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

• Published in: Global change biology 2017-09, Vol.23 (9), p.3501-3512
• Main Authors: Kim, Dohyoung, Oren, Ram, Clark, James S., Palmroth, Sari, Oishi, A. Christopher, McCarthy, Heather R., Maier, Chris A., Johnsen, Kurt
• Format: Article
• Language: English
• Subjects: Atmospheric models; Bayesian state space model; Carbohydrates; Carbon dioxide; climate change; Components; Contraction; Dynamics; Ecosystems; Efflux; Leaf area; Leaves; nitrogen fertilization; Photosynthesis; Reduction; Soil; Soil dynamics; soil respiration; Soils; Temperature effects
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.13713

We evaluated the effect on soil CO2 efflux (FCO2) 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 FCO2. FCO2 did not decrease until 4 months after termination of the long‐term eCO2 treatment, longer than the 10 days observed for decrease of FCO2 after experimental blocking of C flow to belowground, but shorter than the ~13 months it took for increase of FCO2 following the initiation of eCO2. The reduction of FCO2 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 FCO2‐temperature sensitivity. These asymmetric responses pose a tractable challenge to process‐based models attempting to isolate the effect of individual processes on FCO2. We evaluated the effect on soil CO2 efflux (FCO2) of sudden changes in photosynthetic rates by altering CO2 concentration in plots subjected to +200 ppmv for 15 years. FCO2 in elevated CO2 (eCO2) plots was not affected by short‐term (five‐day) manipulation of atmospheric CO2 concentration ranging from ambient to 300 ppmv above ambient. However, prolonged exposure to ambient CO2 (aCO2) after the termination of the long‐term CO2 enrichment reduced FCO2 in previously eCO2 plots to lower than that in aCO2 plots for at least 2 years.