Understanding how plant litter quality modulates carbon and nutrient fluxes across soil–water–microbial–plant interfaces is essential for predicting permafrost climate feedbacks. In Work Package 3 (WP3) of the PEACE project, we designed a suite of complementary in situ and laboratory experiments to elucidate the mechanistic controls of litter stoichiometry on greenhouse gas emissions and nutrient transfers in Arctic permafrost environments.
Labelled Litter Production and Deployment
We first produced uniformly 13C- and 15N-labelled litter of three representative tundra species—Eriophorum vaginatum, Betula nana, and Sphagnum spp.—under controlled ecotron conditions. This isotopic enrichment enables precise tracing of carbon and nitrogen through soil fractions, microbial biomass, and leachates. We deployed these litters at two depths (saturated vs. unsaturated) in experimental plots at Abisko station (Sweden) and monitored them over two years. Periodic sampling allowed us to partition C and N into particulate organic matter, water-extractable fractions, and microbial biomass, while simultaneously characterizing dissolved organic matter (DOM) composition.
In Situ Mesocosm Incubations
To mimic aquatic processing, we submerged barrels containing leachates of labelled and control litters in a tundra pond for three weeks. We measured daily CO₂, CH₄, and N₂O fluxes alongside changes in DOM quality and microbial community structure (via metabarcoding and RT-qPCR). Parallel photodegradation assays—incubating sterile leachates with and without sunlight exposure—clarified the relative contributions of photo-oxidation versus microbial mineralization to DOM transformation and gas emissions.
Laboratory Climate-Simulator Experiments
In our ecotron facility, we replicated seasonal thaw dynamics and future climate scenarios (–20% precipitation, +6 °C, +450 ppm CO₂) on intact soil-plant cores. By simulating active-layer deepening and advanced light regimes, we quantified shifts in GHG emissions and nutrient leaching under present and projected conditions. Microcosm studies further dissected microbial metabolic pathways driving C-N turnover in permafrost soils.
Towards Mechanistic Understanding
Through WP3, we aim to identify the stoichiometric thresholds at which litter quality accelerates or mitigates greenhouse gas production and nutrient mobilization. Our integrative approach—combining isotopic tracing, high-frequency gas flux monitoring, and molecular microbiology—will inform process-based models of permafrost carbon feedback under global change.