6800-18 Aquatic Chamber

The 6800-18 Aquatic Chamber is used to measure steady-state carbon assimilation and chlorophyll a fluorescence from an algal suspension using the LI-6800 Portable Photosynthesis System, the preferred photosynthesis system for terrestrial plant research.

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LI-6800-18 aquatic chamber with algae

The LI-6800 is trusted by leading researchers and institutions around the world to measure carbon assimilation (A) and pulse-amplitude modulated (PAM) chlorophyll a fluorescence in terrestrial plants. With high precision CO2 and H2O gas analyzers and automated system controls, the LI-6800 is used to test novel hypotheses at the forefront of photophysiology research.

The NEW 6800-18 Aquatic Chamber extends these capabilities to aquatic samples, enabling researchers to explore questions related to photosynthesis of algae in suspension.

How it works

In contrast with typical oxygen-based measurements of algal photosynthesis, where photosynthesis is derived from the change in O2 concentration over time, the LI-6800 is an open, flow-through, steady-state gas exchange system where CO2 and O2 concentrations are constant during the measurement.

A differential CO2 measurement

In the 6800-18 Aquatic Chamber, the carbon assimilation rate is determined from the mass balance of an air stream before and after it interacts with a liquid sample. The CO2 and water vapor concentrations of the air stream are measured by a pair of high-precision infrared gas analyzers (IRGA). Assimilation is calculated from the concentration differences and flow rate:

assimilation equation
6800-18 Aquatic Chamber, open, flow-through system diagram
Figure 1. In an open, flow-through system, CO2 and H2O in the sample air are measured before interacting with the sample (Incoming IRGA) and after (Outgoing IRGA). The difference represents biological activity of the sample.

Fundamentally, this mass balance gives the flux of CO2 between the liquid sample and the cuvette headspace. The flux is coupled to the true biological carbon assimilation rate by mass transfer at the air-liquid interface and the kinetics of the carbonate system for the aquatic sample.

When normalized to cell density, mass, or chlorophyll content, the aquatic chamber provides measurements as µmol CO2 cell-1 s-1, µmol CO2 mg-1 s-1, and µmol CO2 µg-1 s-1, respectively.

  • The water vapor difference between the incoming and outgoing airstreams is minimized by a patent-pending method.
  • Water vapor concentrations are included in the carbon assimilation calculation to account for volumetric dilution.

Rapid equilibration of gas-phase CO2 and CO2 in solution through aeration of the aquatic sample

A carefully controlled aeration scheme ensures that the mass transfer coefficient is not limiting and that the measured flux represents the biological assimilation rate of the sample. To keep the carbonate system at a steady state during measurements, carbonic anhydrase (CA) is added to the sample media for rapid hydration of CO2 and interconversion with bicarbonate (HCO3).

CO2 transfer from air to water

Steady state sample conditions

The LI-6800 precisely controls environmental conditions of the sample, including the CO2 concentration in headspace air and the light environment according to your preferences.

  • The CO2 concentration that the sample is subject to is stable during the measurement. The instrument maintains the CO2 concentration with a mixer/scrubber system, preventing either CO2 or O2 from accumulating in the aquatic sample or headspace.
  • The instrument controls light in the chamber – total light, as well as proportions of blue, red, and far-red – enabling a wide variety of light response measurements.
  • With an external recirculating water bath, the sample temperature can be maintained at setpoints from >0 °C to 50 °C. Sample temperature is measured and recorded with the dataset.

These features enable time-series data collection on a sample while environmental conditions are kept stable. This ensures that the measured biological response is in the context of known, steady-state conditions.

screenshot showing steady state sample conditions
Figure 2. The instrument controls variables based on user-configurable setpoints while it records measured parameters in the dataset. Here, CO2 in the reference air is kept at 400 ppm, while temperature is maintained near 25 °C by a recirculating water bath.

Chlorophyll a fluorescence

Simultaneous measurements of CO2 gas exchange and PAM chlorophyll a fluorescence of an aquatic sample provide a more complete impression of photosynthetic processes than either technique alone. CO2 exchange measurements are indicators of the photosynthetic interaction between algae and dissolved inorganic carbon in solution. Chlorophyll a fluorescence is an indicator of the light reactions of the organisms.

When combined, they reveal more about the photochemistry of algae than either technique alone.

flourescence in aquatic sample

“This chamber has many possibilities beyond algae, we are excited to explore coral, bryophytes, lichens and other organisms that are in solution or require constant wetting.”

Dr. Tracy Lawson
Aquatic Chamber Beta Tester
Professor – Plant Physiology
University of Essex, Colchester, UK

Example measurements

From basic irradiance response measurements to complex multifactor experiments, the aquatic chamber can be used to evaluate biological responses to different environmental conditions.

Photosynthetic response to irradiance at constant CO2

Figure 3 shows assimilation measurements on Chlorella at ambient oxygen (21%) and low oxygen (0.5%) in response to light (Q). The CO2 concentration entering the chamber was held constant at 400 µmol mol-1 by the LI-6800 system. Air with 21% oxygen was ambient; low-oxygen air was from a tank of 0.5% oxygen balanced in air. Chamber temperature was held constant at 25 °C using an external water bath. Cells were measured in a saltwater media at 17 ppt salinity.

6800-18 Aquatic Chamber, Net carbon assimilation rate as a function of light intensity (Q)
Figure 3. Net carbon assimilation rate as a function of light intensity (Q). Solid symbols are at 0.5% oxygen; open symbols are at 21% oxygen.

When O2 concentrations are reduced in solution, the likelihood of oxygenation of RuBP by RuBisCO—the first step of photorespiration—is reduced, and the overall efficiency of carbon assimilation relative to energy capture increases. There is little impact on the efficiency of PSII, shown here by the near identical behavior of ΦPSII. Photorespiration impacts the strength of electron sinks such that 1-qL may be expected to decrease some with an increase in photorespiration (Figure 4).

6800-18 Aquatic Chamber, Measurements derived from chlorophyll a fluorescence as a function of light intensity.
Figure 4. Measurements derived from chlorophyll a fluorescence as a function of light intensity. The quantum efficiency of PSIIPSII when Q > 0 or Fv/Fm when Q = 0) is shown (circles) along with the fraction of closed reaction centers (1-qL, triangles). Solid symbols are at 0.5% oxygen; open symbols are at 21% oxygen.

Active regulation of a portion of NPQ related to cyclic electron flow balances the energetic products of photochemistry, ATP, and NADPH—so as photorespiration is suppressed at low oxygen, down regulation of NPQ is observed (Figure 5).

6800-18 Aquatic Chamber, Captured energy being dissipated through non-photochemical processes (NPQ).
Figure 5. Captured energy being dissipated through non-photochemical processes (NPQ). Solid symbols are at 0.5% oxygen; open symbols are at 21% oxygen.

Photosynthesis response to CO2 at constant O2 and light intensity

The photosynthetic response to CO2 was measured on Monoraphidium at ambient O2 concentration and 700 µmol photons m-2 s-1 light intensity. The CO2 concentration entering the chamber was controlled at different setpoints during these measurements. Chamber temperature was held constant at 25 °C using an external water bath. Cells were measured in a freshwater media buffered to pH 7.0 with a TRIS buffer.

The photosynthetic response to CO2 is non-linear in nature (Figure 6). At low concentrations, CO2 is limiting, and assimilation changes proportionally to the concentration.

6800-18 Aquatic Chamber, Net carbon assimilation rate as a function of pCO2 in the sample medium.
Figure 6. Net carbon assimilation rate as a function of pCO2 in the sample medium. Under these conditions, the portion of energy ultimately used in carbon assimilation decreases, leading to a rise in non-photochemical quenching and a rise in 1-qL, indicative of a decreasing electron sink strength. This leads to a reduction in the quantum efficiency of PSIIPSII) as the system becomes progressively limited by energy dissipation (Figure 7).
6800-18 Aquatic Chamber, Measurements derived from chlorophyll a fluorescence as a function of the equilibrium CO2 concentration (pCO2) in the sample cuvette.
Figure 7. Measurements derived from chlorophyll a fluorescence as a function of the equilibrium CO2 concentration (pCO2) in the sample cuvette. The quantum efficiency of PSII is shown PSII, solid symbols) along with the fraction of closed reaction centers (1-qL, open symbols). The lower panel shows the degree of captured energy being dissipated through non-photochemical processes (NPQ). Download the full white paper for more details on the data described here.
6800-18 whitepaper

A novel approach to measuring carbon assimilation and chlorophyll a fluorescence in algal suspensions

A novel approach to measuring carbon assimilation and chlorophyll a fluorescence in algal suspensions

Read the Whitepaper

Features that keep your focus on research

The LI-6800 is a well-developed system for photosynthesis research. It supports advanced configurations, automated controls, simple file management, and other features that let you focus on research.

  • Background Programs provide full programmatic control over all LI-6800 functions. You can write them using the Python programing language or the built-in graphical programming interface.
  • Connector and port allow sample pH to be measured with common 12 mm diameter pH probes. Data are recorded with the dataset.
  • Support for custom gas blends via an auxiliary air inlet to subject the sample to any gas conditions.
  • Onboard graphing of live data lets you observe measured responses in real time.
  • User-configurable prompts allow the operator to enter supplemental information on each measurement. These are recorded in the dataset along with the measurement.
  • Automated system tests verify the performance and operation of the instrument and provide troubleshooting information to help you get the best possible data.
  • Data are logged in text files and Microsoft Excel files with equations for simple evaluation and recalculation.

6800-18 Aquatic Chamber Specifications

Sample Cuvette:

  • Wetted Materials: 316 stainless, float glass, Viton, PTFE, silicone, acetal
  • Cuvette Working Volume: 0 – 20 mL, 15 mL recommended sample volume

CO2 Gas Analyzer:

  • Operating Principle: Non-dispersive Infrared (NDIR)
  • Measurement Range: 0 – 3100 µmol mol-1
  • Precision (1-sigma) @ 4 Second Averaging @ 400 µmol mol-1: < 0.1 µmol mol-1
  • Accuracy: 1% of reading at > 200 µmol mol-1, +/- 2 µmol mol-1 at < 200 µmol mol-1

CO2 Control:

  • Range: 0-2,000 µmol mol-1
  • Support for custom gas blends through external fittings on the air supply

Fluorometer (6800-01A):

  • Red/Blue Actinic Light Output: 0 – 3000 µmol m-2 s-1
  • Far-red Light Output: 0 – 20 µmol m-2 s-1
  • Saturation Flash Intensity: 0 – 16,000 µmol m-2 s-1
  • Red Actinic Peak Wavelength: 625 nm
  • Blue Actinic Peak Wavelength: 475 nm
  • Far-red Peak Wavelength: 735 nm

Temperature:

  • Operating Temperature: 0 to 50 °C with no solar load (non-freezing)
  • Storage Temperature: -20 to 60 °C with chamber clean and dry
  • Temperature Control: User provided water bath. #10-32 threaded connections to chamber.

Operating Fluid Environment:

  • Temperature: non-freezing to 50 °C
  • Salinity: 0 – 35 %

Auxiliary Ports:

  • pH (probe not included): 12 mm diameter O-ring sealed port and integrated amplifier. Passive glass-electrode based pH probe, with BNC connector (nominal -59 mV/pH slope, user calibrated).
  • Septa: Silicone-PTFE septa

Specifications subject to change without notice.

View specifications for the full LI-6800 Portable Photosynthesis System

Ordering

The aquatic chamber can be purchased as a complete stand-alone system, as a new chamber and light source for an existing LI-6800 system (LI-6800 System required), or as a chamber only (LI-6800 System and fluorometer required).

LI-6800AQ Portable Photosynthesis System with Aquatic Chamber

Designed for the primarily aquatic researcher, this package includes the LI-6800 System with console, sensor head, cable assembly, 6800-01A Fluorometer, and 6800-18 Aquatic Chamber. Accessories include the Spares Kit, Power Supply, two batteries, Silica gel, Soda lime, and CO2 cartridges.

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6800FAQ Aquatic Chamber with Fluorometer

Includes the 6800-01A Fluorometer and the 6800-18 Aquatic Chamber. This package is for customers who already have an LI-6800 System and still need a 6800-01A Fluorometer or want a specific 6800-01A Fluorometer for their aquatic work to avoid routine switching back and forth to the leaf level measurements.

Get a Quote for the 6800FAQ

6800-18 Aquatic Chamber

LI-6800 Aquatic Chamber for measuring Photosynthesis and Respiration in an aquatic solution. Must be used with the LI-6800 Portable Photosynthesis System and 6800-01A Fluorometer. Includes the Spares Kit.

Get a Quote for the 6800-18

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