A tipping point in carbon storage when forest expands into tundra is related to mycorrhizal recycling of nitrogen

• Published in: Ecology Letters
• Main Authors: Clemmensen, Karina Engelbrecht, Durling, Mikael Brandström, Michelsen, Anders, Hallin, Sara, Finlay, Roger D., Lindahl, Björn D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Arctic warming; carbon sequestration; decomposition; functional genes; meta-barcoding; mycorrhizal type; nitrogen cycling; soil fungal communities; stable isotopes; treeline ecotone; Arctic; Subarctic; Tundra
• Online Access: https://curis.ku.dk/portal/da/publications/a-tipping-point-in-carbon-storage-when-forest-expands-into-tundra-is-related-to-mycorrhizal-recycling-of-nitrogen(a6f39ce8-e97c-4faf-af28-0ecf7ea61989).html; https://doi.org/10.1111/ele.13735; https://curis.ku.dk/ws/files/262939655/A_tipping_point_in_carbon_storage_when_forest_expands_into_tundra_is_related_to_mycorrhizal_recycling_of_nitrogen.pdf

Tundra ecosystems are global belowground sinks for atmospheric CO 2 . Ongoing warming-induced encroachment by shrubs and trees risks turning this sink into a CO 2 source, resulting in a positive feedback on climate warming. To advance mechanistic understanding of how shifts in mycorrhizal types affect long-term carbon (C) and nitrogen (N) stocks, we studied small-scale soil depth profiles of fungal communities and C–N dynamics across a subarctic-alpine forest-heath vegetation gradient. Belowground organic stocks decreased abruptly at the transition from heath to forest, linked to the presence of certain tree-associated ectomycorrhizal fungi that contribute to decomposition when mining N from organic matter. In contrast, ericoid mycorrhizal plants and fungi were associated with organic matter accumulation and slow decomposition. If climatic controls on arctic-alpine forest lines are relaxed, increased decomposition will likely outbalance increased plant productivity, decreasing the overall C sink capacity of displaced tundra.