Comparative analysis of the phytoplankton communities of a peat bog from Tierra del Fuego (Argentina)

The phytoplankton communities of five water hollows and a river from the Rancho Hambre peat bog (Tierra del Fuego, Argentina) are compared as to species composition and densities, as well as morphological, chemical and physical data.A total of 212 taxa is reported, the river having the highest species richness (105) and algal density (6374 ind. ml^–1). Water hollows showed remarkable differences in the structure of their phytoplankton communities.A cluster analysis, based on species presence-absence, clearly distinguishes the river from the water hollows. The hollows fall into groups. One contains the shallow ones the other, the smallest, deepest ones.Correlation analyses between biotic and abiotic variates shows strong correlations between the relative frequencies of some major groups (Chrysophyceae, Euglenophyceae, Tribophyceae) and the values of abiotic variables (alkalinity, pH, conductivity and dissolved phosphate).     

Human-nature connection and soundscape perception: Insights from Tierra del Fuego,Argentina

Human disconnection from nature is thought to have contributed to the environmental crises we currently face, and increasing connection with nature has been proposed as one way of promoting pro-environmental behavior, nature conservation, and social-ecological sustainability. Some efforts to increase connection with nature (“nature relatedness”) have centered on exploring the social-ecological importance of soundscapes, but there is a paucity of empirical evidence supporting the theoretical linkage between soundscape perception and nature relatedness. Using prerecorded and in situ soundscape prompts, we conducted a street intercept survey in Ushuaia, Tierra del Fuego, Argentina to assess: 1) the relative importance of senses in experiences of nature, 2) the relationship between nature relatedness and soundscape perception, 3) differences in soundscape perception between various soundscapes, and 4) possible sociodemographic influences on sense importance, nature relatedness, and soundscape perception. Participants reported that hearing was of secondary importance to vision in experiences of nature. We also found that nature relatedness was positively correlated with the valuation of soundscapes—particularly more natural ones—but not with the discernment of soundscapes or identification of where soundscapes were recorded. Valuation of more natural soundscapes was higher than valuation of more technophonically dominated soundscapes, while soundscape discernment and location identification were higher for soundscapes that were likely more familiar to listeners. Sociodemographic influences on these variables were minor, but women reported higher sense importance, and having a nature-based occupation was associated with higher nature relatedness and valuation of a soundscape from a penguin colony. Our study highlighted a number of potential research areas concerning soundscape perception, including differences between prerecorded and in situ soundscape prompts, defining various aspects of soundscape perception, and the relative influences of sound sources and quantitative acoustic parameters on soundscape perception. Further research is certainly needed to account for global diversity in cultures and soundscapes, but we found some promising empirical support for the use of natural-soundscape-focused educational programs in efforts to promote nature relatedness.     

Responses to solar ultraviolet-B radiation in a shrub-dominated natural ecosystem of Tierra del Fuego (southern Argentina)

A study was made of the effects of solar ultraviolet‐B radiation (UV‐B) on the growth of the dominant plant species of a shrub‐dominated ecosystem in Tierra del Fuego. This part of southern Argentina can be under the direct influence of the Antarctic ‘ozone hole’ during the austral spring and lingering ozone‐depleted air during the summer. The plant community is dominated by an evergreen shrub (Chiliotrichum diffusum) with an herbaceous layer of Gunnera magellanica and Blechnum penna‐marina in the interspaces between the shrubs. Inspections of ozone trends indicate that the springtime and summertime ozone column over Tierra del Fuego has decreased by 10–13% from 1978/9 to 1998/9. In a set of well‐replicated field plots, solar UV‐B was reduced to approximately 15–20% of the ambient UV‐B using plastic films. Polyester films were used to attenuate UV‐B radiation and UV‐transparent films (～90% UV‐B transmission) were used as control. Treatments were imposed during the growing season beginning in 1996 and continued for three complete growing seasons. Stem elongation of the shrub C. diffusum was not affected by UV‐B attenuation in any of the three seasons studied. However, frond length of B. penna‐marina under attenuated UV‐B was significantly greater than that under near‐ambient UV‐B in all three seasons. Attenuation of solar UV‐B also promoted the expansion of G. magellanica leaves in two of the growing seasons. Differences between treatments in leaf or frond length in B. penna‐marina and G. magellanica did not exceed 12%. Another significant effect of UV‐B attenuation was a promotion of insect herbivory in G. magellanica, with a 25–75% increase in the leaf area consumed. Changes in plant phenology or relative species cover were not detected within the time frame of this study. The results suggest that the increase in UV‐B radiation associated with the erosion of the ozone layer might be affecting the functioning of this ecosystem to some degree, particularly by inhibiting the growth of some plant species and by altering plant–insect interactions.     

Solar UVB and warming affect decomposition and earthworms in a fen ecosystem in Tierra del Fuego, Argentina

Combined effects of co-occurring global climate changes on ecosystem responses are generally poorly understood. Here, we present results from a 2-year field experiment in a Carex fen ecosystem on the southernmost tip of South America, where we examined the effects of solar ultraviolet B (UVB, 280–315 nm) and warming on above- and belowground plant production, C : N ratios, decomposition rates and earthworm population sizes. Solar UVB radiation was manipulated using transparent plastic filter films to create a near-ambient (90% of ambient UVB) or a reduced solar UVB treatment (15% of ambient UVB). The warming treatment was imposed passively by wrapping the same filter material around the plots resulting in a mean air and soil temperature increase of about 1.2 °C. Aboveground plant production was not affected by warming, and marginally reduced at near-ambient UVB only in the second season. Aboveground plant biomass also tended to have a lower C : N ratio under near-ambient UVB and was differently affected at the two temperatures (marginal UVB × temperature interaction). Leaf decomposition of one dominant sedge species ( Carex curta ) tended to be faster at near-ambient UVB than at reduced UVB. Leaf decomposition of a codominant species ( Carex decidua ) was significantly faster at near-ambient UVB; root decomposition of this species tended to be lower at increased temperature and interacted with UVB. We found, for the first time in a field experiment that epigeic earthworm density and biomass was 36% decreased by warming but remained unaffected by UVB radiation. Our results show that present-day solar UVB radiation and modest warming can adversely affect ecosystem functioning and engineers of this fen. However, results on plant biomass production also showed that treatment manipulations of co-occurring global change factors can be overridden by the local climatic situation in a given study year.     

Solar UV-B radiation affects below-ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of stratospheric ozone depletion

Stratospheric ozone depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so‐called ‘ozone hole’). The consequent increase in solar ultraviolet‐B radiation (UV‐B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above‐ground since sunlight does not penetrate effectively below‐ground. Here, we demonstrate that solar UV‐B radiation in a fen in Tierra del Fuego (Argentina), where the ozone hole passes overhead several times during the Austral spring, is causing large changes of below‐ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV‐B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near‐ambient solar UV‐B. There was also an apparent shift toward older age classes of roots under reduced solar UV‐B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.     

Vegetation patterns,plant distribution and life forms across the alpine zone in southern Tierra del Fuego,Argentina

The alpine zone is examined at meso‐ and microscales in southern Tierra del Fuego (54°49′S), where the full zone is expressed. Mesoscale patterns were studied on opposing aspects, and microscale patterns were studied on a series of solifluction terraces, in a hanging valley overlooking the Beagle Channel. Plant cover and life form data were collected within 50‐m altitudinal bands on north and south aspects and comprehensive plant lists were compiled for each band. Topography and associated surface cover were recorded on the terraces. Six alpine plant communities, in lower and upper floristic zones, were differentiated with multivariate analyses and significantly related to five ecological factors. Equivalent communities were separated by approximately 185 m altitude on opposing aspects, which related to a soil temperature difference of approximately 3.0°C. The richness (and range) of 80 local vascular taxa (18.6% of the regional flora), decreased with increasing altitude (6.6 per 100 m); however, richness differed significantly with aspect (north: 5.6, south: 7.5). Upper altitudinal limits (approximately 1250 m a.s.l.), were associated with a midsummer isotherm of approximately 1.7°C. Chamaephytes and hemicryptophytes dominated throughout but the tall tussock form was conspicuously absent. Reasons for this are discussed in the context of the Nothofagus treeline, which conformed to a midsummer isotherm of only approximately 6.0°C. Such patterns are at variance with those found in the oceanic subantarctic islands, other oceanic perhumid temperate mountain regions and tropical high mountains. However, the microscale pattern of fines, pebbles, stones and rock across the active solifluction terraces, with dense vegetation on their steep risers, had a clear affinity with that of other subantarctic regions. Inferences that alpine systems of the Southern Hemisphere are necessarily equivalent to those at similar northern latitudes are cautioned against. Likewise, such comparisons within the Southern Hemisphere may also be invalid.     

Direct and indirect effects of solar ultraviolet-B radiation on long-term decomposition

As a result of stratospheric ozone depletion, more solar ultraviolet-B radiation (UV-B, 280–315 nm) is reaching the Earth's surface. Enhanced levels of UV-B may, in turn, alter ecosystem processes such as decomposition. Solar UV-B radiation could affect decomposition both indirectly, by changes in the chemical composition of leaves during growth, or directly by photochemical breakdown of litter and through changes in decomposer communities exposed to sunlight. In this experiment, we studied indirect and direct effects of solar UV-B radiation on decomposition of barley (Hordeum vulgare). We used barley straw and leaf litter grown under reduced UV-B (20% of ambient UV-B) or under near-ambient UV-B (90% of ambient UV-B) in Buenos Aires, Argentina, and decomposed the litter under reduced or near-ambient solar UV-B for 29 months in Tierra del Fuego, Argentina. We found that the UV-B treatment applied during growth decreased the decay rate. On the other hand, there was a marginally significant direct effect of elevated UV-B during the early stages of decomposition, suggesting increased mass loss. The effect of UV-B during growth on decomposition was likely the result of changes in plant litter chemical composition. Near-ambient UV-B received during plant growth decreased the concentrations of nitrogen, soluble carbohydrates, and N/P ratio, and increased the concentrations of phosphorus, cellulose, UV-B-absorbing compounds, and lignin/N ratio. Thus, solar UV-B radiation affects the decomposition of barley litter directly and indirectly, and indirect effects are persistent for the whole decomposition period.     

Solar ultraviolet-B radiation can affect slug feeding preference for some plant species native to a fen ecosystem in Tierra del Fuego,Argentina

The objectives of this study were to test potential effects of solar ultraviolet-B (UV-B) radiation on (i) foliage nutritional quality and foliage decomposition rates of six plant species of this fen ecosystem (Nothofagus antarctica, Carex curta, C. decidua and C. magellanica; Acaena magellanica and Gunnera magellanica) and (ii) feeding preferences for these plant species of the slug Deroceras reticulatum prevalent in this ecosystem. In a mixed-diet selection slugs were offered leaves of the six species that had been grown for three years in experimental field plots under either near-ambient or reduced solar ultraviolet-B (UV-B) radiation. The chosen characteristics of leaf quality (nitrogen concentration, carbon:nitrogen ratio, specific leaf area) and leaf decomposition rates of the six species varied significantly among species but were not affected by the UV-B treatments. However, there were UV-B treatment effects on slug feeding preference for two plant species. For the tree species, Nothofagus, slugs had consumed only one-third as much foliage grown under near-ambient UV-B radiation as of foliage grown under reduced UV-B by the end of the feeding experiment. In contrast, leaves of the sedge C. decidua that had been grown under near-ambient UV-B were consumed twice as much as leaves grown under reduced UV-B radiation. Consumption of foliage for the other four species was similar for the two UV-B treatments. Additionally, diet selection of the slugs was also significantly affected by prior UV-B conditions under which foliage had been grown. Nothofagus leaves were consumed proportionately less and C. decidua proportionately more if the foliage had been grown under near-ambient UV-B radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solar UV-B decreases decomposition in herbaceous plant litter in Tierra del Fuego, Argentina: potential role of an altered decomposer community

Tierra del Fuego, Argentina (55°S), receives increased solar ultraviolet‐B radiation (UV‐B) as a result of Antarctic stratospheric ozone depletion. We conducted a field study to examine direct and indirect effects of solar UV‐B radiation on decomposition of Gunnera magellanica, a native perennial herb, and on the native community of decomposer organisms. In general, indirect effects of UV‐B mostly occur due to changes in the chemical composition of litter, whereas direct effects during decomposition result from changes in decomposer organisms and/or differences in the photochemical breakdown of litter. We designed a full‐factorial experiment using senescent leaves that had received either near‐ambient or attenuated UV‐B during growth. The leaves were distributed in litterbags and allowed to decompose under near‐ambient or reduced solar UV‐B during the growing season. We evaluated initial litter quality, mass loss, and nutrient release of decomposing litter, and microbial colonization of both initial litter and decomposed litter. We found that litter that decomposed under near‐ambient UV‐B had significantly less mass loss than litter that decomposed under reduced UV‐B. The UV‐B conditions received by plants during growth, which did not affect mass loss and nutrient composition of litter, affected fungal species composition but in different ways throughout the decomposition period. Before the decomposition trial, Beauveria bassiana and Penicillium frequentans were higher under reduced UV‐B, whereas Cladosporium herbarum and pigmented bacteria were more common under the near‐ambient compared to the reduced UV‐B treatment. After the decomposition period, leaves that had grown under reduced UV‐B showed higher frequency of Penicillium thomii and lower frequency of Trichoderma polysporum than leaves that had grown under near‐ambient conditions. The UV‐B condition received during decomposition also affected fungal colonization, with Penicillium chrysogenum being more frequent in leaves that had decomposed under reduced UV‐B, while the other species were not affected. Our results demonstrate that, in this ecosystem, the effects of UV‐B radiation on decomposition apparently occurred mostly through changes in the fungal community, while changes in photochemical breakdown appeared to be less important.     

Assessing genetic variation and population structure of invasive North American beaver (<Emphasis Type="Italic">Castor Canadensis</Emphasis> Kuhl, 1820) in Tierra Del Fuego (Argentina)

The North American beaver (Castor Canadensis) was introduced into Isla Grande de Tierra del Fuego, Argentina in 1946 as a potential source of wild fur. The species showed high growth potential, reaching close to 100,000 individuals from an original founding stock of 25 females and 25 males. Beavers adapted rapidly to their new environment and became invasive, providing an excellent model of successful adaptation of introduced populations to a new habitat. In this study, we used polymorphic mitochondrial (mt) DNA to evaluate genetic variation in the introduced beaver population from Tierra del Fuego. Nucleotide variation in partial sequences of Cytochrome b (500 bp) and 12S rRNA (421 bp) genes and the main non-coding D-loop region (521 bp) were analyzed. Our study allowed to identify 10 different mtDNA lineages in the invasive population, none of them shared among the source populations. The pattern observed is a consequence of cessation of gene flow following expansion of the founding beaver population since the time of its introduction. This approach contributes to the understanding of effects of genetic changes on survival ability and reproductive success of invasive species. It also has important management implications to invasive species.     

Accumulation of DNA damage in Antarctic mosses: correlations with ultraviolet-B radiation, temperature and turf water content vary among species

The susceptibility of three East Antarctic moss species to UV-B radiation was examined by measuring accumulation of cyclobutane pyrimidine dimers under natural sunlight during the austral summer season of 2002/03. The 2002/03 season was characterized by unusually low springtime ozone depletion and as such our results likely underestimate the DNA damage possible in a more typical UV-B radiation season. Despite this all three species accumulated significant DNA photoproducts. We also found a positive association between photoproduct accumulation and incident UV-B radiation in the two cosmopolitan species, Bryum pseudotriquetrum and Ceratodon purpureus , with more DNA damage in samples collected early in the season compared with later in the summer. For B. pseudotriquetrum , negative associations were also observed between photoproduct accumulation and both turf water content and the 10-day mean air temperature. Photoproduct accumulation in the endemic species Schistidium antarctici was similarly high across the season and no significant association with environmental variables was found. Our results are consistent with the two cosmopolitan species having somewhat higher UV-B-screening capabilities and possibly more efficient mechanisms for repairing DNA damage than the endemic S. antarctici .