Bean experiments affirm ozone impact in Hong Kong

22 May 2020

A research team, led by Dr Amos Tai (Croucher Fellowship 2012) at the Chinese University of Hong Kong (CUHK), has found the ozone level in Hong Kong is high enough to cause significant damage to plants, even in the countryside.

Hong Kong is one of the most densely populated cities in the world, with many busy roads with severe air pollution. A 2019 air quality monitoring report showed that the average ozone level has been increasing over the past 20 years, despite the city improving its air quality overall.

Ozone is mostly produced photochemically from manmade gases, such as volatile organic compounds (VOCs) and nitrogen oxides emitted by vehicles; and is known to damage photosynthesis, reduce gas exchange, induce early leaf senescence, and retard growth in both natural vegetation and crops.

As plants play vital roles in regulating the ambient environment, ozone-induced damage in plants may further accelerate environmental degradation, with severe consequences for human health.

Tai, an Associate Professor in the Earth System Science Programme, Faculty of Science, and his team were able to quantify and visualise the impact of ozone pollutant on plants and the environment.

Field site at the ozone garden in CUHK where the beans are exposed to ambient ozone level.

To do so, the scientists established an ozone garden to monitor, quantify, and understand the mechanisms of ozone damage on plants. The team grew cultivars of beans with different ozone sensitivities as a bioindicator of the local air pollution impacts on ecosystems.

While free-air ozone gardens have been built in many locations in the US and Europe, this was the first of its kind in South China, according to Tai. “The data obtained from this garden is essential [for] demonstrating the impact of air pollution on plants under locally specific environmental conditions and deriving important parameters of ecophysiology and biometeorology that can be used to build a regionally relevant earth system model for predictive purposes,” he said.

The species of bean chosen showed distinctive red mottling on the leaves according to the level of ozone in the atmosphere, with two genotypes of beans used – sensitive and resistant to ozone. The beans were supplied by the UK Centre for Ecology & Hydrology, a research institute.

The CUHK project team found the ozone-sensitive genotype bean suffered higher ozone-induced foliar damage, with more red mottles and a higher death rate. These plants also produced 30 per cent more flowers than the resistant genotype. This was a result of stress-induced flowering caused by ozone, which triggered the plant to produce more flowers and therefore maintain its chance of fertilisation and reproduction

The plant’s foliar is damaged by high intensity of ozone, thus showing more red mottles.

The researchers also found that the resistant genotype had a higher success rate (17 per cent more) of fruiting development, from flowering to bean formation, and less immature or dead pods than the sensitive genotype.

Furthermore, even though the experiment took place in spring in a rural area, which would usually have a lower average ozone concentration, the pollutant level was still high enough to do significant damage to the bioindicator plant.

The findings, published in Atmosphere, have important implications for farmers in Hong Kong and South China where their crops suffer from ozone pollution. The experiment also provided evidence in support of a clean air policy that reduces vehicle emissions in Hong Kong.

Further studies are due to be carried out to investigate the physiology of the beans under various ozone concentrations in a controlled environment.

Dr Amos Tai is an Associate Professor in the Earth System Science Programme and Graduate Division of Earth and Atmospheric Sciences in the Faculty of Science at the Chinese University of Hong Kong (CUHK). He graduated from Harvard with a PhD in Environmental Science and Engineering (Atmospheric Science) in 2012 and pursued postdoctoral research in the Department of Civil and Environmental Engineering at Massachusetts Institute of Technology (MIT) from 2012 to 2013. At MIT, he studied impacts of climate change and air pollution on agriculture. Tai joined CUHK in 2013 as an Assistant Professor and became an Associate Professor in 2019. He received his Croucher Fellowship in 2012.

To view Tai’s Croucher profile, please click here.