Deciphering microplastic ecotoxicology:impacts on crops and soil ecosystem functions

Review on microplastic toxicity in agroecosystems is scarce.Thus,we develop a conceptual model(based on literature to date)that describes various microplastic effects using a size-scale.We also classify crops depending on their observed responses,and discuss several conceptual mechanisms of soil functions.The model shows that microplastic effects on crops can be positive,toxic,lethal and no-effect.Predominantly,microfibers in a wide range of sizes can positively affect crops.However,toxic effects of microplastics with/without other pollutants are more common at different sizes.Surprisingly,biodegradable plastic effects are lethal,calling into question their environmental friendliness.No-effect on crops is also possible but less observed.Unlike other crops(e.g.,wheat,maize and bean),only onion seems resistant to microplastics.Crop uptake of micro/nanoplastic demands a clear benchmark to ensure food-safety.Furthermore,mixed effects are observed on soil functions.Alternation in soil enzymes and litter decomposition can affect nutrients and organic matter biogeochemistry.Hydrophobicity can be induced by increasing evaporation.Shifts in microbial community structure and activities are inevitable.

Phosphorus-Mobilizing Rhizobacterial Strain Bacillus cereus GS6 Improves Symbiotic Efficiency of Soybean on an Aridisol Amended with Phosphorus-Enriched Compost

Legume plants are an essential component of sustainable farming systems.Phosphorus(P) deficiency is a significant constraint for legume production, especially in nutrient-poor soils of arid and semi-arid regions.In the present study, we conducted a pot experiment to evaluate the effects of a phosphorus-mobilizing plant-growth promoting rhizobacterial strain Bacillus cereus GS6, either alone or combined with phosphate-enriched compost(PEC) on the symbiotic(nodulation-N_2 fixation) performance of soybean(Glycine max(L.) Merr.) on an Aridisol.The PEC was produced by composting food waste with addition of single super phosphate.The bacterial strain B.cereus GS6 showed considerable potential for P solubilization and mobilization by releasing carboxylates in insoluble P(rock phosphate)-enriched medium.Inoculation of B.cereus GS6 in combination with PEC application significantly improved nodulation and nodule N_2 fixation efficiency.Compared to the control(without B.cereus GS6 and PEC), the combined application of B.cereus GS6 with PEC resulted in significantly higher accumulation of nitrogen(N), P, and potassium(K) in grain, shoot, and nodule.The N:P and P:K ratios in nodules were significantly altered by the application of PEC and B.cereus GS6, which reflected the important roles of P and K in symbiotic performance of soybean.The combined application of PEC and B.cereus GS6 also significantly increased the soil dehydrogenase and phosphomonoesterase activities, as well as the soil available N, P, and K contents.Significant positive relationships were found between soil organic carbon(C) content, dehydrogenase and phosphomonoesterase activities, and available N, P, and K contents.This study suggests that inoculation of P-mobilizing rhizobacteria, such as B.cereus GS6, in combination with PEC application might enhance legume productivity by improving nodulation and nodule N_2 fixation efficiency.