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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.