The "enzymic latch" mechanism in various mangrove swamps and its controlling factors

Mangrove swamps cover a very small area of the land surface ( 0.1%), but they store 5-10 Pg of carbon globally. Recent studies suggested that the "enzymic latch" mechanism may play a substantial role in the accumulation of soil organic matter in mangrove swamps. The waterlogged anoxic soil of mangrove swamps inhibits the activity of phenol oxidase and accumulates phenolic materials, which suppresses the activity of hydrolases, thereby reducing decomposition of soil organic matter. However, there is no global-scale comparison of the activity of extracellular enzymes (hydrolases and phenol oxidase) in various mangrove swamps. In this study, we attempted to test whether "enzymic latch" mechanism is involved in C accumulation in various mangrove swamps. We analyzed chemical properties and extracellular enzyme activities of the soil samples from Okinawa in Japan and Shenzhen in China. The activities of all the hydrolases had significant positive correlations with the activity of phenol oxidase in both Okinawa and Shenzhen. The results of structural equation modeling suggested that the "enzymic latch" mechanism is substantially involved in the accumulation of soil organic matter in mangrove swamps. In particular, soil moisture and pH may take an important role in the mechanism. In addition, a ratio of abundance of fungi to bacteria had a strong correlation to the activities of hydrolases.