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

• Main Authors: Engelbrecht Clemmensen, Karina, Brandström Durling, Mikael, Michelsen, Anders, Hallin, Sara, Finlay, Roger, Lindahl, Björn
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Ecology; Arctic; Subarctic; Tundra
• Online Access: https://pub.epsilon.slu.se/24361/; https://pub.epsilon.slu.se/24361/1/engelbrecht_clemmensen_k_et_al_210602.pdf

Tundra ecosystems are global belowground sinks for atmospheric CO2. Ongoing warming-induced encroachment by shrubs and trees risks turning this sink into a CO2 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.