Cycling and Global Fluxes of Nitrogen in Mangroves

抄録

Recent advances necessitate a critical reappraisal of nitrogen cycling in mangrove ecosystems. Nitrogen concentrations in soil, water and vegetation are low, but N-use and recycling efficiencies are high and N residence times are short, driven by rapid forest production and the need to conserve N. Most mangrove- associated fauna preferentially assimilate benthic algae, phytoplankton, algal detritus or complex mixtures of these forms to meet N demand. Consumer preferences, locations and types of habitat, and the relative availability of other foods determine the trophic significance of mangrove litter. A nitrogen mass balance model of the world’s mangrove forests indicates that: (1) 2687 Gg N yr^-1 is required to sustain global man grove net primary production (NPP); (2) N burial is ≈ 25% of total N input; (3) N2 fixation is ≤ 5% of total N input; (4) production in roots and litter account for 40% and 50% of mangrove NPP, respectively; (5) tidal export equates to ≈ 55% of N input; and (6) denitrification and N2O effluxes account for < 10% of total N losses. Despite proportionately large tidal losses, the global flux of nitrogen in mangrove forests is roughly in balance due to multiple adaptations and strategies to efficiently use and retain nitrogen.