Abstract
Nitrogen (N) deposition and carbon (C) addition significantly influence the dynamics of plant-microbe interactions, particularly altering the symbiotic relationship between plants and arbuscular mycorrhizal fungi (AMF). However, the effects and underlying mechanisms of labile C input on the relationship between AMF and various plant species in a nitrogen-enriched environment remain a knowledge gap. A seven-year field experiment was conducted to examine how six levels of N and three levels of labile C addition impact AMF colonization in four key plant species: Leymus chinensis (Trin. ex Bunge) Tzvelev, Stipa baicalensis Roshev., Thermopsis lanceolata R. Br. and Potentilla bifurca Linn. Our results showed that N and C additions exert significantly different effects on the relationship between AMF and various plant species. Labile C addition mitigated historical N negative effects, particularly for S. baicalensis, enhancing AMF infection and promoting nutrient exchange under high-N and low-C conditions. The relationship between AMF and both L. chinensis and T. lanceolata changed to weak mutualism under low-N and high-C conditions, with significant decreases in vesicular and arbuscular abundance. Plant root stoichiometry plays a critical role in modulating AMF symbiosis, particularly under high-N and -C conditions, as reflected in the increased AMF infection observed in T. lanceolata and P. bifurca. Our findings emphasize the species-specific and nutrient-dependent AMF symbiosis, revealing that targeted C input can mitigate the legacy effects of N enrichment. Effective nutrient management is of crucial importance for ecological restoration efforts in temperate grasslands affected by long-term N enrichment.