Centre for Systems Biology (ZBSA), Core Facility Metabolomics, Albert-Ludwigs-University, Habsburgerstrasse 49, 79104 Freiburg, Germany.
Tree Physiol. 2009 Nov;29(11):1349-65. doi: 10.1093/treephys/tpp066. Epub 2009 Sep 4.
In this study, the effects of different light intensities either in direct sunlight or in the shade crown of adult beech (Fagus sylvatica L.) trees on delta13C and Delta18O were determined under ambient (1 x O3) and twice-ambient (2 x O3) atmospheric ozone concentrations during two consecutive years (2003 and 2004). We analysed the isotopic composition in leaf bulk, leaf cellulose, phloem and xylem material and related the results to (a) meteorological data (air temperature, T and relative humidity, RH), (b) leaf gas exchange measurements (stomatal conductance, g(s); transpiration rate, E; and maximum photosynthetic activity, A(max)) and (c) the outcome of a steady-state evaporative enrichment model. Delta13C was significantly lower in the shade than in the sun crown in all plant materials, whilst Delta18O was increased significantly in the shade than in the sun crown in bulk material and cellulose. Elevated ozone had no effect on delta13C, although Delta18O was influenced by ozone to varied degrees during single months. We observed significant seasonal changes for both parameters, especially in 2004, and also significant differences between the study years. Relating the findings to meteorological data and gas exchange parameters, we conclude that the differences in Delta18O between the sun and the shade crown were predominantly caused by the Péclet effect. This assumption was supported by the modelled Delta18O values for leaf cellulose. It was demonstrated that independent of RH, light-dependent reduction of stomatal conductance (and thus transpiration) and of A(max) can drive the pattern of Delta18O increase with the concomitant decrease of delta13C in the shade crown. The effect of doubling ozone levels on time-integrated stomatal conductance and transpiration as indicated by the combined analysis of Delta18O and delta13C was much lower than the influence caused by the light exposure.
在这项研究中，我们在两年（2003 年和 2004 年）的时间里，在大气臭氧浓度分别为ambient（1 x O3）和 doubled（2 x O3）的情况下，确定了不同光照强度（直射阳光或成年山毛榉（Fagus sylvatica L.）树冠下的阴影）对叶片δ13C 和 δ18O 的影响。我们分析了叶片整体、叶片纤维素、韧皮部和木质部材料的同位素组成，并将结果与（a）气象数据（空气温度，T 和相对湿度，RH）、（b）叶片气体交换测量（气孔导度，g(s)；蒸腾速率，E；和最大光合作用活性，A(max)) 和（c）稳态蒸发浓缩模型的结果相关联。在所有植物材料中，与树冠下的阳光相比，树冠下的 δ13C 明显更低，而在整体材料和纤维素中，树冠下的 δ18O 明显更高。臭氧升高对 δ13C 没有影响，尽管在单个月份，臭氧对 δ18O 的影响程度不同。我们观察到这两个参数都有显著的季节性变化，特别是在 2004 年，而且在研究年份之间也有显著差异。将这些发现与气象数据和气体交换参数相关联，我们得出结论，树冠下的 δ18O 与阳光之间的差异主要是由 Peclet 效应引起的。这一假设得到了叶片纤维素模型 δ18O 值的支持。研究表明，独立于 RH，气孔导度（因此蒸腾）和 A(max)的光依赖性降低会导致树冠下 δ18O 随着 δ13C 的同时降低而增加的模式。臭氧水平加倍对时间积分气孔导度和蒸腾作用的影响，如 δ18O 和 δ13C 的综合分析所示，远低于光暴露引起的影响。
