Near infrared microscopy (NIRM) has been developed as a rapid technique to predict the chemical composition of foods, reduce analytical costs and time and ease sample preparation. In this study, NIRM has been evaluated as an alternative to classical chemical analysis to determine the nitrogen and carbon content of small samples of tomato (Solanum lycopersicum L.) leaf powder. Near infrared spectra were obtained by NIRM for independent leaf samples collected on 216 plants grown under six different levels of nitrogen. From these, 30 calibration and 30 validation samples covering the spectral range of the whole set were selected and their nitrogen and carbon contents were determined by a reference method. The calibration model obtained for nitrogen content proved to be excellent, with a coefficient of determination in calibration (R2c) higher than 0.9 and a ratio of performance to deviation (RPDc) higher than 3. Statistical indicators of prediction using the validation set were also very high (R2p values > 0.90). However, the calibration model obtained for carbon content was much less satisfactory (R2c < 0.50). NIRM appears as a promising and suitable tool for a rapid, non-destructive and reliable determination of nitrogen content of tiny samples of tomato leaf powder.

Elongation rates of maize roots showed to be independant of the root type but dependant on the genotype and steady over time, with a high heritability.The variations in source-sink relationships during the devel-opment of the root system was found to be highly geno-type-dependant according to our indicators.With an increased reliability, better root support and higher image quality, our next aeroponic phenotyping platform will allow us to develop a fully automated, model-assisted analysis pipeline. Aeroponics has proven to be an efficient and cost-effective way to phenotype non-invasively dynamic root traits (e.g. elongation rates, emergence dynamics) in addition to static characteristics on a large number of plants with a high temporal resolution [De Dorlodot

The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens.Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cd- or Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability.Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLD but induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd.Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and species-specific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site.

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity.The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl).Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production.This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings' morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.

Micro-tidal wetlands are subjected to strong seasonal rainfall variations that induce fluctuations in groundwater salinity. In Caribbean mangroves and swamp forests, top-soil salinity may fluctuate by 20 ‰ between wet and dry season. Moreover, climate change is expected to increase seasonal variation by decreasing the amount of rainfall during the dry season. Whereas the effects of salinity levels on the physiology of mangrove seedlings have been widely tested, little is known about the effect of seasonal variations on growth performances of mangrove and swamp forest trees. In this study, we monitored tree physiology responses to climatic seasonal variations on the 4 main tree species of coastal forested wetlands in Guadeloupe. Physiological leaf traits and percent loss of hydraulic conductivity have been monitored on 50 trees during a wet and a dry season in 5 study sites. In addition, variation in trunk circumference of 90 trees, water-table level and groundwater salinity were monitored monthly during 20 months. Decrease of water table and increase of salinity during the dry season were associated to a strong decrease in diameter increment for all species. Leaf water potentials, stomatal conductance and carbon assimilation decreased for all species during the dry season, A. germinans being the most resistant species. At the end of the dry season, all mangrove species reached high embolism levels, L. racemosa and A. germinans being respectively the most and the less sensitive species. These results suggest that stronger dry periods due to climate change may impact mangrove structure and species-specific composition, leading to a possible decline of L. racemosa abundance in Caribbean mangroves.

Les Mangroves des Antilles sont soumises aux variations saisonnieres du climat. Les differences de precipitations entre la saison des pluies et la saison seche induisent de fortes variations edaphiques (inondation, salinite). Les projections du changement climatique prevoient une augmentation de la saisonnalite dans les Antilles. Les saisons seches deviendraient encore plus seches et les variations edaphiques plus importantes. Ces nouvelles conditions pourraient etre des contraintes physiologiques potentielles pour les paletuviers.

Urbanization, industrialization and agricultural practices have resulted in soil contamination with heavy metals in many world areas. Phytostabilisation is an emerging solution to limit pollutant dispersion out of the contaminated area without expensive costs. However, because of the heavy metal phytotoxicity, the implementation of a plant cover could be jeopardized. Therefore, we assessed the impact of Cd and Zn, 2 common metal pollutants, on the setting up of root system of 2 plant models, Lolium perenne and Trifolium repens. After 1 month of metal application, we measured the root mass, length and diameter according to the depth thanks to scanner and image analysis. These results were linked to root metal concentrations. We focused also on ultrastructural modifications by means of histochemical analyses and on quantification of structural polysaccharides and lignin through Van Soest global method and lignin staining. Drastic alterations of root system were highlighted, especially for Lolium perenne.