How are microplastics affecting plant photosynthesis?

A comprehensive meta-analysis conducted by environmental researchers, Earth scientists and pollution specialists from Nanjing University, the Chinese Academy of Sciences and international collaborators has revealed a significant and concerning impact of microplastic pollution on photosynthetic efficiency across terrestrial, marine and freshwater ecosystems.

Some researchers, voicing their opinions in published reports, believe this research underscores the urgent need for proactive mitigation strategies to curtail microplastic pollution.

They hypothesize that, if these data trends prove to be true, microplastics could threaten plant health, agricultural productivity and the stability of the planet’s food supply chains. As an extension, it could negatively affect the greenhouse, nursery and controlled agriculture industries.

Published in March in the Proceedings of the National Academy of Sciences, the study synthesized data from more than 150 investigations, encompassing thousands of observations, to quantify the detrimental effects of ubiquitous microplastics on plant physiology.

According to the research, the findings indicate a substantial reduction in photosynthetic efficiency, ranging from 7% to 12% across diverse plant types, accompanied by decreased chlorophyll production. This translates to alarming projected harvest yield losses of 4% to 14% for staple crops such as maize, wheat and rice globally, and up to a 7% reduction in global aquatic net primary productivity.

Given the reports of escalating levels of microplastic contamination in environmental systems, it is postulated that these proposed yield reductions could pose a direct threat to global food security, potentially placing hundreds of millions of individuals at risk of starvation within the next two decades.

Kristin M. Burkholder, professor and assistant academic director of the School of Biological Sciences, and Carrie J. Byron, associate professor in the School of Marine and Environmental Programs, both at the University of New England, say that while they have not had an opportunity to review the study thoroughly, its findings are a bit “alarmist” and, as a whole, this is a very complex biological issue that warrants addition study. However, ample scientific literature demonstrates that the toxicity from plastics interferes with plants’ photosynthetic machinery, which can have implications for plant growth.

Byron adds that research has shown different types of plastics have different levels of toxicity that could influence plants’ photosynthetic and growth rates.

“So, some types of plastics are going to have a larger impact than other types of plastics,” she says. “And there’s another nuance that not every photosynthetic organism has the exact same photosynthetic machinery. So, depending on what type of plant or algae you are, there may be a different impact, as well.”

Burkholder clarified that the study investigated the potential impact of plastics on food production through a meta-analysis. This comprehensive study synthesized findings from a substantial number of investigations, reportedly more than 150, focusing on the effects of plastics on photosynthesis.

The researchers then developed a model based on this meta-analytic data to extrapolate the potential consequences for agricultural output. While such modeling is a crucial analytical approach, Burkholder believes validating these model-derived conclusions with empirical studies directly examining the impact of plastic-mediated photosynthesis inhibition on food production in terrestrial plants would be highly valuable.

Burkholder further stresses the importance of understanding that the effects of plastics are not uniform but are contingent upon various factors, including the type and size of plastic particles and their concentration within a specific environment. These concentrations, she notes, vary considerably across the globe depending on factors like proximity to industrial activity and population density, leading to a non-uniform distribution of plastic impacts on biological organisms.

“Obviously, photosynthesis is essential for the productivity of terrestrial and aquatic plants,” she says. “So, if this is really happening in the way that their model tells them it could be happening, then that could cause a decrease in plant and food production. But I wouldn’t go so far as to say destruction of the planet.”

In light of the research’s findings, Byron raises the issue of potential plastic contamination within greenhouse and controlled environment agriculture (CEA) systems, as well as in aquaculture. A common assumption, she says, is that these are highly managed environments, where parameters like water and air temperature and water quality are meticulously controlled, and that these environments would inherently be free from contaminants.

However, Byron points out the significant use of plastic materials within these managed growing systems.

“A lot of times, in these controlled environments, there is heavy use of plastic materials,” she says. “I wonder — and I don’t have an answer — but I wonder how plastic loading differs in these controlled systems versus open-environment uncontrolled systems. I haven’t seen very many studies trying to quantify that specifically. There are a lot of benefits to controlled ag and aquaculture, but I also think there are some scary questions that we need to be asking.”

Mike Zawacki is a Cleveland-based journalist and frequent contributor to the GIE Media Horticulture Group who has covered various aspects of the green, horticultural, sports turf and irrigation industries for the last 20 years.