Soil salinization is a growing threat to global agriculture and carbon sequestration, but to date it remains unclear how microbial
processes will respond. We studied the acute response to salt exposure of a range of anabolic and catabolic microbial processes,
including bacterial (leucine incorporation) and fungal (acetate incorporation into ergosterol) growth rates, respiration, and
gross N mineralization and nitrification rates. To distinguish effects of specific ions from those of overall ionic strength, we compared
the addition of four salts frequently associated with soil salinization (NaCl, KCl, Na2SO4, and K2SO4) to a nonsaline soil.
To compare the tolerance of different microbial processes to salt and to interrelate the toxicity of different salts, concentrationresponse
relationships were established. Growth-based measurements revealed that fungi were more resistant to salt exposure
than bacteria. Effects by salt on C and N mineralization were indistinguishable, and in contrast to previous studies, nitrification
was not found to be more sensitive to salt exposure than other microbial processes. The ion-specific toxicity of certain salts could
be observed only for respiration, which was less inhibited by salts containing SO4
2 than Cl salts, in contrast to the microbial
growth assessments. This suggested that the inhibition of microbial growth was explained solely by total ionic strength, while
ion-specific toxicity also should be considered for effects on microbial decomposition. This difference resulted in an apparent
reduction of microbial growth efficiency in response to exposure to SO4
2 salts but not to Cl salts; no evidence was found to
distinguish K and Na salts.