Polystyrene nanoplastics reshape the peatland plants (Sphagnum) bacteriome under simulated wet-deposition pathway: insights into unequal impact of ecological niches

Abstract

Nanoplastics (NPs) enter peatlands through atmospheric deposition, yet their effects on Sphagnum bacterial communities (SBCs) and plant-self remain unknown. We hypothesize that NPs alter the composition, structure, and co-occurrence pattern of epiphytes (Epi) and endophytes (En), thereby differentially affecting the growth and physiological performance of Sphagnum. The 30-day simulated wet deposition experiment was conducted to test this. Here, polystyrene NPs reduced the α-diversity of SBCs, unevenly reshaped the structure of Epi and En. Mfuzz clustering was used to reveal the co-abundance behavior of SBCs, and the null model found SBCs relied on stochastic assembly, formed stable Epi molecular ecological network (MEN) and connected En MEN. NPs disrupted symbiosis of SBCs, with high-abundance phyla reductions impacting MENs and low-abundance phyla affecting the inter-domain ecological network (IDEN) between Epi and En. Increasingly positive NPs (from carboxyl-modified to unmodified, and then to amino-modified NPs) further decreased SBCs abundance. Key clusters of Proteobacteria (Pro.), with α-Pro. and γ-Pro. as module hubs of MENs, and β-Pro. as a network hub in the IDEN, could reflect these changes. Additionally, NPs lowered plant spread area (P < 0.05) and chlorophyll content (P < 0.01), but the reduction in biomass was not significant. Structural equation modeling showed reduced SBCs α-diversity alleviated the NPs phytotoxicity (up to 33.31% offset), as genetic analysis revealed that methane oxidation, carbon fixation, and trace element metabolism may upregulate plant nutrient supply. Our findings offer critical insights into NPs deposition risks in remote areas and highlight the responses of plant-bacteriome symbiosis.