Using a Full Spectral Raytracer for Calculating Light Microclimate in Functional-Structural Plant Modelling

Raytracers that allow the spatially explicit calculation of the fate of light beams in a 3D scene allow the consideration of shading, reflected and transmitted light in functional-structural plant models (FSPM). However, the spectrum of visible light also has an effect on cellular and growth processes. This recently created the interest to extend this modelling paradigm allowing the representation of detailed spectra instead of monochromatic or white light and to extend existing FSPM platforms accordingly. In this study a raytracer is presented which supports the full spectrum of light and which can be used to compute spectra from arbitrary light sources and their transformation at the organ level by absorption, reflection and transmission in a virtual canopy. The raytracer was implemented as an extension of the FSPM platform GroIMP

Fruit and Leaf Response to Different Source–Sink Ratios in Apple, at the Scale of the Fruit-Bearing Branch

International audienceApple fruit growth is the result of several factors: inherent demand (relative sink strength) of the fruit (defined by the demands for cell division and expansion growth, etc.), carbon assimilation by the source leaves (source strength), and the resulting allocation to the organ in question. It is thus a complex process involving source-sink interactions. In the present study, we designed an experimental system in which parts of fruit-bearing branches of two apple cultivars ("Fuji" and "Ariane") were isolated from the rest of the tree by girdling and then subjected to specific pruning and fruit removal treatments to create a wide range of global (branch-level) source-sink ratios. We monitored not only fruit kinetics but also photosynthesis as a response to light in leaves of the three different shoot types (i.e., the rosette, the bourse, and the vegetative shoots) to 1) study the impact of source-sink distance on carbon partitioning between fruits within the same branch and 2) to investigate the impact of source/sink ratio on fruit growth and leaf photosynthetic activity. Our results indicate 1) no significant differences among lateral fruits belonging to different ranks, and this independent of source availability; 2) that a modification of the source/sink ratio seems to be compensated by an alteration of the photosynthetic rate of leaves, with stronger and weaker values obtained for lower and higher ratios, respectively. Moreover, our results seem to suggest that two growing sinks together will upregulate photosynthesis rate more strongly than one growing sink does on its own, and this with the same leaf area per fruit. These results are discussed, and some hypotheses are put forward to explain them

Interspecific variation in leaf traits, photosynthetic light response, and whole-plant productivity in amaranths (Amaranthus spp. L.)

Photosynthetic light response curve parameters help us understand the interspecific variation in photosynthetic traits, leaf acclimation status, carbon uptake, and plant productivity in specific environments. These parameters are also influenced by leaf traits which rely on species and growth environment. In accessions of four amaranth species (Amaranthus. hybridus, A. dubius, A. hypochondriacus, and A. cruentus), we determined variations in the net photosynthetic light response curves and leaf traits, and analysed the relationships between maximum gross photosynthetic rate, leaf traits, and whole-plant productivity. Non-rectangular hyperbolae were used for the net photosynthesis light response curves. Maximum gross photosynthetic rate (Pgmax) was the only variant parameter among the species, ranging from 22.29 to 34.21 μmol m–2 s–1. Interspecific variation existed for all the leaf traits except leaf mass per area and leaf inclination angle. Stomatal conductance, nitrogen, chlorophyll, and carotenoid contents, as well as leaf area correlated with Pgmax. Stomatal conductance and leaf nitrogen explained much of the variation in Pgmax at the leaf level. At the plant level, the slope between absolute growth rate and leaf area showed a strong linear relationship with Pgmax. Overall, A. hybridus and A. cruentus exhibited higher Pgmax at the leaf level and light use efficiency at the whole-plant level than A. dubius, and A. hypochondriacus. Thus, A. hybridus and A. cruentus tended to be more efficient with respect to carbon assimilation. These findings highlight the correlation between leaf photosynthetic characteristics, other leaf traits, and whole plant productivity in amaranths. Future studies may explore more species and accessions of Amaranthus at different locations or light environments

Ausbreitung und Rückgang der Englischen Kratzdistel - Cirsium dissectum (L.) Hill - in Nordwestdeutschland

Es werden die Ausbreitung und der Rückgang der Englischen Kratzdistel, Cirsium dissectum, in Nordwestdeutschland dokumentiert. Hierzu dient eine Verbreitungskarte mit allen rezenten und erloschenen Fundorten. Die Verbreitung der Art wird in Nordwestdeutschland offenbar durch drei klimatische Faktoren festgelegt: Januarmittel > 0°C; Jahresschwankung der Temperatur 0°C; annual fluctuation of mean temperature < 16°C; annual precipitation 600 to 800mm. The Meadow Thistle benefited from the cultivation of peat bogs and fens in the last century, which allowed it to spread strongly. After the intensification of drainage but also manuring in this century, the species declined greatly, especially after 1950. It is nowadays a strongly endangered species in Germany

Meeting present and future challenges in sustainable horticulture using virtual plants.

Article de revue (Article scientifique dans une revue à comité de lecture)International audiencele résumé</p

Simulating the morphology of barley spike phenotypes using genotype information

A computer graphic L-system-model simulating the final morphology of the barley (Hordeum vulgare L.) spike is presented. By applying different parameter sets to growth and branching rules, natural variation in spike morphology can be modelled visually. The biological relevance of the simulated phenotypes is enhanced in various ways: (1) constraints arising from parameter correlations are considered in the growth rules; (2) parameters are chosen to mimic the plant's morphology; (3) their ranges are based on those of real plants. The model is designed to predict and visualize phenotypes corresponding to diploid multigenic genotypes. Those are assembled from lists of alleles belonging to specified genes (or QTLs). Interactions of alleles (dominance, additivity) and of genes (epistasis) are computed from measurements to predict values of morphological variables. Two examples illustrate the principles of the model: spikelet rows and awn length. The use of quantitative data supplied by analysis of QTLs is considered.Simulation de la morphologie des phénotypes de l'épi d'orge à partir de l'information génotypique. Un modèle basé sur des L-systèmes simulant la morphologie finale de l'épi d'orge (Hordeum vulgare L.), est présenté. Les variations naturelles de morphologie de l'épi sont modélisées et reproduites visuellement grâce à l'utilisation de différents jeux de paramètres modifiant les règles de croissance et de ramification. La pertinence biologique des phénotypes simulés est accrue de diverses façons : (1) les contraintes relatives aux corrélations entre paramètres sont prises en considération dans les règles de croissance, (2) les paramètres sont choisis en vue d'imiter la morphologie de la plante, (3) l'étendue de la variation des paramètres repose sur des observations faites sur les plantes réelles. Le modèle vise à prédire et visualiser des phénotypes correspondant à des génotypes diploides multigéniques. Ceux-ci sont créés à partir des listes d'allèles appartenant à des locus spécifiques (ou QTLs). Les interactions entre allèles (dominance/additivité) ou entre gènes (effets epistatiques) sont calculées en utilisant les connaissances fournies par les études génétiques expérimentales et permettent la prédiction des valeurs de variables morphologiques. Deux exemples illustrent les principes du modèle : le nombre de rangs d'épillets et la longueur des barbes. L'intégration dans le modèle des données quantitatives sur les effets des QTLs est envisagée

Modelling temporal variation of parameters used in two photosynthesis models: influence of fruit load and girdling in fruit bearing branches of apple trees

A large number of studies have found seasonal and temporal variability in leaf photosynthesis parameters in different crops. This variability depends upon the environment, the developmental stage of the plant and the presence or absence of sinks. Girdling removes the bark and phloem down to the youngest xylem all around the stem and prevents export of photoassimilates out of the stem. This technique is used to manipulate tree development and growth, as well as fruit growth, in a variety of fruit species. It has been shown to decrease net photosynthesis rate (Pn) in several tree species. Developing fruits and crop load have often been reported to influence individual leaf photosynthesis rate in tree crops. In the literature, numerous studies propose models to simulate photosynthesis. In this "preliminary" study, we have chosen to compare three models: The rectangular and non-rectangular hyperbola model by Thornley, as well as the model by Marshall and Biscoe. Ten-year old apple trees (Malus domestica L. (Borkh.), cv. 'Elstar') were used to study and model the seasonal variation of photosynthetic parameters in leaves of long shoots and rosettes, as a function of global fruit load (at the branch level), with or without girdling, during the growing season of 2015. Three 6-years-old fruit bearing branches were selected in each tree and treated independently. Gas exchange measurements were carried out using a LI-6400XT portable photosynthesis system. For each fruit bearing branch, light response curves of Pn for 2 leaves of a rosette were measured at two different positions, proximal and distal. Our comparison of models indicates that the model of Marshall and Biscoe is the most accurate model for the simulation of photosynthesis rate in bearing branches of apple tree with time (season) and the three treatments applied

Modelling temporal variation of parameters used in two photosynthesis models: influence of fruit load and girdling in fruit bearing branches of apple trees

A large number of studies have found seasonal and temporal variability in leaf photosynthesis parameters in different crops. This variability depends upon the environment, the developmental stage of the plant and the presence or absence of sinks. Girdling removes the bark and phloem down to the youngest xylem all around the stem and prevents export of photoassimilates out of the stem. This technique is used to manipulate tree development and growth, as well as fruit growth, in a variety of fruit species. It has been shown to decrease net photosynthesis rate (Pn) in several tree species. Developing fruits and crop load have often been reported to influence individual leaf photosynthesis rate in tree crops. In the literature, numerous studies propose models to simulate photosynthesis. In this "preliminary" study, we have chosen to compare three models: The rectangular and non-rectangular hyperbola model by Thornley, as well as the model by Marshall and Biscoe. Ten-year old apple trees (Malus domestica L. (Borkh.), cv. 'Elstar') were used to study and model the seasonal variation of photosynthetic parameters in leaves of long shoots and rosettes, as a function of global fruit load (at the branch level), with or without girdling, during the growing season of 2015. Three 6-years-old fruit bearing branches were selected in each tree and treated independently. Gas exchange measurements were carried out using a LI-6400XT portable photosynthesis system. For each fruit bearing branch, light response curves of Pn for 2 leaves of a rosette were measured at two different positions, proximal and distal. Our comparison of models indicates that the model of Marshall and Biscoe is the most accurate model for the simulation of photosynthesis rate in bearing branches of apple tree with time (season) and the three treatments applied