Global overview on nitrogen dynamics in mangroves and consequences of increasing nitrogen availability for these systems

Background and scope Mangroves provide several ecosystem goods and services to society. However, mangroves are frequently subjected to land conversion, overharvesting, and pollution including increased nitrogen (N) availability. Aiming to provide useful information to predict effects of N enrichment on mangroves, we evaluated literature data on N transformation rates in sediment, dissolved N (DN) fluxes across the sedimentwater interface, and natural abundance of N stable isotopes (δ¹⁵N) in the sediment-plant system in conserved mangroves and those subjected to anthropogenic N enrichment. Conclusions Mangroves and terrestrial tropical forests exhibit a great overlap in rates of biological N fixation (BNF) and denitrification and nitrous oxide flux rates. Mangroves can be highly efficient users of DN forms from tidal waters, related to rapid plant uptake and an efficient conservation of DN in sediment by microbial activity. The main factors limiting N transformation rates in mangrove sediment are inorganic DN availability and microbial immobilization. The δ¹⁵N data indicated that fringe forests exhibit higher N transformation rates in sediment and higher N losses to atmosphere, compared to other mangrove types. Except for BNF, all other N transformation and flux rates seem to be intensified by increasing N availability.