Multi-scale datasets for monitoring Mediterranean oak forests from optical remote sensing during the SENTHYMED/MEDOAK experiment in the north of Montpellier (France).

Mediterranean forests represent critical areas that are increasingly affected by the frequency of droughts and fires, anthropic activities and land use changes. Optical remote sensing data give access to several essential biodiversity variables, such as species traits (related to vegetation biophysical and biochemical composition), which can help to better understand the structure and functioning of these forests. However, their reliability highly depends on the scale of observation and the spectral configuration of the sensor. Thus, the objective of the SENTHYMED/MEDOAK experiment is to provide datasets from leaf to canopy scale in synchronization with remote sensing acquisitions obtained from multi-platform sensors having different spectral characteristics and spatial resolutions. Seven monthly data collections were performed between April and October 2021 (with a complementary one in June 2023) over two forests in the north of Montpellier, France, comprised of two oak endemic species with different phenological dynamics (evergreen: Quercus ilex and deciduous: Quercus pubescens) and a variability of canopy cover fractions (from dense to open canopy). These collections were coincident with satellite multispectral Sentinel-2 data and one with airborne hyperspectral AVIRIS-Next Generation data. In addition, satellite hyperspectral PRISMA and DESIS were also available for some dates. All these airborne and satellite data are provided from free online download websites. Eight datasets are presented in this paper from thirteen studied forest plots: (1) overstory and understory inventory, (2) 687 canopy plant area index from Li-COR plant canopy analyzers, (3) 1475 in situ spectral reflectances (oak canopy, trunk, grass, limestone, etc.) from ASD spectroradiometers, (4) 92 soil moistures and temperatures from IMKO and Campbell probes, (5) 747 leaf-clip optical data from SPAD and DUALEX sensors, (6) 2594 in-lab leaf directional-hemispherical reflectances and transmittances from ASD spectroradiometer coupled with an integrating sphere, (7) 747 in-lab measured leaf water and dry matter content, and additional leaf traits by inversion of the PROSPECT model and (8) UAV-borne LiDAR 3-D point clouds. These datasets can be useful for multi-scale and multi-temporal calibration/validation of high level satellite vegetation products such as species traits, for current and future imaging spectroscopic missions, and by fusing or comparing both multispectral and hyperspectral data. Other targeted applications can be forest 3-D modelling, biodiversity assessment, fire risk prevention and globally vegetation monitoring.

Carotenoid responses to environmental stimuli: integrating redox and carbon controls into a fruit model.

Carotenoids play an important role in plant adaptation to fluctuating environments as well as in the human diet by contributing to the prevention of chronic diseases. Insights have been gained recently into the way individual factors, genetic, environmental or developmental, control the carotenoid biosynthetic pathway at the molecular level. The identification of the rate-limiting steps of carotenogenesis has paved the way for programmes of breeding, and metabolic engineering, aimed at increasing the concentration of carotenoids in different crop species. However, the complexity that arises from the interactions between the different factors as well as from the coordination between organs remains poorly understood. This review focuses on recent advances in carotenoid responses to environmental stimuli and discusses how the interactions between the modulation factors and between organs affect carotenoid build-up. We develop the idea that reactive oxygen species/redox status and sugars/carbon status can be considered as integrated factors that account for most effects of the major environmental factors influencing carotenoid biosynthesis. The discussion highlights the concept of carotenoids or carotenoid-derivatives as stress signals that may be involved in feedback controls. We propose a conceptual model of the effects of environmental and developmental factors on carotenoid build-up in fruits.

Responses of epidermal phenolic compounds to light acclimation: in vivo qualitative and quantitative assessment using chlorophyll fluorescence excitation spectra in leaves of three woody species.

Chlorophyll fluorescence (ChlF) excitation spectra were measured to assess the UV-sunscreen compounds accumulated in fully expanded leaves of three woody species belonging to different chemotaxons, (i.e. Morus nigra L., Prunus mahaleb L. and Lagerstroemia indica L.), grown in different light microclimates. The logarithm of the ratio of ChlF excitation spectra (logFER) between two leaves acclimated to different light microclimates was used to assess the difference in epidermal absorbance (EAbs). EAbs increased with increasing solar irradiance intercepted for the three species. This epidermal localisation of UV-absorbers was confirmed by the removal of the epidermis. It was possible to simulate EAbs as a linear combination of major phenolic compounds (Phen) identified in leaf methanol extracts by HPLC-DAD. Under UV-free radiation conditions, shaded leaves of M. nigra accumulated chlorogenic acid. Hydroxybenzoic acid (HBA) derivatives and hydroxycinnamic acid (HCA) derivatives greatly increased with increasing PAR irradiance under the low UV-B conditions found in the greenhouse. These traits were also observed for the HCA of the two other species. Flavonoid (FLAV) accumulation started under low UV-A irradiance, and became maximal in the adaxial epidermis of sun-exposed leaves outdoors. A decrease in the amount of HCA was observed concomitantly to the intense accumulation of FLAV for both leaf sides of the three species. Judging from the logFER, under low UV-B conditions, larger amounts of HCA are present in the epidermis in comparison to FLAV for the three species. Upon transition from the greenhouse to full sunlight outdoors, there was a decrease in leaf-soluble HCA that paralleled FLAV accumulation in reaction to increasing solar UV-B radiation in the three species. In M. nigra, that contains large amounts of HCA, the logFER analysis showed that this decrease occurred in the adaxial epidermis, whereas the abaxial epidermis, which is protected from direct UV-B radiation, continued to accumulate large amounts of HCA.

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon-nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

Mapping meristem respiration of Prunus persica (L.) Batsch seedlings: potential respiration of the meristems, O2 diffusional constraints and combined effects on root growth.

Root system architecture partially results from meristem activities, which themselves depend on endogenous and environmental factors, such as O2 depletion. In this study, meristem respiration and growth was measured in the root systems of three Prunus persica (L.) Batsch seedlings. The spatial distribution of meristem respiration within the root system was described, and the relationship between the respiration rates and meristem radii was analysed, using a model of radial O2 diffusion and consumption within the root. Histological observations were also used to help interpret the results. Respiration rates were linearly correlated to the root growth rates (rho 2 = 0.9). Respiration reached values greater than 3.5 x 10(-13) mol O2 s-1 for active meristems. The taproot meristem consumed more O2 than the rest of the entire root system meristems. Similarly, the first order lateral meristems used more O2 than the second order ones. A near hyperbolic relationship between respiration rates and meristem radii was observed. This can be explained by a model of radial O2 diffusion and consumption within the root. Therefore, only one maximum potential respiration rate and one O2 diffusion coefficient was estimated for all the meristems.