PEPR FairCN PEACE

The northern circumpolar permafrost land area is warming four times faster than the globe average and stores ~1500 gigatons of organic carbon (C). Climate change is rapidly altering vegetation communities and the hydrology of northern watersheds by disrupting snow cover and degrading permanently frozen soil layers (permafrost). The Arctic experiences vegetation changes controlled by the ground ice content; woody vegetation increasing in ice-poor uplands, graminoids in ice-rich lowlands. Changes in plant communities will modify the amount and composition of litter added to soils as well as the N and P availability. Permafrost degradation through thickening of the seasonal thawing active layer and melting of ground ice will modify water transfers and the export of nutrients and organic matter (OM). All these processes will further modify the C-N-P cycles from plants to soils and hydrosystems, further regulating the high latitude ecosystem C balance. Therefore, understanding the consequences of changes in OM and N-P inputs on microbial activity, carbon storage, transfers and emissions along the land-water-atmosphere continuum is crucial to predict the permafrost C feedback to climate change. The proposed project will tackle the following question: how do climate-driven degradation of permafrost and vegetation changes affect Arctic ecosystem C-N-P dynamics and transfers along the plant-soil-hydrosystem continuum? To do so, we aim to 1) characterise the current states of the different compartments of the continuum using field monitoring and sampling, and quantify the C-N-P fluxes (dissolved, particulate and gaseous) at the catchment scale, and 2) gain access to a fine understanding of the processes involved in the evolution of C-N-P cycles under changes in temperature and substrate composition using intensive laboratory experiments, including ecosystem-level manipulation (Ecotron) while improving our modeling capacities. The consortium will deploy a multi-disciplinary approach (geomorphology, soil science, geochemistry, hydrology, climate science, microbiology) and will build directly upon the experiences and previous research of the team members in permafrost ecosystems. The coupling of the C-N-P cycles in the plant-soil-hydrosystems continuum will be assessed using state-of-the-art infrastructures and analyses. Plants and permafrost soils (i.e., active layer + permafrost) will be studied in multiple sites encompassing the pan-Arctic area based on samples collected by team members and partners in the past. The most intensive sampling, monitoring and modelling efforts will be conducted in three ecosystem observatories in Canada (Churchill in Manitoba) and Europe (Zackenberg in Greenland, Abisko in Sweden) while sharing fieldwork efforts and cost with ongoing projects from French and international partners. The PEACE project is organised in six work packages (WP). WP0 will coordinate the whole project. WP1 will build an open standardised long-term database of the cycle of C-N-P in the plant-soil-hydrosystems continuum in the Arctic. WP2 will characterise litter and permafrost OM in 20 locations representing the diversity of circumpolar permafrost ecosystems. WP3 will experiment the evolution of OM decomposition and N-P release and immobilisation in soils and waters using in-situ mesocosms and laboratory incubations. WP4 will quantify current C-N-P transfers and characterise dissolved OM and N-P forms at high-frequency in the soil-hydrosystems continuum. Finally, WP5 will statistically analyse the links between the different variables measured in WPs, and model the impact of changes in litter stoichiometry on C stocks at the site scale. This project will provide a comprehensive framework for evaluating the controls of OM composition on C emissions and its evolution with climate change in permafrost ecosystems.

LSCE contribution: using isotopic organic geochemistry (¹³C, ¹⁴C), LSCE provides elements for the characterization of dissolved and particulate organic matter in water.