The Tundra is a Net Source of CO2 Measured by Autochambers and Eddy Covariance Techniques During Five Years in a Site With Permafrost Thawing.

Abstract:

Current and future warming of high latitude tundra ecosystems will play an important role in climate change through feedbacks to the global carbon (C) cycle. Long-term observational and experimental studies are pivotal for detecting and understanding changes in the coming decades. Yet studies of the C feedbacks from observational studies and manipulative experiments made on tundra plant communities often have significantly different conclusions with regards to impacts of warming on the ecosystem. Comparing results from these two study types, however, often involves integrating CO₂ flux measurements that were collected on different spatial scales using a variety of methods. The process of data assimilation for landscape level analysis is often complicated by the fact that many projects only utilize one method for measuring CO₂ fluxes at a given site. This study compares five years of C dynamics in a moist acidic tundra from control plots in a manipulative warming experiment (CiPEHR – plot-scale) and landscape-level natural permafrost thaw gradient (Gradient – Eddy covariance) observations all within a 1km distance from each other. We found net ecosystem exchange (NEE) to be an annual net source of carbon using both methods (Gradient 12.3 – 125.6 g CO₂-C m^-2 and CiPEHR warming manipulation 80.2 – 175.8 g CO₂-C m^-2). The differences between sites were biggest in the first three years of observation, and can be explained by lower growing season gross primary production (GPP – first three years) from the manipulation (CiPEHR), and lower ecosystem respiration (R_eco) from CiPEHR in the first year only. Suppressed GPP and R_eco could be from the impact of experimental setup (chamber soil collars – root damage), which lowered the plant community’s capacity to fix C, but recovered within three years. This warrants caution of making generalization of short-term experiments in the tundra and more research is needed evaluating coupling of belowground and aboveground C dynamics.