The presented study concerns the delayed response of photosynthetic performance to summer drought. Increasing drought events are thought to be one of the most detrimental and expensive natural disasters. For that reason, we studied the condition of urban trees, which are especially susceptible to water deficit. Three species of linden trees (T. tomentosa, T. × europaea and T. cordata) growing in the city area of Krakow, Poland, were investigated for two consecutive years to compare their response to a precipitation deficit. For the first time, the physiological traits of linden urban trees were compared in years with and without a natural summer drought. For evaluation of the photosynthetic performance, we used measurements of the chlorophyll a fluorescence concerning the OJIP transients and derived parameters. The contents of photosynthetic pigments, such as chlorophylls and carotenoids, were analysed, and stress-sensible parameter ratios, such as chl a/b and chl/carot, were calculated. The most common method of research conduction assumes examination close to the presence of a stressor. We chose an innovative method of prolonged investigation after relief from the stress conditions. While there was no evident reaction of PSII to meteorological drought during the stress occurrence, all of the investigated species of linden revealed delayed reaction of PSII to precipitation deficit in summer. Changes in PSII were connected with the decrease of active reaction centres (RCs), which was evident in the increase of the ABS/RC, DI₀/RC and TR₀/RC, and the decrease of ET₀/RC. T. × europaea demonstrated a more intense decrease of certain parameters during late senescence compared with other species. Despite the close relation of T. cordata and T. × europaea, species showed different physiological traits during senescence after a summer drought. Our results underline the need for monitoring tree conditions not only during stress but also in the wider perspective.

中文翻译：

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光合性能的延迟抑制——城市环境中的三种菩提树种

所提出的研究涉及光合性能对夏季干旱的延迟反应。越来越多的干旱事件被认为是最具破坏性和代价最高的自然灾害之一。出于这个原因，我们研究了城市树木的状况，这些树木特别容易缺水。对生长在波兰克拉科夫市区的三种菩提树（T. tomentosa、T. × europaea和T. cordata）连续两年进行了调查，以比较它们对降水不足的反应。首次比较了有和无自然夏季干旱年份的椴树城市树木的生理特征。为了评估光合性能，我们使用了叶绿素a 的测量值关于 OJIP 瞬变和衍生参数的荧光。分析了光合色素的含量，如叶绿素和类胡萝卜素，并计算了胁迫敏感参数比，如 chl a/b和 chl/carot。最常见的研究传导方法假设检查接近压力源的存在。在摆脱压力后，我们选择了一种创新的长期调查方法。虽然在胁迫发生期间PSII对气象干旱没有明显反应，但所有被调查的椴树种都显示PSII对夏季降水不足的反应延迟。PSII 的变化与活性反应中心 (RC) 的减少有关，这在 ABS/RC、DI ₀的增加中很明显/RC 和 TR ₀ /RC，以及 ET ₀ /RC的减少。与其他物种相比，T. × europaea在衰老晚期表现出某些参数的更强烈下降。尽管T. cordata与T. × europaea的亲缘关系密切，但在夏季干旱后的衰老过程中，物种表现出不同的生理特征。我们的结果强调了不仅在压力期间而且在更广泛的角度监测树木状况的必要性。