Abstract: Understanding the variations of plant-soil carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) stoichiometry under N-enriched conditions is crucial for elucidating the homeostasis mechanisms of these biogenetic elements in estuarine marsh ecosystems. In this study, a field experiment with four N enrichment treatments was conducted from March 2021 to July 2023 in a typical Cyperus malaccensis marsh in the Minjiang River estuary, Southeast China. Following more than 2 yr of sustained N enrichment, this study aimed to investigate how N enrichment affects C, N, P and S concentrations and stoichiometric relationships within the plant-soil system and to elucidate the potential mechanisms underlying plant-soil elemental coupling and homeostatic adjustment. Results showed that N enrichment noticeably increased the C and P concentrations in leaves but reduced those in roots. With increasing N enrichment, the concentrations of N and S in plant organs generally increased, whereas the concentrations of C, N, P and S in soils also showed increasing trends. The ratios of C/N, C/P, C/S, N/S and P/S in plant organs and soil generally declined under N-enriched conditions, whereas those of N/P generally increased. Both N and S concentrations between plant and soil showed positive correlations, while the P concentrations between plant roots and soil exhibited negative associations, implying that the N, S and P nutrient linkages in the plant-soil system might be markedly altered by N enrichment. The overall positive correlations between the C/N, C/P and C/S ratios of plants and soil showed a pivotal mechanism of plant-soil feedback, highlighting the impacts of soil N, P and S availability on plant nutrient absorption. Concurrently, the positive correlations of plant-soil N/S ratios indicated a relative balance relationship and tightly coupled synergistic mechanism between N and S in the plant-soil system. This study found that, under N-enriched scenarios, the imbalances of C, N, P and S stoichiometry (especially N and S) within the plant-soil system of C. malaccensis marsh might be mitigated by their potential positive feedback loop, which probably re-established the ecosystem homeostasis.