Canopy chlorophyll fluorescence applied to stress detection using an easy-to-build micro-lidar

Abstract

LEDFLEX is a micro-lidar dedicated to the measurement of vegetation fluorescence. The light source consists of 4 blue Light-Emitting Diodes (LED) to illuminate part of the canopy in order to average the spatial variability of small crops. The fluorescence emitted in response to a 5-μs width pulse is separated from the ambient light through a synchronized detection. Both the reflectance and the fluorescence of the target are acquired simultaneously in exactly the same field of view, as well as the photosynthetic active radiation and air temperature. The footprint is about 1 m2 at a distance of 8 m. By increasing the number of LEDs longer ranges can be reached. The micro-lidar has been successfully applied under full sunlight conditions to establish the signature of water stress on pea (Pisum Sativum) canopy. Under well-watered conditions the diurnal cycle presents an M shape with a minimum (Fmin) at noon which is Fmin > Fo. After several days withholding watering, Fs decreases and Fmin < Fo. The same patterns were observed on mint (Menta Spicata) and sweet potatoes (Ipomoea batatas) canopies. Active fluorescence measurements with LEDFLEX produced robust fluorescence yield data as a result of the constancy of the excitation intensity and its geometry fixity. Passive methods based on Sun-Induced chlorophyll Fluorescence (SIF) that uses high-resolution spectrometers generate only flux data and are dependent on both the 3D structure of vegetation and variable irradiance conditions along the day. Parallel measurements with LEDFLEX should greatly improve the interpretation of SIF changes.

Active in situ and passive airborne fluorescence measurements for water stress detection on a fescue field

“…This instrument has already been described by Moya et al (2019). Briefly, Ledflex is a hardened fluorometer for continuous chlorophyll fluorescence measurements under natural illumination at distances up to 8 m. It has been designed to integrate the fluorescence emission of a target diameter of about 1 m. The light source consists of a group of pulsed blue Light Emitting Diodes (LEDs) (Thorlabs, Maisons-Laffitte, France) with peak emission at 470 nm and a full width at half maximum (FWHM) of 22 nm.…”

“…Fs variations are much smaller in amplitude than the maximum fluorescence (Fm); however, obtaining qualitative but valuable information on the vegetation's physiological state by measuring Fs continuously from a fixed and constant position is possible. For example, one can consider the Fs/Fo ratio (Fo is the Fs signal measured during the night) to characterize water stress, as shown by Moya et al (2019). In the present work, the authors used the same "Ledflex," a LED-based micro-LIDAR able to measure Fs continuously at several meters, in full sunlight, and over a target size of up to 1m 2 .…”

Responses of photosynthesis and chlorophyll fluorescence during light induction in different seedling ages of Mahonia oiwakensis

“…Chlorophyll uorescence (ChlF) is a noninvasive technique offering highly accurate measurements that illustrate the function of the photosynthetic apparatus in plants, and uorescence is often used in physiological studies to investigate a plant's response to various environmental stresses in controlled environments and in the eld (Kałuzewicz et al 2018). ChlF values re ect photosynthetic potential and the potential for photochemical dissipation, and they demonstrate the percentage of PSII that is open and its effectiveness in capturing photo energy from light-harvesting complexes (LHC)II, and the subsequent transfer of quanta (Moya et al 2019). However, few studies have described their eco-physiological responses under controlled light conditions, and the function of the photosynthetic apparatus has not yet been examined with respect to the occurrence of ChlF indicators in Mahonia leaves under eld conditions to explain the development and distribution of Mahonia species.…”

Site Characteristics Mediate the Relationship Between Forest Productivity and Satellite Measured Solar Induced Fluorescence

“…Differences in SIF responses can also stem from SIF measurement methods, which can be either active, i.e., groundbased through pulse amplitude-modulated measurements (Goulas et al, 2017), or passive (remote sensing) methods. Active measurements can directly estimate the yield as they emit an active signal, but this can only be done at a local level (Moya et al, 2019). Passive measurements, such as from satellites, have a wider spatial coverage but they are available at a much lower temporal frequency (depending on satellite pass time) and cannot directly control the incoming PAR.…”