Elevated atmospheric CO2 concentration (eCO2) and climate change may significantly affect ecosystem structure and functioning, and alter soil carbon (C) dynamics and thus affect feedback to future climate. However, our understanding of these changes is still limited, especially with respect to the interaction between elevated CO2 and the climate change factors. Nevertheless, only very few field experiments world-wide have combined eCO2 with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of carbon cycling in ecosystems. We exposed a temperate heath/grassland in Denmark to eCO2 (510 ppm) by Free Air Carbon Enrichment, warming (c. +1 oC) by passive night time warming, and drought (c. 1 mth. summer drought) by automatic roll out screens, in all combinations for 8 years. We measured the consequent changes in the major carbon pools and fluxes.
Results/Conclusions
Soil C stocks remained constant under ambient CO2 over time, whereas soil C stocks increased by 0.167 kg C m-2 yr-1 on average across all treatment combinations with eCO2. Soil C stocks showed no sign of slowed accumulation over time. Further, the response of soil C stocks to eCO2 was not affected by simultaneous exposure to warming and drought. The increase in soil C observed here under eCO2 were robust, even when combined with other climate change factors. This suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems. This soil C accumulation adds to mitigate increasing atmospheric CO2 concentrations under future climate conditions.
The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Consequently, globally coordinated and distributed experiments manipulating the three major climate change-related global drivers, CO2, warming, and changes in precipitation patterns are urgently needed, including studies of long-term changes in soil C.