Abstract

The absence of pines from tropical forests is a puzzling biogeographical oddity potentially explained by traits of shade intolerance. Pinus krempfii (Lecomte), a flat-leaved pine endemic to the Central Highlands of Vietnam, provides a notable exception as it seems to compete successfully with shade-tolerant tropical species. Here, we test the hypothesis that successful conifer performance at the juvenile stage depends on physiological traits of shade tolerance by comparing the physiological characteristics of P. krempfii to coexisting species from two taxa: the genus Pinus, and a relatively abundant and shade-tolerant conifer family found in pantropical forests, the Podocarpaceae. We examined leaf photosynthetic, respiratory and biochemical traits. Additionally, we compiled attainable maximum photosynthesis, maximum RuBP carboxylation (V_cmax) and maximum electron transport (J_max) values for Pinus and Podocarpaceae species from the literature. In our literature compilation, P. krempfii was intermediate between Pinus and Podocarpaceae in its maximum photosynthesis and its V_cmax. Pinus exhibited a higher V_cmax than Podocarpaceae, resulting in a less steep slope in the linear relationship between J_max and V_cmax. These results suggest that Pinus may be more shade intolerant than Podocarpaceae, with P. krempfii falling between the two taxa. However, in contrast, Vietnamese conifers’ leaf mass per areas and biochemical traits did not highlight the same intermediate nature of P. krempfii. Furthermore, regardless of leaf morphology or family assignation, all species demonstrated a common and extremely high carbon gain efficiency. Overall, our findings highlight the importance of shade-tolerant photosynthetic traits for conifer survival in tropical forests. However, they also demonstrate a diversity of shade tolerance strategies, all of which lead to the persistence of Vietnamese juvenile conifers in low-light tropical understories.

中文翻译：

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越南热带森林原生的松树和罗汉松的耐荫性生理特征相反：来自异常平叶松的见解

摘要

热带森林中没有松树是令人费解的生物地理奇特现象，可能是由不耐荫性特征所解释。松krempfii（勒孔特），平坦的阔叶松地方性越南中部高地，提供了一个显着的例外，因为它似乎与耐荫热带种类竞争中取得成功。在这里，我们通过比较克雷姆菲氏菌与两种分类单元（松属）共存物种的生理特征，来检验幼年阶段针叶树的成功表现取决于耐荫性的生理特征的假设。，在泛热带森林罗汉松科中发现了一个相对丰富且耐荫的针叶树科。我们检查了叶片的光合，呼吸和生化特性。此外，我们从文献中汇编了松树和罗汉松科植物可获得的最大光合作用，最大RuBP羧化（V _cmax）和最大电子传递（J _max）值。在我们的文献汇编，P. krempfii是之间的中间松和罗汉松在其最大光合作用和V_{的C max}。松树表现出更高的V _cmax与罗汉松科相比，J _max和V _cmax之间的线性关系的斜率_较小。这些结果表明，松树可能比罗汉松更耐荫，而克雷伯氏杆菌属于两个类群。但是，相比之下，越南针叶树的单位面积叶片叶面积和生化特性并未突出克雷伯氏菌的相同中间性质。。此外，无论叶片的形态或家族分配如何，所有物种均表现出共同且极高的碳获取效率。总体而言，我们的发现突出了耐荫光合性状对于热带森林中针叶树生存的重要性。但是，它们还展示了多种耐荫策略，所有这些策略都导致越南少年针叶树在低光照的热带林下存在。