Abstract
Climate warming is occurring fastest at high latitudes. Based on short-term field experiments, this warming is projected to stimulate soil organic matter decomposition, and promote a positive feedback to climate change. We show here that the tightly coupled, nonlinear nature of high-latitude ecosystems implies that short-term (<10 year) warming experiments produce emergent ecosystem carbon stock temperature sensitivities inconsistent with emergent multi-decadal responses. We first demonstrate that a well-tested mechanistic ecosystem model accurately represents observed carbon cycle and active layer depth responses to short-term summer warming in four diverse Alaskan sites. We then show that short-term warming manipulations do not capture the non-linear, long-term dynamics of vegetation, and thereby soil organic matter, that occur in response to thermal, hydrological, and nutrient transformations belowground. Our results demonstrate significant spatial heterogeneity in multi-decadal Arctic carbon cycle trajectories and argue for more mechanistic models to improve predictive capabilities.
Highlights
Climate warming is occurring fastest at high latitudes
Permafrost soils contain more carbon between 0 and 3 m depth[2,3] (1035 ± 150 PgC) than in the current atmosphere. These soils are warming at twice the global average (0.6 °C per decade)[4], and empirical observations and model predictions indicate that this warming leads to a consistent release of greenhouse gases (i.e., CO2 and CH4) from soils, leading to a positive feedback to climate change[5]
Observational experiments are invaluable for improving conceptual understanding of the mechanisms underpinning ecosystem responses to climate change
Summary
Based on short-term field experiments, this warming is projected to stimulate soil organic matter decomposition, and promote a positive feedback to climate change. Permafrost soils contain more carbon between 0 and 3 m depth[2,3] (1035 ± 150 PgC) than in the current atmosphere These soils are warming at twice the global average (0.6 °C per decade)[4], and empirical observations and model predictions indicate that this warming leads to a consistent release of greenhouse gases (i.e., CO2 and CH4) from soils, leading to a positive feedback to climate change[5]. Increase in tundra respiration under short-term warming, while recent ecosystem manipulation experiments focusing on winter and summer warming have demonstrated carbon effluxes via heterotrophic respiration outweigh inputs via plant productivity as the active layer depth increases[18]. While drying or anoxic microsite formation under saturating conditions can reduce microbial activity[6,9], a slight decrease in soil moisture has been shown to increase microbial activity[19]
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