Table 2: Evaporation from individual shoots of antarctic mosses

Experimental observations on pathways of water movement are discussed in relation to anatomical and micromorphological features of five moss species from Signy Island, South Orkney Islands. Significant internal uptake of water was recorded only in the mesic species Polytrichum alpinum (internal=>60% of total) and Bartramia patens (internal=c.30% of total), in experiments in which uptake by cut shoots was compared in individuals with the external pathway blocked, and others with both external and internal pathways open. Internal uptake maintained shoot water content close to full turgor in P. alpinun and at 30% of full tugor in B. patens, whereas water content fell to 12-15% dry wt. in the lithophytes Andreaea gainii and Schistidium antarctici and in the mesic/hydric species Drepanocladus uncinatus, with the external pathway blocked. Where both pathways were open water uptake from below maintained water content at or above full turgor in shoots of all five species. External water uptake by capillarity occurred most rapidly in the lithophytes, and was slower in initially air-dry than in hydrated shoots of the other species. The spreading limbs of leaves in B. patens and P. alpinum are water-repellent, as are the bright green leaves in the apical 1-2 mm of dry shoots of the lithophytes. A central strand of hydroids is well-developed only in B. patens and P. alpinum. These two species have deposits of surface wax on parts of the leaves, and surface wax also occurs on the green apical leaves in some specimens of S. antarcticum and other lithophytes from Signy Island.

Tab. 1: Mean water loss by mosses and lichens at 40%

The loss of water in a desiccating atmosphere (c.40% r.h. at 10°C) and uptake of water from a saturated atmosphere (100% r.h. at 10°C) was recorded at intervals over periods of many hours or days in the dominant mosses and macroiichens occurring near the Australian Casey Station. Wilkes Land, continental Antarctica. While major differences exist in the water holding capacity and rates of water loss between mosses and lichens, the minimum levels attained after prolonged exposure to desiccating conditions are remarkably similar. By contrast, the volume of water absorbed from a saturated atmosphere is very similar in both groups of cryptogams. Morphological and anatomical characters are responsible for many of the differences, both between species, and within species exhibiting different growth features. Thus, significantly larger amounts of water are held by colonies of Bryum algens with a dense tomentum of rhizoids than those with sparse rhizoids; similarly, the rhizinate Umbilicaria aprina held a greater volume of water than the erhizinate U. decussata. The filamentous mat form of Alectoria mimiscula permits a much higher water content to be attained than in the coarser fruticose forms of Usnea sphacelata and U. antarctica. The dense shoot arrangement in Schistidium antarcticum accounts for the high water holding capacity in the hydric turf form whereas the less densely packed shoots and thicker cell walls of the xeric cushion form maintain a lower water content. The rate of water loss (as percentage dry weight) was much faster in the turf form of Schistidium and tomenlose form of Bryum, although this trend was reversed when expressed as percentage of the initial water content. Minimal water contents arc achieved by the lichens in desiccating conditions within 6-12 hours, whereas the mosses take several times longer. The water relations characteristics of these cryptogams are considered in the light of their distribution in the field and of their metabolic activity under prevailing Antarctic conditions.

Environment and habitat characteristics of wintering lemmings in the Arctic

Snow cover has dramatic effects on the structure and functioning of Arctic ecosystems in winter. In the tundra, the subnivean space is the primary habitat of wintering small mammals and may be critical for their survival and reproduction. We have investigated the effects of snow cover and habitat features on the distributions of collared lemming (Dicrostonyx groenlandicus) and brown lemming (Lemmus trimucronatus) winter nests, as well as on their probabilities of reproduction and predation by stoats (Mustela erminea) and arctic foxes (Vulpes lagopus). We sampled 193 lemming winter nests and measured habitat features at all of these nests and at random sites at two spatial scales. We also monitored overwinter ground temperature at a subsample of nest and random sites. Our results demonstrate that nests were primarily located in areas with high micro-topography heterogeneity, steep slopes, deep snow cover providing thermal protection (reduced daily temperature fluctuations) and a high abundance of mosses. The probability of reproduction increased in collared lemming nests at low elevation and in brown lemming nests with high availability of some graminoid species. The probability of predation by stoats was density dependent and was higher in nests used by collared lemmings. Snow cover did not affect the probability of predation of lemming nests by stoats, but deep snow cover limited predation attempts by arctic foxes. We conclude that snow cover plays a key role in the spatial structure of wintering lemming populations and potentially in their population dynamics in the Arctic.

Carbon/Nitrogen ratio of plant tissues and biomass of belowground consumers after 11 years of experimental treatment, Toolik lake

Theory and observation indicate that changes in the rate of primary production can alter the balance between the bottom-up influences of plants and resources and the top-down regulation of herbivores and predators on ecosystem structure and function. The Exploitation Ecosystem Hypothesis (EEH) posited that as aboveground net primary productivity (ANPP) increases, the additional biomass should support higher trophic levels. We developed an extension of EEH to include the impacts of increases in ANPP on belowground consumers in a similar manner as aboveground, but indirectly through changes in the allocation of photosynthate to roots. We tested our predictions for plants aboveground and for phytophagous nematodes and their predators belowground in two common arctic tundra plant communities subjected to 11 years of increased soil nutrient availability and/or exclusion of mammalian herbivores. The less productive dry heath (DH) community met the predictions of EEH aboveground, with the greatest ANPP and plant biomass in the fertilized plots protected from herbivory. A palatable grass increased in fertilized plots while dwarf evergreen shrubs and lichens declined. Belowground, phytophagous nematodes also responded as predicted, achieving greater biomass in the higher ANPP plots, whereas predator biomass tended to be lower in those same plots (although not significantly). In the higher productivity moist acidic tussock (MAT) community, aboveground responses were quite different. Herbivores stimulated ANPP and biomass in both ambient and enriched soil nutrient plots; maximum ANPP occurred in fertilized plots exposed to herbivory. Fertilized plots became dominated by dwarf birch (a deciduous shrub) and cloudberry (a perennial forb); under ambient conditions these two species coexist with sedges, evergreen dwarf shrubs, and Sphagnum mosses. Phytophagous nematodes did not respond significantly to changes in ANPP, although predator biomass was greatest in control plots. The contrasting results of these two arctic tundra plant communities suggest that the predictions of EEH may hold for very low ANPP communities, but that other factors, including competition and shifts in vegetation composition toward less palatable species, may confound predicted responses to changes in productivity in higher ANPP communities such as the MAT studied here.

Initial biomass and biomass change of tundra and forest plants in three herbivore treatments in Norway and Sweden

Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana, has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (> 0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (< 0.3 m) and mosses. In contrast to short-term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.

Plant frequency and cover abundance at three sites on Disko Island in 1967/1970 and 2009

We report on a revisit in 2009 to sites where vegetation was recorded in 1967 and 1970 on Disko Island, West Greenland. Re-sampling of the same clones of the grass Phleum alpinum after 39 years showed complete stability in biometrics but dramatic earlier onset of various phenological stages that were not related to changes in population density. In a fell-field community, there was a net species loss, but in a herb-slope community, species losses balanced those that were gained. The type of species establishing and increasing in frequency and/or cover abundance at the fell-field site, particularly prostrate dwarf shrubs, indicates a possible start of a shift towards a heath, rather than a fell-field community. At the herb-slope site, those species that established or increased markedly in frequency and/or cover abundance indicate a change to drier conditions. This is confirmed both by the decrease in abundance of Alchemilla glomerulans and Epilobium hornemanii, and the drying of a nearby pond. The causes of these changes are unknown, although mean annual temperature has risen since 1984.

(Table 1) Chlorophyll concentration and pigment composition of carotenoids in three heathland bryophytes, northern Sweden

Background and Aims: Anthropogenic depletion of stratospheric ozone in Arctic latitudes has resulted in an increase of ultraviolet-B radiation (UV-B) reaching the biosphere. UV-B exposure is known to reduce aboveground biomass and plant height, to increase DNA damage and cause accumulation of UV-absorbing compounds in polar plants. However, many studies on Arctic mosses tended to be inconclusive. The importance of different water availability in influencing UV-B impacts on lower plants in the Arctic has been poorly explored and might partially explain the observed wide variation of responses, given the importance of water in controlling bryophyte physiology. This study aimed to assess the long-term responses of three common sub-Arctic bryophytes to enhanced UV-B radiation (+UV-B) and to elucidate the influence of water supply on those responses. Results: Responses were species specific: H. splendens responded most to +UV-B, with reduction in both annual growth (-22%) and sporophyte production (-44%), together with increased b-carotene, violaxanthin, total chlorophyll and NPQ, and decreased zeaxanthin and de-epoxidation of the xanthophyll cycle pool (DES). Barbilophozia lycopodioides responded less to +UV-B, showing increased b-carotene and sclerophylly and decreased UV-absorbing compounds. Polytrichum commune only showed small morphogenetic changes. No effect of UV-B on bryophyte cover was observed. Water availability had profound effects on bryophyte ecophysiology, and plants showed, in general, lower growth and ETR, together with a higher photoprotection in the drier site. Water availability also influenced bryophyte responses to +UV-B and, in particular, responses were less detectable in the drier site. Conclusions: Impacts of UV-B exposure on Arctic bryophytes were significant, in contrast to modest or absent UV-B effects measured in previous studies. The impacts were more easily detectable in species with high plasticity such as H. splendens and less obvious, or more subtle, under drier conditions. Species biology and water supply greatly influences the impact of UV-B on at least some Arctic bryophytes and could contribute to the wide variation of responses observed previously.

Plant Functional Type (PFT) map over Siberia derived from GlobCover 2005 dataset, link to dataset in NetCDF format

High-latitude ecosystems play an important role in the global carbon cycle and in regulating the climate system and are presently undergoing rapid environmental change. Accurate land cover data sets are required to both document these changes as well as to provide land-surface information for benchmarking and initializing Earth system models. Earth system models also require specific land cover classification systems based on plant functional types (PFTs), rather than species or ecosystems, and so post-processing of existing land cover data is often required. This study compares over Siberia, multiple land cover data sets against one another and with auxiliary data to identify key uncertainties that contribute to variability in PFT classifications that would introduce errors in Earth system modeling. Land cover classification systems from GLC 2000, GlobCover 2005 and 2009, and MODIS collections 5 and 5.1 are first aggregated to a common legend, and then compared to high-resolution land cover classification systems, vegetation continuous fields (MODIS VCFs) and satellite-derived tree heights (to discriminate against sparse, shrub, and forest vegetation). The GlobCover data set, with a lower threshold for tree cover and taller tree heights and a better spatial resolution, tends to have better distributions of tree cover compared to high-resolution data. It has therefore been chosen to build new PFT maps for the ORCHIDEE land surface model at 1 km scale. Compared to the original PFT data set, the new PFT maps based on GlobCover 2005 and an updated cross-walking approach mainly differ in the characterization of forests and degree of tree cover. The partition of grasslands and bare soils now appears more realistic compared with ground truth data. This new vegetation map provides a framework for further development of new PFTs in the ORCHIDEE model like shrubs, lichens and mosses, to represent the water and carbon cycles in northern latitudes better. Updated land cover data sets are critical for improving and maintaining the relevance of Earth system models for assessing climate and human impacts on biogeochemistry and biophysics.

Species occurrence and richness of lichen, bryophytes and vascular plants near Abisko, Sweden and Toolik lake, Alaska

Little is known about the impact of changing temperature regimes on composition and diversity of cryptogam communities in the Arctic and Subarctic, despite the well-known importance of lichens and bryophytes to the functioning and climate feedbacks of northern ecosystems. We investigated changes in diversity and abundance of lichens and bryophytes within long-term (9-16 years) warming experiments and along natural climatic gradients, ranging from Swedish subarctic birch forest and subarctic/subalpine tundra to Alaskan arctic tussock tundra. In both Sweden and Alaska, lichen diversity responded negatively to experimental warming (with the exception of a birch forest) and to higher temperatures along climatic gradients. Bryophytes were less sensitive to experimental warming than lichens, but depending on the length of the gradient, bryophyte diversity decreased both with increasing temperatures and at extremely low temperatures. Among bryophytes, Sphagnum mosses were particularly resistant to experimental warming in terms of both abundance and diversity. Temperature, on both continents, was the main driver of species composition within experiments and along gradients, with the exception of the Swedish subarctic birch forest where amount of litter constituted the best explanatory variable. In a warming experiment in moist acidic tussock tundra in Alaska, temperature together with soil ammonium availability were the most important factors influencing species composition. Overall, dwarf shrub abundance (deciduous and evergreen) was positively related to warming but so were the bryophytes Sphagnum girgensohnii, Hylocomium splendens and Pleurozium schreberi; the majority of other cryptogams showed a negative relationship to warming. This unique combination of intercontinental comparison, natural gradient studies and experimental studies shows that cryptogam diversity and abundance, especially within lichens, is likely to decrease under arctic climate warming. Given the many ecosystem processes affected by cryptogams in high latitudes (e.g. carbon sequestration, N2-fixation, trophic interactions), these changes will have important feedback consequences for ecosystem functions and climate.

Age determination and sedimentology of sediment core Lz1101 from the Melles Lake

A lacustrine sediment core from Store Koldewey, northeast Greenland, was biogeochemically, biologically and sedimentologically investigated in order to reconstruct long- and short-term climatic and environmental variability. The chronology of the uppermost 189 cm of the record is based on ten 14C AMS age determinations of aquatic mosses. The record covers almost the entire Holocene and revealed changes on multidecadal to centennial scales. Dating of the oldest mosses shows that lacustrine biogenic productivity already began at around 11 cal. kyr BP. This age pre-dates the onset of biogenic productivity in other lakes on Store Koldewey by about 2 kyr. In spite of the early onset of biogenic production organic matter accumulation remained low and minerogenic sedimentation dominated. At about 9.5 cal. kyr BP moss, sulphur, organic carbon and biogenic silica content started to increase, indicating that the environment stabilized and the biogenic production in the lake adjusted to more preferable conditions. Subsequently, the biogenic productivity experienced repeated changes and varied both on long- and short-term scales. The long-term trend shows a maximum during the early Holocene thus responding to increased temperatures during the Holocene Thermal Maximum. Superimposed on the long-term trend, biogenic productivity also experienced repeated short-term fluctuations that match partly the NGRIP temperatures. The most pronounced decrease of biogenic productivity occurred at around 8.2 cal. kyr BP. Perennial lake ice coverage resulting from low temperatures is supposed to have caused decreased lacustrine biogenic productivity. From the middle Holocene to the present repeated decreases of productivity occurred that could be related to periods with severe sea-ice conditions of the East Greenland Current. Besides the dependence on air temperature it therefore demonstrates the sensitivity of lacustrine biogenic productivity in coastal high arctic areas to short-term cold spells that are mediated by the currents emanating from the Arctic Ocean. However, the data also emphasize the difficulties associated with the interpretation of lacustrine records.

Rock magnetic properties and radiocarbon dates of samples obtained on Ile de Possession, South Indian Ocean

A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates. When combining all the proxy data the following changes could be inferred. From the onset of the peat formation (6200 cal yr BP) until ca. 5550 cal yr BP, biological production was high and climatic conditions must have been relatively warm. At ca. 5550 cal yr BP a shift to low biological production occurred, lasting until ca. 4600 cal yr BP. During this period the organic matter is well preserved, pointing to a cold and/or wet environment. At ca. 4600 cal yr BP, biological production increased again. From ca. 4600 cal yr BP until ca. 4100 cal yr BP a 'hollow and hummock' micro topography developed at the peat surface, resulting in the presence of a mixture of wetter and drier species in the macrobotanical record. After ca. 4100 cal yr BP, the wet species disappear and a generally drier, acidic bog came into existence. A major shift in all the proxy data is observed at ca. 2800 cal yr BP, pointing to wetter and especially windier climatic conditions on the island probably caused by an intensification and/or latitudinal shift of the southern westerly belt. Caused by a stronger wind regime, erosion of the peat surface occurred at that time and a lake was formed in the peat deposits of the crater, which is still present today.

Lignin and chemical elements in the surface layer of bottom sediments from the Kandalaksha Bay of the White Sea

Chemical composition of the upper layer of sediments (0-1 cm) in the Kolvits and Knazhaya inlets, and also in the deep-water part of the Kandalaksha Bay is considered. It is shown that silts are richer in Fe, TOC, and heavy metals, than sands. The highest concentration of these elements is found in sediments under mixing zones of riverine and sea waters. Correlations of P, Zn, Cd, and Cu with iron are high, and correlations of Pb and Cu with organic carbon are also high. Very high concentration of Pb in the Kandalaksha Bay indicate technogenic pollution of sediments. Lignin makes significant contribution to formation of organic matter in the sediments. Composition of lignin in bottom sediments of the Kandalaksha Bay is defined by composition of lignin in soils and aerosols. Vanillin and syringyl structures prevail in molecular composition of lignin in bottom sediments. Their sources are coniferous vegetations, soils, and mosses. Ratios of certain types of phenol compounds indicate pollution of the upper layer of sediments by technogenic lignin. Lead and copper correlate well with this technogenic lignin.