Fire in lichen-rich subarctic tundra changes carbon and nitrogen cycling between ecosystem compartments but has minor effects on stocks

• Main Authors: Heim, Ramona Julia, Yurtaev, Andrey, Bucharova, Anna, Heim, Wieland, Kutskir, Valeriya, Knorr, Klaus-Holger, Lampei, Christian, Pechkin, Alexandr, Schilling, Dora, Sulkarnaev, Farid, Hölzel, Norbert
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; Climate change; Subarctic; Tundra
• Online Access: https://doi.org/10.5194/bg-2021-277; https://bg.copernicus.org/preprints/bg-2021-277/

Fires are predicted to increase in Arctic regions due to ongoing climate change. Tundra fires can alter carbon and nutrient cycling and release a substantial amount of greenhouse gases with global consequences. Yet, the long-term effects of tundra fires on carbon (C) and nitrogen (N) stocks and cycling are still unclear. Here we used a space-for-time approach to investigate the long-term fire effects on C and N stocks and cycling in soil and aboveground living biomass. We collected data from three large fire scars (> 44, 28 and 12 years old) and corresponding control areas and used linear mixed-effects models in a Bayesian framework to analyse how the stocks and cycling were influenced by fire. We found that tundra fires did not affect total C and N stocks because a major part of the stocks was located belowground in soils, which were largely unaltered by fire. However, fire had a strong effect on stocks in the aboveground vegetation, mainly due to the reduction of the lichen layer. Fire reduced N concentrations in graminoids and herbs on the younger fire scars, which affected respective C / N ratios and indicated an increased post-fire competition between vascular plants. Aboveground plant biomass was depleted in 13 C in all three fire scars. This could be related to a lower 13 C abundance in CO 2 in the ambient air because of increased post-fire decomposition, providing a source of 13 C-depleted CO 2 . In soil, the relative abundance of 13 C changed with time after fire because of the combined effects of microbial decomposition and plant-related fractionation processes. Our results indicate that in lichen-rich subarctic tundra ecosystems, the contribution of fires to the release of additional carbon to the atmosphere might be relatively small as soil stocks appear to be resilient.