Functional Resistance of Microbiome to Differently Charged Nanoplastics in Rhizosphere Hotspots Soil

Nanoplastics (NPs) pose greater soil ecological risks than microplastics due to their surface charge-dependent uptake, transport, and accumulation in plants. However, how differently charged NPs affect maize growth and microbial functional resistance in rhizosphere hotspots remains unclear. Here, we investigated the effect of positively (PS-NH₂) and negatively (PS-SO₃H) charged NPs on maize growth, enzyme activities and gene abundance, microbial resistance, and functional properties in acidic soil using soil zymography, 16S rRNA sequencing, and metagenomics. PS-NH₂ showed stronger inhibitory effects on maize growth than PS-SO₃H, mainly through reducing microbial diversity and weakening N and P cycling-related enzyme activities and resistance. Conversely, PS-SO₃H maintained higher microbial resistance. Functional hotspots microbial species (particularly in Actinobacteria) alleviated NPs toxicity by accelerating N and P cycling to meet the demand for nutrients limiting maize growth. This study provides a mechanistic basis for assessing soil NPs risk with implications for agricultural sustainability and food safety.