Department of Forestry and Wood Technology, Linnaeus University, 351 95 Växjö, Sweden.
Department of Geosciences and Natural Resource Management, University of Copenhagen, Rolighedsvej 23, Frederiksberg C, 1958 Copenhagen, Denmark.
Tree Physiol. 2021 Aug 11;41(8):1450-1461. doi: 10.1093/treephys/tpab016.
The percentage of respiratory and photorespiratory CO2 refixed in leaves (Pr) represents part of the CO2 used in photosynthesis. The importance of Pr as well as differences between species and functional types are still not well investigated. In this study, we examine how Pr differs between six temperate and boreal woody species: Betula pendula, Quercus robur, Larix decidua, Pinus sylvestris, Picea abies and Vaccinium vitis-idaea. The study covers early and late successional species, deciduous broadleaves, deciduous conifers, evergreen conifers and evergreen broadleaves. We investigated whether some species or functional types had higher refixation percentages than others, whether leaf traits could predict higher Pr and whether these traits and their impact on Pr changed during growing seasons. Photosynthesis CO2 response (A/Ci)-curves, measured early, mid and late season, were used to estimate and compare Pr, mesophyll resistance (rm) and stomatal resistance (rs) to CO2 diffusion. Additionally, light images and transmission electron microscope images were used to approximate the fraction of intercellular airspace and cell wall thickness. We found that evergreens, especially late successional species, refixed a significantly higher amount of CO2 than the other species throughout the entire growing season. In addition, rm, rs and leaf mass per area, traits that typically are higher in evergreen species, were also significantly, positively correlated with Pr. We suggest that this is due to higher rm decreasing diffusion of (photo) respiratory CO2 out of the leaf. Cell wall thickness had a positive effect on Pr and rm, while the fraction of intercellular airspace had no effect. Both were significantly different between evergreen conifers and other types. Our findings suggest that species with a higher rm use a greater fraction of mitochondria-derived CO2, especially when stomatal conductance is low. This should be taken into account when modeling the overall CO2 fertilization effect for terrestrial ecosystems dominated by high rm species.
叶片中呼吸和光呼吸固定的 CO2 比例（Pr）代表光合作用中使用的部分 CO2。Pr 的重要性以及不同物种和功能类型之间的差异仍未得到充分研究。在这项研究中，我们检查了六个温带和北方木本物种之间的 Pr 差异：欧洲白桦、欧洲山毛榉、欧洲落叶松、欧洲赤松、挪威云杉和越橘。该研究涵盖了早期和晚期演替物种、落叶阔叶树、落叶针叶树、常绿针叶树和常绿阔叶树。我们研究了某些物种或功能类型的 Pr 是否高于其他物种，叶片特性是否可以预测更高的 Pr，以及这些特性及其对 Pr 的影响是否在生长季节发生变化。使用光合作用 CO2 响应（A/Ci）曲线，分别在早期、中期和晚期进行测量，以估计和比较 Pr、叶肉阻力（rm）和 CO2 扩散的气孔阻力（rs）。此外，还使用了光图像和透射电子显微镜图像来近似细胞间气腔和细胞壁厚度的分数。我们发现，常绿树种，尤其是晚期演替物种，在整个生长季节都比其他物种固定了更多的 CO2。此外，rm、rs 和叶面积质量，这些特性通常在常绿物种中更高，也与 Pr 呈显著正相关。我们认为这是由于 rm 较高，减少了（光）呼吸 CO2 从叶片中扩散出来的量。细胞壁厚度对 Pr 和 rm 有积极影响，而细胞间气腔的分数则没有影响。这两个参数在常绿针叶树和其他类型之间有显著差异。我们的研究结果表明，rm 较高的物种会使用更多的线粒体衍生 CO2，尤其是在气孔导度较低时。在以高 rm 物种为主的陆地生态系统中，建模整体 CO2 施肥效应时应考虑到这一点。
