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Alight-induced fluorescence transient (LIFT) is a device to remotely measurechlorophyll fluorescence in plants in a fast and non-destructive way. By using a series of excitation light pulses, LIFT combines chlorophyll fluorescence data with spectral andRGB information to provide insights into variousphotosynthetic traits andvegetation indices. LIFT combines thepump-probe method with the principle oflaser-induced fluorescence.^{[citation needed]}

A LIFT measures photosynthesis by exposing the plant to short flashes of blue light and analyzing the changes influorescence over time by the help of the FRR technique.

The LIFT fast repetition rate (FRR) fluorescence technique is a method for measuring plant fluorescence. It uses a series of short bursts of blue light pulses from aLED to excite photosystem II in the plant. When thequinone acceptor A (Q_A) reaches its capacity for binding electrons, the system becomes saturated and consequently red fluorescence is emitted. This is regulated by a precise excitation protocol, which consists of a saturation sequence (SQA) and a relaxation sequence (RQA) with a set of short excitation flashes (1 μs).

The fluorescence can then be measured with FRRfluorometry. For that purpose, the LIFT instrument has a built-inoptical interference filter to separate the red chlorophyll fluorescence from reflected light, with a wavelength of 685 ± 10 nm.

The fluorescencetransient resulting from this excitation protocol shows the kinetics of the reduction ofQ_A and its subsequent re-oxidation, and can be used to calculate various photosynthetic indicators.^[1] These indicators provide information on the level of photosynthetic activity, such as the efficiency of light utilization, thequantum yield of photochemical conversion, and the rate of electron transport.

The LIFT system measureschlorophyll fluorescence by stimulating the plant with excitation light, leading to an increase in fluorescence to its maximum (Fm'). The naturally occurring fluorescence (F') can also be measured without the excitation light. The variable fluorescence (Fq') can be calculated as the difference between Fm' and F'. The Photosystem II operating efficiency can be calculated using the equation:

${\displaystyle {\text{Fq}}^{\prime }/{\text{Fm}}^{\prime }=({\text{Fm}}^{\prime }-{\text{F}}^{\prime })/{\text{Fm}}^{\prime }}$

For the relaxation sequence (RQA), different relaxation parameters^[1] can be calculated according to different time sections:

• F_r1, ~ 0.625 ms after the maximum Fluorescence has occurred and
• F_r2, ~ 6.5 ms after the maximum Fluorescence has occurred.

These parameters can be used for calculating the reoxidation efficiency ofQ_A i.e. the kinetics of electron transfer between QA to PQ pool to photosystem I for light-adapted plants.

The concept for an airborne LIFT instrument was developed by Zbigniew Kolber atRutgers University in 1998. The first field test was conducted atBiosphere 2 in Arizona in 2002 using a stationary large LIFT setup equipped with a laser operating at a distance of up to 50 meters.^[2] The prototype instrument was later refined and improved at the Carnegie Institute, Stanford, and the Agricultural Research Center in Arizona, where the first attempt to operate it on a tractor frame was made.^[3] In 2010 several instruments were transferred from Carnegie to theForschungszentrum Jülich where they are used for laboratory and field research in robotic positioning systems for non-invasive, high-throughput data acquisition.

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In recent research, LIFT has been used in laboratory settings to explore the kinetics of photosynthesis and was also implemented in high-throughputphenotyping platforms for early drought detection.^[4] In a more recent publication, the device has been used to study the effects of future elevated atmosphericCO₂ concentrations on the seasonalphotosynthesis dynamics of differentwheat cultivars. The authors showed that the elevated CO₂ concentration increased the photosynthetic efficiency, mainly during vegetative growth.^[5]

• Photosynthesis
• Fluorescence techniques
• Measurement

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