area at the transition zone between the Karakoram and Himalayas (TKH) have occurred since 1968 in response to a significant global climate change. Glacial areas in the Songmuxi Co basin, Zepu Co basin, Mang Co basin and Unnamed Co decreased by -1.98 ± 0.02 km², -5.39 ± 0.02 km², -0.01 ± 0.02 km², and -0.12 ± 0.02 km² during the study period, corresponding to losses of -1.42%, -2.86%, -1.54%, and -1.57%, respectively. The lake area of the Songmuxi Co, Zepu Co, Mang Co and Unnamed Co increased by 7.57 ± 0.02 km², 8.53 ± 0.02 km², 1.35 ± 0.02 km², and 0.53±0.02 km², corresponding to growths of 30.22%, 7.55%, 11.39%, and 8.05%, respectively. Increases in temperature was the main reason for glacier retreat, whereas decreases in potential evapotranspiration of lakes, increases in precipitation, and increases in melt water from glaciers and frozen soil all contributed to lake area expansion.     

Effects of chlorophyll a, chlorophyll b, and xanthophylls on the in vitro assembly kinetics of the major light-harvesting chlorophyll a/b complex, LHCIIb

The major light-harvesting chlorophyll a/b complex (LHCIIb) of photosystem II in higher plants can be reconstituted with pigments in lipid-detergent micelles. The pigment-protein complexes formed are functional in that they perform efficient internal energy transfer from chlorophyll b to chlorophyll a. LHCIIb formation in vitro, can be monitored by the appearance of energy transfer from chlorophyll b to chlorophyll a in time-resolved fluorescence measurements. LHCIIb is found to form in two apparent kinetic steps with time constants of about 30 and 200 seconds. Here we report on the dependence of the LHCIIb formation kinetics on the composition of the pigment mixture used in the reconstitution. Both kinetic steps slow down when the concentration of either chlorophylls or carotenoids is reduced. This suggests that the slower 200 seconds formation of functional LHCIIb still includes binding of both chlorophylls and carotenoids. LHCIIb formation is accelerated when the chlorophylls in the reconstitution mixture consist predominantly of chlorophyll a although the complexes formed are thermally less stable than those reconstituted with a chlorophyll a:b ratio < or = 1. This indicates that although chlorophyll a binding is more dominant in the observed rate of LHCIIb formation, the occupation of (some) chlorophyll binding sites with chlorophyll b is essential for complex stability. The accelerating effect of various carotenoids (lutein, zeaxanthin, violaxanthin, neoxanthin) on LHCIIb formation correlates with their affinity to two lutein-specific binding sites. We conclude that the occupation of these two carotenoid binding sites but not of the third (neoxanthin-specific) binding site is an essential step in the assembly of LHCIIb in vitro.     

LIPOPHILIC PIGMENTS FROM CYANOBACTERIAL (BLUE-GREEN ALGAL) AND DIATOM MATS IN HAMELIN POOL,SHARK BAY,WESTERN AUSTRALIA1

Lipophilic pigments were examined in microbial mat communities dominated by cyanobacteria in the intertidal zone and by diatoms in the subtidal and sublittoral zones of Hamelin Pool, Shark Bay, Western Australia. These microbial mats have evolutionary significance because of their similarity to lithified stromatolites from the Proterozoic and Early Paleozoic eras. Fucoxanthin, diatoxanthin, diadinoxanthin, β-carotene, and chlorophylls a and c characterized the diatom mats, whereas cyanobacterial mats contained myxoxanthophyll zeaxanthin, echinenone, β-carotene, chlorophyll a and, in some cases, sheath pigment. The presence of bacteriochlorophyll a with in the mats suggest a close association of photosynthetic bacteria with diatoms and cyanobacteria. The high carotenoids: chlorophyll a ratios (0.84–2.44 wt/wt) in the diatom mats suggest that carotenoids served a photoprotective function in this high light environment. By contrast, cyanobacterial sheath pigment may have largely supplanted the photoprotective role of carotenoids in the intertidal mats.     

冰川消退带微生物群落演替及生物地球化学循环

冰川是生物圈重要组分之一。由于全球气候变化世界多地冰川加速消融,暴露原本被冰盖覆盖的区域,这些区域被称为冰川消退区域(glacier retreat area)或冰川前部区域(glacier foreland)。自暴露开始消退区随即发生初生演替,随着演替进行,物质循环逐步建立,生物量和土壤C、N总量逐步增加。生态系统C、N输入最初以矿化外来物为主,逐渐转变为以生物固C、固N为主。演替早期生态系统的发育主要受土壤C、N含量的限制,而演替后期的限制性营养物转变为P。演替区域土壤逐渐发育并促进生态位的分化,细菌、真菌、古菌,病毒及其他微生物群落的生物量和多样性不断增加直至达到该地区可承受的极值。随着生存条件的改善,不同生态策略物种的更替导致每个演替阶段微生物群落结构的差异。整体上,伴随演替进行微生物群落丰度、结构和活性呈现梯度性变化。气候变化对冰川消退带生态演替结果产生多方面的影响,而这些影响结果又综合反馈气候变化,因此目前难以准确估计气候变化对消退带生态演替的净效应。综述了近年冰川消退带微生物群落演替方面相关的研究结果,同时分别对该区域物质循环的建立、微生物群落演替和气候变化造成的影响这三个方面进行详细描述,并指出当前研究的不足。     

Microbial Communities on Glacier Surfaces in Svalbard: Impact of Physical and Chemical Properties on Abundance and Structure of Cyanobacteria and Algae

Microbial communities occurring in three types of supraglacial habitats—cryoconite holes, medial moraines, and supraglacial kames—at several glaciers in the Arctic archipelago of Svalbard were investigated. Abundance, biovolume, and community structure were evaluated by using epifluorescence microscopy and culturing methods. Particular emphasis was laid on distinctions in the chemical and physical properties of the supraglacial habitats and their relation to the microbial communities, and quantitative multivariate analyses were used to assess potential relationships. Varying pH (4.8 in cryoconite; 8.5 in a moraine) and texture (the proportion of coarse fraction 2% of dry weight in cryoconite; 99% dw in a kame) were found, and rather low concentrations of organic matter (0.3% of dry weight in a kame; 22% dw in cryoconite) and nutrients (nitrogen up to 0.4% dw, phosphorus up to 0.8% dw) were determined in the samples. In cryoconite sediment, the highest numbers of bacteria, cyanobacteria, and algae were found, whereas relatively low microbial abundances were recorded in moraines and kames. Cyanobacterial cells were significantly more abundant than microalgal ones in cryoconite and supraglacial kames. Different species of the cyanobacterial genus Leptolyngbya were by far the most represented in all samples, and cyanobacteria of the genera Phormidium and Nostoc prevailed in cultures isolated from cryoconite samples. These species are considered opportunistic organisms with wide ecological valency and strong colonizing potential rather than glacial specialists. Statistical analyses suggest that fine sediment with higher water content is the most suitable condition for bacteria, cyanobacteria, and algae. Also, a positive impact of lower pH on microbial growth was found. The fate of a microbial cell deposited on the glacier surface seems therefore predetermined by the physical and chemical factors such as texture of sediment and water content rather than spatial factors or the origin of sediment.     

THE EFFECTIVENESS OF THE SPECTRUM IN CHLOROPHYLL FORMATION

1. Although the carotenoid pigments are present in large concentration in the plastids of etiolated Avena seedlings as compared with protochlorophyll, the pigment precursor of chlorophyll, it is possible to show that the carotenoids do not act as filters of the light incident on the plant in the blue region of the spectrum where they absorb heavily. This suggests that the carotenoids are located behind the protochlorophyll molecules in the plastids. 2. Since the carotenoids do not screen and light is necessary for chlorophyll formation, an effectiveness spectrum of protochlorophyll can be obtained which is the reciprocal of the light energy necessary to produce a constant amount of chlorophyll with different wavelengths. The relative effectiveness of sixteen spectral regions in forming chlorophyll was determined. 3. From the effectiveness spectrum, one can conclude that protochlorophyll is a blue-green pigment with major peaks of absorption at 445 mµ, and 645 mµ, and with smaller peaks at 575 and 545 mµ. The blue peak is sharp, narrow, and high, the red peak being broader and shorter. This differs from previous findings where the use of rougher methods indicated that red light was more effective than blue and did not give the position of the peaks of absorption or their relative heights. 4. The protochlorophyll curve is similar to but not identical with chlorophyll. The ratio of the peaks of absorption in the blue as compared to the red is very similar to chlorophyll a, but the position of the peaks resembles chlorophyll b. 5. There is an excellent correspondence between the absorption properties of this "active" protochlorophyll and what is known of the absorption of a chemically known pigment studied in impure extracts of seed coats of the Cucurbitaceae. Conclusive proof of the identity of the two substances awaits chemical purification, but the evidence here favors the view that the pumpkin seed substance, which is chemically chlorophyll a minus two hydrogens, is identical with the precursor of chlorophyll formation found in etiolated plants.     

Abundance and Diversity of Glacial Bacteria on the Tibetan Plateau with Environment

The relation of glacial microorganism and their living environment is concerned but less understood for both glaciologists and microbiologists. Here we present the results about glacial snow bacteria from 3 glaciers on the Tibetan Plateau. The concentrations and diversity of bacteria collected from snow pit samples of East Rongbuk, Laohugou and Hailuogou glaciers on the Tibetan Plateau were investigated by epifluorescence microscope, denaturing gradient gel electrophoresis and Shannon-Weaver index. Concentrations and community diversity of bacteria in the East Rongbuk glacier with lower concentration and smaller size of microparticle were lower than in the Laohugou with higher concentration and larger size of microparticle. Bacterial concentration in East Rongbuk Glacier was close to that in polar regions, suggesting that Mt. Everest is a bacterial background for remote regions away from direct influence of anthropogenic sources. In addition, altitude difference was another factor for higher concentrations and community diversity of bacteria in Hailuogou and Laohugou glaciers than in East Rongbuk Glacier. The highest concentrations and community diversity of bacteria in Hailuogou Glacier were attributed to its most diverse atmospheric circulations and highest temperature among the 3 glaciers. We suggest a complicated correlation between glacial bacteria and their regional living environments.     

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.     

Microbial Assemblages in Soil Microbial Succession After Glacial Retreat in Svalbard (High Arctic)

Microbial community composition (cyanobacteria and eukaryotic microalgae abundance and diversity, bacterial abundance, and soil respiration) was studied in subglacial and periglacial habitats on five glaciers near Ny-Alesund, Svalbard (79 degrees N). Soil microbial communities from nonvegetated sites (subglacial, recently deglaciated, and cryoconite sediments) and sites with plant cover (deglaciated some hundreds of years ago) were analyzed. Physicochemical analyses (pH, texture, water content, organic matter, total C and N content) were also performed on the samples. In total, 57 taxa of 23 genera of cyanobacteriaand algae were identified. Algae from the class Chlorophyceae (25 species) and cyanobacteria (23 species) were richest in biodiversity. The numbers of identified species in single habitat types were 23 in subglacial, 39 inbarren, 22 in cryoconite, and 24 in vegetated soils. The highest cyanobacterial and algal biovolume and cell numbers, respectively, were present in cryoconite (13x10(4) microm3 mg-1 soil and 508 cells per mg of soil), followed by barren (5.7x10(4) and 188), vegetated (2.6x10(4) and 120), and subglacial (0.1x10(4) and 5) soils. Cyanobacteria prevailed in all soil samples. Algae (mainly green algae) were present only as accessory organisms. The density of bacteria showed a slightly different trend to that of the cyanobacterial and algal assemblages. The highest number of bacteria was present in vegetated (mean: 13,722x10(8) cells per mg of soil dry wt.), followed by cryoconite (3802x10(8)), barren (654x10(8)), and subglacial (78x10(8)) soils. Response of cyanobacteria and algae to physical parameters showed that soil texture and water content are important for biomass development. In addition, it is shown that nitrogen and water content are the main factors affecting bacterial abundance and overall soil respiration. Redundancy analysis (RDA) with forward selection was used to create a model explaining variability in cyanobacterial, algal, and bacterial abundance. Cryoconites accounted for most of the variation in cyanobacteria and algae biovolume, followed by barren soils. Oscillatoriales, desmids, and green coccoid algae preferred cryoconites, whereas Nostocales and Chroococcales occurred mostly in barren soils. From the data obtained, it is evident that of the studied habitats cryoconite sediments are the most suitable ones for the development of microbial assemblages. Although subglacial sediments do not provide as good conditions as cryoconites, they support the survival of microbial communities. Both mentioned habitats are potential sources for the microbial recolonization of freshly deglaciated soil after the glacier retreat.     

Gradient analysis of cryoconite ecosystems from two polar glaciers

The cylindrical meltholes present in the ablation zones of many glaciers (termed cryoconite holes) contain complex microbial communities. A canonical correspondence analysis (CCA) of community structure and environmental gradients for cryoconite holes on two glaciers was undertaken. The Canada Glacier (77°37S, 162°55E) is located in the McMurdo Dry Valleys of Antarctica. The White Glacier (79°27N, 90°40W) is located on Axel Heiberg Island, Nunavut Territory, Canada. These glaciers are at similar, yet antipodal latitudes, are roughly the same size and endure approximately the same mean annual temperature. The Canada Glacier cryoconite communities were found to be significantly (P=0.001) associated with six environmental variables, which together explained 55% of the biological variation. The White Glacier cryoconite communities were not significantly associated with environmental variables. The differences in CCA results were attributed to the relative amount of disturbance and isolation between each glaciers cryoconite holes. Canada Glacier cryoconite holes were mostly ice-covered and undisturbed by meltwater flow, whereas high meltwater production and open cryoconite holes on the White Glacier may continually reset the community structure and habitat variability due to inter-hole mixing.     

Light‐induced pigment degradation in leaves and ripening fruits studied in situ with reflectance spectroscopy

Pigment breakdown mediated by activated oxygen species is a consequence and a general symptom of oxidative stress and injury to plants. We have attempted to estimate the patterns of pigment bleaching and follow pigment susceptibility to irradiation as related to the process of senescence/ripening. Light‐induced pigment breakdown was studied in situ in the leaves of a shade‐requiring plant, wax flower ( Hoya carnosa R. Br.), as well as in apple ( Malus domestica Borlh. cv. Zhigulevskoe) and lemon ( Citrus limon Burm. cv. Pavlovsky) fruits, using reflectance spectroscopy. It was found that the sensitivity of plant pigments to photobleaching increases as ripening progresses in lemon fruit. Kinetic analysis showed that in all systems a rapid breakdown of the pigment occurs after a lag‐phase. The signature analysis revealed a common pattern of chlorophyll and carotenoid changes, but degradation of the individual pigments was found to be inhomogeneous. Both in lemon and apple fruits a decrease in reflectance in the band of carotenoid absorption preceded pigment photodestruction. In the fruits, the bulk of chlorophyll b and the long‐wavelength chlorophyll a forms were degraded at early stages of the process whereas the breakdown of both chlorophylls in H. carnosa leaves was more synchronous. Prolonged irradiation induced bleaching of the main chlorophyll a band with maximum at 678 nm in the difference spectra, as well as carotenoids. Some features of reflectance spectra in the bands of chlorophyll and carotenoid absorption were found to be suitable for the differentiation of photo‐induced pigment breakdown from the transformation of the pigments taking place during senescence.     

Leaf senescence in a non-yellowing mutant of Festuca pratensis: Degradation of carotenoids

The loss of pigments was assessed in detached leaves of Festuca pratensis Huds. kept in permanent darkness. Two genotypes, a normal yellowing cultivar Rossa and a non-yellowing mutant Bf 993 were compared with each other. Analysis of individual pigments, chlorophylls. β-carotene, lutein, violaxanthin and neoxanthin was performed using HPLC. In the non-yellowing genotype the high retention of chlorophylls was associated with an equally high retention of total carotenoids. Although the two genotypes differ markedly with regard to the rate of pigment loss, the ratios of yellow to green pigments did not change significantly during dark-induced senescence. At the end of the senescence period β-carotene was retained to a higher degree than the xanthophylls, particularly in the yellowing genotype. In the mutant leaves the ratio of chlorophyll a to b remained nearly constant, whereas in leaves of the normal genotype a preferential retention of chlorophyll b was observed towards the end of the senescence period. It is concluded that the thylakoids of the non-yellowing genotype retain all the principal components of protein-pigment complexes, i.e. chlorophylls, carotenoids and apoproteins. Possible explanations for the stability of these complexes in the mutant are discussed.