Chlorophyll fluorescence meter is a crucial tool in plant physiological and ecological research. By measuring the fluorescence signal of photosystem II (PSII), it can non destructively reveal the photosynthetic performance, stress resistance, and health status of plants. Mastering its standardized operations is the key to obtaining reliable data.

　　1、 Preparation before measurement

1. Instrument calibration and setup

After turning on the instrument, perform dark adaptation calibration first. Insert the blade clamp into the calibration base, ensure all light is blocked, and run the calibration program. After calibration, set measurement parameters according to experimental requirements, including saturation light intensity (usually 3000-4000 μ molm ⁻² s ⁻¹), modulation frequency, measurement light intensity, etc. Modern fluorescence meters (such as PAM series) often have built-in standard programs, such as Fast Light Curve (RLC) or Induced Curve measurement modes.

2. Sample dark adaptation

Dark adaptation is a prerequisite for accurately measuring Fv/Fm (maximum photochemical efficiency). Use specialized shading clips or aluminum foil to completely shade the tested leaves for at least 20-30 minutes (C3 plants), ensuring that all reaction centers are open. Insufficient dark adaptation can significantly underestimate Fv/Fm values.

　　2、 Measurement process

1. Basic fluorescence measurement

Quickly place the dark adapted leaves under the measuring head, ensuring that the leaf clamp is tightly closed to avoid light leakage. Firstly, weak measurement light (<1 μ molm ⁻² s ⁻¹) is applied to obtain the minimum fluorescence (Fo) under dark adaptation. Subsequently, a saturation pulse (approximately 0.6-1 seconds) is triggered to obtain maximum fluorescence (Fm). The instrument automatically calculates Fv/Fm=(Fm Fo)/Fm, which is the core indicator for evaluating the degree of light suppression.

2. Measurement of light adaptation parameters

Remove the shading device and allow the leaves to undergo photosynthesis under actin light. After the fluorescence signal stabilizes (usually taking 3-5 minutes), apply saturation pulses again to obtain the maximum fluorescence (Fm ') and steady-state fluorescence (Fs) under light adaptation. Then turn off the action light and immediately turn on the far red light to measure the minimum fluorescence (Fo '). From this, it can be calculated that:

-Φ PSII=(Fm '- Fs)/Fm' (actual quantum yield of photosystem II)

-QP=(Fm '- Fs)/(Fm' - Fo ') (photochemical quenching coefficient)

-NPQ=(Fm-Fm ')/Fm' (non photochemical quenching coefficient)

3. Construction of Fast Light Response Curve

Select RLC mode, and the instrument will automatically gradually increase the light intensity (such as 0, 50, 100, 200, 500, 1000, 1500 μ molm ⁻² s ⁻¹). After stabilizing at each light intensity, apply saturation pulses to obtain a series of fluorescence parameters for fitting the response of photosynthetic electron transfer rate (ETR) to light intensity.

　　3、 Key precautions

1. Leaf selection: The measurement site should be representative and avoid leaf veins and damaged areas. At least 5-6 repetitions should be measured for the same treatment.

2. Environmental control: During measurement, try to avoid severe fluctuations in ambient light, preferably indoors or in a shaded environment. Outdoor measurements should be taken on cloudy days or in the morning and evening.

3. Measurement consistency: Different treatments should maintain the same dark adaptation time, measurement location, and instrument settings to ensure data comparability.

4. Data recording: Detailed recording of sample information, measurement time, environmental conditions (temperature, light), and instrument parameters for subsequent analysis.

　　4、 Data Processing and Interpretation

After the measurement is completed, export the data to professional software such as WinControl and PyChlorophyll for analysis. Key focus:

Fv/Fm: Healthy plants typically range from 0.75 to 0.85, with values below 0.75 indicating the presence of photoinhibition or photodamage.

2. Φ PSII and ETR: reflect the photosynthetic efficiency under actual light conditions.

3. NPQ: It characterizes the heat dissipation capacity of plants and is an important indicator of stress resistance.

Conclusion

Standardizing the operation of chlorophyll fluorescence meters can not only obtain high-quality data, but also truly reveal the physiological state of plants. From rigorous dark adaptation to precise parameter interpretation, each step is a crucial step in converting fluorescent signals into biological insights. Mastering this technique proficiently will provide strong support for plant physiological and ecological research.