Growing urbanization is triggering the evolution of plants, reveals a new study.
Scientists in Japan have discovered how the spread of towns and cities is having a major impact on flora as they adapt to urban environments.
Some species even change the color of their leaves when they grow in urban areas, reveals the study published in the journal Science Advances.
The researchers explained that a key characteristic of such environments is the presence of impermeable, heat-retaining surfaces created using brick, stone, asphalt, and concrete.
Such surfaces form urban “heat islands” – regions with elevated surface temperatures.
An unexpected result of heat stress is the impact on the behavior, physiology, and evolutionary trajectories of resident organisms, according to the findings.
Although previous studies have investigated the role of urban heat stress on evolution in animals, the researchers said its effects on plants remain largely unexplored.
They investigated how urban heat islands affect the leaf colors of Oxalis corniculata, also known as the creeping woodsorrel.
The plant displays diverse leaf colors – ranging from green to red – and is found in both urban and rural areas around the world.
Research suggests that the color variations serve as an evolutionary adaptation to protect the plant from environmental stress.
Moreover, red pigments, called anthocyanins, in the leaves are thought to reduce heat and light-induced damage by intercepting light and forming antioxidants.
Dr. Yuya Fukano and his team conducted field observations of the leaf color distribution in the creeping woodsorrel, across urban and rural regions at the local, landscape, and global scales.
Dr. Fukano said: “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.”
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.
Further examination of an online database showed that the geographical findings were “consistent” across the globe, thereby confirming a link between urbanization and leaf color variations in the creeping woodsorrel.
To quantify the adaptive benefits of the leaf color variations, the research team examined their influence over biomass growth and photosynthetic ability under heat stress and non-heat stress conditions across controlled and uncontrolled cultivation experiments.
The researchers found that the red-leaf variants showed superior growth rates and higher photosynthetic efficiency under high temperatures, whereas green-leaf variants thrived in lower temperatures.
As a result, red-leaf variants tend to thrive in urban areas with low plant density due to high stress tolerance.
The opposite is true for their green-leaf counterparts, which display higher growth competitiveness in lush green areas.
Dr. Fukano is an Associate Professor at the Graduate School of Horticulture at Chiba University, said: “Although these findings will not change much in the immediate future, this study showcases one of the most popular examples of ongoing evolution that can be observed in urban areas.”
The team also conducted genome-wide genetic analyses, which indicated that the red-leaf variant of O. corniculata may have evolved “multiple times” from the ancestral green-leaf plant.
Dr. Fukano added: “Urban heat islands are precursors to global warming.
“Understanding the rapid adaptive evolution of urban organisms to high temperatures will provide valuable insights on ecosystem dynamics and sustainable crop production.”
He said adaptations to high-temperature stress likely extend beyond leaf color, thereby warranting further research into various plant traits.
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