Methods for Nitrogen Fixation Measurement

This chapter introduces the acetylene reduction assay (ARA) and 15N2 technique, two commonly used methods for the measurement of N2-fixation rates of aquatic samples in the field and laboratory. As a simple, low-cost, and relatively sensitive technique, the AR assay determines the acetylene (C2H2) reduction or ethylene (C2H4) production rate in samples using gas chromatography and yields the N2-fixation rate by converting the C2H4 production rate. A detailed protocol of the ARA is described in this chapter, including the principles, acetylene preparation, sample collection and incubation, and quantification and conversion of the C2H4 production rate.