Department of Ecology, Evolution and Environmental Biology, Columbia University, 10th Floor Schermerhorn Extension, 1200 Amsterdam Ave., New York, NY 10027, USA.
New York Botanical Garden, 2900 Southern Boulevard, Bronx, NY 10458, USA.
Tree Physiol. 2021 Feb 2;41(2):223-239. doi: 10.1093/treephys/tpaa123.
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 (Vcmax) and maximum electron transport (Jmax) 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 Vcmax. Pinus exhibited a higher Vcmax than Podocarpaceae, resulting in a less steep slope in the linear relationship between Jmax and Vcmax. 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.
热带森林中没有松树是一个令人费解的生物地理奇异现象，这可能可以用不耐荫的特性来解释。越南中高原特有物种平叶松（Lecomte），作为一个显著的例外，似乎成功地与耐荫的热带物种竞争。在这里，我们通过比较平叶松与两个类群（松属和一种在泛热带森林中丰富且耐荫的柏科）共存物种的生理特征，来检验其幼年阶段成功的针叶树表现取决于耐荫性的生理特征的假说。我们研究了叶片光合作用、呼吸和生化特征。此外，我们还从文献中为松属和柏科物种编译了可达到的最大光合作用、最大 RuBP 羧化（Vcmax）和最大电子传递（Jmax）值。在我们的文献编译中，平叶松在最大光合作用及其 Vcmax 方面介于松属和柏科之间。松属的 Vcmax 高于柏科，导致 Jmax 和 Vcmax 之间的线性关系斜率较小。这些结果表明，松属可能比柏科更不耐荫，而平叶松则介于两者之间。然而，相反的是，越南针叶树的比叶面积和生化特征并没有突出平叶松的中间性质。此外，无论叶片形态或科归属如何，所有物种都表现出共同的、极高的碳获取效率。总的来说，我们的研究结果强调了耐荫性光合作用特征对热带森林中针叶树生存的重要性。然而，它们也展示了各种耐荫策略，所有这些策略都导致了越南幼年针叶树在低光照的热带林下的持续存在。
