Impact of silicon nitride nanoparticles on soil organic carbon dynamics in subtropical evergreen forest ecosystems of China: An incubation study

Abstract

Ensuring the stability of soil organic carbon (SOC) is vital for effective long-term carbon storage in forest ecosystems. While nanoparticles (NPs) have shown the potential to enhance SOC stability and reduce cumulative carbon mineralization rates (CCMR) in agricultural soils, their effects on forest soils remain largely unexplored. This study addresses this gap through an incubation experiment that evaluated the impact of silicon nitride nanoparticles (Si₃N₄-NPs) at varying concentrations [control, 0 mg kg⁻¹ (NP₀); 50 mg kg⁻¹ (NP₁); 100 mg kg⁻¹ (NP₂)] on SOC stability, CCMR, enzymatic activities, and microbial diversity across three forest ecosystems in the Dinghushan region of Guangdong, China: coniferous forest (CF), mixed conifer–broadleaf forest (MCBF), and monsoon evergreen broadleaf forest (MEF). The results revealed that Si₃N₄-NP application at the NP₂ concentration significantly reduced CCMR by 40.82 % compared to the control (NP₀). Moreover, NP₂ substantially decreased the activities of key soil enzymes: β-glucosidase by 13.81 %, N-acetylglucosaminidase by 32.62 %, cellobiohydrolase by 59.12 %, and phenol oxidase by 26.40 %, relative to NP₀. The NP₂ treatment also enhanced total SOC retention by 24.62 % compared to NP₀. Within SOC fractions, NP₂ significantly impacted the less labile (C3) and non-labile (C4) fractions, which increased by 46.83 % and 57.84 %, respectively, compared to NP₀. Meanwhile, the very labile C (C1) and labile C (C2) fractions showed non-significant changes. Furthermore, the Si₃N₄-NP applications induced distinct shifts in bacterial (Actinobacteriota) and fungal (Ascomycota) microbiomes, which correlated significantly with CCMR and total SOC. These findings indicate that Si₃N₄-NPs improve SOC stability and reduce mineralization in forest soils. However, field-scale validation is essential to assess the long-term impacts of Si₃N₄-NPs on microbial communities and overall ecosystem functioning. This study highlights the significance of NP concentration and forest type in developing effective strategies for SOC management to mitigate climate change.