Is peat accumulation in mangrove swamps influenced by the “enzymic latch” mechanism?

Abstract

Mangrove swamps accumulate a significant amount (45–98 %) of organic carbon in sediments; however, there is a knowledge gap in explaining the mechanism behind this. Through the analysis of substrate samples from a red mangrove (Rhizophora mangle) swamp in southwest Florida, USA, this study investigated whether the “enzymic latch”, which suppresses decomposition in northern peatlands, is prevalent in mangrove soils. Laboratory analyses were performed to investigate the four hypotheses of the “enzymic latch”. Results showed that under aerobic conditions mangroves soil samples have significantly higher phenol oxidase activity (two-fold, p < 0.05), but lower phosphatase activity (−33 %, p < 0.05), β-glucosidase activity (−14 %) and glucosaminidase activity (−11 %) compared to anaerobic conditions. Soil samples supplemented with phenol oxidase showed significantly lower phenolic concentration (−8.3 %, p < 0.01), but increased β-glucosidase (+79 %, p < 0.05), xylosidase (+99 %, p < 0.01) and glucosaminidase (+102 %, p < 0.01) activities. Supplementation of lignin-based solution significantly lowered β-glucosidase (−55 %, p < 0.001), sulphatase (−82 %, p < 0.001) and glucosaminidase (−45 %, p < 0.01) activities. Based on these findings, it is concluded that the “enzymic latch” is highly likely to play a key role in suppressing decomposition rates in red mangrove covered areas of mangrove swamps.