Patterns and drivers of soil organic carbon fractions and persistence in coastal wetlands of China

Abstract

Coastal wetlands have disproportionately high carbon (C) sequestration rates and long-term sustainable C sequestration capacity, contributing to the mitigation of global climate change. Previous studies have mainly focused on the assessment of bulk soil organic C (SOC) in coastal wetlands, neglecting the form in which C is stored, its stability and driving factors, which hinders our in-depth understanding of C sequestration capacity and underlying mechanisms. In this study, we sampled 157 plots across coastal wetlands in China, covering tropical, subtropical, and temperate climates to gain a detailed understanding of the distribution, stability, and control mechanisms of SOC fractions. Our results showed that the SOC in the topsoil (0–10 cm) was co-dominated by mineral-associated organic C (MAOC) and particulate organic C (POC) in mudflats, temperate and subtropical salt marshes, and subtropical mangroves, but not in tropical mangroves. The content of dissolved organic C (DOC, 0.12 ± 0.08 g kg⁻¹) was only 1.15 ± 0.06 % of bulk SOC. The POC became more dominant relative to MAOC and DOC as SOC content increased. We found that soil properties (total nitrogen, bulk density, and particle size, etc), were the primary explanatory variables for SOC fractions content and persistence, accounting for 58 %, 64 %, 38 %, 53 %, and 34 % of total variation in MAOC, POC, DOC, MAOC/SOC, and C/N, respectively. Although climate and vegetation factors did not directly control C contents in soil matrix and persistence, they interacted strongly with edaphic variables explaining 8 %, 16 %, 11 %, 12 %, and 13 % of the total variation in the above variables, respectively. Our results suggest that the increase in SOC, especially POC, reduced its persistence, so the implementation of C management strategies in coastal wetlands should integrate SOC sequestration and stability to maximize benefits.