While the ARA is often the method o

While the ARA is often the method of choice for quantifying N2 fixation potential in environmental samples, we were unable to detect any nitrogenase activity in this forest soil using the ARA and illustrated that the 15N2-tracer assay was more sensitive. However, this may depend on the amount of nitrogen already present in the system. Similar results, showing that 15N2-tracer assays can be more sensitive than ARA, have been obtained for oligotrophic marine samples . Taken together, our results demonstrate that measuring the isotopic incorporation (15N2 tracer assay) can be more sensitive than the ARA, highlighting the difficulty in applying ARA to environments where diazotrophic activity is expected to be low or sporadic, such as in soils.