Synchronic recovery of soil carbon, nitrogen, and phosphorus depends on restoration type in mangrove wetlands

Restoration has emerged as a critical need to ensure the critical function and economic benefits of mangrove ecosystems. Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) can help assess the effectiveness of restoration. However, it remains unclear whether active restoration (AR) with planting results in better recovery of these nutrients than does passive restoration (PR) without planting (natural regeneration). We empirically assessed the SOC, TN, and TP contents in four soil layers (0‒10, 10‒20, 20‒30, and 30‒40 cm) in the Qinglan Harbor mangroves of Hainan Island, China. We compared sites subjected to different pond-to-mangrove restoration methods over three years (AR and PR) to nearby reference sites with natural mangrove forests. We found that the SOC, TN, and TP contents in restored mangroves were considerably lower than those in natural mangroves, highlighting the long-term nature of ecosystem recovery. However, the nutrient content did not differ between the AR and PR sites. The scaling slopes of the C:N:P stoichiometric relationships remained consistent (slope =1) across the whole study area and at each site and soil depth, indicating tight coupling of these elements post-restoration. Soil salinity and bacterial community richness were identified as significant determinants of nutrient level. Consistent stoichiometric slopes across conditions imply a synchronized recovery of soil nutrients that is crucial for the sustainable management and restoration of mangrove ecosystems.

红树林生态系统修复已成为保障其核心生态功能与经济价值的关键需求。土壤有机碳（soil organic carbon, SOC）、全氮（total nitrogen, TN）与全磷（total phosphorus, TP）是评估修复成效的核心指标。然而，采用人工种植的主动修复（active restoration, AR）是否比无种植的被动修复（passive restoration, PR，即自然再生）更能有效促进上述营养元素的恢复，目前尚无定论。本研究以中国海南岛清澜港红树林为研究对象，实测了0-10 cm、10-20 cm、20-30 cm及30-40 cm四层土壤的SOC、TN与TP含量；将开展三年塘基转红树林修复模式的主动修复与被动修复样地，与邻近的天然红树林参照样地进行对比分析。结果表明，修复后红树林的土壤SOC、TN与TP含量显著低于天然红树林，凸显了生态系统恢复的长期性特征。但主动修复与被动修复样地间的营养元素含量并无显著差异。研究区整体、各样地及各土壤深度的碳氮磷化学计量比缩放斜率均稳定维持为1，表明修复后各营养元素间存在紧密的耦合关系。土壤盐度与细菌群落丰富度被确定为调控土壤营养水平的关键因素。不同条件下化学计量比斜率的一致性，意味着土壤营养元素实现了同步恢复，这对于红树林生态系统的可持续管理与修复具有重要的指导意义。