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Hypoxia is common in marine environments and a major stressor for marine organisms inhabiting benthic and intertidal zones. Several studies have explored the responses of these organisms to hypoxic stress at the whole organism level with a focus on energy metabolism and mitochondrial response, but the instrinsic mitochondrial responses that support the organelle’s function under hypoxia and reoxygenation (H/R) stress are not well understood. We studied the effects of acute H/R stress (10 min anoxia followed by 15 min reoxygenation) on mitochondrial respiration, production of reactive oxygen species (ROS) and posttranslational modifications (PTM) of the proteome in a marine facultative anaerobe, the blue mussel Mytilus edulis. The mussels’ mitochondria showed increased OXPHOS respiration and suppressed proton leak resulting in a higher coupling efficiency after H/R stress. ROS production decreased in both the resting (LEAK) and phosphorylating (OXPHOS) state indicating that M. edulis was able to prevent oxidative stress and mitochondrial damage during reoxygenation. Hypoxia did not lead to rearrangement of the mitochondrial supercomplexes but impacted the mitochondrial phosphoproteome including the proteins involved in OXPHOS, amino acid- and fatty acid catabolism, and protein quality control. This study indicates that mussels’ mitochondria possess intrinsic mechanisms (including regulation via reversible protein phosphorylation) that ensure high respiratory flux and mitigate oxidative damage during H/R stress and contribute to the hypoxia-tolerant mitochondrial phenotype of this metabolically plastic species.
Carbon dioxide (CO2) is one of the most important factors of the Earth’s carbon cycle. Peatlands are well-known to be a long term sink for atmospheric carbon dioxide. Under changing environmental conditions, the carbon balance and hence the CO2 fluxes can be significantly changed, and peatlands may even become a significant atmospheric carbon source. To be able to predict the changes in climatic conditions and their effects on ecosystems, it is important to understand the contemporary CO2 exchange of the ecosystems. Many studies on peatland CO2 fluxes have been conducted in the boreal zone of North America and Scandinavia. Still little scientific evidence is available from peatland ecosystems of boreal Russia. This dissertation presents the detailed investigation of CO2 dynamics and the relevant processes and environmental factors from the boreal peatland site Ust-Pojeg (61°56'N, 50°13'E) in Komi Republic, northwest Russia. On the small spatial scale (microform), the investigated peatland was characterised by high variability in vegetation composition and coverage as well as in water table level which resulted in large variability in CO2 fluxes not only between the microform types but also within one microform type. The cumulative flux over the investigation period for the different microforms ranged from strong CO2 sources to CO2 sinks. An area-weighted estimate for the entire peatland showed that it was a CO2 source for the investigation period, which was characterised by average conditions in terms of precipitation and temperature. The CO2 fluxes were measured at different scales: by the closed chamber method at the microform scale and by the eddy covariance technique at the ecosystem scale. Three different upscaling methods were used to compare the fluxes. Irrespective of the upscaling methods, the discrepancies between the estimates based on the upscaled chamber measurements and estimates based on measurements by the eddy covariance technique were high. The high spatial heterogeneity of the vegetation and the water table level and thus of the CO2 fluxes were recognised as reasons for high potential errors when upscaling CO2 fluxes from the microform to the ecosystem level. Large discrepancies were also observed in comparison between measured CO2 fluxes and CO2 estimates based on the mechanistic ecosystem model LPJ-GUESS. Insufficient model forcing may have led to errors in the timing of the onset and the end of the growing season, and the modelled vegetation did not always reproduce the observed vegetation. These two factors may have led to the discrepancies in the model-measurement comparison. Although the closed chamber technique is widely used for measurements of CO2 fluxes between ecosystems and the atmosphere, the errors which might occur during the measurement itself or which are associated with the used measurement devices as well as the flux calculation from chamber-based CO2 concentration data are still under discussion. The study showed that the CO2 fluxes measured by the closed chamber method can be overestimated during low-turbulence nighttime conditions and can be seriously biased by inappropriate application of linear regression for the flux calculation. The methodological studies were conducted at the boreal peatland Salmisuo in eastern Finland (62°46'N, 30°58'E). The methods developed in this dissertation could contribute significantly to improved CO2 flux estimates. VI