MEASUREMENT OF NITROGENASE ACTIVITY IN LEGUME ROOT-NODULES - IN DEFENSE OF THE ACETYLENE-REDUCTION ASSAY - REPLY

This article is in response to that of Vessey (1994) who argues that t he traditional, closed acetylene reduction assay can still be a valuab le tool for measuring relative differences in nitrogenase activity of legumes. To counter this assertion we consider the practical uses of t he traditional assay procedure in relation to real research situations . This requires the use of the assay to be considered separately in th e different circumstances of pot-grown and field-grown plants. We conc lude that for pot-grown legumes there are a few practical applications where the use of the traditional, closed assay procedure is valid and we accept that these can be extended by the careful use of calibratio ns against open, flow-through systems. However, we doubt that there ar e many situations where such a calibration approach would have practic al advantages over using the flow-through system to obtain the actual measurements. We cannot recommend any form of the uncalibrated acetyle ne reduction assay for field-based studies and suggest that researcher s consider the merits of simple, alternative measurements such as dry weight, yield and total nitrogen.