Researchers at the University of Hong Kong have found that fine particulate pollution reduces plants' capacity to absorb carbon dioxide and use water efficiently. The team studied how PM2.5, particles smaller than 2.5 micrometers, interferes with plant physiology at the Faculty of Social Sciences.

Fine particles accumulate on leaf surfaces and in the atmosphere, blocking sunlight from reaching plant tissues. This reduction in light availability forces plants to close their stomata, the microscopic pores through which they exchange gases and water vapor with the environment. When stomata close, plants absorb less carbon dioxide while simultaneously losing their ability to conserve water through transpiration.

The findings carry implications for global carbon cycles and plant health in polluted regions. As plants absorb less CO2, their contribution to removing greenhouse gases from the atmosphere diminishes. Simultaneously, impaired water conservation stresses plants during dry periods, making them more vulnerable to drought and reducing agricultural productivity.

PM2.5 pollution stems from vehicle emissions, industrial processes, and fossil fuel combustion. Major cities across Asia, including Hong Kong, regularly experience high PM2.5 concentrations that exceed international air quality standards. The research demonstrates a direct physiological pathway linking air pollution to ecosystem dysfunction.

The study adds to growing evidence that fine particle pollution affects not just human health but entire ecosystems. Previous research focused primarily on respiratory impacts in humans, but this work highlights cascading ecological consequences. Plants struggling to photosynthesize and conserve water experience reduced growth and yield, affecting food security and carbon storage in vegetation.

The HKU researchers measured stomatal conductance, photosynthetic rates, and water-use efficiency in plants exposed to varying PM2.5 levels. Their results show a clear dose-response relationship, where higher pollution concentrations produce greater physiological impairment.

Addressing this challenge requires reducing particulate emissions through stricter industrial