This paper explores the effects of three types of admixture treatments: (1) monospecific (M: European beech surrounded by six European beech seedlings), (2) single-admixture (S: European beech surrounded by six Norway spruce seedlings), and (3) group-admixture (G: European beech surrounded by three Norway spruce and three European beech seedlings), and two different CO2 concentrations ([CO2]): ambient [AMBCO2, 385 μmol (CO2) mol−1] and elevated [ELECO2, 770 μmol (CO2) mol−1] on the stem diameter increment (DI), based on a 7-year monitoring of the diameter growth of European beech (Fagus sylvatica L.) seedlings. Furthermore, to improve our understanding of the influence of climatic variables, we assessed the effects of precipitation and temperature on radial growth. After 7 years’ experience (irrespective of admixture treatment), our data were not able to confirm the effect of elevated CO2 on the diameter growth (p value = 0.35), but the result was changed when the effect of elevated CO2 was considered under the different types of admixture. Elevated CO2 along with single-admixture increased the diameter increment significantly (p value = 0.001). In contrast, we characterized a significant effect of AMBCO2 × G interaction on DI (p value = 0.002). But DI was unaffected by elevated CO2 in M (p value = 0.77). In both [CO2], inter-specific competition with spruce resulted in the highest radial growth. The inter-specific interaction was most pronounced in the lower proportion with spruce (S) in ELECO2, while in ambient CO2, the higher proportion with spruce (G) had the greatest effect on the radial growth. With respect to the climatic factors, our observations showed that temperature had a stronger influence than precipitation in ELECO2, but in AMBCO2, precipitation had the strongest effect on the radial growth as indicated by the statistically significant correlation between climatic variables and radial growth. Overall, our result suggested that seedlings growth was more under the control of climate and edaphic factors than dependent on tree species diversity and CO2 concentrations.

中文翻译：

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二氧化碳升高和邻里竞争对欧洲山毛榉 (Fagus sylvatica L.) 幼苗径向生长的交互作用

本文探讨了三种外加剂处理的效果：（1）单种（M：欧洲山毛榉被六棵欧洲山毛榉幼苗包围），（2）单一混合物（S：欧洲山毛榉被六棵挪威云杉树苗包围），以及3) 组混合物（G：被三棵挪威云杉和三棵欧洲山毛榉幼苗包围的欧洲山毛榉），以及两种不同的 CO2 浓度（[CO2]）：环境 [AMBCO2, 385 μmol (CO2) mol−1] 和升高的 [ELECO2 , 770 μmol (CO2) mol−1] 在茎直径增量 (DI) 上，基于对欧洲山毛榉 (Fagus sylvatica L.) 幼苗直径增长的 7 年监测。此外，为了提高我们对气候变量影响的理解，我们评估了降水和温度对径向增长的影响。经过7年的经验（不考虑外加剂处理），我们的数据无法证实 CO2 升高对直径增长的影响（p 值 = 0.35），但是当在不同类型的外加剂下考虑 CO2 升高的影响时，结果发生了变化。升高的 CO2 以及单一混合物显着增加了直径增量（p 值 = 0.001）。相比之下，我们描述了 AMBCO2 × G 相互作用对 DI 的显着影响（p 值 = 0.002）。但 DI 不受 M 中 CO2 升高的影响（p 值 = 0.77）。在 [CO2] 中，与云杉的种间竞争导致最高的径向生长。在 ELECO2 中，与云杉 (S) 的较低比例的种间相互作用最明显，而在环境 CO2 中，与云杉 (G) 的较高比例对径向生长的影响最大。从气候因素来看，我们的观察表明，在 ELECO2 中，温度的影响比降水的影响更大，但在 AMBCO2 中，降水对径向增长的影响最强，气候变量与径向增长之间的统计显着相关性表明。总的来说，我们的结果表明，幼苗的生长更多地受气候和土壤因素的控制，而不是依赖于树种多样性和 CO2 浓度。