Urbanization-Driven Anthropogenic and Environmental Factors Shape Soil Dissolved Organic Matter in Mangrove Ecosystems

Abstract

Mangrove ecosystems play a critical role in supporting ecological service values and regulating the global carbon cycle. They have become one of the most highly vulnerable ecosystems in the Anthropocene under the long-term influence of diverse human perturbations. Soil dissolved organic matter (DOM) is an active fraction within the carbon cycle in mangrove ecosystems. However, it remains unclear how human perturbations regulate DOM dynamics. Here, we used the fluorescence method and structural equation modeling to quantify the anthropogenic and environmental influence on soil DOM across the urban development gradient on a national scale in China. Anthropogenic activities (urban construction and sewage discharge) and environmental factors (salinity, metals, pH, and soil organic carbon) were striking forces that shaped DOM quality in mangrove soils. Both indirect and direct effects played critical roles in the soil DOM heterogeneity across the gradient of urbanization. Environmental factors can act as cofactors mediating human impact on DOM pools and as promoters transforming soil DOM in mangroves. Our study provided novel insights into the relationship between coastal developments and mangrove soil DOM heterogeneity and improved knowledge of coastal ecosystems as blue carbon sinks.