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

Abstract

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.

Plant Leaf Functional Adaptions along Urban–Rural Gradients of Jinhua City

“…This stability may be attributed to urban tree growth trajectories being better suited to high-temperature conditions, coupled with the complexity of growth-driving factors for urban plants. A study found that urban environments promote plant resistance to high temperatures [ 13 ], which might be associated to diverse planting methods, soil types, and fertilization practices, each significantly influencing plant growth [ 25 ].…”

“…These differences could be attributed to their distinct resource allocation strategies [ 13 ]. Our research demonstrated that evergreen tree species adopted a more conservative resource allocation approach ( Figure 4 a), progressively favoring structural components as they transitioned from rural to urban areas.…”

“…Our research demonstrated that evergreen tree species adopted a more conservative resource allocation approach ( Figure 4 a), progressively favoring structural components as they transitioned from rural to urban areas. This adaptation allowed them to better withstand urban challenges [ 13 , 27 ]. In contrast, deciduous species, located on the resource acquisition end of the spectrum, demonstrated increasing investment in resource acquisition as they moved from rural to urban environments ( Figure 4 b).…”

“…However, in urban areas, city irrigation can significantly reduce plant stress induced by heat and dry spells. Suburban areas with less frequent irrigation may show different plant responses to drought stress due to varying watering patterns [13].…”

“…Evergreen and deciduous tree species have leaves with distinct life forms and resource allocation strategies. Generally, evergreen species typically follow a ‘slow investment-return’ strategy, while deciduous trees follow a ‘fast investment-return’ approach [ 13 ]. It has been thought that deciduous species would be more sensitive to rising temperatures considering the changes in the SLA, net photosynthetic rate (A), leaf nitrogen content, chlorophyll (Chl), and stomatal conductance [ 14 ].…”