<p>Biochar has been proposed as a soil amendment in vegetable fields, where the widespread use of plastic film leads to significant retention of microplastics (MPs) in the soil. However, the interactive effect of biochar and MPs on plant growth and soil functions remains poorly understood. Here, we conducted a pot experiment to examine the effects of biochar application in the presence of conventional and biodegradable microplastics (0.05% <i>w/w</i>) on the growth of coriander, soil nitrogen (N) cycling processes, and microbial communities. The results showed that biochar application increased aboveground biomass by increasing plant available N of NH₄⁺, regardless of the presence&#xa0;of MPs. Biochar also significantly reduced soil nitrous oxide (N₂O) emissions by an average of 16% without MPs. However, when MPs were present, the effect of biochar on N₂O emissions was lessened depending on the MP type. Polylactic acid consistently reduced soil N₂O emissions and the abundance of N₂O production genes, irrespective of biochar application. Conversely, polyethylene without biochar reduced N₂O emissions primarily by inhibiting N-related functional genes responsible for nitrification and denitrification. This inhibitory effect was reversed when biochar was applied, leading to a 26% increase in N₂O emissions due to increased <i>nifH</i> and <i>nirK</i> gene abundance. Although biochar and MPs did not significantly alter microbial α-diversity, they altered the composition and structure of bacterial and fungal communities, linked to changes in soil N turnover. Our study underscores the critical role of MP type in assessing the effects of biochar on soil N cycling and N₂O emissions. Consequently, plastic pollution may complicate the ability of biochar to improve plant growth and soil functions, depending on the characteristics of the MPs.</p> Graphical Abstract <p></p>