Responses and Post-Recovery of Physiological Traits after Drought-Heatwave Combined Event in 12 Urban Woody Species

The frequency and intensity of droughts combined with heatwave events have increased under climate change, increasing destruction in urban areas and leading to severe impacts on urban plants. These impacts remain poorly understood at the species level. Here, we investigate the effects of a drought-heatwave event on 12 urban woody species using in situ records of the dynamic changes in physiological traits in the field before, during and after the drought-heatwave event to assess resistance and resilience to hot drought. We found the following: (1) Hydraulic and photosynthesis traits showed an instantaneous decline during the hot drought event in the 12 species, with severe drought-induced xylem embolism in hydraulic systems and a high percentage loss of hydraulic conductivity (PLC). (2) The two conifer species were less resistant to hot droughts than broadleaves but capable of post-stress recovery, suggesting that conifers showed better resilience and that broadleaves showed better resistance under hot drought stress. (3) The evergreen species showed strong resistance, while three deciduous species showed strong resilience to hot drought stress. (4) The three shrubs may be more vulnerable to hot droughts than trees, as they showed lower resistance and were not able to recover the current year's growth.