Accelerated terrestrial ecosystem carbon turnover and its drivers.

The terrestrial carbon cycle has been strongly influenced by human-induced CO ₂ increase, climate change, and land use change since the industrial revolution. These changes alter the carbon balance of ecosystems through changes in vegetation productivity and ecosystem carbon turnover time (τ _eco ). Even though numerous studies have drawn an increasingly clear picture of global vegetation productivity changes, global changes in τ _eco are still unknown. In this study, we analyzed the changes of τ _eco between the 1860s and the 2000s and their drivers, based on theory of dynamic carbon cycle in non-steady state and process-based ecosystem model. Results indicate that τ _eco has been reduced (i.e., carbon turnover has accelerated) by 13.5% from the 1860s (74 years) to the 2000s (64 years), with reductions of 1 year of carbon residence times in vegetation (r _veg ) and of 9 years in soil (r _soil ). Additionally, the acceleration of τ _eco was examined at biome scale and grid scale. Among different driving processes, land use change and climate change were found to be the major drivers of turnover acceleration. These findings imply that carbon fixed by plant photosynthesis is being lost from ecosystems to the atmosphere more quickly over time, with important implications for the climate-carbon cycle feedbacks.
(© 2020 John Wiley & Sons Ltd.)