Vitali Valentina, Klesse Stefan, Weigt Rosemarie, Treydte Kerstin, Frank David, Saurer Matthias, Siegwolf Rolf T W
Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, CH-8903 Birmensdorf, Switzerland.
Swiss Forest Protection, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, CH-8903 Birmensdorf, Switzerland.
Tree Physiol. 2021 Nov 8;41(11):2046-2062. doi: 10.1093/treephys/tpab062.
Picea abies (L.) Karst. and Fagus sylvatica (L.) are important tree species in Europe, and the foreseen increase in temperature and vapour pressure deficit (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 10 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. In addition, we observed a strikingly high coherence of the high-frequency δ18O variations across long distances with significant correlations above 1500 km, whereas 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.
欧洲云杉（Picea abies (L.) Karst.）和欧洲山毛榉（Fagus sylvatica (L.)）是欧洲重要的树种，预计气温升高和水汽压亏缺（VPD）增加会使这些树种的脆弱性上升。然而，它们在温带和高产地区气候变化下的生理表现尚未完全明晰，尤其是在异龄林中。因此，我们沿着中欧的气候梯度，在10个地点研究了这两个树种的年轮宽度和稳定同位素年表（δ13C/δ18O）。在这些异龄林中，我们比较了过去80年优势木和被压木逐年变化情况，并与地点的空间分布和气候相关联。δ18O和δ13C在各地点和树种间总体一致，对夏季VPD表现出高敏感性，而与径向生长的气候相关性差异更大，且取决于当地平均气候。我们发现，稳定同位素比率对气候变化的响应中，优势木和被压木之间没有显著差异，特别是在年度高频信号内。此外，我们观察到长距离上高频δ18O变化具有惊人的高一致性，在1500公里以上存在显著相关性，而δ13C变化的空间一致性较弱（约700公里）。我们采用了一种基于同位素分馏已知理论理解的双同位素方法，将观测到的变化转化为生理成分，主要是光合同化率和气孔导度。当在两个时间窗口分离年表并研究同位素比率的变化时，可以观察到在过去几十年中，一种或两种同位素比率有显著富集。通过双同位素方法转化后的这些结果表明，气孔导度普遍受气候驱动而下降。对控制同位素特征短期变化的生理机制的这种深入理解，将有助于确定这些树种在未来气候下的表现。
