Shade Avoidance and Light Foraging of a Clonal Woody Species, Pachysandra terminalis

(1) Background: A central subject in clonal plant ecology is to elucidate the mechanism by which clones forage resources in heterogeneous environments. Compared with studies conducted in laboratories or experimental gardens, studies on light foraging of forest woody clonal plants in their natural habitats are limited. (2) Methods: We investigated wild populations of an evergreen clonal understory shrub, Japanese pachysandra (Pachysandra terminalis Siebold & Zucc.), in two cool-temperate forests in Japan. (3) Results: Similar to the results of herbaceous clonal species, this species formed a dense stand in a relatively well-lit place, and a sparse stand in a shaded place. Higher specific rhizome length (i.e., length per unit mass) in shade resulted in lower ramet population density in shade. The individual leaf area, whole-ramet leaf area, or ramet height did not increase with increased light availability. The number of flower buds per flowering ramet increased as the canopy openness or population density increased. (4) Conclusions: Our results provide the first empirical evidence of shade avoidance and light foraging with morphological plasticity for a clonal woody species.

The properties of terrestrial laser system intensity for measuring leaf geometries: a case study with Conference Pear trees (Pyrus communis)

Light Detection and Ranging (LiDAR) technology can be a valuable tool for describing and quantifying vegetation structure. However, because of their size, extraction of leaf geometries remains complicated. In this study, the intensity data produced by the Terrestrial Laser System (TLS) FARO LS880 is corrected for the distance effect and its relationship with the angle of incidence between the laser beam and the surface of the leaf of a Conference Pear tree (Pyrus commmunis) is established. The results demonstrate that with only intensity, this relationship has a potential for determining the angle of incidence with the leaves surface with a precision of ±5° for an angle of incidence smaller than 60°, whereas it is more variable for an angle of incidence larger than 60°. It appears that TLS beam footprint, leaf curvatures and leaf wrinkles have an impact on the relationship between intensity and angle of incidence, though, this analysis shows that the intensity of scanned leaves has a potential to eliminate ghost points and to improve their meshing.

Shoot morphology of Aucuba japonica incurred by anisophylly: ecological implications

Anisophylly, having leaves different in size and/or shape, was quantified in adult Aucuba japonica and simulations were carried out to evaluate the effects of anisophylly on the extent of self-shading at the single-shoot level as well as at the whole-canopy level. Clear anisophylly was observed in the individual after switching from the single-stemmed juvenile stage to the multi-stemmed adult stage. In such plants, leaf area in the canopy abruptly increased. The effective display of adult foliage involved a variety of morphological changes in addition to anisophylly, most prominently reduction in leaf size compared to juveniles. The simulation results indicate that diversity of leaf size and shape is an effective means of minimizing self-shading as well as allowing the efficient exploitation of a larger canopy volume in adult plants. Anisophylly also increased the biomass use efficiency of individual plants at maturity. Taken together, having diverse leaf forms is superior to having a single leaf form for maximizing area acquisition and for efficiently filling the acquired area. We therefore conclude that the anisophylly expressed in A. japonica is adaptive.

Plasticity in leaf-area density within the crown of Aucuba japonica growing under different light levels

We assessed leaf-area density (LAD; m(2) m(-3)) within the crown of Aucuba japonica (Cornaceae) growing under different light regimes and analyzed the components of crown architecture that most influenced variation in LAD. At a whole-crown level, extension-unit (EU) density (EUs/m(3)) had the greatest impact on LAD. The number of leaves per unit EU length and EU length had a wide range of impacts depending on the degree of crowding of foliage on the EU. Leaf size had a lesser impact on LAD. LAD was higher in the uppermost crown and declined towards the base. The non-uniformity of LAD among crown layers was much greater under high irradiance. Individuals under high irradiance achieved greater LAD by increased branching, well-marked EU dimorphism and a larger number of leaves per unit EU length; the reverse was true for the individuals under low irradiance. We identified two distinct modes of growth response to light regime. Under high irradiance, individuals responded by differential growth between the layers of crowns with the lower crown suppressed and growth in the upper crown increased. Conversely, shaded individuals did not respond by differential growth between crown layers.

Crown architecture in sun and shade environments: assessing function and trade-offs with a three-dimensional simulation model

Sun and shade environments place markedly different constraints on the photosynthetic performance of plants. Leaf-level photosynthetic responses to sun and shade have been extensively investigated, whereas there has been much less research on the functional role of crown architecture in these environments. This paper focuses on the role of architecture in maximizing light capture and photosynthesis in shaded understories and in minimizing exposure to excess radiation in open high light environments. Understanding these contrasting roles of architecture is facilitated by application of a three-dimensional structural-functional model, Y-plant. Surveys of understory plants reveal a diversity of architectures but a strong convergence at only modest light-capture efficiencies because of significant self-shading. Simulations with Psychotria species revealed that increasing internode lengths would increase light-capture efficiencies and whole plant carbon gain. However, the costs of the additional required biomechanical support was high, which, in terms of relative growth rates, would override the advantage provided by higher light-capture efficiencies. In high light environments, leaf angles and self-shading provide structural photoprotection, minimizing potential damage from photoinhbition. Simulations reveal that without these structural protections photoinhibition of photosynthesis is likely to be much greater with daily carbon gain significantly reduced.

Rice morphogenesis and plant architecture: measurement, specification and the reconstruction of structural development by 3D architectural modelling

BACKGROUND AND AIMS

The morphogenesis and architecture of a rice plant, Oryza sativa, are critical factors in the yield equation, but they are not well studied because of the lack of appropriate tools for 3D measurement. The architecture of rice plants is characterized by a large number of tillers and leaves. The aims of this study were to specify rice plant architecture and to find appropriate functions to represent the 3D growth across all growth stages.

METHODS

A japonica type rice, 'Namaga', was grown in pots under outdoor conditions. A 3D digitizer was used to measure the rice plant structure at intervals from the young seedling stage to maturity. The L-system formalism was applied to create '3D virtual rice' plants, incorporating models of phenological development and leaf emergence period as a function of temperature and photoperiod, which were used to determine the timing of tiller emergence.

KEY RESULTS

The relationships between the nodal positions and leaf lengths, leaf angles and tiller angles were analysed and used to determine growth functions for the models. The '3D virtual rice' reproduces the structural development of isolated plants and provides a good estimation of the tillering process, and of the accumulation of leaves.

CONCLUSIONS

The results indicated that the '3D virtual rice' has a possibility to demonstrate the differences in the structure and development between cultivars and under different environmental conditions. Future work, necessary to reflect both cultivar and environmental effects on the model performance, and to link with physiological models, is proposed in the discussion.