LI-600 Porometer/ Fluorometer

Rapid insights into stomatal conductance and chlorophyll fluorescence

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LI-600 Porometer/Fluorometer

The LI-600 is a compact porometer with an optional Pulse-Amplitude Modulation (PAM) fluorometer that measures stomatal conductance and chlorophyll a fluorescence over the same leaf area. Capable of completing a measurement in seconds, the LI-600 provides the speed and precision required by researchers today.

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Why measure stomatal conductance and chlorophyll a fluorescence?

Stomatal openings regulate the exchange of water vapor and CO2 between a leaf and the air. Stomatal conductance to water (gsw), which responds to light, CO2, temperature, and humidity, among others, is a measure of the degree of stomatal openness and the number of stomata. It is an indicator of a plant’s genetic makeup and physiological response to environmental conditions.

Measurements of chlorophyll a fluorescence can provide information about the leaf’s quantum efficiency, electron transport rate (ETR), non-photochemical quenching (NPQ), as well as an assortment of reactions that collectively protect a leaf when it absorbs excessive light energy.

diagram showing how conductance and fluoresence in a single leaf

Combined measurements of stomatal conductance and chlorophyll a fluorescence present a more complete picture of a plant’s physiological state than either technique alone.

Understanding these processes is important to many research applications, including genetic screening, agronomy, plant physiology, ecology, climate change research, and stress tolerance.

How it works

The LI-600 brings together numerous innovative technologies to deliver fast, accurate, and dependable measurements in a compact, handheld device.

Stomatal conductance

The LI-600 uses an open flow-through differential measurement for quantifying transpiration (E) and stomatal conductance that enhances its measurement process. First, E is quantified by measuring the flow rate and water vapor mole fraction of air that enters and leaves the chamber. Meanwhile, total conductance to water vapor (gtw) is computed as a function of E and vapor pressures in the leaf and cuvette. Finally, stomatal conductance to water (gsw) is computed as a function of gtw and the boundary layer conductance to water vapor (gbw).

The advantages of the LI-600 measurement flow path include the following:

  • Flow rates that quickly flush through the small chamber volume and result in rapid stabilization for quick measurements
  • A differential measurement that is close to ambient conditions
  • Minimally disturbed light, CO2, and H2O during the measurement that eliminate the need for desiccant chambers or corrections for large diffusion gradients
  • Automatic matching that accounts for drift between the reference and sample sensors

Chlorophyll a fluorescence

Measurements of chlorophyll a fluorescence provide insights into photosynthesis, and, when combined with stomatal conductance, results in a more complete picture of the overall plant physiology and health. In addition to rectangular flashes, the LI-600 supports multiphase flashes (MPF), which can prevent underestimation of Fm’ (Loriaux et al., 2013) and thereby reduce bias in numerous fluorescence parameters.

Loriaux SD, et al. (2013). Closing in on maximum yield of chlorophyll fluorescence using a single multiphase flash of sub-saturating intensity. Plant Cell Environ 36:1755-1770.

diagram showing how the LI-600 Porometer/Fluorometer makes measurements

Light-adapted leaves

For light-adapted leaves, the LI-600 measures the quantum yield of fluorescence (ΦPSII), or the proportion of light absorbed by PSII used in biochemistry.

equation for light adapted leaves with the LI-600 Porometer Fluorometer

Fm’ is maximum fluorescence yield in a light-adapted leaf; Fs is steady-state fluorescence yield in a light-adapted leaf.

Dark-adapted leaves

For dark-adapted leaves, the LI-600 measures maximum quantum yield (Fv/Fm), or the maximum proportion of absorbed light that can be used to drive photochemistry.

equation for dark adapted leaves with the LI-600 Porometer Fluorometer

Fv is variable fluorescence yield in a dark-adapted leaf; Fm is maximum fluorescence yield in dark-adapted leaf; Fo is minimum fluorescence yield in a dark-adapted leaf.

LI-600 Testimonial

See what Aaron Hogan learned while measuring 40 different tree species with the LI-600 Porometer/ Fluorometer!

Read About His Experience

How it is different

The LI-600 is designed to quickly survey plants under ambient conditions. You can configure the instrument to log a measurement automatically when parameters are stable, or you can log manually with the press of a button.

diagram showing the features of the LI-600 Porometer/Fluorometer

Time-saving features for fast surveys

  • Automatic logging to complete a single measurement in seconds, typically.
  • Simple, intuitive display shows the instrument status and most recent measurement.
  • Ergonomic and light weight for easy handling.
  • Barcode scanner to enter sample information and reduce manual data entry errors.
  • Built-in rechargeable battery provides 8 hours or more of active use.

Reaches stability in seconds for speed and consistency

  • Reaches stability in seconds across a range of gsw rates
  • Provides fast measurements on different species.
  • User-configurable stability criteria and automatic logging to record each measurement when it is stable.
LI-600 data set
Figure 1: Three time series of measurements taken at different times of day on three adjacent leaves of three plants. The series are overlaid to show that the instrument can complete measurements in 6 to 9 seconds at a range of gsw values. Data points when not clamped between leaves not shown for clarity. Measurements are one-side stomatal conductance (gsw) made on three adjacent leaves (orange is soy shortly after sunrise; gsw = 0.055, blue is soy near midday; gsw = 0.17, and green is tobacco at midday; gsw = 0.51). Data are the 2 Hz measurements from the LI-600.

Dependable data, day after day

  • Automatic, user-configurable matching of RH sensors ensures measurement of the true differential.
  • Pliable gasket material conforms to the leaf to minimize diffusion and bulk flow leaks.
  • Automatic leak detection to prevent measurement errors.
  • Infrared thermometer for fast, accurate leaf temperature measurements.
  • Built-in light sensor measures ambient photosynthetically active radiation (PAR) near the leaf.

Fast-track your research

Watch the LI-600 complete six measurements in 60 seconds.

Software that simplifies your work

You can configure the LI-600 with ease – just set a few parameters in the computer software and you are ready to collect data. Each LI-600 can store up to four configurations, making it easy to switch from one protocol to another. You can save numerous configurations on your Mac or PC and share configuration files with colleagues. Configurations are easily loaded from the software onto the device through a USB connection.

Whether you are preparing for measurements, evaluating data files, or verifying the calibration, the computer software presents a simple, intuitive interface that lets you focus on the task at hand.

Keeps your focus on measurements

The instrument display presents you with the information that matters without distractions, so you can keep moving from sample to sample. You can view live data, the most recent measurement, and configuration settings, among others.

Pair the LI-600 and LI-6800 for two tiers of analysis

While the LI-600 Porometer/Fluorometer is for quickly surveying many plants in ambient conditions, the LI-6800 Portable Photosynthesis System provides an in-depth analysis by characterizing carbon assimilation and numerous other parameters under controlled conditions.

The LI-6800 precisely controls conditions in the leaf chamber in order to subject a leaf to specific temperature, CO2, water vapor, and light conditions. Advanced automatic controls enable response curves for variables, including CO2, light, temperature, and vapor pressure deficit (VPD). The LI-6800 fluorometer has red and blue actinic LEDs, along with far-red LEDs, for controlled-lighting measurements, providing capabilities that complement those of the LI-600. The LI-6800 also includes various chambers for different leaf morphologies and applications such as soil CO2 flux and insect respiration.

Learn more about the LI-6800

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