Uwe Rascher

Measuring photosynthetic parameters at a distance: laser induced fluorescence transient (LIFT) method for remote measurements of photosynthesis in terrestrial vegetation

We have developed a laser induced fluorescence transient (LIFT) technique and instrumentation to remotely measure photosynthetic properties in terrestrial vegetation at a distance of up to 50xa0m. The LIFT method uses a 665xa0nm laser to project a collimated, 100xa0mm diameter excitation beam onto leaves of the targeted plant. Fluorescence emission at 690xa0nm is collected by a 250xa0mm reflective telescope and processed in real time to calculate the efficiency of photosynthetic light utilization, quantum efficiency of PS II, and the kinetics of photosynthetic electron transport. Operating with peak excitation power of 125xa0Wxa0m−2, and duty cycle of 10–50%, the instrument conforms to laser safety regulations. The LIFT instrument is controlled via an Internet connection, allowing it to operate from remote locations or platforms. Here we describe the theoretical basis of the LIFT methodology, and demonstrate its applications in remote measurements of photosynthetic properties in the canopy of cottonwood and oak trees, and in the rosette of Arabidopsis mutants.

Assessing photosynthetic efficiency in an experimental mangrove canopy using remote sensing and chlorophyll fluorescence

This study examined the ability of the photochemical reflectance index (PRI) to track changes in effective quantum yield (Δ F/Fm′), non-photochemical quenching (NPQ), and the xanthophyll cycle de-epoxidation (DPS) in an experimental mangrove canopy. PRI was correlated with (Δ F/Fm′) and NPQ over the 4-week measurement period and over the diurnal cycle. The normalised difference vegetation index (NDVI) was not correlated with any aspect of photochemical efficiency measured using chlorophyll fluorescence or xanthophyll pigments. This study demonstrated that photochemical adjustments were responsible for controlling the flow of energy through the photosynthetic apparatus in this mangrove forest canopy rather than canopy structural or chlorophyll adjustments.

Photosynthetic field capacity of cyanobacteria of a tropical inselberg of the Guiana Highlands

Photosynthesis of cyanobacteria is well characterized under laboratory conditions. We present a detailed study of photosynthetic capacity of cyanobacterial communities measured under natural conditions using chlorophyll fluorescence techniques. Cyanobacteria of extensive and diverse communities grow epi- and endolithically on the bare rock of inselbergs in the tropics where they are exposed to extreme and rapid fluctuations in irradiance, temperature and water availability. Extreme and rapidly changing environmental conditions impose various stresses on cyanobacteria and lead to small-scale niches of different communities along the furrows of an inselberg in French Guiana. These different cyanobacterial communities can easily be separated from each other by their species composition. Moreover, cyanobacteria of these zonal areas show significantly different rates of apparent quantum yield of photosystem II (PSII), are differently adapted to utilize early morning light energy and have different strategies to face rapid cycles of desiccation. These different physiological strategies have led to the development of different cyanobacterial communities in distinct zones which are determined by different resistance to dehydration, water transport and storage capacity. In spite of the extreme environmental conditions with very high solar radiation, predawn measurements of potential quantum yield of PS II showed that they are not photoinhibited. We describe the manifold photosynthetic strategies that have developed in cyanobacteria under these extreme and highly fluctuating natural conditions.

Temperature profiles for the expression of endogenous rhythmicity and arrhythmicity of CO2 exchange in the CAM plant Kalanchoë daigremontiana can be shifted by slow temperature changes

Abstract. The crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie shows an endogenous circadian rhythm of net CO2 exchange (JCO2) under constant conditions in continuous light. Previous studies have shown, however, that above a certain threshold temperature JCO2 changes from rhythmic to arrhythmic behaviour and that this is reversible when the temperature is lowered again. It is now demonstrated here, that this re-initiation of rhythmic JCO2 from arrhythmicity needs a sufficiently strong temperature signal as defined by its abruptness. Rhythmicity reappears only if the temperature is reduced rather rapidly. If the temperature is reduced slowly then arrhythmicity is retained even at a low temperature level which normally would allow rhythmicity. Under these circumstances, however, a distinct temperature increase followed by an abrupt temperature decrease immediately elicits regular oscillations of JCO2 at this lower temperature. We suggest that the strong temperature signals function as a definite synchronizer (“zeitgeber”) which synchronizes different cells and/or different leaf areas which remain desynchronized after application of only slow temperature changes. This is further supported by Fourier transform analyses, revealing a harmonic structure of the superficially arrhythmic time series of JCO2 after application of slow temperature reductions. This conclusion adds a spatial dimension to the otherwise purely time-dependent rhythmicity and arrhythmicity of JCO2 in CAM.

Remote Monitoring of Photosynthetic Efficiency Using Laser Induced Fluorescence Transient (LIFT) Technique

The Interaction Of Phototrophic Organisms With Their Environment Is A Dynamic And Variable System. Studying The Underlying Processes Is Important For Understanding And Modeling The Response To Changing Environmental Conditions And Requires Continuous And Spatially Distributed Monitoring. Limited Access To Many Canopies And Scale Of Observation With Portable Instrumentation Make It Difficult To Examine Dynamics Of Canopy Photosynthesis. We Report Here On The Application Of A Recently Developed Technique, Laser Induced Fluorescence Transient (Lift), For Continuous Remote Measurement Of Photosynthetic Efficiency Of Selected Leaves Within An Oak Tree Canopy, Grass Community Below This Tree And, Thalli Of Lichen On Branches Of The Tree Over 50 Days In Spring. While The Oak Tree Showed Very Little Variation Of Quantum Yield Throughout The Measuring Period, A Reduction Of Photosynthetic Efficiency Of The Grass Community Was Observed And, The Photosynthetic Efficiency Of Lichens Was Strongly Correlated With Relative Humidity.