Urbanization Triggers Evolution of plants, reveals study

Researchers from Japan have been studying the impact of urban heat islands on the evolution of the creeping woodsorrel plant, Oxalis corniculata. Urban environments, characterized by impermeable, heat-retaining surfaces, create unique selective pressures on resident organisms.

These environments often result in elevated surface temperatures, affecting the behavior, physiology, and evolutionary trajectories of these organisms.

Urbanization influences plant leaf coloration

The team, led by Associate Professor Yuya Fukano from the Graduate School of Horticulture, Chiba University, Japan, focused on the leaf color variations of Oxalis corniculata. This plant exhibits a range of leaf colors from green to red and is found in both urban and non-urban spaces globally. The color variations are thought to be an evolutionary adaptation to protect the plant from environmental stress.

 “We noticed that the red-leaved variants of the creeping woodsorrel commonly grew near impervious surfaces in urban areas but rarely grew in farmlands or green spaces in and around the city,” says Dr. Fukano, while discussing their observations. 

The team identified a pattern where green-leaved variants of the creeping woodsorrel dominated green spaces while their red-leaf counterparts dominated the urban sites of Tokyo at both the local and landscape levels. Upon further examination of an online database, the team discovered that these geographical findings were consistent across the globe, thereby confirming a link between urbanization and leaf color variations in the creeping woodsorrel.

The researchers observed the leaf color distribution of creeping woodsorrel across urban and non-urban regions at local, landscape, and global scales. They discovered that urban areas near impervious surfaces commonly had red-leaved variants growing, but these were rarely present in farmlands or green spaces. Green-leaved variants were the predominant type in green spaces, while their red-leaf counterparts primarily dominated urban sites.

Plant adaptation to Urban Heat Islands

The team then quantified the adaptive benefits of these leaf color variations by examining their influence over biomass growth and photosynthetic ability under heat stress and non-heat stress conditions. Their findings provide valuable insights into how plants might adapt to elevated temperatures due to urbanization.

The research team discovered that red-leaf variants of the creeping woodsorrel plant exhibited superior growth rates and higher photosynthetic efficiency under high temperatures, making them more suited to urban environments. Conversely, green-leaf variants thrived in lower temperatures, making them more prevalent in lush green areas.

Genome-wide genetic analyses conducted by the team suggested that the red-leaf variant of O. corniculata may have evolved multiple times from the ancestral green-leaf plant. This study provides valuable insights into the ongoing evolution observable in urban areas and the rapid adaptive evolution of urban organisms to high temperatures.

Dr. Fukano, who led the research, highlighted the importance of these findings for understanding ecosystem dynamics and sustainable crop production. He noted that urban heat islands are precursors to global warming, and understanding how organisms adapt to these conditions can provide valuable insights.

The team believes that adaptations to high-temperature stress likely extend beyond leaf color, indicating a need for further research into various plant traits to fully understand plant adaptation to urban heat islands.

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