Sun-induced fluorescence - a new probe of photosynthesis: First maps from the imaging spectrometer HyPlant

Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO2 uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun-induced fluorescence signal on the ground and on a coarse spatial scale using space-borne imaging spectrometers. Intermediate-scale observations using airborne-based imaging spectroscopy, which are critical to bridge the existing gap between small-scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun-induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun-induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun-induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun-induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.

[Consideration on the King-Armstrong method and on the kinetic method for the measurement of the alkaline phosphatase activity in serum (author's transl)]

The comparative study of a determined time method, according to King-Armstrong, for the measurement of the alkaline phosphatase activity in serum and of a kinetic method consents us to make the following points: 1) the reagents used in the King-Armstrong method are easily prepared and are stable for months, with the sole addition of cloroform to the substrate and to the buffer to avoid the growth of moulds. 2) The substrate used for the kinetic method undergoes spontaneous Xydrolysis in acqueous solution, which makes it possible to keep it refrigerated for a limited number of days. Freezing at - 20 degrees C does not improve the situation. 3) The degree of precision within the series and between the series is the same for the two methods, and very good. 4) From the working point of view the method of "determined time" is advantageous for few samples, while the kinetic method becomes preferable when the number of samples goes over 20 and 30 a day, provided that it is linked with the suitable automatic apparatus. 5) The results of the measurement of the enzyme activity found with the two methods on 120 sera of normal and pathological subjects have shown good correlation, confirming the clinical diagnostic value of the results obtained by the kinetic method, which uses a transphosphorilant buffer and their congruency with those obtained by the classical King-Armstrong method.