There are several methods of measuring nitrogen fixation ability of bacterial cells (like acetylene reduction assay etc) , but is there any protocol or research paper from which we can directly find out nitrogen fixing ability of root nodule.
You can also perform ARA measurements on the root system, by placing the roots in a closed bottle in which you inject acetylene. After incubation you can analyze the ethylene produced.
The following link could be of help.
http://www.colorado.edu/lab/barger/sites/default/files/attached-files/acetylene_reduction_assay.pdf
Alternatively, you could use some N15 isotope experiments to demonstrate fixed N in the plant biomass.
Nitrogenase activity (N2 -ase) in roots were measured as described by Hardy et al. (1973) and Somasegaran and Hoben (1985). Samples of roots were taken from all the treatments and kept in paper bags still be transferred later to 600 ml serum bottles. The bottles were then fitted with 5 ml glucose (1 % w/v) to accelerate the bacteria in the(roots). Bottles were sealed with silicon rubber (suba seal) to prevent any air gas leakage . Ten percent of bottle air was then replaced by acetylene gas . the samples were then incubated at 280 C for 24 hrs Nitrogenase activity (ARA) was then calculated according to the following formula
Container volume
µ mol C2H4 = R X ---------------------------------------------------------- X 103
Time of incubation.X Inj.Vol. X d.w. X 22.4
Where :
Ing . vol = Injection volume
R = Reading.
d.w. = The dry weight of roots
The results are presented as µ mole / C2H4 / g dry weight / day, µ mole / C2H4 / g dry weight of roots / day.
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