Physiological responses of Tilia tomentosa, Liriodendron tulipifera, and Liquidambar styraciflua to urban stress: implications for roadside tree selection

Water scarcity is a critical environmental constraint in urban ecosystems, making tree species selection highly dependent on drought tolerance and adaptability to site-specific microclimatic conditions. In the present study, the adaptational response of two introduced species, namely Liquidambar styraciflua L. and Liriodendron tulipifera L., was assessed in parallel with a native species , Tilia tomentosa Moench, towards drought in the open lab environment at two largest cities in Serbia (Belgrade and Novi Sad), through quantification of photosynthetic and fluorescence parameters and structural leaf traits during the growing season of 2019 (from June to September). Beyond inducing stomatal closure, low water availability reduced gas exchange in the plants by downregulating transpiration and net photosynthesis, limiting photochemical energy conversion, and increasing the dissipation of excess light energy, thereby protecting the photosynthetic apparatus. Differences were detected among localities, with species exhibiting generally a stronger decrease in photosynthetic efficiency at the Belgrade site compared to Novi Sad, showing consistently low values, corresponding to the content of soil water availability. Adaptive responses were species-specific: L. styraciflua exhibited enhanced water-use efficiency, T. tomentosa showed superior cooling capacity, and L. tulipifera displayed non-stomatal regulation of photosynthesis across both urban sites, indicating high susceptibility to urban environmental stress. Overall, T. tomentosa and L. styraciflua are recommended for planting along streets with extensive impervious surfaces, while L. tulipifera is more suitable for parks or low-stress urban areas such as swale bottoms. These findings highlight the importance of species-specific physiological traits in guiding urban tree selection under increasing drought pressures.