PRIMETIME · Rhizosphere priming: Quantifying plant impacts on carbon dioxide emissions from a warming Arctic

Rapid warming is accelerating Arctic carbon cycling, including CO2 release by degradation of thawing soil organic matter and CO2 uptake by better-growing plants. Projections of future Arctic greenhouse gas fluxes retain large uncertainties and do not consider plant-soil interactions that can substantially affect CO2 release - the RHIZOSPHERE PRIMING EFFECT. Theoretical considerations, comparison of ecosystem carbon stocks and model extrapolation of temperate studies suggest a high potential for globally-relevant, priming-induced CO2 emissions from a warming Arctic following shifts in vegetation and rooting patterns. PRIMETIME aims to provide the first observation-based estimate of total plant effects on circum-Arctic soil and ecosystem carbon stocks in a changing climate. Central questions include:(1) How do different vegetation types affect soil and ecosystem carbon stocks and CO2 balance?(2) How do changes in rooting depth interact with depth gradients of soil properties to affect carbon stocks and CO2 fluxes?(3) What is the net effect of expected changes in plant productivity, vegetation distribution and rooting on ecosystem carbon storage across the circum-Arctic?The EXPERIMENTAL MODULE will quantify plant-soil carbon fluxes and plant impacts on soil CO2 release for different vegetation types and soil depths, combining a novel living-plant macrocosm experiment with field observations, cutting-edge 14C-dating (high risk) and 13C-labelling. The MODELLING MODULE will take our recent model to the next level and integrate experimental data to calculate the combined plant effect on ecosystem CO2 sink/source strength in a changing Arctic. The model will be validated against Eddy Covariance-observed CO2 fluxes (high risk). The integrated PRIMETIME approach will break new ground by shedding light on plant impacts on belowground carbon cycling, and provide a tool box to quantify and integrate these fine-scale processes in large-scale emission estimates.