As an agent interfering with the biophysical environment perceived by roots, microplastics have the potential to affect the whole plant performance, and our experiments started to demonstrate how.
Have you ever tried to go jogging wearing flip-flops? Or you are on a business trip to a beautiful mountainous area and then you realize to have forgotten the hiking boots. All left are those serious and stiff social shoes. Would you still go? Most of us, at some point, were limited by not having the right footwear for a desirable activity. Not wearing the right shoes will likely not kill you (although some serious accidents have been attributed to the footwear). However, it can certainly cause great discomfort, affect your performance, and influence your decision on engaging several activities essential for your general well-being. We all know why this happens: the footwear determines the environment directly interacting with our feet, and thus influences the function of support and motion that these parts of our body perform. Thus, your ability to remain upstanding or how comfortably (or oddly) you walk can be a direct whole-body consequence of the what is around your feet.
Interestingly, a very similar analogy could be made for the effects of microplastics in plants according to our recent study entitled “Microplastics can change soil properties and affect plant performance” published at Environmental Science &Technology. Everything started in 2018 when we first proposed in a review published at Global Change Biology that microplastics could represent a threat to terrestrial ecosystems by changing the properties of the soil biophysical environment. Later, we could demonstrate that microplastics could change very fundamental environmental properties of the soil that would potentially interact with the roots of plants. At that point, we learned that microplastics could influence how tight or loose would be the environment that roots would face (e.g. via soil bulk density). We also learned that microplastics could affect the resistance of soil to disaggregation and how much water the soil would hold. As an agent interfering with the biophysical environment perceived by roots, microplastics have the potential to affect the whole plant performance, and our experiments started to demonstrate how. In other words, we knew that some effects could happen, but had no data about how the changes in soil properties caused by microplastics could affect soil-plant interactions.
We wanted to know what would be the impacts of this microplastic footwear in the soil environment perceived by the plant (including soil properties and microbial communities).
We wanted to know what would be the impacts of this microplastic footwear in the soil environment perceived by the plant (including soil properties and microbial communities). So we started an experiment using spring onions as a plant model. Also, we were interested in how those shifts would translate into impacts on their roots and whole plant. It is very important to know these impacts since microplastic pollution continues to increase and environmental concentrations might be as high as 7% of soils. Moreover, such relationships among the soil, the roots, and the whole plants are determining the function of entire plant communities and influencing all terrestrial ecosystems. Thus we investigated the impacts of six different microplastics (polyester fibers, polyamide beads, and four fragment types- polyethylene, PET, polypropylene, and polystyrene) on various parameters that inform about soil health and plant performance.
We observed several significant changes in the plants that were caused by the microplastic exposure at levels as low as 0.2% for polyester fibers. These included shifts of root characteristics that impacted plant growth (biomass), as well as the proportions between the different above and below-ground parts of the plants. Remarkably, each microplastic caused a very different effect, with the primary polyamide beads even increasing plant biomass. These novel results enabled us to formulate a conceptual causal model of how certain properties, particularly shape/size and composition affected soil and plants. Just as sneakers, sandals, heels, and boots will make some activities more favorable than others by altering the interaction of terrain and floors with our feet, each microplastic type had its own characteristic effects on the interaction of plant roots and soil.
We observed several significant changes in the plants that were caused by the microplastic exposure at levels as low as 0.2% for polyester fibers. These included shifts of root characteristics that impacted plant growth...
Such straight analogy of roots and feet can be misleading in a point, however. Roots are actually much more important, and performing a broader range of vital functions for the plant than the lower extremities of our legs is doing for us. In fact, it seems that the microplastic contamination would interfere with the plant performance by affecting how roots physically support plants but also in its functional role in absorbing water and nutrients. That is because, microplastics that caused more effects were those affecting more drastically soil structure, chemistry, and water cycling.
We did not detect any lethal effects, but microplastic-exposed spring onions were clearly functioning differently. And now our next question in this direction is whether natural plant communities, where each individual is competing for water and nutrients, could be affected by microplastic exposure. The first results are yielding very interesting insights. In any case, our unprecedented results imply that the pervasive contamination of soils with microplastics may have consequences for plant performance, and thus, for the terrestrial ecosystems.