Field decomposition study (Emelie Winquist, PhD student) 2022-2023
For this filed litter bag study, we aim to explore the interactive effects of warming, grubbing and ROS events on plant litter decomposition and nutrient availability to plants. We use leaves of two different plant species, a fast-decomposing plant Bistorta Vivipara and a slow-decomposing plant Salix Polaris, placed into nylon bags of two different mesh sizes. The smaller mesh size only allows microbes and spores to enter, while the bigger mesh size also allows small invertebrates. The bags were buried in September 2022, and one set will be harvester in June 2023 (decomposition during the cold season) and the second batch in September 2023 (decomposition during the growing season). Our hypothesis is that geese grubbing will amplify the effect of warming on litter decomposition and soil N availability only if hydrological conditions are favourable for microbial decomposition. We have also used Plant Root Simulator probes (PRS® Western Innovation AG), buried at a close location from the litter bags. A first set of probes was inserted in September 2022 and a second set will be inserted in June 2023 to investigate soil nutrient availability to plants during winter and summer separately.
Laboratory soil incubation (Hélène Barthelemy, postdoctoral researcher and Millie Johnson, master student) 2022-2023
For this lab soil incubation study, we aim to explore the effects of grubbing, warming and changes in soil hydrology on N mineralization, organic carbon decomposition, carbon (C) fluxes and microbial community composition. In early autumn 2022, rhizosphere and permafrost soils were collected from two vegetation types (wet and moss tundra) and natural grubbing (high and low). The top 10 cm of the permafrost cores (the soil horizon expected to thaw under climate warming) is used for the incubations. Three types of soils will be incubated, rhizosphere soils, permafrost soils and rhizosphere soils mixed with 10% of permafrost soils to provide an inoculum with the permafrost microbial community. Soil will be incubated for 4 months (snow free period at the study site in Adventdalen) either at 5 °C (field summer soil temperatures or 10 °C (warming scenario). Soils will be also subjected to ambient or reduced moisture content (warming scenario). CO2 release will be measured at regular intervals. Soil microbial community composition (both fungal and bacterial communities) will be determined by Next Generation Sequencing and soil will be analyzed for C and N chemistry (C quality, dissolved organic C, total inorganic N etc.…) prior and at the end of the incubations.
