In 2018—2020, Central-European forests suffered from extremely hot and dry summers. We used data from long-term forest monitoring of six stands of European beech () and two stands of oak (/) growing on different geological substrates in the climatically uniform state of Saarland (south-western Germany) for analyzing leaf traits of the period 2004—2021. We aimed at detecting overall effects of the drought on foliar morphology, nutrient concentrations, and injury, and long-term alterations in these traits. Across sites, drought resulted in a decrease in leaf size and specific leaf area (SLA) and increased fruiting in the beech and a decrease in the foliar nitrogen (N) concentrations in both tree genera. During drought, foliar calcium and manganese concentrations were lower and potassium (K) concentrations higher across the beech stands, whereas in the oak stands, drought led to a reduction in the foliar phosphorus (P) and magnesium (Mg) concentrations. High rates of anthropogenic N deposition during recent decades have resulted in high foliar N concentrations and low to deficient concentrations of P and, in the beech, of Mg. However, a significant (negative) long-term trend in leaf traits across the study sites was only found for the K concentration and necroses of the beech leaves. Foliar N correlated positively with SLA in the beech and with leaf size in the oak but was not related to herbivory. Chlorosis was the only leaf trait that, in the beech, correlated (negatively) with the climatic water balance. We conclude that even severe drought during three consecutive years does not seem to critically affect the nutrient supply to the two most important deciduous forest tree genera of Central Europe. In the beech, a decrease in leaf size and SLA might be used as an early indication of severe drought stress effects in regular monitoring programs.

中文翻译：

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中欧山毛榉（Fagus sylvatica）和橡树（Quercus petraea/robur）的叶子性状：严重干旱和长期动态的影响

2018年至2020年，中欧森林遭受了极其炎热和干燥的夏季。我们使用了气候均匀的萨尔州（德国西南部）不同地质基质上生长的六片欧洲山毛榉 () 和两片橡树 (/) 的长期森林监测数据来分析该时期的叶子特征2004—2021。我们的目的是检测干旱对叶片形态、养分浓度和损伤的总体影响，以及这些性状的长期变化。在各个地点，干旱导致山毛榉的叶片尺寸和比叶面积 (SLA) 减小，结果增加，并且两个树属的叶面氮 (N) 浓度降低。在干旱期间，山毛榉林的叶面钙和锰浓度较低，钾 (K) 浓度较高，而在橡树林中，干旱导致叶面磷 (P) 和镁 (Mg) 浓度降低。近几十年来，人为氮沉积率高，导致叶面氮浓度高，磷浓度低甚至不足，山毛榉中镁浓度低甚至不足。然而，仅在山毛榉叶子的钾浓度和坏死方面发现了整个研究地点叶子性状的显着（负）长期趋势。叶面氮与山毛榉的 SLA 和橡树的叶子大小呈正相关，但与草食性无关。褪绿是山毛榉唯一与气候水平衡（负相关）相关的叶子性状。我们的结论是，即使连续三年严重干旱，似乎也不会严重影响中欧两种最重要的落叶林树属的养分供应。在山毛榉中，叶子尺寸和 SLA 的减小可以用作定期监测计划中严重干旱胁迫影响的早期指示。