Climate warming and soil carbon cycling: Emergent responses across time and space

1) Background/Question/Methods

Warming temperatures have immediate, direct effects on decomposition rates, for example through effects on enzyme activity, binding energies, and reaction kinetics. The strength of the decomposition feedback to global warming, however, remains highly uncertain, in part due to the difficulty in integrating the different time scales of ecosystem temperature-response. Here we discuss some of the complexity in predicting climate impacts on soils and share recent results from two plot- to landscape-scale studies. We are conducting multi-year whole-profile soil-warming experiments in the field in a temperate forest and a grassland and beginning a short-term warming study in permafrost tundra as part of an integrated investigation of how geomorphology, hydrology, geophysics, and vegetation influence biogeochemical cycles and CO₂ and CH₄ fluxes.

2) Results/Conclusions .

In the first year of field treatments, we see expected effects of warming on soil CO₂ production, and the whole-profile manipulation allows us to estimate robust temperature sensitivities of decomposition. At slightly longer timescales, evidence is emerging for microbial acclimation and changes in carbon use efficiency. Perhaps, even more challenging, longer time scales of warming will lead to changes in vegetation, soil properties, other factors that influence soil carbon cycling. For example, interactions among roots, microbes, and mineral phases may allow climate to alter organo-mineral associations that control decomposition on long timescales. Moreover, in permafrost regions, large changes in landscape topography, inundation, and active layer depth will affect carbon cycling. These ecosystem- and landscape-level impacts of warming may dominate the effects of climate change decomposition and soil carbon losses, and need to be integrated into our experimental and predictive frameworks.