RESOLVING CO2 FLUXES IN A WARMING ARCTIC ENVIRONMENT

Sammanfattning

The Arctic is warming faster than the global average. As a key influencer of the Earth’s biogeochemical cycles, its vast quantities of stored Carbon risk being released into the atmosphere which could significantly accelerate the already rapidly warming Arctic. However, Ecosystem Respiration (ER), through which the stored carbon is released, is not fully understood in terms of partitioning. In this study, the effects of experimental warming on ER were studied across 5 distinct plant communities in the sub-arctic site of Latnjajure in Northern Sweden. It aimed to identify the biotic and abiotic regulators of ER, compare the fluxes during the day and night, and evaluate the accuracy of different measurement techniques. Passive warming was simulated using Open Top Chambers (OTCs) over the 2025 growing season. CO2 fluxes were measured using a trace gas analyser connected to a closed chamber, biotic and abiotic factors were measured alongside.Experimental warming resulted in a significant 30.5% mean increase in ER across all communities, regardless of their structural differences. Vascular plant height emerged as the strongest biotic predictor, with every centimetre increase in height associated with a 28.7% increase in CO2 efflux. While soil temperature was a dominant driver, warming reduced the sensitivity of ER to incremental thermal fluctuations by 23.9%, suggesting thermal acclimation. Notably, nighttime CO2 fluxes were higher than daytime levels under similar low-light conditions. The dark hood method used to determine ER did not align with the derived ER from Light Response Curves, which could indicate for a bias in estimating ER by measuring CO2 fluxes in dark conditions. These findings indicate that while warming increases ER, this is modulated by soil temperature and affected by vegetation structure. The discrepancy between measurement methods indicates that current Arctic carbon budgets may be systematically biased. Refining measurement protocols is essential for accurately quantifying the net carbon balance of the tundra and predicting future climate-carbon feedback