The New Standard in
The most common parameters used for stress measurement are Fv/Fm and Quantum Photosynthetic Yield (ΔF/Fm’) or Y(II). Both parameters are very robust and have volumes of supporting research regarding their value and sensitivity in plant stress measurement. Fv/Fm is a dark adapted measurement that reveals the maximum quantum efficiency of PSII under existing stress conditions. Yield of PSII is taken during photosynthesis and taken at steady state photosynthetic conditions to reveal actual achieved quantum efficiency under existing stress conditions.
Yield, the more versatile parameter, has been shown to correlate well with to CO2 assimilation rates under most stress conditions. C4 plants correlate in a linear manner and C3 plants correlate in a curve-linear manner. Parameter sensitivity to stress can vary with the type of stress and in some cases with the type of plant. There are some types of stress do not immediately affect PSII and therefore Quantum Photosynthetic Yield and Fv/Fm do not normally detect these types of stress until levels are moderate, severe or even at starvation levels. For example , Quantum Photosynthetic Yield has been shown to measure early water stress in C4 plants, while a special fluorescence assay is required to measure early water stress in C3 plants. Solutions now exist for difficult to measure early water stress in C3 plants, and early nitrogen stress in C3 and C4 plants.
Other modulated parameters are also valuable for stress measurement , such as Electron Transport Rate (ETR) and the various quenching parameters involved in photo-protection, and heat dissipation. For further details please refer to the Stress Guide.