Incubation assay metrics describe different aspects of dissolved carbon degradation

Dissolved organic matter (DOM) incubation experiments are an important method for disentangling the effects of dissolved organic carbon (DOC) characteristics and microbial community composition on carbon (C) bioreactivity. However, common quantification metrics (ΔDOC, biodegradability, C removal rate) measure different aspects of C degradation and can change through time, suggesting experimental conclusions may depend on the metric used and the time of measurement. We performed an incubation experiment crossing varying DOM sources and microbial communities and synthesized published experimental data to explore (1) whether the interpretation of C degradation activity changed with the metric used, (2) how incubation duration impacted measures of degradation, and (3) how these different metrics compared across studies. Through our incubation experiment, we found that all metrics agreed regarding which treatments were associated with the greatest amounts of C degradation, and in all cases we observed peak C removal rates within 24 h of incubation initiation. However, our literature synthesis found that just 10% of studies sampled within the first 24 h of incubation initiation, suggesting common measurement intervals may miss peak C removal rates. Using these findings, we propose combinations of C degradation metrics and sampling frequencies that may be especially effective for detecting differences in C bioavailability, microbial activity, or C degradation.