A review of properties of organic matter fractions in soils of mangrove wetlands: Implications for carbon storage

Soil organic matter (SOM) is partitioned among structurally and functionally distinct pools. Information on these different SOM fractions in mangrove environments are emerging and the three-pool classification of SOM into particulate organic matter (POM), mineral-associated organic matter (MAOM) and dissolved organic matter (DOM) has become the operational framework of most mangrove studies. The differences in degree of protection provided by physical and chemical mechanisms against microbial decomposition of these fractions lay a strong foundation for empirical SOM studies in mangroves. In this review, we discuss the formation and transformation pathways and stabilization mechanisms of these SOM fractions in mangroves under different environmental conditions. We also show that further studies on lesser-known forms of SOM such as FeS-MAOM, pyrite-MAOM, and Al-MAOM could set a path better understanding long-term stabilization of mangrove SOM. The binding capacity of sediments with DOM points to a hidden potential of mangroves to store soil carbon, which is not accounted in traditional sediment and carbon accumulation models. In addition, incorporating the feedback from SOM fractions to different physiochemical and climatic conditions can improve carbon dynamic projections in mangrove ecosystems using carbon models. • Mangrove soils contain particulate, mineral-associated, and dissolved organic matter fractions. • In low sediment supply conditions, particulate organic matter (POM) fractions dominate the soils. • Metal and clay mediated mechanisms preserve soil C as mineral-associated organic matter (MAOM). • Dissolved organic matter (DOM) fraction is important for MAOM formation. • Soil organic matter fractionation elucidates the capacity of mangroves for long-term carbon storage.