Baoguo Li

Comparison of architecture among different cultivars of hybrid rice using a spatial light model based on 3-D digitising

Modification of plant types (i.e. plant architecture) is an important strategy to enhance the yield potential of crops. The aims of this study were to specify rice plant types using 3-D modelling methodology. The architecture of three typical hybrid rice cultivars were measured in situ in a paddy field using a 3-D digitiser at four development stages from the panicle initiation to the filling stage. The structural parameters of the rice canopies were calculated and their light capture and potential carbon gain were simulated based on a 3-D light model. The results confirmed that a plant type with steeper leaf angles let light penetrate more deeply with relatively uniform light distribution in the canopy at higher sun elevation angles, although this result was related to leaf area index. The variations of plant types, however, did not convert into differences of light distribution across rice varieties at lower sun elevation angles. Light use efficiency at the higher leaf area index could be enhanced by reducing mutual-shading. These results indicate that a promising approach to quantify the rice architecture in situ is to combine 3-D digitising and a 3-D light model to evaluate light interception and photosynthesis of rice plant types.

Three-dimensional distribution of vessels, passage cells and lateral roots along the root axis of winter wheat (Triticum aestivum)

BACKGROUND AND AIMS The capacity of a plant to absorb and transport water and nutrients depends on anatomical structures within the roots and their co-ordination. However, most descriptions of root anatomical structure are limited to 2-D cross-sections, providing little information on 3-D spatial relationships and hardly anything on their temporal evolution. Three-dimensional reconstruction and visualization of root anatomical structures can illustrate spatial co-ordination among cells and tissues and provide new insights and understanding of the interrelation between structure and function. METHODS Classical paraffin serial-section methods, image processing, computer-aided 3-D reconstruction and 3-D visualization techniques were combined to analyse spatial relationships among metaxylem vessels, passage cells and lateral roots in nodal roots of winter wheat (Triticum aestivum). KEY RESULTS 3-D reconstruction demonstrated that metaxylem vessels were neither parallel, nor did they run directly along the root axis from the root base to the root tip; rather they underwent substitution and transition. Most vessels were connected to pre-existent or newly formed vessels by pits on their lateral walls. The spatial distributions of both passage cells and lateral roots exhibited similar position-dependent patterns. In the transverse plane, the passage cells occurred opposite the poles of the protoxylem and the lateral roots opposite those of the protophloem. Along the axis of a young root segment, the passage cells were arranged in short and discontinuous longitudinal files, thus as the tissues mature, the sequence in which the passage cells lose their transport function is not basipetal. In older segments, passage cells decreased drastically in number and coexisted with lateral roots. The spatial distribution of lateral roots was similar to that of the passage cells, mirroring their similar functions as lateral pathways for water and nutrient transport to the stele. CONCLUSIONS With the 3-D reconstruction and visualization techniques developed here, the spatial relationships between vessels, passage cells and lateral roots and the temporal evolution of these relationships can be described. The technique helps to illustrate synchronization and spatial co-ordination among the roots radial and axial pathways for water and nutrient transport and the interdependence of structure and function in the root.

A stochastic model of tree architecture and biomass partitioning: application to Mongolian Scots pines

BACKGROUND AND AIMS Mongolian Scots pine (Pinus sylvestris var. mongolica) is one of the principal species used for windbreak and sand stabilization in arid and semi-arid areas in northern China. A model-assisted analysis of its canopy architectural development and functions is valuable for better understanding its behaviour and roles in fragile ecosystems. However, due to the intrinsic complexity and variability of trees, the parametric identification of such models is currently a major obstacle to their evaluation and their validation with respect to real data. The aim of this paper was to present the mathematical framework of a stochastic functional-structural model (GL2) and its parameterization for Mongolian Scots pines, taking into account inter-plant variability in terms of topological development and biomass partitioning. METHODS In GL2, plant organogenesis is determined by the realization of random variables representing the behaviour of axillary or apical buds. The associated probabilities are calibrated for Mongolian Scots pines using experimental data including means and variances of the numbers of organs per plant in each order-based class. The functional part of the model relies on the principles of source-sink regulation and is parameterized by direct observations of living trees and the inversion method using measured data for organ mass and dimensions. KEY RESULTS The final calibration accuracy satisfies both organogenetic and morphogenetic processes. Our hypothesis for the number of organs following a binomial distribution is found to be consistent with the real data. Based on the calibrated parameters, stochastic simulations of the growth of Mongolian Scots pines in plantations are generated by the Monte Carlo method, allowing analysis of the inter-individual variability of the number of organs and biomass partitioning. Three-dimensional (3D) architectures of young Mongolian Scots pines were simulated for 4-, 6- and 8-year-old trees. CONCLUSIONS This work provides a new method for characterizing tree structures and biomass allocation that can be used to build a 3D virtual Mongolian Scots pine forest. The work paves the way for bridging the gap between a single-plant model and a stand model.

A Functional and Structural Mongolian Scots Pine (Pinus sylvestris var. mongolica) Model Integrating Architecture, Biomass and Effects of Precipitation

Mongolian Scots pine (Pinus sylvestris var. mongolica) is one of the principal tree species in the network of Three-North Shelterbelt for windbreak and sand stabilisation in China. The functions of shelterbelts are highly correlated with the architecture and eco-physiological processes of individual tree. Thus, model-assisted analysis of canopy architecture and function dynamic in Mongolian Scots pine is of value for better understanding its role and behaviour within shelterbelt ecosystems in these arid and semiarid regions. We present here a single-tree functional and structural model, derived from the GreenLab model, which is adapted for young Mongolian Scots pines by incorporation of plant biomass production, allocation, allometric rules and soil water dynamics. The model is calibrated and validated based on experimental measurements taken on Mongolian Scots pines in 2007 and 2006 under local meteorological conditions. Measurements include plant biomass, topology and geometry, as well as soil attributes and standard meteorological data. After calibration, the model allows reconstruction of three-dimensional (3D) canopy architecture and biomass dynamics for trees from one- to six-year-old at the same site using meteorological data for the six years from 2001 to 2006. Sensitivity analysis indicates that rainfall variation has more influence on biomass increment than on architecture, and the internode and needle compartments and the aboveground biomass respond linearly to increases in precipitation. Sensitivity analysis also shows that the balance between internode and needle growth varies only slightly within the range of precipitations considered here. The model is expected to be used to investigate the growth of Mongolian Scots pines in other regions with different soils and climates.

Estimating photosynthetically active radiation distribution in maize canopies by a three-dimensional incident radiation model

The three-dimensional (3-D) radiation distribution model in plant canopy is pivotal for understanding and modelling plant eco-physiological processes. Diffuse and direct radiations penetrate into plant canopies in different ways and may present different intensity and wavelength composition. Sunfleck (the canopy surfaces where the direct radiation reaches) distribution in the plant canopy is usually regarded as an important index for crop development, especially under dense canopy conditions. Distributions of direct and diffuse components of photosynthetically active radiation (PAR) in maize (Zea mays L.) canopies were estimated respectively using a 3-D incident radiation model (3DIRM). The 3DIRM model was set up for computing incident radiation in crop canopies by applying a parallel-projection based submodel for direct solar radiation and a central-projection based submodel for incident diffuse radiation simulation in crop canopy. It was well assessed with a field experiment with multi-point PAR measurement in maize canopies with relative errors of 2.6, 4.5 and 2.6%, respectively, for sunfleck area ratio, diffuse PAR and total PAR. The results suggest that the 3DIRM model could be used to estimate the direct, diffuse and total PAR at any specific surface part in the 3-D canopy space. The exponential distinction model for direct, diffuse and total PAR along with leaf area index in different heights in maize canopies was also evaluated based on the 3DIRM simulation results.

Calibration of Topological Development in the Procedure of Parametric Identification: Application of the Stochastic GreenLab Model for Pinus sylvestris var. mongolica

Climate, biophysical conditions and human activities all contribute to the occurrences of ecosystem and environment problems, i.e. water scarcity, desertification, salinization, in arid and semiarid zone of North China. Mongolian Scots pine tree (Pinus sylvestris var. mongolica) is one of the principal species of the windbreak and sand-fixing forest in this area. In this paper, we presented the calibration process of stochastic GreenLab model based on experiment data. Specific plant topology and sink–source parameters were estimated for Mongolian Scots pine trees through optimizing procedure. The fitting results showed that the calibration process were reasonable and acceptable. The model produced a variety of three-dimensional visual representations of Mongolian Scots pine trees with different topological structures simulated by Monte Carlo methods. This model can be used to describe the plant development and growth in a stand level, taking into accounts the variations in plant topology and biomass.

Calibration of GREENLAB Model for Maize with Sparse Experimental Data

Simplification of field measurement to reduce the time-consuming data collection for calibration is important to facilitate the application of the GREENLAB model. The effect of such simplifications on the accuracy of parameter values should be quantified in order to define to what extent simplifications are valid. This study introduced a new method for model parameter optimization with sparse data of maize using a multi-fitting technique, evaluated the effect of such simplifications on the parameter values, and validated the calibrated model with four independent field data sets. The results showed that coefficients of variance (CV) among different simplifications were below 15% for most parameter values. The parameter values of the beta function varied more compared with those of relative sink strength for different simplifications. Organ biomass under four different climate regimes was simulated based on parameter values optimized with a sparse dataset. Significant (P<0.05) deviations of simulation vs. observation correlations from the 1:1 relationship were only observed for internodes of second experiment in 2003. Thus, multi-fitting with sparse data can provide reasonable accuracy of parameter values.

Three-Dimensional Reconstruction and Visualization of Xylem Vessels of Wheat Nodal Root

Descriptions of root internal structure are often limited to 2D cross-sections, with little information about three dimensions, and the evolution of xylem vessels along root axis has not been clearly presented. A computer-aided 3D-reconstrution method was developed based on paraffin serial slices techniques. The image processing protocol involved slice images alignment, registration, and 3D reconstruction. The stability of this approach was quantified and proven to be satisfactory. The 3D reconstruction conducted on wheat nodal roots illustrated that metaxylem vessel number decreased along root axis. Most vessels connected to the existent or new-formed vessels by lateral cell walls before disappearing. Thus metaxylem vessels in longitudinal profiles were not straightforward. The proposed imaging technique was low cost. It allowed various visualizations and quantitative comparisons of root structures. In the ongoing work, the technique is used to illustrate the spatial coordination of the radial pathway (passage cells, lateral roots), and longitudinal conduits (xylem vessels) of water and nutrient transport.

Towards Modeling and Analyzing Stem Lodging for Two Contrasting Rice Cultivars

Mechanical properties of two contrasting rice cultivars, P64S/E32 and SY63, were measured using 3-point bending tests performed on segments taken at the base and top of plant stems. The parameters of an elastic-plastic material constitutive law were fitted using a finite beam element model reproducing the 3-point bending tests. Both measured data and constitutive laws were compared between cultivars. The finite element model was used to perform numerical analyses of 3D virtual rice lodging. The results showed that there is a significant difference between the material properties of the two rice cultivars, P64S/E32 being more resistant than SY63 due to both material and structural characteristics.

Modelling three‐dimensional architecture of pine tree (Pinus sylvestris linn, van mongolica litv.) in a semiarid area

Abstract A dynamic model for three‐dimensional (3D) simulation of pine tree (Pinus sylvestris Linn, var. mongolica Litv) architecture based on dual‐scale automata is presented. The developmental sequence of pine trees was analysed qualitatively by identification of types of organs and elementary units. A dual‐scale automata model was used to describe the topological structure of the pine tree. The model is a collection of a large number of elementary units corresponding to the organs of the tree. The time step of simulation is set for 1 year. The model stochastically simulates the 3D architecture of a pine tree crown based on the Monte Carlo method and has been pa‐ram eterised for juvenile pine trees. Topological and geometrical parameters were calculated using a large amount of field data of branch number and internode lengths and diameters for 1‐ to 6‐year‐old pine trees. Visualisation of a 3D pine tree is presented. The model provides a good quantitative description of the 3D architecture of a single pine tree crown.