Laboratory of Plant Ecology, Department of Plant and Crops Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium.
Polish Academy of Sciences, Institute of Dendrology, Parkowa 5, 62-035 Kórnik, Poland.
Tree Physiol. 2020 Oct 29;40(11):1572-1582. doi: 10.1093/treephys/tpaa085.
Woody tissue photosynthesis (Pwt) contributes to the tree carbon (C) budget and generally stimulates radial stem growth under ambient atmospheric CO2 concentration (aCO2). Moreover, Pwt has potential to enhance tree survival under changing climates by delaying negative effects of drought stress on tree hydraulic functioning. However, the relevance of Pwt on tree performance under elevated atmospheric CO2 concentration (eCO2) remains unexplored. To fill this knowledge gap, 1-year-old Populus tremula L. seedlings were grown in two treatment chambers at aCO2 and eCO2 (400 and 660 ppm, respectively), and woody tissues of half of the seedlings in each treatment chamber were light-excluded to prevent Pwt. Radial stem growth, sap flow, leaf photosynthesis and stomatal and canopy conductance were measured throughout the growing season, and the concentration of non-structural carbohydrates (NSC) in stem tissues was determined at the end of the experiment. Fuelled by eCO2, an increase in stem growth of 18 and 50% was observed in control and light-excluded trees, respectively. Woody tissue photosynthesis increased radial stem growth by 39% under aCO2, while, surprisingly, no impact of Pwt on stem growth was observed under eCO2. By the end of the growing season, eCO2 and Pwt had little effect on stem growth, leaf photosynthesis acclimated to eCO2, but stomatal conductance did not, and homeostatic stem NSC pools were observed among combined treatments. Our results highlight that eCO2 potentially fulfils plant C requirements, limiting the contribution of Pwt to stem growth as atmospheric [CO2] rises, and that radial stem growth in young developing trees was C (source) limited during early phenological stages but transitioned towards sink-driven control at the end of the growing season.
木质部组织光合作用（Pwt）有助于树木的碳（C）预算，并且通常在环境大气 CO2 浓度（aCO2）下刺激径向茎生长。此外，Pwt 通过延迟干旱胁迫对树木水力功能的负面影响，具有增强树木在气候变化下生存的潜力。然而，Pwt 在高大气 CO2 浓度（eCO2）下对树木性能的相关性尚未得到探索。为了填补这一知识空白，我们将 1 年生的欧洲山杨（Populus tremula L.）幼苗在两个处理室中于 aCO2 和 eCO2 下（分别为 400 和 660 ppm）生长，并且每个处理室中一半的幼苗的木质部组织被遮光以防止 Pwt。在整个生长季节中测量了径向茎生长、液流、叶片光合作用以及气孔和冠层导度，并且在实验结束时测定了茎组织中非结构性碳水化合物（NSC）的浓度。在 eCO2 的推动下，对照和遮光树的茎生长分别增加了 18%和 50%。在 aCO2 下，木质部组织光合作用增加了 39%的径向茎生长，而令人惊讶的是，在 eCO2 下，Pwt 对茎生长没有影响。在生长季节结束时，eCO2 和 Pwt 对茎生长的影响很小，eCO2 使叶片光合作用适应，但气孔导度没有，并且在综合处理中观察到了同化物茎 NSC 库的平衡。我们的研究结果表明，eCO2 可能满足了植物的 C 需求，限制了 Pwt 对随着大气[CO2]升高的茎生长的贡献，并且在早期物候阶段，年轻发育树木的径向茎生长受到 C（源）限制，但在生长季节结束时向源驱动控制转变。
