Main content area

Dynamics of soil CO2 efflux under varying atmospheric CO2 concentrations reveal dominance of slow processes

Kim, Dohyoung, Oren, Ram, Clark, James S., Palmroth, Sari, Oishi, A. Christopher, McCarthy, Heather R., Maier, Chris A., Johnsen, Kurt
Global change biology 2017 v.23 no.9 pp. 3501-3512
carbon dioxide, ecosystems, leaf area, models, photosynthesis, soil
We evaluated the effect on soil CO₂ efflux (FCO ₂) of sudden changes in photosynthetic rates by altering CO₂ concentration in plots subjected to +200 ppmv for 15 years. Five‐day intervals of exposure to elevated CO₂ (eCO₂) ranging 1.0–1.8 times ambient did not affect FCO ₂. FCO ₂ did not decrease until 4 months after termination of the long‐term eCO₂ treatment, longer than the 10 days observed for decrease of FCO ₂ after experimental blocking of C flow to belowground, but shorter than the ~13 months it took for increase of FCO ₂ following the initiation of eCO₂. The reduction of FCO ₂ upon termination of enrichment (~35%) cannot be explained by the reduction of leaf area (~15%) and associated carbohydrate production and allocation, suggesting a disproportionate contraction of the belowground ecosystem components; this was consistent with the reductions in base respiration and FCO ₂‐temperature sensitivity. These asymmetric responses pose a tractable challenge to process‐based models attempting to isolate the effect of individual processes on FCO₂.