Measurements & Applications

Designed for cutting-edge research, yet easy to learn, the LI-6800 is both a remarkable teaching tool and a powerful research instrument that provides the ability to answer new questions.

An entirely new design, the LI-6800 Portable Photosynthesis System is a technological innovation that can reveal the mechanisms of photosynthesis.


Does your photosynthesis system eliminate the confounding effects of uncontrolled environmental conditions?

By controlling environmental conditions in the chamber for the duration of a measurement, the LI-6800 prevents multiple parameters from confounding the plant responses, ensuring more repeatability and confidence in the results.

CO2 Response Curves

By controlling chamber conditions, the photosynthetic response to changes in intercellular CO2 concentration is not confounded by other independent variables. The LI-6800 controls the leaf chamber environment at the setpoints with low variance (n = 3; ± standard error of the means).

LI-6800 graph showing leaf-level control of temperature

Automated leaf-level control of temperature holds the biochemistry constant for the entire response, even as transpirational cooling changes with stomatal conductance changes.

LI-6800 graph showing constant vapor pressure difference

The LI-6800 maintains a constant vapor pressure difference (VPD) between the leaf and chamber air to eliminate stomatal changes to VPD even as they respond to changing CO2.

LI-6800 graph showing flow rate

The flow rate is maintained precisely, decreasing moment-to-moment variation that impacts calculated carbon assimilation rates.

LI-6800 graph showing light-dependent biochemical reaction rates

Leaves are illuminated with constant irradiance, ensuring consistent light-dependent biochemical reaction rates.

LI-6800 graph showing CO2 assimilation

As the substrate for the dark reactions, photosynthetic responses to CO2 concentration provide information about the biochemical limitations. In C3 species, these data are used to assess Amax (maximum photosynthesis rate), Vc,max (maximum rate of Rubisco carboxylation), Jmax (maximum rate of electron transport for RuBP regeneration), and triose phosphate utilization (TPU) limitations.

Diurnal Measurements

LI-6800 graph showing Diurnal carbon assimilation

The LI-6800 controls chamber environmental conditions to maintain ambient or growth conditions around the sample of diurnal or survey measurements. Diurnal carbon assimilation for field-grown bok choy (Brassica rapa) with a slight depression at mid-day (n = 24 to 28; ± standard error of the means).

LI-6800 graph showing leaf illumination

The 6800-02 light source consistently illuminates the leaf with intensities that mirror ambient light levels.

LI-6800 graph showing chlorophyll fluorescence

The ΦPSII, measured from chlorophyll fluorescence, reflects the leaf illumination across the day, driving changes in electron transport.

Light Responses in Uniform Illumination

The chamber light sources illuminate the leaf with uniform light. Variation typically is less than ± 10% over 90% of the aperture, ensuring that photosynthesis is even across the entire chamber aperture. The average photosynthetic carbon assimilation reflects the true spot-to-spot rate across the enclosed leaf area when the leaf is uniformly illuminated (n = 3; ± standard error from the means).

LI-6800 graph showing light intensity distribution
False-color map (left) indicating the light intensity distribution from an LI-6800 fluorometer. A transect (right) of light intensity across the light field at the Multiphase Flash Fluorometer midline shows that illumination is highly uniform across the entire aperture.
LI-6800 histogram showing heat map of light uniformity distribution
Histogram of the heat map, indicating the light uniformity distribution is 10% over 90% of the area (counts).
LI-6800 graph showing Light response of Nicotiana tabacum
Light response of Nicotiana tabacum. Error bars are standard error of the means (n = 3).

Quantum Efficiency

LI-6800 graph showing steady leaf

Leaf temperature is held steady across a range of light intensities (Qabs), from 0 to 100 µmol m-2 s-1, ensuring that temperature is not a confounding variable.

LI-6800 graph showing changing carbon assimilation rate

Precisely controlled leaf chamber CO2 concentrations prevent alterations to the carbon assimilation rate that result from a changing CO2 concentration.

LI-6800 graph showing constant  leaf vapor pressure difference

Constant control of leaf vapor pressure difference (VPD) during light-driven changes in stomatal conductance, which removes the confounding effect of changing chamber H2O concentration.

LI-6800 graph showing steady flow rate

The flow rate is maintained precisely at the setpoint, which prevents flow from confounding the calculated carbon assimilation rate.

LI-6800 graph showing photosynthesis quantum efficiency

At low light intensities, the carbon assimilation rate is limited by light capture to drive linear electron transport in the light harvesting complex. Assessing the gross carbon assimilation response to absorbed light (Qabs) is a measure of the quantum efficiency of photosynthesis. The quantum efficiency for Nicotiana tabacum in non-photorespiratory conditions (0.5% O2 air) is consistent with theoretical and empirically measured values (n = 2, ± standard error of the means).


The LI-6800 Portable Photosynthesis System and accessories provide unprecedented capabilities to advance research in many different applications.


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