Reply to ?Measurement of nitrogenase activity in legume root nodules: In defense of the acetylene reduction assay? by J.K. Vessey

Abstract

This article is in response to that of Vessey (1994) who argues that the traditional, closed acetylene reduction assay can still be a valuable tool for measuring relative differences in nitrogenase activity of legumes. To counter this assertion we consider the practical uses of the traditional assay procedure in relation to real research situations. This requires the use of the assay to be considered separately in the different circumstances of pot-grown and field-grown plants. We conclude 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 calibrations against open, flow-through systems. However, we doubt that there are many situations where such a calibration approach would have practical advantages over using the flow-through system to obtain the actual measurements. We cannot recommend any form of the uncalibrated acetylene reduction assay for field-based studies and suggest that researchers consider the merits of simple, alternative measurements such as dry weight, yield and total nitrogen.

Effect of weed management on weeds, and on the nodulation, nitrogenase activity, growth and yield of pea (Pisum sativum)

“…Similarly the nitrogenase activity did not correlate well with shoot dry weight at different periods of measurement (r = 0.576, 0.656, 0.352 and 0.127 at 6, 8, 10 and 12 weeks after sowing, respectively). Witty and Minchin (1988) and Minchin et al (1994) suggested that a closed acetylene reduction assay should not be used for measuring nitrogenase activity due to the errors (plant disturbance and acetylene-induced decline) associated with this technique. They suggested the use of simple alternative measurements such as dry weight, yield and total nitrogen.…”

“…It is possible that the inoculation of seed with rhizobia might decrease this variability. As a flow-through gas system cannot be used for measuring nitrogenase activity in field experiments (Vessey, 1994) and plant disturbance also decreases nitrogenase activity (Minchin et al, 1986(Minchin et al, , 1994Witty and Minchin 1988) better and cheaper methods need to be developed for measuring biological nitrogen fixation under field conditions.…”

“…However, for field studies the roots have to be excavated for incubating in closed containers. Although researchers have criticised the use of the closed acetylene reduction assay (Minchin et al, 1983(Minchin et al, , 1986Witty and Minchin, 1988;Minchin et al, 1994), no better methods, which are also cheap, have been developed for measuring the nitrogenase activity of field-grown plants. These workers have suggested the use of simple parameters such as plant dry weight, yield and total nitrogen, rather than nitrogenase activity, to determine the effect of given treatments.…”

Glutamine synthetase and glutamate synthase activities in relation to nitrogen fixation in Lotus spp.

“…Despite the criticisms of the method (Vessey, 1994, Minchin et al, 1994 it is still used in comparative experiments under controlled conditions (Buttery and Dirks, 1987;Vessey, 1994).…”

N2 Fixation of Common and Hairy Vetches when Intercropped into Switchgrass

“…These techniques must be performed in a controlled environment and are therefore unsuitable for quantifying N 2 fixation of field-grown legumes [23,24]. On the other hand, 15 N isotope dilution, 15 N natural abundance, N-balance and N-difference methods all are suitable for in situ experiments; however, each technique has inherent advantages and disadvantages.…”