Contrasting control strategies of Spartina alterniflora reconfigure blue carbon processes and stability in salt marshes

Large-scale control of invasive Spartina alterniflora is widely implemented to restore coastal biodiversity and native habitats, yet its blue carbon consequences remain poorly resolved. Aligned with global efforts to integrate blue carbon into climate mitigation and coastal management, resolving these consequences is important for reconciling invasive-species management with carbon conservation. Here, we investigated how two contrasting control strategies—herbicide application (chemical control) and cutting combined with continuous flooding (physical control)—reconfigure blue carbon dynamics in salt marshes of eastern China, considering atmospheric carbon exchange, carbon storage, and soil carbon stability. The following results were obtained: (1) Both control strategies resulted in a significant shift from substantial net carbon uptake (–13.49 Mg C ha⁻ 1 yr⁻ 1 ) to net carbon release (1.78–4.94 Mg C ha⁻ 1 yr⁻ 1 ; P < 0.05), via distinct carbon processes. (2) Chemical control disproportionately enhanced methane (CH₄) emissions by 79.6% relative to unmanaged marshes and amplified warming potential, whereas physical control resulted in a lower global warming potential ( P < 0.05). (3) Total organic carbon density declined from 71.55 ± 5.04 Mg C ha⁻ 1 in unmanaged marshes to 53.62–55.84 Mg C ha⁻ 1 following control, with particularly severe reductions in surface soil organic carbon (SOC) content (0–30 cm: 38.3–51.5%, P < 0.05). Concurrently, the carbon pool management index (CPMI) decreased by 55.4–64.2%, indicating reduced carbon stability, which was associated with altered hydrological conditions and shifts in microbial carbon-processing potential. (4) Physical control largely retained residual carbon pools but redistributed them into more labile dissolved forms, increasing potential lateral carbon export, while chemical control maintained standing dead biomass yet accelerated SOC loss and carbon release. This study demonstrates that contrasting S. alterniflora control strategies can produce distinct carbon consequences, with greater SOC retention not necessarily corresponding to greater carbon stability. These findings underscore the importance of considering the carbon costs of intervention and the stability of retained carbon in control-strategy choice, with broader implications for S. alterniflora management across invaded regions and for efforts to reconcile invasive-plant control with long-term blue carbon conservation.