Plant invasion reshapes the latitudinal pattern of soil microbial necromass and its contribution to soil organic carbon in coastal wetlands

An emerging consensus is reached that microbial necromass carbon (MNC) significantly contributes to the formation and stabilization of soil organic carbon (SOC). Yet less is known about how plant invasion regulates MNC accumulation in coastal “Blue Carbon” ecosystems, and the environmental and microbial controls on MNC distribution across large scales are not well revealed. Here, we evaluated the contribution of MNC to SOC across a broad scale in coastal habitats including salt marshes and mangroves before and after exotic Spartina alterniflora Loisel. invasion. Specifically, we explored the influence of biotic and abiotic factors on soil MNC accumulation in paired native and invaded soils. The MNC pool was quantitatively inferred by analyzing soil microbial amino sugar content. We found that soil MNC contents significantly increased from temperate salt marshes to tropical mangroves, and the average MNC in mangrove soils was 1.3–5.0 times that in salt marshes. In native soils, the estimated contribution of MNC to SOC decreased along the climatic gradient, ranging from 13.4% to 61.2%. However, the invasion homogenized the latitudinal variation of MNC/SOC as the invasion reduced the contribution of soil MNC to SOC in salt marshes but increased the accumulation of microbial residues in mangrove habitats. Furthermore, MNC derived from fungi was 3.6–19.0 times that of bacteria and the contribution of fungal MNC to total MNC decreased against the increasing mean annual temperatures. The soil carbon-to-nitrogen ratio and soil texture had significant negative effects on MNC/SOC, indicating that soil nutrient status and physical protection are vital abiotic controls in regulating MNC accumulation in coastal wetlands. In summary, these findings revealed that MNC considerably contributes to soil carbon sequestration in coastal ecosystems, and emphasized that plant invasion can change the latitudinal pattern of MNC accumulation by altering environmental and microbial attributes and thus influencing soil carbon stabilization.