Soil warming generally increases soil organic carbon (SOC) decomposition. The presence of plants can also stimulate SOC decomposition through labile carbon inputs from the roots, which is often defined as rhizosphere priming effect (RPE). It remains unclear whether root-soil interactions alter the temperature sensitivity of SOC decomposition (as measured in Q₁₀ value) through RPE. We carried out three separate continuous ¹³C-labeling experiments in a growth chamber and assessed temperature sensitivities of decomposition of an organic farm soil with RPE (planted with sunflower or soybean) and without RPE (unplanted). We partitioned total soil respiration in planted treatment to rhizosphere respiration and SOC decomposition using a two end-member mixing model. We then determined the Q₁₀ value by measuring the response of SOC decomposition to continuous soil warming throughout the experimental period (51-57 days) in the first two experiments, and to temporary entire plant-soil system warming for 48 hours in the third experiment. The warming magnitude was 2.7^oC, 4.5^oC, and 5^oC for the three experiments respectively.

Results/Conclusions

In experiment-1, when sunflower was at maturity stage (49-51 days after planting or DAP) with relatively large plant biomass, RPE significantly increased Q₁₀ value from 1.38 to 1.99. In experiment-2, when sunflower was at vegetative stage (42-43 DAP) with relatively small biomass, RPE did not significantly change Q₁₀ value (1.48 vs. 1.66). However, when sunflower was at maturity stage (56-57 DAP) with relatively large biomass, RPE significantly increased Q₁₀ value from 1.24 to 1.77. These results suggest that the role of RPE in modifying the temperature sensitivity of SOC decomposition is dependent on plant growth stage and biomass. In the third experiment, when both sunflower and soybean were at maturity stage (47-50 DAP) with relatively large biomass, RPE significantly increased Q₁₀ value from 1.80 in unplanted treatment to 2.84 in sunflower treatment and 2.61 in soybean treatment. These results suggest that different warming methods don’t change the role of RPE in shaping the temperature sensitivity of SOC decomposition. Overall, our results indicated that RPE can significantly increase the temperature sensitivity of SOC decomposition. More attention should be paid to RPE in experimental and modeling studies of soil organic matter decomposition.