LIFT · Laser-Induced Fluorescence Transient: a remote sensing approach to scale and quantify photosynthetic light use efficiency in ecosystems

Final Activity Report Summary - LIFT (LIFT - Laser-Induced Fluorescence Transient: a remote sensing approach to scale and quantify photosynthetic light use efficiency in ecosystems)

Light energy absorbed by chlorophyll molecules in a leaf can undergo three different fates: it can drive photosynthesis, it can be dissipated as heat or re-emitted as fluorescence. These three processes compete with each other so that an increase in the efficiency of one inevitably decreases the yield of the other two and, by non-invasive measurement of chlorophyll fluorescence we gain information on the efficiency of photochemistry and non-photochemical heat dissipation. The most commonly used technique to measure chlorophyll fluorescence is the Pulse Amplitude Modulated (PAM) fluorometry which uses saturating pulses to retrieve a maximum fluorescence level which in relation to the fluorescence level at ambient illumination or in absence of any light can be related to the efficiency with which absorbed photons are being used for photosynthesis, the rates of electron transport, and the degree of non-photochemical protection. This approach provides a possible route to obtain the leaf by leaf measurements of photosynthesis required to estimate carbon uptake and validate canopy carbon uptake models. However, the application of saturating pulses requires measurements very close to the leaf so that this technique is mostly used in laboratory experiments being not practical for measurements in inaccessible plant canopies. With this project we have proposed to bridge the gap between laboratory and field measurements by further develop and apply a Laser Induced Fluorescence Transient (LIFT) approach for remote measurement of chlorophyll fluorescence of selected leaves in a distance of up to 50m. The instrument makes use a low power laser to manipulate the light regime of the target and a telescope to collect the re-emitted fluorescence from target leaves. Constraints on the power of the laser for use in open environments make it impossible to use the same protocols that have been used with PAM flourometers. New approaches take advantage of a laser to make much small but highly replicated modification of the light regime on a selected leaf. The LIFT instrument is required to make measurements that are at the noise limit and computer assisted fitting of the data to a theoretical model are substituted for brute force and simple analysis used in PAM fluorometery. The LIFT was extensively tested under laboratory conditions with gas exchange measurements as the gold standard. We developed protocols which allowed measurements of chlorophyll fluorescence transients under high and variable background illumination which enabled us to use the system in the field. The LIFT has proved successful for mapping of photosynthetic efficiency in trees, it has the potential for monitoring the productivity in agricultural fields, it was used to quantify cold and light stress in a variety of plants and, currently the LIFT has been monitoring the seasonal dynamics in photosynthetic efficiency in deciduous and evergreen trees. The ability to make continuous, automatic and remote measurements of photosynthetic efficiency of leaves with the LIFT provides a new approach for studying and monitoring of the effects of the variable environment on plant performance on the canopy scale.

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