Microplastics lead to behavioral disorders in soil nematode movement, foraging and food choice

Generally, studies related to microplastic (MP) effects on soil nematodes use agar plate assays, while test conditions with soil are scarce. The overlooked fact is that nematodes can behave differently in their natural soil environment. This study investigated three common soil species, Acrobeloides buetschlii , Cephalobus sp., and Diploscapter coronatus, and the model nematode Caenorhabditis elegans in a modular soil system. The responses in movement, foraging and food choice to two MP types, i.e. non-biodegradable low-density polyethylene (LDPE) and a biodegradable blend of poly(lactic acid) and poly(butylene adipate- co -terephthalate) (PLA/PBAT), were evaluated. Additionally, food choice assays on agar plates were performed to compare these with the test under soil conditions. MP presence in soil reduced nematode movement, with the extent of effect depending on MP amount and nematode species. The foraging behavior of A . buetschlii and C . elegans was more affected by MP than that of Cephalobus sp. and D. coronatus . Soil phospholipid fatty acid analysis indicated that microbial diet was consumed by all nematodes, most prominent by D. coronatus in the presence of LDPE. The food choice index in soil was not dependent on MP type and nematode species, while on agar plate it was affected by all factors: MP amount and type, nematode species and time. Linear regression revealed a dose-response relationship between the choice index on agar and increasing MP amounts. In conclusion, MPs in soil hampered nematode movement and had the potential to change food foraging and choice. The effects of MPs in agar plate and soil assays differed, highlighting the importance of using semi-natural test conditions. Finally, species-specific responses drive the ecological impact of MPs on soil nematodes. Note:A non-biodegradable plastic of low-density polyethylene (LDPE) and a blend of biodegradable plastics of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were tested in soil using four nematode species. Movement, foraging and food choice were evaluated. • Microplastic reduced nematode movement with species-specific response • Foraging had a potential to be affected by microplastic • Food choice differed between agar plates and soil conditions • Microplastic amount and type, nematode species, and observation time influenced significantly food choice on agar plates