Consequences of climate change for ecosystem functioning mediated by plant responses across the tundra

Abstract

Climate change is among the biggest challenges of our time, with its consequences already reshaping ecosystems across the planet. In the tundra, amplified warming trends of almost four times the global average poses a significant threat to ecosystems that have historically acted as a large carbon sink. Climate warming is altering the structure and composition of tundra plant communities. As primary producers, plants play a central role in terrestrial carbon cycling, yet the direction and magnitude by which ongoing vegetation change will alter ecosystem carbon dynamics remain poorly understood. Combining field-based and site-specific studies with tundra biome-wide syntheses, this thesis aims to assess how indirect drivers of climate warming, mediated by plant responses, will influence ecosystem functioning across the tundra. Specific focus is on the relationship between warming-induced vegetation changes and decomposition, an important ecosystem function that has the potential to significantly influence the carbon balance of the region. Paper I and II focus on decomposition responses to warming from local to large-scale patterns across the tundra biome and together demonstrate the importance of vegetation composition as a driver of decomposition. Paper III further quantifies tundra community decomposability, linking plant functional traits that reflect litter quality to decomposition, to ultimately assess if warming-induced shifts in plant species composition, and in turn their traits, produce directional shifts in ecosystem function. Paper IV finally explores plant functional consequences of climate change by estimating within-species trait responses to experimental warming treatments across the tundra. Collectively, this research demonstrates the potential for warming-induced vegetation shifts in one of the coldest biomes on Earth to shape future carbon dynamics in the region with potential global consequences.