Constraints on the spatial variations of soil carbon fractions in a mangrove forest in Southeast China

Abstract

Mangroves, carbon-rich ecosystems, store significant amounts of carbon in the soil to mitigate climate change. For better mangrove carbon management, the spatial distributions and driving factors of distinct soil carbon fractions, notably soil inorganic carbon (IC) and labile carbon, require clarification. Here, we quantified variations in the soil carbon fractions (total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), permanganate-oxidizable carbon (POC), and IC) with landward distance and soil depth, and identified the means by which edaphic and biotic factors affect soil carbon fractions in a mangrove forest in Southeast China. Average TOC, IC, POC, DOC, and MBC densities were 15.22 kg/m3, 1.39 kg/m3, 4.23 kg/m3, 43.49 g/m3, and 63.25 g/m3, respectively. Soil total nitrogen was the most important factor affecting TOC, POC, and MBC. Soil IC was found to be controlled by pH, and plant biomass was the main factor explaining soil DOC variation. Except for MBC, landward distance was negatively correlated with organic carbon fractions and positively correlated with IC via soil nutrients, pH, bulk density, and plant biomass. Soil depth directly or indirectly altered soil carbon fractions via soil nutrients, pH, clay, and salinity, resulting in negative relationships with TOC, POC, and MBC and a positive relationship with IC. Collectively, our results indicate that future changes in soil total nitrogen content and pH are likely to impact carbon storage in mangroves, and that the conservation of landward mangroves is important with respect to their high labile carbon contents.