Evaluation of the 18O-H2O incubation method for measurement of soil microbial carbon use efficiency

The 18O-labelled water approach has been widely used to estimate microbial carbon use efficiency (CUE). However, this approach assumes that oxygen in microbial DNA synthesis is 100% from water while this assumption has not been tested. We tested this assumption using 18O-labelled glucose and 18O-labelled water to see their contributions to the oxygen in microbial DNA synthesis. Results showed microbes used less than 8.3% glucose-oxygen and more than 91.7% water-oxygen for their DNA synthesis. The 18O-labelled water method for estimation of CUE has proven to be reliable under low enrichment of 18O in soil water. We suggest to use a correction factor (i.e., 1.1 in this study) to account for oxygen incorporated into DNA from other sources than water.