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The peatlands of Tierra del Fuego are subject to increased solar ultraviolet-B radiation (UV-B) due to the influence of the Antarctic ‘ozone hole’. Research into the effects of climate change and ozone depletion on peatlands has predominantly focused on the higher plant community and neglected other organisms. In the second 3-year portion of a 6-year experiment, we intensified our investigations of the response of the peatland surface microfaunal community to current and attenuated solar UV-B, and assessed possible links to changes in the microenvironment. Near-ambient UV-B and reduced UV-B treatments were realised by stretching plastic film filters that differentially attenuate UV-B over peatland sample plots. We extracted the microfauna and analysed the dissolved nutrients held within Sphagnum capitula removed from the top 1-cm of the peatland. In line with previous findings in this system, testate amoebae were more abundant under near-ambient UV-B than under reduced UV-B. Populations of the most common genus, Assulina, and other less prominent amoebae species of Heleopera and Euglypha, were consistently increased under near-ambient UV-B. Overall diversity of testate amoebae was also higher under near-ambient UV-B than under reduced UV-B, whereas rotifers, nematodes and mites were less abundant under near-ambient UV-B. Concentrations of DOC and P were generally higher under near-ambient UV-B than under reduced UV-B. These changes, combined with the changes previously reported in the plant and fungal communities, have the potential to influence peatland C storage, and surface nutrient availability. The peatland microfaunal community under near-ambient solar UV-B may be regulated by the plant community through the leaching of nutrients from leaf cells, and changes in Sphagnum morphology that affect the capitulum microenvironment.

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.

Background Nothofagus pumilio (Poepp & Endl.) Krasser, known as “lenga” is the most important timber wood species in southernmost Patagonia (Argentina). Humicolopsis cephalosporioides Cabral & Marchand is a soil fungus associated with Nothofagus pumilio forests, which has outstanding cellulolytic activity. However, there is no information about the ability of this fungus to use organic substrates other than cellulose, and its ability to produce different enzyme systems, as well as its response to temperature. Aims The aim of this study was to examine the role of H. cephalosporioides in degradation processes in N. pumilio forests in detail by evaluating the in vitro ability of four isolates of this fungus to grow and produce different lytic enzyme systems, and their response to incubation temperature. Methods The ability of the fungi to grow and produce enzyme systems was estimated by inoculating them on agar media with specific substrates, and the cultures were incubated at three temperatures. Results A differential behavior of each strain in levels of growth and enzyme activity was found according to the medium type and/or incubation temperature. Conclusions A intra-specific variability was found in H. cephalosporioides. Likewise a possible link between the saprotrophic role of this fungus in N. pumilio forests and the degradation of organic matter under stress conditions, such as those from frosty environments, was also discussed. Antecedentes Nothofagus pumilio (Poepp & Endl) Krasser (N. pumilio), conocido como «lenga», es la especie maderable más importante en el extremo sur de Patagonia (Argentina). Humicolopsis cephalosporioides Cabral & Marchand es un hongo del suelo asociado a bosques de N. pumilio, que tiene una actividad celulolítica excepcional. Sin embargo, no hay información acerca de la capacidad de este hongo para utilizar otros sustratos orgánicos distintos de la celulosa, o para producir diferentes sistemas enzimáticos, así como su respuesta a la temperatura. Objetivos El objetivo de este estudio fue profundizar en el rol que Humicolopsis cephalosporioides tiene en los procesos de degradación en los bosques de N. pumilio a través de la evaluación de la capacidad in vitro de 4 aislamientos de este hongo para crecer y producir diferentes sistemas enzimáticos líticos y su respuesta a la temperatura de incubación. Métodos La capacidad de los hongos para crecer y producir sistemas enzimáticos se estimó a través de su inoculación sobre medios de agar con sustratos específicos, siendo incubados a 3 temperaturas. Resultados Se observó un comportamiento diferencial de cada cepa en el crecimiento y la actividad enzimática de acuerdo con el tipo de medio o la temperatura de incubación. Conclusiones Se observó variabilidad intraespecífica en Humicolopsis cephalosporioides. Asimismo, se discutió la posible relación entre el rol saprotrófico de este hongo en los bosques de N. pumilio y la degradación de la materia orgánica en condiciones estresantes, como las existentes en ambientes fríos. Fil: Eliades, Lorena Alejandra. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina Fil: Cabello, Marta N.. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina Fil: Pancotto, Veronica Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Moretto, Alicia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Rago, María Melisa. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina Fil: Saparrat, Mario Carlos Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Fisiología Vegetal; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Instituto de Botánica Spegazzini; Argentina

Fil: Pancotto, Veronica Andrea. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Instituto de Investigaciones Fisiologicas y Ecologicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomia. Instituto de Investigaciones Fisiologicas y Ecologicas Vinculadas a la Agricultura; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina