ALBERT

Description: Peatland soils are projected to respond to rising global temperatures with an increase in microbial respiration rates. At the same time, nutrients that were previously bound in undecomposed organic matter will increasingly become available to the decomposer microbial communities. The pathway and magnitude of response in respiration rates to a changing nutrient status remains an open question, especially given that these ecosystems are typically limited in nutrients like nitrogen. In my ongoing Master thesis, I investigate the effects of adding nitrate and ammonium to incubated peat samples from Siikaneva bog in boreal Finland. While the site itself is not affected by permafrost, this study provides an analogue for the future of peatlands at the edge of the permafrost zone. Preliminary results from 190 days of incubation indicate that carbon dioxide production was reduced by ammonia additions. Data on methane production were less conclusive, but also point to an average reduction of total C respiration. Samples from above and below the water table exhibit different trajectories, which may be an expression of different microbial communities: most prominently, a complete lack of methanogenenis in the surface samples. In summary, this implies that the peatland carbon sink is not endangered by nutrient release.

Description: The future of terrestrial carbon found in permafrost is not yet well understood, but this soil carbon may be a potential significant contributor to positive-feedback loop of climatic warming. In the (sub)arctic, the annual freeze-thaw cycles and thick peat accumulation harbor ideal conditions for palsa formation. Although, a recent study at our site in Arctic Lapland found that the area of the carbon-rich palsa mounds have already decreased by -77 % to -90 % since 1960. Here, we investigate potential greenhouse gas (CO2, CH4, N2O) production from a palsa sampled along a transect with 60+ years of documented thaw. During the annual cycle of freeze-thaw, one of the largest unknowns in the life cycle of a palsa mound is the biogeochemical cycles during the shoulder season. This transition time between growing, and non-growing seasons that have previously been assumed to be times of relative dormancy for GHG flux in high-latitude wetlands. However, recent studies find that there is in fact a significant amount of GHG flux during this time. We aim to isolate shoulder season variables (increased N from plant senescence, temperature change) and explore how they each affect the potential CO2 and CH4 production using ex-situ incubations, coupled with microbial community cell counts sampled in tandem. Here, we test whether N addendums increase the GHG, as n-poor habitat has been shown to respond with increased microbial activity to the release of this metabolic bottleneck. In addition to the N-treatments, the samples will also be separated into three incubation temperature groups (4 , 15, 20C) to be able to link increasing temperatures with the N response. Overall, we aim to fill knowledge gaps on these habitats response to changing climatic conditions, and use our findings to better earth system models permafrost carbon predictions.