My talk at the AGA was centered around light and CO2 mostly. As nutrients, or light or CO2 go from no growth and then severe limiting levels, up to moderate limitations, to critical level(90% or more max potential growth) to non limiting................this relations ship is Non linear.
In other words, at the lower levels of light, say the change from 30 umols to 40umol is HUGE.
At 150 vs 160 umols, the change is virtually non existent.
The CO2 demand also behaves precisely the same way. There are huge differences between say 30 and 40 umols of light on the CO2 demand. There is very good support in the research specific to aquatic submersed plants(Bowes, Haller and Van, 1976).
Ole and Troels also presented such evidence, but did not discuss it in this context, but they both know about it and could fill folks in if asked.