Woody tissue photosynthesis (P_wt) contributes to the tree carbon (C) budget and generally stimulates radial stem growth under ambient atmospheric CO₂ concentration (aCO₂). Moreover, P_wt has potential to enhance tree survival under changing climates by delaying negative effects of drought stress on tree hydraulic functioning. However, the relevance of P_wt 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 P_wt. 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 P_wt on stem growth was observed under eCO₂. By the end of the growing season, eCO₂ and P_wt 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 P_wt 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.

中文翻译：

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木质组织的光合作用在环境大气CO2的作用下增加了年轻杨树的径向茎生长，但在CO2升高时其作用就停止了。

木质组织的光合作用（P _wt）有助于树木碳（C）的收支，并通常在环境大气CO ₂浓度（aCO ₂）下刺激radial茎的生长。此外，P _wt可以通过延迟干旱胁迫对树木水力功能的负面影响来提高气候变化下树木的生存能力。然而，在大气CO ₂浓度升高（eCO ₂）下，P _wt与树木性能的相关性尚待探索。为了填补这一知识差距，1岁的欧洲山杨幼苗是在两个治疗室中ACO增长₂和ECO ₂（分别为400和660 ppm）和每个处理室中一半幼苗的木质组织被光排除以防止P _wt。在整个生长季节测量measured茎的生长，汁液流动，叶片的光合作用以及气孔和冠层的导度，并在实验结束时确定茎组织中非结构性碳水化合物（NSC）的浓度。以eCO _2为燃料，在对照树和避光树中分别观察到茎生长增加18％和50％。在aCO _2下，木质组织的光合作用使径向茎的生长增加了39％，而令人惊讶的是，在eCO ₂下，未发现P _wt对茎生长的影响。到生长季节结束时，eCO₂和P _wt对茎的生长几乎没有影响，叶片的光合作用适应了eCO ₂，但气孔导度没有，并且在联合处理之间观察到了稳定的茎NSC库。我们的结果表明，eCO ₂可能满足植物C的要求，随着大气[CO ₂ ]的升高，限制了P _wt对茎生长的贡献，并且在早期物候期中，发育中的幼树的径向茎生长受到C（源）的限制，但过渡在生长季节结束时向水槽驱动的控制迈进。