Priming effect of substrate addition in soil-based biodegradation tests.

To test whether substrate addition changes background CO2 evolution of soil, we measured both 14CO2 and net CO2 evolution from various test compounds. Glucose caused a priming effect, defined as substrate-stimulated soil organic matter mineralization. Formate, benzoate, n-hexadecane, and bis(2-ethylhexyl)phthalate caused no priming, and phenol caused only a transient one. The priming effect of glucose appears to be unusual and does not require a general rejection of net CO2 evolution measurements in biodegradability testing.