Root functional traits determine the magnitude of the rhizosphere priming effect among eight tree species

Rhizosphere priming effect can accelerate or decelerate the
decomposition of soil organic matter. Using a natural abundance
13C tracer method allowing partitioning of native soil organic carbon
(SOC) decomposition and plant rhizosphere respiration, we studied the
effects of eight tree species on the strength of the rhizosphere priming.
All tree species enhanced the rate of SOC decomposition, by 82% on
average. Mean diameter of first-order roots and root
exudate-derived respiration were positively correlated with the RPE,
together explaining a large part of the observed variation in the RPE (R2
= 0.72), whereas root branching density was negatively associated with the
RPE. Path analyses further suggested that mean diameter of first-order
roots was the main driver of the RPE owing to its positive direct effect
on the RPE and its indirect effects via root exudate-derived respiration
and root branching density. These results demonstrate that the magnitude
of the RPE is regulated by complementary aspects of root morphology,
architecture and physiology, implying that comprehensive approaches are
needed to reveal the multiple mechanisms driving plant effects on the RPE.