An integrated fluorometer is a system that measures the light reaction and the dark reaction of photosynthesis. Software allows combined operation of gas exchange measurement and chlorophyll fluorescence measurement of a leaf. These parameters are used to non-destructively measure the photosynthetic efficiency of plants. The use of an integrated chlorophyll fluorometer provides the opportunity to measure additional measuring parameters that allow for a more exact measurement of photosynthesis than with gas exchange alone. Advanced gas exchange instrumentation, by itself, is capable of measuring A/Ci curves, commonly used for plant characterization. “A” is the term for photosynthetic rate (rate of CO2 exchange in the leaf chamber), and Ci is Sub-stomatal CO2 concentration or intracellular CO2 level within the leaf. When measured over a range of CO2 levels above and below ambient conditions, A/Ci curves become possible. With the addition of an integrated chlorophyll fluorometer, it becomes possible to measure more accurate A/CC curves, or photosynthetic rate at the site of carboxylation in chloroplasts. The integrated fluorometer allows measurement of mesophyll conductance, or the opposite of the resistance to CO2 transfer from intracellular air spaces to the site of carboxylation in chloroplasts. Various integrated chlorophyll fluorometer measuring protocols, such as the Laisk Protocol, the Kok protocol and the Yin Protocol are used to measure or estimate gm or mesophyll conductance. For example: the Laisk protocol allows the measurement of Γ* or compensation point, and Rd or respiration in the dark. Both values are required to calculate gm or mesophyll conductance and CC or CO2 at the site of carboxylation. Parameters typically measured by the gas exchange portion of the system include: “A” or photosynthetic rate, “gs” or stomatal conductance, “Ci” or sub stomatal CO2 concentration, and “E” or transpiration.
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Components and Design
Typically, integrated chlorophyll fluorometers consist of a leaf chamber in which the sample to be measured is sealed. Inside may be a thermistor to monitor the air and leaf temperature and a PAR sensor to measure the photosynthetically active radiation (400-700 nm) reaching the surface of the leaf. This chamber is part of an gas exchange system, typically used to measure photosynthesis and transpiration of leaves. It is also common to have a programmable actinic light source to allow various types of research including the use of A/Q curves or photosynthetic rate at different actinic light levels. This highly specialized light unit is held above the clear window of the chamber. This not only supplies the light to drive the photosynthesis of the leaf but also houses a sensitive chlorophyll fluorometer. Furthermore, integrated systems include software to control the integrated use of both the chlorophyll fluorometer, and gas exchange components of the system. For more information please visit the article photosynthesis systems.
Although highly complex, modern systems are relatively compact, portable and easy to use. With modern battery technology, it is normal for integrated chlorophyll fluorometers to operate for 8 hours in the field before recharging is necessary.
Uses
Integrated chlorophyll fluorometers are being used by leading plant physiologists to probe the photosynthetic process in plants. The results of this research will enable scientists to improve the efficiency of CO2 utilization by crops and estimate the capacity of grasslands, forests and ecosystems to mitigate climate change. It is hoped that these devices will enable us to screen genetic mutants to identify plants with an increased capacity to assimilate CO2.