5 research outputs found
Microbial iron reduction and greenhouse gas production in response to organic matter amendment and temperature increase of periglacial sediments, Bolterdalen, Svalbard
Arctic permafrost soils store substantial reserves of organic matter (OM) from which microbial transformation contributes significantly to greenhouse gas emissions of CH4 and CO2. However, many younger sediments exposed by glacier retreat and sea level change in fjord landscapes lack significant organic carbon resources, so their capacity to promote greenhouse gas emissions is unclear. We therefore studied the effects of increased temperatures (4°C and 21°C) and OM on rates of Fe(III) reduction, CO2 production, and methanogenesis in three different Holocene sedimentary units from a single site within the former marine limit of Adventdalen, Svalbard. Higher temperature and OM addition generally stimulated CH4 production and CO2 production and an increase in Bacteria and Archaea abundance in all units, whereas an equal stimulation of Fe(II) production by OM amendment and an increase in temperature to 21°C was only observed in a diamicton. We observed an accumulation of Fe(II) in beach and delta deposits as well but saw no stimulating effect of additional OM or increased temperature. Interestingly, we observed a small but significant production of CH4 in all units despite the presence of large reservoirs of Fe(III), sulfate, and nitrate, indicating either the availability of substrates that are primarily used by methanogens or a tight physical coupling between fermentation and methanogenesis by direct electron transfer. Our study clearly illustrates a significant challenge that comes with the large heterogeneity on a narrow spatial scale that one encounters when studying soils that have complex histories.publishedVersio
Влияние семантики локализованности на текстовую внешнетемпоральную транспозицию
Языковая временная семантика в лингвистических исследованиях последних лет рассматривается как широкая сфера языковых/речевых отношений различных категорий (грамматических, функционально-
семантических, текстовых), т.е. как область пересечения, иногда концентрации аспектуального, собственно темпорального, таксисного и другого аналогичного содержания, где центральное место принадлежит
глагольной единице, потенциальные функциональные возможности которой и определяют указанные грамматические отношения
Silicates Eroded under Simulated Martian Conditions Effectively Kill Bacteria—A Challenge for Life on Mars
The habitability of Mars is determined by the physical and chemical environment. The
effect of low water availability, temperature, low atmospheric pressure and strong UV
radiation has been extensively studied in relation to the survival of microorganisms. In
addition to these stress factors, it was recently found that silicates exposed to simulated
saltation in a Mars-like atmosphere can lead to a production of reactive oxygen species.
Here, we have investigated the stress effect induced by quartz and basalt abraded
in Mars-like atmospheres by examining the survivability of the three microbial model
organisms Pseudomonas putida, Bacillus subtilis, and Deinococcus radiodurans upon
exposure to the abraded silicates. We found that abraded basalt that had not been in
contact with oxygen after abrasion killed more than 99% of the vegetative cells while
endospores were largely unaffected. Exposure of the basalt samples to oxygen after
abrasion led to a significant reduction in the stress effect. Abraded quartz was generally
less toxic than abraded basalt. We suggest that the stress effect of abraded silicates
may be caused by a production of reactive oxygen species and enhanced by transition
metal ions in the basalt leading to hydroxyl radicals through Fenton-like reactions. The
low survivability of the usually highly resistant D. radiodurans indicates that the effect of
abraded silicates, as is ubiquitous on the Martian surface, would limit the habitability of
Mars as well as the risk of forward contamination. Furthermore, the reactivity of abraded
silicates could have implications for future manned missions, although the lower effect
of abraded silicates exposed to oxygen suggests that the effects would be reduced in
human habitats