Coastal wetlands are crucial global "blue carbon" reservoirs, within which allochthonous pre-aged carbon derived from land-ocean transport can account for over 50% of the total carbon. However, the storage mechanisms of this pre-aged carbon within coastal ecosystems remain unclear. In particular, the interplay between mineral association and microbial processing represents a significant knowledge gap in blue carbon science. There is an urgent need to establish relevant mechanistic models to guide blue carbon management and assessment.

Associate Professor Yuan Li and Professor Guangxuan Han from the Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), in collaboration with Professor Zhaoliang Song from Tianjin University, Professor Yongming Luo from the Institute of Soil Science, CAS, and several other domestic and international institutions, conducted a systematic survey of 36 mangrove and saltmarsh wetlands across a 20-degree latitudinal gradient along the Chinese coastline. By comprehensively analyzing topsoils and 1-meter-deep sediment cores, combined with ¹⁴C isotopic dating, biomarker analysis, and model interpretation, the research team systematically revealed the joint regulatory mechanisms of mineral-microbial synergy on blue carbon turnover and storage.

Figure 1 Sampling locations and the distribution of soil organic carbon characteristics in coastal mangroves and saltmarshes.

The study found significant differences in carbon turnover times between saltmarshes and mangroves. Saltmarsh wetlands, characterized by high mineral accretion rates, exhibited significantly longer soil organic carbon (SOC) turnover times than mangroves (averaging ~2,200 years vs. ~500 years in topsoils). This disparity is primarily attributed to higher proportions of pre-aged carbon (~50%) and petrogenic carbon (fossil carbon) (~20%) in saltmarshes. Regarding fractional distribution, the proportion of mineral-associated organic carbon (MAOC) in saltmarsh topsoils reached 81.5%, significantly higher than the 66.6% found in mangroves. Furthermore, saltmarshes contained higher proportions of lignin phenols (3.5% vs. 3.1%) and microbial necromass carbon (21% vs. 14%). These findings indicate that in ecosystems dominated by allochthonous inputs, SOC is primarily derived from a highly degraded, pre-aged carbon pool.

Figure 2 ¹⁴C-based soil organic carbon composition and turnover in coastal mangroves and saltmarshes.

Further analyses utilizing linear mixed-effects models (LMM) and structural equation modeling (SEM) revealed a significant, depth-dependent shift in the mineral-microbial synergy. In topsoils (0–20 cm), where fresh organic matter inputs are abundant, the accumulation of microbial necromass carbon is the key driver of carbon turnover (coefficient = 0.36). In contrast, in deep soils (1 m), the degree of lignin degradation supersedes microbial biomass to become the primary predictor dictating the multi-millennial persistence of organic carbon (coefficient = 0.45).

Figure 3 Controlling factors of soil organic carbon turnover in topsoils and deep soils of coastal mangroves and saltmarshes.

This study proposes a novel blue carbon sequestration mechanism based on joint mineral-microbial regulation: microbes transform and degrade allochthonous organic matter into relatively stable components, which are subsequently physically protected by reactive minerals. This finding challenges the traditional paradigm that blue carbon storage is predominantly driven by the direct burial of recent plant biomass. It demonstrates the critical role of coupled mineral-microbial processes in the sequestration of pre-aged allochthonous carbon, emphasizing that future blue carbon accounting and ecological management frameworks must incorporate this mechanism.

Figure 4 Conceptual model of mineral-microbial synergy driving the composition and turnover of coastal blue carbon.

The research findings were published in the journal Global Change Biology. This study was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Natural Science Foundation of Shandong Province.

Paper Information:

Yuan Li, Chuancheng Fu, Peng Ren, Zhaoliang Song, Lingfang Ni, Ting Wang, Changxun Yu, Ji Chen, Laodong Guo, Iain P. Hartley, Ding He, Xiaoguang Ouyang, Wei Zhi, Shaopan Xia, Weiqi Wang, Mingliang Zhao, Guangxuan Han, Yongming Luo. Mineral Association and Microbial Processing Jointly Prolong Carbon Turnover in Coastal Wetlands. Global Change Biology, 2026, 32: e70763. https://doi.org/10.1111/gcb.70763