## 4 Impact of Plastic Particles on Soil Properties
### Impact of Plastic Particles on the Soil Microbiome and Implication for Soil Metabolism  
When MPs enter the soil ecosystem, they can negatively impact the soil's microbiome. This disruption can lead to detrimental changes in soil metabolism and an increase in soil pathogens [83], significantly affecting agricultural crop production. Therefore, the impact of MPs on soil should not be underestimated. Table S5 (SI) offers a comprehensive summary of the current knowledge on this topic. The interaction between MPs and soil microbiota is complex, influenced by numerous factors. First, factors such as soil structure, pH, and the presence of metal ions and organic chemicals significantly affect the development of microbial biofilms on MP surfaces [84]. Second, the type, shape, and size of plastic particles play crucial roles in biofilm formation [85]. Research shows [86; 87; 88; 89; 90] that MPs of different chemical composition origins create habitats for various microorganisms. The properties of these polymers, including surface roughness, free energy, specific surface area, hydrophobicity, and bioavailability influence the differentiation among microbial communities associated with different polymer types [91; 92]. This effect is a form of chemotaxis [93]. Studies summarized in Table S5 (SI) indicate that the morphology of microorganisms and their microcolonies on MP surfaces differ from those in bulk soil. The difference arises from the unique properties of MPs, particularly their hydrophobicity [77; 94], which creates distinct habitats for specific bacterial and fungal species [95]. Additionally, MPs can act as a physical barrier, limiting the movement and dispersal of soil microorganisms. They can also change the availability and distribution of nutrients in the soil [96; 97; 98]. Consequently, MPs in soil can lead to alterations in the soil microbiome composition by modifying the soil microclimate and creating new ecological niches [3; 98; 99]. While current data do not precisely describe how MPs impact the soil microbiome and subsequently affect broader properties like soil fertility (Table S5, SI), three related factors must be considered in understanding soil microbiome changes due to MP contamination (see Figure 4). The first factor concerns the destabilization of the soil microbiome structure, leading to imbalances in soil metabolic pathways. Studies suggest that MPs' presence tends to reduce the alpha diversity of bacteria and fungi in specific areas of soil while increasing the beta diversity [88; 91; 96; 100]. This indicates that while MPs reduce the diversity of bacterial and fungal genera in their immediate vicinity, they do not significantly affect the microbiome in areas without MPs. This supports the idea that MPs create distinct ecological niches with different microbiome structures compared to the surrounding soil, possibly enabling new species to colonize the soil matrix. The concept of the 'plastigh sphere', microbial communities that form biofilms on MPs' surface, is a prominent topic in environmental research. It is believed that the plastigh sphere alters soil metabolism by changing the microbiome structure and composition [96; 101; 102], leading to significant metabolic differences compared to unaffected soil, impacting nutrient availability, cycling, and microbial activity [102]. [PERSON] et al. [77] reported that the plastigh sphere can influence soil metabolism by changing the microbiome structure and composition, resulting in significant differences in metabolic pathways and functions compared to the surrounding soil that can lead to changes in nutrient availability, nutrient cycling and microbial activity in the soil. Furthermore, plastigh sphere bacteria may more significantly  
Figure 4: Summary of 93 studies from Table S5 (SI) related to impacts of microplastics in soil according to three related factors (Microbial resistance—Mr, Microbial diversity—Md, Pathogenic proliferation—P): A: Mr. B: Md + Mr. []: not mentioned. C: Md + Mr + P. D: Md + P. E: Md.