Microplastic effects on carbon cycling processes in soils.

Matthias C Rillig,Johannes Lehmann,Eva Leifheit

doi:10.1371/journal.pbio.3001130

Abstract

Microplastics (MPs), plastic particles <5 mm, are found in environments, including terrestrial ecosystems, planetwide. Most research so far has focused on ecotoxicology, examining effects on performance of soil biota in controlled settings. As research pivots to a more ecosystem and global change perspective, questions about soil-borne biogeochemical cycles become important. MPs can affect the carbon cycle in numerous ways, for example, by being carbon themselves and by influencing soil microbial processes, plant growth, or litter decomposition. Great uncertainty surrounds nano-sized plastic particles, an expected by-product of further fragmentation of MPs. A major concerted effort is required to understand the pervasive effects of MPs on the functioning of soils and terrestrial ecosystems; importantly, such research needs to capture the immense diversity of these particles in terms of chemistry, aging, size, and shape.

Highlights

Microplastic as a factor of global changePlastic in the environment is an issue that was first reported from ocean observations several decades ago [1,2,3]
While this addition to the canon of factors of global change might take time to be fully appreciated [11], it is important for MP research. This is the case for 3 reasons: (i) target concentrations of MP for experiments should not be just informed by current levels of contamination, but should be based on future, presumably higher levels. (ii) Proximate effects can be nominally positive, just as is the case for other factors of global change, such as elevated CO2 or warming. This does not mean that the effects are desirable; it merely means that increases in certain performance parameters can occur, but that these still represent deviations from the natural state. (iii) This realization of MP as a factor of global change shifts the research focus more toward ecosystems [12], with questions about feedbacks to the Earth system becoming more important and how MP might alter the functioning of terrestrial ecosystems, the cycling of nutrients and carbon
We finish by briefly discussing nanoplastics (NPs) in a separate section, since effects are primarily expected to be toxicological in nature