Warming stimulates mangrove carbon sequestration in rising sea level at their northern limit: An in situ simulation

Global warming and sea-level rise are directly influencing the growth, distribution, and greenhouse gas emissions of mangrove forests. However, mangrove forests growing at their latitudinal limits are relatively susceptible to warming; nevertheless, few studies have focused on GHG emissions of latitudinal limits mangrove forests as related to global climate change. To address this knowledge gap, a multiyear in situ control experiment was established in a restored plantation at the northern distribution limit of Kandelia obovata, the most cold-tolerant mangrove species in China, to simulate both warming and sea-level rise. We investigated the growth patterns and sediment greenhouse gas emissions of a K. obovata population and identified the primary factors contributing to these changes. The results showed that warming and moderate sea-level rise enhanced biomass by more than 18%, indicating that warming stimulated plant growth while excessive sea-level rise inhibited it. The sediment greenhouse gas emissions ranged from 45.5 to 484.6 mgCO₂ m⁻² h⁻¹, 5.6 to 590.3 μgCH₄ m⁻² h⁻¹, and 11.4 to 385 μgN₂O m⁻² h⁻¹, which increased with warming while decreased with sea-level rise, acting as the net source of greenhouse gas emission. Our study predicted that sea-level rise, while directly changing sediment properties, had combined effects with warming on these studied mangrove forests that were predicted to emit more greenhouse gases from sediments in the future. These findings indicated that K. obovata plantations within their latitudinal limits tend to accumulate more CO₂ for biomass carbon storage under warming conditions, while stimulating sediment greenhouse gas emissions, which will offset their climate mitigating effect in future climatic scenarios.