Radial growth and cell wall structure of trees grown under elevated carbon dioxide concentrations

我们估计了二氧化碳浓度升高对树木生理和解剖特性（即茎生长、木材结构和光合作用特性）的长期影响。将西伯利亚落叶松（Larix sibirica）和日本落叶松（Betula platyphylla var. japonica）幼苗分别生长在co2浓度为360 ppm和720 ppm的环境中，并在1 - 3个生长季节中分别添加高或低水平的养分。升高CO_2对茎高和茎粗无显著影响。然而，高水平的养分增加了茎高和茎粗，而这种增加是由[CO_2]升高引起的。随着[CO_2]浓度的升高，年轮宽、细胞数和细胞直径有增加的趋势，细胞壁厚度有减小的趋势，而细胞壁相对面积无统计学差异，且与木材比重密切相关，说明[CO_2]浓度升高对木材质量变化的影响不大。综上所述，提高[CO_2]对植物的固碳能力没有明显的增强作用。然而，在CO_2升高的情况下，茎生长的时间模式和茎的解剖特征会发生变化。虽然升高[CO_2]条件下幼苗的净同化率高于环境[CO_2]，但升高[CO_2]条件下全冠光合速率的提高并不明显，这是由于幼苗生长的叶片比叶面积较小，且叶片光合特性对[CO_2]已经适应。这种光合作用的驯化与叶片中可溶性蛋白和Rubisco（光合作用的关键酶）的减少密切相关。

We estimated long-term effects of elevated carbon dioxide concentrations [CO_2] on physiological and anatomical characteristics of trees, namely the stem growth, wood structure and characteristics of photosynthesis. Seedlings of larch (Larix sibirica and Larix kaempferi) and white birch (Betula platyphylla var. japonica) trees were grown in growth chambers under two [CO_2], ambient (360 ppm) and elevated (720 ppm), and with high or low levels of nutrients for one-three growing seasons. Elevated [CO_2] had no significant effects on stem height and stem diameter. However, the stem height and stem diameter were enhanced by the high level of nutrients and these increases were stimulated by elevated [CO_2]. Annual ring widths, cell numbers and cell diameters tended to increase, whereas cell wall thickness tended to decrease slightly in response to elevated [CO_2] , By contrast, there were no statistically significant differences in the relative area of cell wall, which was closely related to specific gravity of wood, indicating that elevated [CO_2] had few effects of changes in wood quality. In conclusion, there is no obvious enhancement in the capacity of carbon fixation by elevated [CO_2]. However, changes in the temporal pattern of stem growth and in anatomical features of the stem would occur under elevated [CO_2]. Although net assimilation rate under which seedlings grew was higher in elevated [CO_2] than in ambient [CO_2], little enhancement of photosynthesis rate of whole crown under elevated [CO_2] was observed because of the smaller specific leaf area and the acclimation of photosynthetic characteristics of leaves to [CO_2] which seedling grew. Such acclimation of photosynthesis was closely related to the decrease in amounts of soluble proteins and Rubisco, which is a key enzyme of photosynthesis, in leaves.