Department of Biology, College of Science and Technology, University of Rwanda, Avenue de l'Armée, PO Box 3900, Kigali, Rwanda.
Center of Excellence in Biodiversity Conservation and Natural Resources Management, College of Science and Technology, University of Rwanda, Avenue de l'Armée, PO Box 3900, Kigali, Rwanda.
Tree Physiol. 2023 Jul 9;43(7):1104-1117. doi: 10.1093/treephys/tpad035.
The productivity and climate feedbacks of tropical forests depend on tree physiological responses to warmer and, over large areas, seasonally drier conditions. However, knowledge regarding such responses is limited due to data scarcity. We studied the impact of growth temperature on net photosynthesis (An), maximum rates of Rubisco carboxylation at 25 °C (Vcmax25), stomatal conductance (gs) and the slope parameter of the stomatal conductance-photosynthesis model (g1), in 10 early successional (ES) and 8 late-successional (LS) tropical tree species grown at three sites along an elevation gradient in Rwanda, differing by 6.8 °C in daytime ambient air temperature. The effect of seasonal drought on An was also investigated. We found that warm climate decreased wet-season An in LS species, but not in ES species. Values of Vcmax25 were lower at the warmest site across both successional groups, and An and Vcmax25 were higher in ES compared with LS species. Stomatal conductance exhibited no significant site differences and g1 was similar across both sites and successional groups. Drought strongly reduced An at warmer sites but not at the coolest montane site and this response was similar in both ES and LS species. Our results suggest that warming has negative effects on leaf-level photosynthesis in LS species, while both LS and ES species suffer photosynthesis declines in a warmer climate with more pronounced droughts. The contrasting responses of An between successional groups may lead to shifts in species' competitive balance in a warmer world, to the disadvantage of LS trees.
热带雨林的生产力和气候反馈取决于树木对温暖和大面积季节性干旱条件的生理响应。然而，由于数据稀缺，对于这些响应的知识有限。我们研究了生长温度对净光合速率（An）、25°C 时最大 Rubisco 羧化速率（Vcmax25）、气孔导度（gs）和气孔导度-光合作用模型斜率参数（g1）的影响，在卢旺达海拔梯度上的三个地点种植了 10 种早期演替（ES）和 8 种晚期演替（LS）热带树种，日间环境空气温度相差 6.8°C。还研究了季节性干旱对 An 的影响。我们发现，温暖的气候降低了 LS 物种在湿季的 An，但对 ES 物种没有影响。在两个演替组中，最温暖的地点的 Vcmax25 值都较低，而 ES 物种的 An 和 Vcmax25 值都高于 LS 物种。气孔导度没有明显的地点差异，g1 在两个地点和两个演替组中都相似。干旱在温暖的地点强烈降低了 An，但在最凉爽的山地地点没有降低，ES 和 LS 物种的反应相似。我们的结果表明，变暖对 LS 物种的叶片水平光合作用有负面影响，而 LS 和 ES 物种在更温暖和更干旱的气候下都会经历光合作用下降。在更温暖的世界中，An 对不同演替组的反应可能导致物种竞争平衡的转变，对 LS 树木不利。
