Well, they are all important to some degree, but as you go down the scale of % of plant biomass of each micro nutrient, Mo is not needed much Wereas Fe is far more. This pattern extends to your question, in decreasing order, the relative importance and effects on plant health are noted in a similar manner.
Light=> CO2=> NO3/NH4 => etc on down the line. See Epstien 1972 for the mineral % break down in a common terrestrail plant. While these amounts vary plant to plant, nutriental status of said plant and submersed plants are different as well, the rough ranges of relative % ratios are not too far off.