Roots Increase the Temperature Sensitivity of Soil Carbon Decomposition.

The temperature sensitivity of soil CO₂ efflux underlies a potentially important feedback mechanism in the global carbon cycle, yet remains a subject of debate.  Total soil CO₂ efflux originates from two main sources, rhizosphere respiration of root-derived carbon by roots and associated rhizosphere microbes and microbial respiration of soil organic carbon (SOC).  The two sources also interact through a process known as the rhizosphere priming effect in which root-derived carbon stimulates microbial respiration of soil organic carbon.  Here we ask which component of soil CO₂ efflux is more sensitive to warming, rhizosphere respiration, SOC decomposition, or rhizosphere-primed SOC decomposition?  Past studies excluding roots from soil or soil incubations totally without plants omit the rhizospere respiration component and the rhizosphere priming effect, while field-warming experiments that measure total soil CO₂ efflux cannot discern the temperature sensitivity of rhizosphere respiration from that of SOC decomposition.  Results from a continuous ¹³C-labeling experiment show that, with 3ºC warming, rhizosphere-primed SOC decomposition increases 50% and exhibits the highest temperature sensitivity; whereas total soil CO₂ efflux, rhizosphere respiration, and SOC decomposition from soil incubation without plants are virtually insensitive.  These results indicate that root-soil interactions play a pivital role in determining the overall temperature sensitivity of SOC decomposition.