I'm using the IRGA to assess physiological characteristics in the cactus, but with the IRGA can not identify the photosynthetic mechanism that the plant is performing.
It depends on the physiological characteristics which you are studying. there are so many differences among C3,C4, and CAM plants which could you use,CO 2 compensation point,optimum temperature, leaf anatomy,chlorophyll a to chlorophyll b ratio . Please, see Plant Physiology text by Hoopkins and Muner, 2008.