Figure 1.

Hypothetical relationship between soil nutrient availability and rhizosphere priming. Three nutrient-centered hypotheses are illustrated: Microbial mining: microbes utilize rhizodeposition to mine for nutrients in SOM thereby causing a positive rhizosphere priming effect when nutrient availability is low; Preferential substrate utilization: microbes switch from decomposing SOM to utilizing rhizodeposition when nutrient availability is high; Competition: microbes compete for nutrients with plants causing a negative rhizosphere priming effect because microbial growth and decomposition are nutrient limited. Both positive and negative rhizosphere priming can occur under low nutrient availability (gray area).