Introducing the Argon-Hydrogen Method to Measure Biological Nitrogen Fixation

In the mid-1960s, the acetylene reduction assay was introduced as a simple and straightforward technique to determine rates of nitrogenase activity. It quickly gained acceptance and became the default method for estimating rates of biological nitrogen fixation. An alternative procedure, whereby the sample is flushed with a gaseous mixture of argon:oxygen:carbon dioxide and the resulting hydrogen gas is quantified, did not receive such wide acceptance by the research community. This most likely reflects the ease of handling and quantifying trace quantities of ethylene compared to hydrogen. However, fast forward to the present day and the current generation of gas analyzers with their micro-fluidic control are able to handle trace gases more precisely. We compare the acetylene reduction and the argon-hydrogen methods using laboratory cultures of diazotrophs and discuss the advantages and disadvantages of each method. We also demonstrate the applicability of these methods to obtaining real-time at-sea measurements of nitrogen fixation in the open ocean.