The importance of moisture in regulating soil organic carbon content based on a comparison of “enzymic latch” and “iron gate” in Zoige Plateau peatland

Due to the enormous amount of carbon (C) stored in peatlands, understanding the regulator of soil organic carbon (SOC) in peatlands is critical for global C cycling. Currently, "enzymic latch" and "iron gate" are the frequently debated mechanisms that propose phenol oxidase (PHO) and Fe2+ as important regulators driving SOC cycling in peatland. Therefore, this study compared "enzymic latch" and "iron gate" in the same peatland (Zoige Plateau, the largest peatland in China) to figure out the crucial regulator of SOC content via investigating the interrelationships among soil properties, C-related enzymes, phenolics, and iron (Fe) oxides. Moreover, waterlogged and non-waterlogged soils were chosen to take samples in both dry and wet season to understand the potential role of moisture in regulating SOC content. It was found that the contents of dissolved organic C, phenolics, SOC, Fe oxides, and β-glucosidase (BG) activities in waterlogged soils were higher than those in non-waterlogged soils. Compared to the dry season, soils in the wet season had higher phenolics, SOC, and Fe oxides contents. Also, this study observed an insignificant relationship between PHO and SOC (p > 0.05) and the small amounts of Fe2+ to total Fe (<2‰) in soils. Meanwhile, the highest effect of moisture (0.89) and negligible effect of PHO (0.04) and Fe2+ (-0.08) on SOC based on pathway analysis suggested that moisture might be the crucial regulator of SOC. Furthermore, pathway analysis implied that moisture could indirectly affect SOC by adjusting BG (p < 0.05) and soluble phenolics (p < 0.05). This study provided valuable information for understanding the importance of moisture in driving C cycling and helping against soil C loss by moisture management in Zoige Plateau.