Smallest microplastics intensify maize yield decline, soil processes and consequent global warming potential.

Area of Science:

• Environmental Science
• Soil Science
• Agricultural Science

Background:

• Microplastic pollution poses a significant threat to global agroecosystems, affecting soil processes and crop development.
• The impact of microplastics on soil is potentially size-dependent, but field data are limited.

Purpose of the Study:

• To investigate the effects of different microplastic types (polyethylene, polystyrene) and sizes (75, 150, 300 µm) on a soil-maize agroecosystem under field conditions.
• To assess microplastic interactions with soil properties, biogeochemical cycling, greenhouse gas emissions, and maize productivity.

Main Methods:

• Field experiment involving the addition of polyethylene and polystyrene microplastics of varying sizes to maize cultivation soils.
• Analysis of soil carbon, nitrogen, biogeochemical cycling, CO2 and N2O emissions, and maize yield.
• Scanning electron microscopy to observe microplastic uptake and translocation in maize plants.

Main Results:

• Microplastic contamination generally increased soil carbon, nitrogen, and biogeochemical cycling.
• Polyethylene microplastics, especially the smallest size (75 µm), were more detrimental than polystyrene.
• Smallest polyethylene microplastics (75 µm) caused a two-fold increase in CO2 and N2O emissions, reduced soil carbon and nitrogen pools by 1-1.5%, and decreased maize productivity by approximately two-fold.
• Microplastics were observed to be taken up by maize roots and translocated to stems and leaves.

Conclusions:

• Microplastic contamination, particularly smaller sizes, significantly alters soil biogeochemical processes, increases greenhouse gas emissions, and reduces crop yield.
• The findings raise concerns for soil health, food security, and climate change, with potential for increased impacts as microplastics degrade.
• Soil microplastic pollution poses a growing threat to planetary boundaries and sustainable agriculture.