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.
摘要：
叶子是重要的植物器官，形状和大小有许多变化。在海拔较高和年平均温度较低的地区茁壮成长的植物中，叶子的大小通常较小。青藏高原的海拔>4000m，年平均气温相对较低。在青藏高原发现的大多数植物物种都有小叶子，与大黄tangutumMaxim。前Balf.是一个例外。这里,我们表明，具有独特三维（3D）形状的唐古特R.的大叶子可能是温度调节的理想解决方案，能耗很小。随着年龄的增长,唐古汀叶片的形状从小椭圆形平面变为大掌部3D形状。因此,曲根草是一种高度异源性物种。在金根草从幼体到成体发育阶段的过渡过程中，叶片形状的变化是植物表型可塑性表现的一个突出例子。叶片不同部位的温度变化是5岁以上植物叶片的明显特征。在强烈的太阳辐射下，单平面叶片的温度会迅速积聚热量，并导致温度远高于环境温度。然而,超过5岁的植物的叶子可以通过避免直接暴露于太阳辐射和促进局部气流来降低叶片温度，以防止晒伤对组织的严重损害。此外，净光合速率与叶片表面温度的异质性相关。我们的结果表明，叶片的鲁棒3D形状是Tangutum进化发展的策略，以适应青藏高原强烈的太阳辐射和低温。
