The LI-6400XT Portable Photosynthesis and Fluorescence System is the most referenced photosynthesis system worldwide in peer-reviewed literature. It has several advantages that make it the top choice for researchers.
- Accurate and Precise: accurate to 1.5%; precision of ±0.09% at CO2 350 ppm
- Gas analysers in the sensor head provide rapid response and eliminate time delays
- Portable: Laboratory-quality measurements in a field-portable system
- Rugged: Used in environments ranging from the moist tropics to the dry arctic
- A variety of applications are supported by many chambers and light sources
- An unprecedented level of automation and flexibility is provided through the open-source software
- Powerful networking capability provides a variety of data output, file-sharing, remote diagnostics and training possibilities
- Complete Solution: The LI-6400XT measures fluorescence and gas exchange simultaneously over the same leaf area with full control of environmental variables
- Reliable: LI-COR's commitment to continuous innovation and quality products (ISO 9001:2001 certified) ensures your LI-6400XT remains a smart choice for years to come
LI-6400XT Performance: Technology
CO2/H2O Analysers in the Sensor Head
The LI-6400 was the first photosynthesis measurement system to put the gas analysers in the sensor head - eliminating measurement time delays due to tubing. These analysers feature a novel, open-path design with the optical bench of the sample analyser open directly to the leaf chamber mixing volume.
Leaf dynamics are measured in real time because the return tubing between the leaf chamber and the console has been eliminated. There are no time delays to confound correlations between gas exchange and changes in environmental driving variables such as light, CO2 mole fraction, etc.
The absence of time delays allows fast, automatic control of chamber humidity at user-defined set points, even when the transpiration rate is changing. The absence of return tubing to the analysers also eliminates equilibration times due to water vapor sorption on the tubing walls.
The LI-6400XT sensor head has two complete, dual-path, non-dispersive infrared analysers, which both measure absolute concentrations of CO2 and H2O.
Infrared radiation from the sample analyser source passes into the leaf chamber mixing volume and is twice reflected 90° by mirrors. The mirrors are gold plated to enhance IR reflection and provide long-term stability.
After being reflected through the leaf chamber mixing volume where IR absorption occurs, infrared radiation passes through a chopping filter wheel and into the sample analyser detector. Absorbtion and optical reference wavelengths for CO2 and H2O are filtered by 1 of 4 narrow pass filters on the chopping wheel. These filters provide excellent rejection of IR radiation outside the wavelengths of interest, eliminating the effects of other IR absorbing gases.
The reference analyser measures incoming gas concentrations and is located directly below the sample analyser. The sample and reference analysers can be matched at any time, either manually or automatically, without altering environmental conditions in the leaf chamber.
The sample analyser detector, reference analyser detector, and chopping filter wheel are sealed in a housing that is continuously purged of CO2 and water vapor to prevent interference.
Through years of experience, LI-6400 systems have been proven to be robust and reliable, even in the most rigorous field conditions.
Spare Input and Output Channels
User-programmable analog and digital I/O channels are available to support external sensors. Input channels include five differential analog, two digital, and one pulse counting. Digital outputs: 8 open drain. Analog outputs: 7 D/A 8-bit, 1 D/A 12-bit, uncalibrated CO2 and H2O reference and sample analyser outputs, +5V regulated power supply (100 ma), battery voltage (fused, 200 ma).
A fan in the mixing volume of the optical bench pushes air through inlet ports into the upper and lower sections of the leaf chamber. The fan draws air from the leaf chamber through a central flow path. The entire flow path is plated to minimise water sorption and can be disassembled and cleaned in the field without affecting factory calibration.
The LI-6400XT system console combines a data acquisition system with a high speed computer for dedicated data logging and computations. High speed analog to digital converters support fast response applications. The backlit graphical display allows any 12 experimental variables or 3 real-time graphs to be displayed at once. All computed variables are calculated and displayed in real-time @ 2 Hz.
The 66 key ASCII keyboard is membrane sealed and designed to be used under harsh field conditions.
The LI-6400XT System, including optional accessories like the LED light source, are powered by 12VDC batteries stored in the console. Four batteries and a battery charger are included with the system, providing 4-8 hours of operation. The optional 6400-70 AC Adapter fits in the battery compartment.
Precise and Accurate
The LI-6400XT has two absolute CO2 and two absolute H2O non-dispersive infrared analysers that provide unparalleled accuracy and precision over systems which use other analysis methods. This gives you laboratory-quality measurements in a field-portable system.
Mounting the analysers in the sensor head allows for real-time measurements with leaf-level feedback control, which is not possible when analysers are placed in the console.
The analysers are robust and user-cleanable, leading to long-term reliability.
Changes in leaf dynamics are measured in real-time. To avoid delays caused by tubing, the analysers are placed within the chamber mixing volume. This allows you to measure the effects of subtle changes in environmental variables such as light and CO2 concentration. This architecture allows the LI-6400XT to precisely control the chamber CO2 concentration to within 1 µmol mol-1, which is critical for measurements like light response curves.
Flexible and Complete Solutions: Environmental Control
The LI-6400XT's flow through design allows automatic, independent control of leaf chamber conditions including:
The integrated CO2 Injector System provides a constant CO2 input from 50 to 2000 µmol mol-1 and can be controlled to within 1 µmol mol-1 of a target value at the leaf surface.
This system facilitates measurements at elevated CO2 concentrations and easily generates CO2 response curves. CO2 levels can be set manually from the console or automatically with the use of Autoprograms to make measurements at a series of concentrations.
The Red/Blue LED Light Source, RGB (Red, Green, Blue) Light Source, and Leaf Chamber Fluorometer (all optional accessories) are integrated with the hardware and software of the LI-6400XT System.
Light intensity is controlled over the entire range (0-2000 µmol m-2 s-1) through an automatic feedback algorithm. Light curves can be generated automatically using Autoprograms and user-selectable light set points.
Leaf temperature is controlled by integrated Peltier coolers. Chamber temperature can be set to any value within ±6°C of ambient temperature. Temperature control is a standard feature of the LI-6400XT; no external power supplies or accessories are required.
An optional Expanded Temperature Control Kit is available.
The LI-6400XT controls user-specified chamber humidity through the use of desiccant and by automatically varying the flow rate to null-balance. The input flow rate can also be held constant.
Inaccuracies and time delays due to water sorption on the air lines are eliminated by measuring the reference and sample water vapor concentrations in the sensor head.
The LI-6400XT's flexible software and user controls allow for a variety of measurements, from quick snapshots of photosynthetic rate to diurnal analyses. Photosynthetic responses to environmental variables such as light, CO2, humidity and temperature can also be measured to examine the underlying biochemical limitations.
Table of midday leaf-level gas exchange and chlorophyll fluorescence measured for biological replicates of experimental-plot grown Zea mays (corn). Gas exchange and fluorescence were measured simultaneously, over the same leaf area. Parameters measured or calculated include: photosynthetic carbon assimilation (Photo), stomatal conductance (Cond), intercellular CO2 concentration (Ci), maximum fluorescence during saturating pulse in the light (Fm'), steady state fluorescence (Fs), the fraction of absorbed photons (quantum yield) used in photochemistry (PhiPS2), leaf transpiration (Trmmol), vapor pressure deficit calculated from measure leaf temperature (VpdL), measured air temperature (Tair), measured leaf temperature (Tleaf), and photosynthetically active radiation inside the chamber (PARi).
Diurnal measurements are a series of discrete measurements taken throughout the day. This measurement tracks plant responses to changing temporal and environmental conditions.
Figure of photosynthetic assimilation rate of Glycine max (soybean) measured across a day. Soybeans were treated either with ambient air (control, blue), elevated CO2 (550ppm) in ambient air (black), or elevated O3 (1.25x ambient) in ambient air (orange) in a free-air gas concentration enrichment (FACE) system. Errors bars are the standard error of the means (n=4). Bernacchi et al., 2006, Plant, Cell and Environment 29(11): 2077-2090.
CO2 Response Curves
CO2 response curves measure plant response(s) to CO2 concentrations, which provides information on the biochemical and stomatal limitations to photosynthesis. This data can be used to assess Amax (maximum photosynthesis rate), VCmax (maximum rate of Rubisco carboxylation) and Jmax (maximum rate of electron transport).
Figure of the photosynthetic response to increasing CO2. Glycine max (soybean) leaf was excised from experimental-garden grown plant and then light acclimated at 1500 µmol m-2 s-1 (saturating) in a lab. Experimental data (circles) was modeled using the equations of Farquhar, von Caemmerer and Berry (1980) for maximum velocity of carboxlation (VCmax, black line) and the maximum electron transport rate for RuBP regeneration (Jmax, cyan line). The intercellular CO2 (Ci) at which photosynthesis transitions from VC-limited to J-limited is 216 µmol CO2 mol-1 air. Stomatal limitation to photosynthesis (l ) is the effect of the stomata resistance restricting photosynthesis decreasing CO2 available for photosynthesis at growth CO2 concentration.
Light Response Curves
Light response curves measure plant response(s) to light intensity. These measurements explore the difference in Rd (dark respiration rate), FCO2, maximum apparent quantum efficiency, Asat (light saturated photosynthesis) and light compensation point (the light level at which photosynthesis equals respiration).
Figure of the photosynthetic response to increasing absorbed light (αPAR). Glycine max (soybean) leaf was excised from experimental-garden grown plant and then light acclimated at 1400 µmol m-2 s-1 (saturating) in 385 µmol CO2 mol-1 air. The incident light was corrected to account for absorption (93%) of the light-source wavelengths. Experimental data (circles) was fit (cyan line) using a nonrectangular empirical function to estimate the light saturated rate of photosynthesis at growth CO2 (Asat, see Long and Hällgren, 1993). The 95% confidence intervals for the regression are plotted (black line).
Temperature Response Curves
Temperature response curves measure photosynthetic responses to temperature. These measurements can be used to study temperature effects on biochemistry including protein kinetics and membrane fluidity.
Humidity Response Curves
Humidity or Vapor Pressure Deficit (VPD) response curves measures the plant response to changing water vapor. Stomatal dynamics in response to H2O concentraion can be studied without altering photosynthetic assimilation.
Figure of the stomatal and photosynthetic response to vapor pressure deficit (VPD, difference in vapor pressure between leaf and chamber air). The photosynthetic rate (dashed lines) and stomatal conductance (solid lines) were measured at steady state at over a range of VPD's as driven by changing the water mole fraction in the chamber. Intact leaves were measured in an experimental garden at growth CO2 and 1300 µmol m-2 s-1 until steady state was reached at each water mole fraction. Helianthus annuus (sunflower, blue) and Glycine max (soybean, orange) had very different (~10x) stomatal conductances and the percentage decreases in stomatal conductance were greater in sunflower.
Gas Exchange & Fluorescence
Combined gas exchange and fluorescence measurements give researchers a more complete picture of how a plant is using absorbed energy (eg, qP and qN). As can be 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.
Figure of the 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 (qP, closed triangle) decrease with increasing light, whereas the theoretical maximal quenching of fluorescence by non-photochemical processes (qN).
The LI-6400XT Portable Photosynthesis System provides a stable platform for a variety of applications. Designed for publication-quality research, the flexibility and versatility of the LI-6400XT make it ideal for a wide range of studies from broad leaf gas exchange to insect respiration. LI-COR's chambers for the LI-6400XT are carefully designed and constructed to provide the highest accuracy and precision with minimal environmental disturbance.
The wide use of Arabidopsis thaliana in genetic and molecular studies has generated an extensive collection of point mutations, knockout, knockdowns, over-expressers and other mutant lines. Physiological assessment of these lines can demonstrate loss or gain of function necessary to demonstrate involvement of your favorite gene (AtYFG) or mutant allele (Atyfg). When equipped with a collection of alleles, researchers can explore expression effects on physiological carbon assimilation, water transpiration, and light capture and energy utilisation.
For secondary screening and comparisons of experimental lines, rapid assessments of physiological processes can be accomplished by non-destructive measurement of whole-plant gas exchange of CO2 assimilation and H2O transpiration. Leaf-level gas-exchange measurements directly assess stomatal function, carbon assimilation and utilisation biochemistry, and stress-signal transduction responses. Additionally, chlorophyll-fluorescence measurements provide non-destructive assessment of light-capture capacity by chlorophyll, efficiency of energy capture and utilisation in photosynthesis and other processes, and effectiveness of protective mechanisms in preventing oxidative damage. Leaf area can be quantified by very rapid destructive measurements.
The LI-6400XTA Portable Photosynthesis System for Arabidopsis Package is designed for molecular biologists, plant physiologists, and geneticists who study Arabidopsis thaliana. It provides a platform for physiological assessment of in situ function to validate regulatory or functional genes identified by genomic, molecular, or bioinformatics studies. In addition to the LI-6400XT Portable Photosynthesis System, the LI-6400XTA package includes the 6400-01 CO2 Injector System, 9901-013 External Quantum Sensor, Whole Plant Arabidopsis Chamber, the Red/Green/Blue (RGB) Light Source, and an AC power supply.
Solar energy powers our ecosystem through the exquisite process of photosynthesis, which converts solar energy into chemical energy that is utilised by a series of enzymes to assimilate atmospheric CO2 into carbon skeletons used to build all organs of a plant, algae, etc. Infrared detection of CO2 and H2O gases is a means of quantifying CO2 assimilation, but this information directly pertains to only a portion of the photosynthetic process.
Fluorescence techniques have been developed to quantify the absorption and conversion of solar energy into the chemical energy used by the CO2 assimilatory reactions. Combining information from these independent measurements can provide critical information about how: 1) the CO2 and light absorption reactions are coupled; 2) plants tolerate various biological and environmental stresses; 3) light capture is regulated at the leaf level; and 4) all of these processes are impacted by genetic manipulation, a process that has resulted in increased yield of various species over the past several decades.
LI-COR's Solution for Studying Chlorophyll Fluorescence
The LI-6400XT Portable Photosynthesis System combined with the 6400-40 Leaf Chamber Fluorometer allows the user to take simultaneous measurement of gas exchange and fluorescence over the same leaf area. The Leaf Chamber Fluorometer is a pulse-amplitude modulated (PAM) fluorometer that can be used to take measurements on both dark- and light-adapted samples. Measured parameters include Fo, Fm, F, Fm', and Fo', and calculated parameters include Fv, Fv/Fm, dF/Fm, qP, qN, NPQ, and ETR.
The unique design of the 6400-40 Leaf Chamber Fluorometer eliminates the need for fragile, awkward fiber optic light guides. Lightweight design and low power consumption make it possible for one person to gather data quickly and easily. Calibration information for the Leaf Chamber Fluorometer is stored onboard, making it easy to move between different LI-6400XT consoles.
Many entomologists work with plants nearly as much as they do with insects, since many insects are important pests of economically important plants. Insect respiration rates can be measured to assess insect health and growth. Insect herbivory can affect ecosystems by decreasing photosynthesis and net primary production. The herbivory can cause disruption of water and nutrient transport as well as directly affecting performance of photosynthetic enzymes within the tissue. Insect feeding may detrimentally affect plants' photosynthetic capabilities by interfering with light capture and energy transfer, regulation of H2O loss and CO2 uptake, and by disrupting the biochemical reactions that involve CO2 assimilation.
It can be argued that photosynthesis is the most important reaction occurring on this planet, since nearly all life on earth depends on solar energy captured by plants. Scientists want to study how plants grow, which drives the question of how ecosystems work. Global Climate Change research examines how rising levels of CO2, temperature and other alterations in climate or atmosphere could affect the ecology as well as agriculture.
Measuring photosynthesis is a short-term, fast response tool. The effect(s) of light, CO2, humidity, temperature, chemical, or biological factors on leaf gas exchange can be measured within seconds or just a few minutes. Measuring changes in plant growth responses is simple and very useful, but researchers may also want to investigate short-term physiological responses. For example, some plants are more drought tolerant because they can reduce water loss by closing down stomates, while others deal with water stress by having deeper roots to exploit a larger volume of the soil reserve. Leaf-level gas exchange measurement will quickly distinguish between these two strategies.
LI-COR's Solution for Studying Photosynthesis
The LI-6400XT system is a compact, rugged, field portable instrument able to provide researchers with detailed information on plant responses such as CO2 assimilation rates, stomatal conductance, intercellular CO2 concentrations, carboxylation and light use efficiencies, and CO2 and light compensation points.
Stressed Plants? Then the 6400-40 Leaf Chamber Fluorometer is an ideal complement to expand the analysis capabilities of the LI-6400 Portable Photosynthesis System.
LI-6400XT System: Photosynthesis, Fluorescence, Respiration