Gas Exchange & Fluorescence

Combined gas exchange and fluorescence measurements give researchers a more complete picture of how a plant is using absorbed energy (e.g. q_P and q_N). As seen in the figure below, photosynthesis measured with fluorescence (electron transport through PSII, ETR) agrees well with photosynthesis measured with gas exchange under some conditions. Under other conditions, especially in the presence of certain stresses, the two measurements reveal different results, highlighting the role of alternative electron sinks.

Simultaneous gas exchange and chlorophyll fluorescence over the same leaf area for Zinnia elegans (Zinnia). Intact leaves were measured in an experimental garden at growth CO₂ and increasing irridance until steady state. The photosynthetic carbon assimilation rate (grey circles) tracked closely with the electron transport rate (ETR, open circles) indicating a closely linked relationship. The theoretical maximal quenching of fluorescence by photosynthesis (q_P, closed triangle) decreases with increasing light, whereas the theoretical maximal quenching of fluorescence by non-photochemical processes (q_N) increases with light.