Abstract
Leaf shape is an important leaf trait, with ovate leaves common in many floras. Recently, a new leaf shape model (referred to as the MLRF equation) derived from temperature-dependent bacterial growth was proposed and demonstrated to be valid in describing leaf boundaries of many species with ovate leaf shape. The MLRF model’s parameters can provide valuable information of leaf shape, including the ratio of lamina width to length and the lamina centroid location on the lamina length axis. However, the model wasn’t tested on a large sample of a single species, thereby limiting its overall evaluation for describing leaf boundaries, for evaluating lamina bilateral asymmetry and for calculating lamina centroid location. In this study, we further test the model using data from two Lauraceae species, Cinnamomum camphora and Machilus leptophylla, with >290 leaves for each species. The equation was found to be credible for describing those shapes, with all adjusted root-mean-square errors (RMSE) smaller than 0.05, indicating that the mean absolute deviation is smaller than 5% of the radius of an assumed circle whose area equals lamina area. It was also found that the larger the extent of lamina asymmetry, the larger the adjusted RMSE, with approximately 50% of unexplained variation by the model accounted for by the lamina asymmetry, implying that this model can help to quantify the leaf bilateral asymmetry in future studies. In addition, there was a significant difference between the two species in their centroid ratio, i.e., the distance from leaf petiole to the point on the lamina length axis associated with leaf maximum width to the leaf maximum length. It was found that a higher centroid ratio does not necessarily lead to a greater investment of mass to leaf petiole relative to lamina, which might depend on the petiole pattern.
Highlights
A leaf of a woody plant usually consists of a lamina, a petiole and a sheath
Whether it is necessary to introduce a parameter to control the curvature in the MLRF equation was answered here; Figure 5A showed that most estimates of δ for Cinnamomum camphora (CC) were larger than 1, and the mean estimated δ of CC was significantly larger that of Machilus leptophylla (ML)
There was no significant difference in the goodness of fit between the two species according to the calculated adjusted root-mean-square errors (RMSE) values (Figure 5B)
Summary
A leaf of a woody plant usually consists of a lamina, a petiole (or a pseudo-petiole) and a sheath. Ovate Leaves and Bilateral Symmetry thickness, leaf shape, and lamina vein patterns are widely studied because those measures are intimately associated with the responses of plants to climate and environmental stress (Wright et al, 2004, 2017; Chitwood and Sinha, 2016; Baird et al, 2021). Previous studies have shown that there is a tradeoff between the photosynthetic returns from increasing lamina area and the investment in leaf physical support and hydraulic systems from increasing lamina mass (Niklas et al, 2007; Huang et al, 2019a,b, 2020; Guo et al, 2021). Lamina thickness and leaf shape have been demonstrated to affect such a tradeoff (Niinemets et al, 2007; Lin et al, 2018, 2020). The centroids of ovate leaves are closer to the lamina base than those of elliptical and obovate leaves, and the support costs of petioles for ovate leaves tend to be lower (Niinemets et al, 2007)
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