The Potential Roles of Unique Leaf Structure for the Adaptation of Rheum tanguticum Maxim. ex Balf. in Qinghai-Tibetan Plateau.

Yanping Hu,Qian Qian,Gonghua Lin,Wenjing Li,Jyan-Chyun Jang,Yi Li,Jun Wang,Jing Sun,Huixuan Zhang

doi:10.3390/plants11040512

Abstract

Leaves are essential plant organs with numerous variations in shape and size. The leaf size is generally smaller in plants that thrive in areas of higher elevation and lower annual mean temperature. The Qinghai–Tibetan Plateau is situated at an altitude of >4000 m with relatively low annual average temperatures. Most plant species found on the Qinghai–Tibetan Plateau have small leaves, with Rheum tanguticum Maxim. ex Balf. being an exception. Here, we show that the large leaves of R. tanguticum with a unique three-dimensional (3D) shape are potentially an ideal solution for thermoregulation with little energy consumption. With the increase in age, the shape of R. tanguticum leaves changed from a small oval plane to a large palmatipartite 3D shape. Therefore, R. tanguticum is a highly heteroblastic species. The leaf shape change during the transition from the juvenile to the adult phase of the development in R. tanguticum is a striking example of the manifestation of plant phenotypic plasticity. The temperature variation in different parts of the leaf was a distinct character of leaves of over-5-year-old plants. The temperature of single-plane leaves under strong solar radiation could accumulate heat rapidly and resulted in temperatures much higher than the ambient temperature. However, leaves of over-5-year-old plants could lower leaf temperature by avoiding direct exposure to solar radiation and promoting local airflow to prevent serious tissue damage by sunburn. Furthermore, the net photosynthesis rate was correlated with the heterogeneity of the leaf surface temperature. Our results demonstrate that the robust 3D shape of the leaf is a strategy that R. tanguticum has developed evolutionarily to adapt to the strong solar radiation and low temperature on the Qinghai–Tibetan Plateau.

Highlights

Licensee MDPI, Basel, Switzerland.Leaves are essential organs for photosynthesis and transpiration of all higher plants.The size and shape of the leaf affect the growth, reproduction, survival and adaptive strategies of plants [1]
We investigated the structure of R. tanguticum leaves in younger versus older plants and determined how the surface temperatures of the leaves varied as the structure of the leaves changed in older plants
We propose that the 3D shape of leaves plays a key role in plant thermoregulation of R. tanguticum for the following reasons: (1) the temperature was highly heterogeneous in leaves of over-5-year-old plants of R. tanguticum under solar radiation; (2) the degree of temperature variation was dependent on leaf position; (3) the local leaf temperature change was rather fast upon the transition from sun exposure to shade and vice versa; (4) the rate of temperature change may be affected by leaf position; and

Summary

Introduction

Leaves are essential organs for photosynthesis and transpiration of all higher plants. The size and shape of the leaf affect the growth, reproduction, survival and adaptive strategies of plants [1]. In order to adapt to different environments, leaves have high plasticity. Both leaf shape and size show a great variation across biomes [2,3,4,5,6]. The leaves of cacti convert to spines for adaptation to the arid dessert [7]. The leaf area is the most common measure of leaf size [8,9,10]. Leaf sizes vary by over 100,000-fold among published maps and institutional affil-

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