Urban plant physiology: adaptation-mitigation strategies under permanent stress

•Urban plants offer a unique opportunity for physiological studies.•Urban plant physiology studies the response and the adaptation of plants to urban conditions.•Responses of plants along the urban–rural gradient simulate responses to climate change.•Urban plant physiology assesses the capacity of urban vegetation to provide key environmental services.

Urban environments that are stressful for plant function and growth will become increasingly widespread in future. In this opinion article, we define the concept of ‘urban plant physiology’, which focuses on plant responses and long term adaptations to urban conditions and on the capacity of urban vegetation to mitigate environmental hazards in urbanized settings such as air and soil pollution. Use of appropriate control treatments would allow for studies in urban environments to be comparable to expensive manipulative experiments. In this opinion article, we propose to couple two approaches, based either on environmental gradients or manipulated gradients, to develop the concept of urban plant physiology for assessing how single or multiple environmental factors affect the key environmental services provided by urban forests.