Abstract
Background and Aims
The dynamics of plant architecture is a central aspect of plant and crop models. Most models assume that whole shoot development is orchestrated by the leaf appearance ...rate, which follows a thermal time schedule. However, leaf appearance actually results from leaf extension and taking it as an input hampers our ability to understand shoot construction. The objective of the present study was to assess a modelling framework for grasses, in which the emergence of leaves and other organs is explicitly calculated as a result of their extension.
Methods
The approach builds on a previous model, which uses a set of rules co-ordinating the timing of development within and between phytomers. We first assessed rule validity for four experimental datasets, including different cultivars, planting densities and environments, and accordingly revised the equations driving the extension of the upper leaves and of internodes. We then fitted model parameters for each dataset and evaluated the ability to simulate the measured phenotypes across time. Finally, we carried out a sensitivity analysis to identify the parameters that had the greatest impact and to investigate model behaviour.
Key Results
The modified version of the model simulated correctly the contrasting maize phenotypes. Co-ordination rules accounted for the observations in all studied cultivars. Factors with major impact on model output included extension rates, the time of tassel initiation and initial conditions. A large diversity of phenotypes could be simulated.
Conclusions
This work provides direct experimental evidence for co-ordination rules and illustrates the capacity of the model to represent contrasting phenotypes. These rules play an important role in patterning shoot architecture and some of them need to be assessed further, considering contrasting growth conditions. To make the model more predictive, several parameters could be considered in the future as internal variables driven by plant status.
Plants react to their environment and to management interventions by adjusting physiological functions and structure. Functional–structural plant models (FSPM), combine the representation of ...three-dimensional (3D) plant structure with selected physiological functions. An FSPM consists of an architectural part (plant structure) and a process part (plant functioning). The first deals with (i) the types of organs that are initiated and the way these are connected (topology), (ii) co-ordination in organ expansion dynamics, and (iii) geometrical variables (e.g. leaf angles, leaf curvature). The process part may include any physiological or physical process that affects plant growth and development (e.g. photosynthesis, carbon allocation). This paper addresses the following questions: (i) how are FSPM constructed, and (ii) for what purposes are they useful? Static, architectural models are distinguished from dynamic models. Static models are useful in order to study the significance of plant structure, such as light distribution in the canopy, gas exchange, remote sensing, pesticide spraying studies, and interactions between plants and biotic agents. Dynamic models serve quantitatively to integrate knowledge on plant functions and morphology as modulated by environment. Applications are in the domain of plant sciences, for example the study of plant plasticity as related to changes in the red:far red ratio of light in the canopy. With increasing availability of genetic information, FSPM will play a role in the assessment of the significance towards plant performance of variation in genetic traits across environments. In many crops, growers actively manipulate plant structure. FSPM is a promising tool to explore divergent management strategies.
Time projection chambers for the T2K near detectors Abgrall, N.; Andrieu, B.; Baron, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2011, Letnik:
637, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector ...located 295
km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280
m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.
► First large scale time projection chambers with micropattern gas detectors. ► Incorporates new ASIC for electronic readout. ► Includes a pressure equalizing gas system and a photoelectron calibration system. ► Specifications achieved as deduced from neutrino, cosmic, and calibration tests. ► Will play an important role in T2K to measure neutrino oscillations.
Plant architectural traits have been reported to impact pest and disease, i.e., attackers, incidence on several crops and to potentially provide alternative, although partial, solutions to limit ...chemical applications. In this paper, we introduce the major concepts of plant architecture analysis that can be used for investigating plant interactions with attacker development. We briefly review how primary growth, branching and reiteration allow the plant to develop its 3D structure which properties may allow it (or not) to escape or survive to attacks. Different scales are considered: (i) the organs, in which nature, shape and position may influence pest and pathogen attack and development; (ii) the individual plant form, especially the spatial distribution of leaves in space which determines the within-plant micro-climate and the shoot distribution, topological connections which influence the within-plant propagation of attackers; and (iii) the plant population, in which density and spatial arrangement affect the micro-climate gradients within the canopy and may lead to different risks of propagation from plant to plant. At the individual scale, we show how growth, branching and flowering traits combine to confer to every plant species an intrinsic architectural model. However, these traits vary quantitatively between genotypes within the species. In addition, we analyze how they can be modulated throughout plant ontogeny and by environmental conditions, here considered
lato sensu
, i.e. including climatic conditions and manipulations by humans. Examples from different plant species with various architectural types, in particular for wheat and apple, are provided to draw a comprehensive view of possible plant protection strategies which could benefit from plant architectural traits, their genetic variability as well as their plasticity to environmental conditions and agronomic manipulations. Associations between species and/or genotypes having different susceptibility and form could also open new solutions to improve the tolerance to pest and disease at whole population scale.
Abstract
A low-energy electronic recoil calibration of XENON1T, a dual-phase xenon time projection chamber, with an internal
$^{37}$$
37
Ar source was performed. This calibration source features a ...35-day half-life and provides two mono-energetic lines at 2.82 keV and 0.27 keV. The photon yield and electron yield at 2.82 keV are measured to be (
$$32.3\,\pm \,0.3$$
32.3
±
0.3
) photons/keV and (
$$40.6\,\pm \,0.5$$
40.6
±
0.5
) electrons/keV, respectively, in agreement with other measurements and with NEST predictions. The electron yield at 0.27 keV is also measured and it is (
$$68.0^{+6.3}_{-3.7}$$
68
.
0
-
3.7
+
6.3
) electrons/keV. The
$^{37}$$
37
Ar calibration confirms that the detector is well-understood in the energy region close to the detection threshold, with the 2.82 keV line reconstructed at (
$$2.83\,\pm \,0.02$$
2.83
±
0.02
) keV, which further validates the model used to interpret the low-energy electronic recoil excess previously reported by XENON1T. The ability to efficiently remove argon with cryogenic distillation after the calibration proves that
$^{37}$$
37
Ar can be considered as a regular calibration source for multi-tonne xenon detectors.
Background and AimsExperimental evidence challenges the approximation, central in crop models, that developmental events follow a fixed thermal time schedule, and indicates that leaf emergence events ...play a role in the timing of development. The objective of this study was to build a structural development model of maize (Zea mays) based on a set of coordination rules at organ level that regulate duration of elongation, and to show how the distribution of leaf sizes emerges from this.MethodsA model of maize development was constructed based on three coordination rules between leaf emergence events and the dynamics of organ extension. The model was parameterized with data from maize grown at a low plant population density and tested using data from maize grown at high population density.Key ResultsThe model gave a good account of the timing and duration of organ extension. By using initial conditions associated with high population density, the model reproduced well the increase in blade elongation duration and the delay in sheath extension in high-density populations compared with low-density populations. Predictions of the sizes of sheaths at high density were accurate, whereas predictions of the dynamics of blade length were accurate up to rank 9; moderate overestimation of blade length occurred at higher ranks.ConclusionsA set of simple rules for coordinated growth of organs is sufficient to simulate the development of maize plant structure without taking into account any regulation by assimilates. In this model, whole-plant architecture is shaped through initial conditions that feed a cascade of coordination events.
Between flowering and maturity, leaf senescence reduces green leaf area while grains are filled from photosynthesis, nitrogen (N) uptake by roots and remobilisation from shoots. The question arises ...of possible effects of leaf senescence on photosynthesis, N uptake and remobilisation and their modification through genetic variations in senescence. To address this question, we compared three cultivars showing different behaviours. Tarro and Nicco are two modern hybrids presenting the same important grain sink but showing different time course of senescence, the former being normally senescent the latter “stay-green”. Déa hybrid, very well known by many previous experiments was the reference hybrid.
The purpose was to monitor precisely the carbon (C) and N repartition in the main organs of the plant in connection with the progress of leaf senescence (experiment 1) and to measure the changes created by variations of N supply and soil-climate conditions (experiment 2).
In experiment 1, time course of leaf senescence of the different leaf stages and weight of leaves, shoots and grains and N concentration of shoots and grain were measured weekly. In experiment 2, the same three cultivars were grown at limiting and non-limiting N supply in four locations in France during 2 years. At flowering, silage and harvest stage, dry matter and N concentration were measured in the main parts of the plant, and leaf senescence was evaluated at silage stage.
On soil well supplied with N, Tarro had an identical rate of leaf senescence than Nicco for leaves below the ear, but higher for leaves above the ear. After flowering, Nicco accumulated more biomass than Tarro, but kept a larger part of this total biomass in the stem. In contrast, Tarro accumulated a larger part of total biomass in the grain.
After flowering, N uptake was larger in Nicco than Tarro. Shoot N concentration decreased earlier and more completely in Tarro than Nicco, indicating a larger remobilisation to the grain. Though Tarro began and finished grain filling simultaneously with Nicco, it reached 70% of final grain weight 25
°C
d sooner than Nicco.
The senescence due to N stress differed from the physiological senescence of a senescent hybrid. The time course of the reproductive phase and the N repartition in the plant suggest that a threshold in grain filling or in shoot nitrogen decrease could be the internal signal triggering senescence of uppermost leaves.
A 3D architectural and process-based model of maize development was implemented on the basis of the L-system software Graphtal, interfaced with physical models computing microclimate distributed on ...the 3D canopy structure. In a first step, we incorporated in the software Graphtal additional functions that enable bi-directional communication with external modules. A simple model for distributed photosynthetically active radiation and the model for apex temperature by Cellieret al. (Agricultural and Forest Meteorology63: 35–54, 1993) were interfaced with Graphtal. In a second step we developed a L-system model for maize, where production rules for growth and development of organs are based on the current state of knowledge of maize development as a function of temperature. Visual representation of the plant is based on the geometrical model of leaf shape by Prévot, Aries and Monestiez (Agronomie11: 491–503, 1991). Finally, various data sets were used to evaluate the physiological aspects and the geometrical representation. It is concluded that environmental L-systems are a convenient tool to integrate biophysical processes from organ to canopy level, and provide a framework to model growth of individual plants in relation to local conditions and ability to forage for resources. However, progress is needed to improve both the knowledge of physiological processes at the organ level and the calculation of physical environmental parameters; some directions for future research are proposed.
• The emergence of a regular phyllochron from the dynamic processes of leaf initiation, leaf elongation and whorl construction suggests causal relationships between leaf elongation and leaf ...emergence. This paper presents a hypothesis as to how the ontogeny of the growth zone of leaves is triggered by emergence events, and implements it in a dynamic model of leaf elongation. • Two different experiments, presenting two contrasted cases of relationships between leaf emergence and kinetics of leaf elongation, were analysed and interpreted with the model in terms of the functioning of the growth zone. • Analysis of elongation kinetics revealed that the hypothesis allows for several contrasted elongation patterns that were observed, and for a regular phyllochron emerging from the variable dynamic of elongation. The model was able to simulate these patterns, and helped to identify the mechanisms underlying the key points of the analysis. • The hypothesis is not demonstrated, but its coherence and robustness are established, which should inform a renewal of the modelling of leaf elongation in architectural models.
The PROSPECT leaf optical properties and SAIL canopy reflectance models were coupled and inverted using a set of 96 AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) equivalent spectra gathered ...in afield experiment on sugar beet plots expressing a large range in leaf area index, chlorophyll concentration, and soil color. In a first attempt, the model accurately reproduced the spectral reflectance of vegetation, using six variables: chlorophyll a + b concentration (C
ab), water depth (C
w), leaf mesophyll structure parameter (N), leaf area index (LAI), mean leaf inclination angle (θ
l), and hot-spot size parameter (s). The four structural parameters (N, LAI, τ
l, and s) were poorly estimated, indicating instability in the inversion process; however, the two biochemical parameters (C
ab and C
w) were evaluated reasonably well, except over very bright soils. In a second attempt, three of the four structure variables were assigned a fixed value corresponding to the average observed in the experiment. Inversions performed to retrieve the remaining structure variable, leaf area index, and the two biochemical variables showed large improvements in the accuracy of LAI, but slightly poorer performance for C
ab and C
w. Here again, poor results were obtained with very bright soils. The compensations observed between the LAI and C
ab or C
w led us to evaluate the performance of two more-synthetic variables, canopy chlorophyll content or canopy water content, for these the inversions produced reasonable estimates. The application of this approach to Landsat TM (Thematic Mapper) data provided similar results, both for the spectrum reconstruction capability and for the retrieval of canopy biophysical characteristics.
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