How are limiting factors determined once the first limiting factor has plateaued?

Once a limiting factor no is no longer increasing, it plateaus on the graph and now something else is a limiting factor. This limiting factor is determined by recording the rate of photosynthesis against another limiting factor such as testing out the CO2 concentration. If the increase of the rate of photosynthesis and CO2 concentration increases past the light intensity, this is the new limiting factor until the graph plateaus again.