Spatial distribution and driving factors of microbial necromass carbon in coastal wetlands of China

Microbial necromass carbon (MNC) constitutes a vital component of soil
carbon pools and is integral to the global soil carbon cycle. However, the
mechanisms driving MNC accumulation in large-scale coastal wetlands,
particularly across different habitat types (such as mangroves,
saltmarshes, and mudflats), remain poorly understood. In this study, we
conducted extensive sampling across 101 sites in China's coastal
wetlands, covering a latitudinal gradient of over 2,500 km, to investigate
variations in MNC and its drivers. Additionally, we integrated global data
from farmland, forest, grassland, and coastal wetland habitats for a
comparative analysis to explore the specificity of carbon storage
mechanisms in coastal wetlands. Our results reveal significant differences
in MNC content among the three coastal wetland habitats, with mangroves
exhibiting the highest MNC levels and saltmarshes the lowest. We found
that primary productivity, especially plant biomass, is the dominant
driver of MNC accumulation in coastal wetlands, while climatic factors
have an indirect effect. Furthermore, after accounting for the influence
of plant biomass, we observed that edaphic properties also played an
important role in driving MNC accumulation within mudflat and saltmarsh
habitat. Compared to other habitats, i.e., grasslands, forests, and
farmlands, coastal wetlands exhibited lower MNC levels (8.44 mg/g) and a
reduced contribution to soil organic carbon (32.16%). In conclusion, these
findings demonstrate that plant primary productivity significantly
regulates MNC accumulation in coastal wetlands. Furthermore, coastal
wetlands exhibit distinct characteristics in carbon storage compared to
other ecosystems, underscoring the unique role of blue carbon ecosystems
in the soil carbon cycle.