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Abstract: Mathematical models to describe crop–environment interaction on organ scale need to take crop or plant architecture into account. Up to now, architectural plant models are largely descriptive and parameters need to be estimated for each species, cultivar and environment. Required measurements are extensive and time-consuming. Hence investigating morphological patterns and their modulation as a response to environmental conditions may help to reduce measurement efforts and to predict plant architecture in crop models. In this paper, we describe the plasticity of winter wheat – expressed as the dimensions and sizes of leaf blades, sheaths and internodes in relation to their position on a stem – under the climatic conditions of the Paris region. Results are discussed with respect to: (i) genotypic variability, (ii) inter-annual variability, (iii) sowing date and plant population density, (iv) Nitrogen fertilisation and (v) tiller rank. Eight wheat cultivars grown in the same season showed similar patterns of leaf and internodes dimensions in relation to their position on the stem. For the cultivar ‘Soissons’, main stem architecture at flowering was remarkably stable when similar growth conditions were reproduced in the different seasons. Increased plant population density yielded longer juvenile, but shorter adult leaf blades and sheaths. Earlier sowing led to an increase in the number of juvenile phytomers – growing before the onset of stem elongation – on the main stem, whereas the number of adult phytomers was almost identical. Further there were little differences in the size of leaf blades, sheaths and internodes between the main stem and axillary tillers. We found remarkable differences in the size of adult leaf blades and sheaths in different growing seasons, with different timing of nitrogen fertilisation and we discuss decreased availability of nitrogen in the soil in spring as a likely cause. Data presented here can be used to enlarge the understanding of wheat plasticity regarding the regulation of organ size by temperature, light, plant-available nitrogen and size-mediated effects towards a mechanistic modelling of these responses. [Copyright &y& Elsevier]

Abstract: Leaf mass per area (LMA) is a parameter the variability of which contributes to architectural plasticity. However its variations according to environment remain not completely understood. We hypothesise that LMA variations of winter oilseed rape (WOSR) follow an ontogenetic trajectory that can be modified by the environment. This was assessed at plant and leaf levels comparing four genotypes field-grown under different environmental conditions characterised by year and nitrogen nutrition. Leaves of the main stem of plants sampled between emergence and harvest were surfaced, oven-dried and weighed to calculate LMA of each individual leaf. At the plant level, LMA presented a common ontogenetic trajectory, which increases from seedling emergence to bolting and from then on decreases. Variations in LMA were related to the variations in plant demand, LMA decreased when demand increased. The trajectory was modified by low N nutrition that increased LMA but differently according to year and genotype, reflecting the plant plasticity. At the leaf level, variations for each individual leaf were related to the variations at the plant level. Plant plasticity and genotypic variability of the responses of LMA to N deficiency seemed to be related to differences in biomass allocation between leaves and stems. [Copyright &y& Elsevier]

Abstract: ADELwheat is an architectural model that describes development of wheat in 3D. This paper analyzes the robustness of the parameterization of ADELwheat for spring wheat cultivars in relation to plant population density and shading. The model was evaluated using data from two spring wheat experiments with three plant population densities and two light regimes. Model validation was done at two levels of aggregation: (a) by comparing parameterization functions used as well as parameter values to the data (leaf and tiller appearance, leaf number, blade dimensions, sheath length, internode length) and (b) by comparing ground cover (GC) and leaf area index (LAI) of simulated virtual wheat plots with GC and LAI calculated from data. A sensitivity analysis was performed by modulating parameters defining leaf blade dimensions and leaf or tiller appearance rate. In contrast to population density, shading generally increased phyllochron and delayed tiller appearance. Both at the level of the organ and at the level of the canopy the model performed satisfactorily. Parameterization functions in the model that had been established previously applied to independent data for different conditions; GC and LAI were simulated adequately at three population densities. Sensitivity analysis revealed that calibration of phyllochron and blade area needs to be accurate to prevent disproportional deviations in output. The robustness of the model parameterization and the simulation performance confirmed that the model is a complete architectural model for aboveground development of spring wheat. It can be used in studies that require simulation of spring wheat structure, such as studies on plant–insect interaction, remote sensing, and light interception. [Copyright &y& Elsevier]