Abstract

Picea abies and Fagus sylvatica are important tree species in Europe, and the foreseen increase in temperature and VPD could increase the vulnerability of these species. However, their physiological performance under climate change at temperate and productive sites is not yet fully understood, especially in uneven aged stands.Therefore, we investigated tree-ring width and stable isotope chronologies (δ¹³C/δ¹⁸O) of these two species at ten sites along a climate gradient in Central Europe. In these uneven-aged stands, we compared the year-to-year variability of dominant and suppressed trees for the last 80 years in relation to the sites’ spatial distribution and climate.δ¹⁸O and δ¹³C were generally consistent across sites and species, showing high sensitivity to summer VPD, whereas climate correlations with radial growth varied much more and depended on mean local climate. We found no significant differences between dominant and suppressed trees in the response of stable isotope ratios to climate variability, especially within the annual high-frequency signals. Additionally, we observed a strikingly high coherence of the high-frequency δ¹⁸O variations across long distances with significant correlations above 1,500 km, while the spatial agreement of δ¹³C variations was weaker (~700 km). We applied a dual-isotope approach that is based on known theoretical understanding of isotope fractionations to translate the observed changes into physiological components, mainly photosynthetic assimilation rate and stomatal conductance. When separating the chronologies in two time windows and investigating the shifts in isotopes ratios, a significant enrichment of either or both isotope ratios over the last decades can be observed. These results, translated by the dual-isotope approach, indicate a general climate-driven decrease in stomatal conductance. This improved understanding of the physiological mechanisms controlling the short-term variation of the isotopic signature will help to define the performance of these tree species under future climate.

中文翻译：

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不均匀森林中的高频稳定同位素信号作为中欧气候生理反应的代表

摘要

Picea abies和Fagus sylvatica是欧洲重要的树种，预计温度和 VPD 的升高可能会增加这些物种的脆弱性。然而，它们在温带和高产地的气候变化下的生理表现尚不完全清楚，尤其是在不均匀的老化林分中。因此，我们研究了这两个物种的年轮宽度和稳定同位素年代学（δ ¹³ C/δ ¹⁸ O）在中欧沿气候梯度的十个地点。在这些年龄不均的林分中，我们比较了过去 80 年中优势树和抑制树的逐年变化与场地空间分布和气候的关系。δ ¹⁸ O 和 δ ¹³C 在不同地点和物种之间基本一致，对夏季 VPD 表现出高度敏感性，而与径向生长的气候相关性变化更大，并且取决于当地平均气候。我们发现，在稳定同位素比率对气候变化的响应方面，优势树和抑制树之间没有显着差异，尤其是在年度高频信号中。^{此外，我们观察到高频 δ 18} O 变化在长距离上具有惊人的高相干性，在1,500 公里以上具有显着相关性，而 δ ^{13的空间一致性}C 变化较弱（~700 km）。我们应用了双同位素方法，该方法基于对同位素分馏的已知理论理解，将观察到的变化转化为生理成分，主要是光合同化速率和气孔导度。当在两个时间窗口中分离年表并研究同位素比率的变化时，可以观察到过去几十年中一种或两种同位素比率的显着富集。通过双同位素方法翻译的这些结果表明，气孔导度普遍受到气候驱动的下降。这种对控制同位素特征短期变化的生理机制的更好理解将有助于确定这些树种在未来气候下的表现。