respiration chambers for Gas Flux measurEments in the lab or Field

Vienna Scientific Instruments offers customised Ecosystem Respiration Chambers for field and laboratory use, constructed of transparent polycarbonate (high PAR transmission) in various sizes. If required, a modular design allows the chamber size to be increased as the plant grows. Gaskets around each collar and the hole in the base plate (when a mesocosm is used) ensure adequate gas tightness. For field use, a metal frame can be installed under the chambers to ensure gas tightness to the soil. Chamber air is stirred by one or more adjustable (direction and speed) fans to homogenise the air. Fan size, speed and angle can be adjusted to avoid interfering with plants or IRGA measurements. A range of pipe fittings/connection plates are available for common IRGA systems. An environmental monitoring system consisting of temperature (air/leaf), rH and possibly PAR sensors can be added on request or appropriate positions for entering clables or fixing sensors can be foreseen during the chamber designing phase.The chamber shown inside the glassland (50 cm x 50 cm x 30-80 cm, w x d x h) is a version built for the University of Vienna to approximate the NEE of different ecosystems during a graduate course. Other versions (see below) have an aluminium frame for convenient and self-sealing placement of the pots / mesocosm. Various shapes and sizes are available to suit your mesocosm, pot, growth tube or field sampling campaign. See below for a list of key considerations when planning your ecosystem respiration chamber systems.

Images for illustration purposes only, design subject to change without notice

There are a number of important considerations when designing a customised gas flow measurement chamber:

• Chamber size and shape: The chamber should be large enough to provide sufficient headspace for gas exchange, but small enough to fit over the study area. The shape of the chamber should be appropriate for the study system, whether it's a circular, square or rectangular shape for rhizoboxes, pots or vegetation plots in situ. An internal fan may help to homogenise the air within larger chamber (consider the flow speed of externally connected devices suc has IRGAs). 
• Chamber materials: The chamber material should be inert, non-reactive and often transparent (for plant studies). Acrylic (PMMA) is a commonly used material for chambers. Other suitable materials are glass, polycarbonate or PTFE (for measurements of reactive substances incl. volatiles). Consider the reduction of radiation (PAR) by any transparent material - and the consequences for photosynthetic assimilation. 
• Gas-tight seal: A gas-tight seal is required to prevent loss or gain of gases from the chamber. Sealing can be achieved by the use of O-rings or gaskets and a clamp or screw system to hold the chamber in place. For field use, metal connection plates are often used at the bottom of the chambers, inserted a few centimetres into the ground. To avoid the build-up of overpressure, an overpressure vent should be considered (this can be a tiny needle or a tube connected to a bottle of water).
• Gas sampling ports: Sampling ports allow the measurement of gas concentrations within the chamber using common analysers, e.g. IRGA. The sampling ports should be positioned at an appropriate position within the chamber and may be fitted with tubing for devices or syringes for automatic gas collection. Appropriate diffusers and spacing, together with internal mixing (particularly in larger chambers), will prevent inflow/outflow loops towards analyzers.
• Manipulation: Potentially insets of gas-tights gloves and airlocks (to enter tools or remove samples) can be useful to manipulate the chamber content, i.e. plants, while the respiration chamber is remaining closed. This is particular importent when using the chambers for isotope labeling. 
• Environment: Environmental variables such as temperature, humidity and light intensity can greatly affect gas flow measurements. A fully functional respiration chamber should include sensors to monitor these variables, such as a temperature probe, humidity sensor and light sensor. In a closed chamber system operated over longer periods, monitoring of CO2 and O2 is required. Take appropriate measures to control environmental variables by placing chambers in growth rooms, scrubbing CO2 or removing rH with Peltier elements, etc. 

Overall, the construction of a gas flow / respiration chamber requires careful consideration of the materials used and environmental factors relevant in the study. Consultation with Vienna Scientific can be helpful to ensure that the chamber design is appropriate for your specific research objectives.

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