Labile carbon retention compensates for CO2 released by priming in forest soils

Increase of belowground C allocation by plants under global warming or elevated CO2 may promote decomposition of soil organic carbon (SOC) by priming and strongly affects SOC dynamics. The specific effects by priming of SOC depend on the amount and frequency of C inputs. Most previous priming studies have investigated single C addi-tions, but they are not very representative for litterfall and root exudation in many terrestrial ecosystems. We evalu-ated effects of 13C-labeled glucose added to soil in three temporal patterns: single, repeated, and continuous on dynamics of CO2 and priming of SOC decomposition over 6 months. Total and 13C labeled CO2 were monitored to analyze priming dynamics and net C balance between SOC loss caused by priming and the retention of added glu-cose-C. Cumulative priming ranged from 1.3 to 5.5 mg C g1 SOC in the subtropical, and from 0.6 to 5.5 mg C g1 SOC in the tropical soils. Single addition induced more priming than repeated and continuous inputs. Therefore, sin-gle additions of high substrate amounts may overestimate priming effects over the short term. The amount of added glucose C remaining in soil after 6 months (subtropical: 8.1–11.2 mg C g1 SOC or 41-56 % of added glucose; tropical: 8.7–15.0 mg C g1 SOC or 43–75 % of glucose) was substantially higher than the net C loss due to SOC decompositio