Planting oats to study the effects of air pollution

What role does air pollution play in plant growth? That’s the question a cross-disciplinary team of EPFL scientists has set out to answer. Their research method involves planting oats in boxes in Bois-Chamblard park, which is owned by the Bois-Chamblard Foundation, and measuring how the plants’ exposure to different atmospheric conditions affects their growth. The team has just completed the first part of the experiment by harvesting the oats and soil samples and freezing them for subsequent laboratory analysis.

This project is being supported by the Foundation and carried out by two labs at EPFL’s School of Architecture, Civil and Environmental Engineering (ENAC): the Laboratory of Atmospheric Processes and their Impacts (LAPI), and the Plant Ecology Research Laboratory (PERL). The work is being supervised by EPFL Professor Emeritus Alexandre Buttler.

Field testing

To conduct their experiment, the scientists designed and built 18 sealed, transparent boxes roughly 1 meter high and 50 centimeters wide. Oat plants were grown on natural soil inside the boxes, either under controlled atmospheric conditions with continuous particle filtration and pure water only, or exposed to unfiltered air or rainwater – or a combination of the two. As a control, some boxes contained only potting soil. The objective of the experiment is to compare the plants that grew with and without the influence of nutrients from the deposition of air pollutants.

From left to right: Andrea Arangio, Megan He, André Welti, Kalliopi Violaki, Athanasios Nenes. © Alain Herzog / EPFL

The scientists turned the picturesque park into a high-tech research station where ambient instruments were used to collect air and soil samples. The air samples consisted of nutrient-containing gases and particles (nitrogen, phosphorous and iron) as well as other compounds, while the soil samples held compounds and particles that fell to the ground both when it was raining (wet deposition) and when it wasn’t (dry deposition). The samples’ chemical compositions will be analyzed later on in the lab. The researchers will use the information they gather, together with meteorological data collected by a portable weather station, to study the nutrient content of air pollution and investigate where the pollution actually came from.

Lab analysis

Now that the plant harvesting and air-and-soil sampling is complete, the scientists are embarking on the analysis phase. “Our goal is to quantify the nutrients contained in air pollution and determine how much of them – especially nitrogen and phosphorus – are captured by the plants as they grow,” says Andrea Arangio, a scientist at LAPI. The head of LAPI, Prof. Athanasios Nenes, adds: “Pollution is typically associated with adverse effects on the environment, but in this case it may provide nutrients that actually promote crops and plant growth.” The scientists will also analyze the composition of both the soil in which the oat plants grew and the surrounding soil.

Fertile pollution

Oddly enough, pollution may bring other benefits as well. According to LAPI scientist Dr. Kalliopi Violaki: “What’s interesting is that pollution, apart from providing nutrients itself, can also interact with other nutrients that are usually locked inside naturally occurring particles and make them more ‘bioavailable.’ An example of this is the phosphorous that’s locked in dust particles carried to Europe from the Sahara.” Prof. Nenes adds: “The acidity resulting from air pollution also determines how long atmospheric nitrogen, a key nutrient, can remain in the air and be carried by wind before falling to the ground.”

The harvest: Alexandre Buttler and Andrea Arangio. © Alain Herzog / EPFL

Plant strategies

Human activity has already boosted concentrations of nutrients like carbon, nitrogen, phosphorous, iron and many other elements, and scientists tend to study these nutrients’ effects on plants by adding inorganic fertilizer to the soil. The EPFL team takes a different approach: “In our experiment, we wanted to analyze the effects of macronutrients present in the air as a result of human activity,” says Arangio. “We hope this will give us insight into the strategies that plants use upon receiving these additional nutrients and how the nutrients affect their environments, and more generally for its feedback to ecosystem functioning. These are phenomena that we know little about but that can occur almost anywhere in the world.”