Difference in the sediment carbon stabilization during the early stages of mangrove restoration

Abstract

Sediment carbon fractions, representing carbon stabilization, are pivotal mechanisms underpinning long‐term carbon sequestration. However, their dynamics during the early phases of mangrove restoration remain poorly understood. In this study, sediment carbon fractions were investigated across four sites in Kandelia obovata mangrove forests: a bare flat (K0), and sites restored 2 years (K2, K. obovata propagules planted in 2022), 8 years (K8, K. obovata propagules planted in 2016), and 12 years (K12, K. obovata propagules planted in 2012), through an integrative assessment of vegetation growth parameters, sediment physicochemical properties, enzymatic activities, and organic carbon (OC) fractions. The K2 site exhibited the highest sediment labile organic carbon (LOC) content and the greatest sediment carbon destabilization (LOC/OC] ratio: 0.79), alongside lower invertase activity and higher polyphenol oxidase and catalase activities. The K12 site showed the lowest LOC/OC ratio (0.08), with higher protease activity. Sediment physicochemical properties and enzymatic activities proved to be more robust proxies of restoration trajectory than vegetation metrics. The first 8 years following planting were characterized by suppressed carbon stabilization due to increased LOC pools, followed by the recovery of stabilization by 12 years, coincident with the accumulation of recalcitrant carbon forms. This temporal pattern indicated that planting‐induced disturbance transiently impaired carbon stabilization, with subsequent forest maturation reinstating stabilization through the modulation of sediment biogeochemical conditions. Sediment carbon stabilization varied significantly during the early stages of mangrove restoration, and this process warranted greater attention in the future assessments of mangrove restoration.