Mowing enhances the sensitivity of arbuscular mycorrhizal mycelial carbon pools to nitrogen enrichment in grassland ecosystem

Abstract Arbuscular mycorrhizal (AM) fungi are pivotal mediators of plant nutrient acquisition and depend on host‐derived carbon (C). However, how plant C allocation to AM fungi responds to below‐ground (e.g. soil nutrient availability) and above‐ground drivers (e.g. plant C availability) remains poorly understood. We used a long‐term (2015–2023) factorial field experiment in a meadow steppe in northern China, with six N addition rates (0, 2, 5, 10, 20 and 50 g N m −2 yr. −1 ) crossed with mowing (mown vs. unmown) to test how N enrichment and mowing alter plant–fungus C allocation strategies. In 2023, plant and fungal biomass, C content and AM fungal community composition were quantified. In unmown plots, plants preferentially allocated C to roots while maintaining relatively stable C allocation to mycelium, although mycelium biomass declined with N addition. By contrast, mowing intensified plant P limitation and altered C allocation strategies, with declines in mycelium biomass becoming evident only under relatively high‐N levels (above 10 g N m −2 yr. −1 ). In mown plots, receiving low‐N inputs increased C allocation to mycelium, whereas at higher N inputs, soil acidification sharply reduced C transfer to fungi. Changes in C allocation were tightly associated with the abundance of the dominant taxon Glomus VT387. Synthesis . Together, our findings demonstrate that mowing mediates N addition effects on plant C allocation to AM fungi, thereby providing mechanistic insight into plant–microbial interactions in grassland subject to global change and management.