Nitrogen-limited mangrove ecosystems conserve N through dissimilatory nitrate reduction to ammonium

Abstract

Earlier observations in mangrove sediments of Goa, India have shown denitrification to be a major pathway for N loss However, percentage of total nitrate transformed through complete denitrification accounted for less than 0�72% of the pore water nitrate reduced Here, we show that up to 99% of nitrate removal in mangrove sediments is routed through dissimilatory nitrate reduction to ammonium (DNRA) The DNRA process was 2x higher at the relatively pristine site Tuvem compared to the anthropogenically-influenced Divar mangrove ecosystem In systems receiving low extraneous nutrient inputs, this mechanism effectively conserves and re-circulates N minimizing nutrient loss that would otherwise occur through denitrification In a global context, the occurrence of DNRA in mangroves has important implications for maintaining N levels and sustaining ecosystem productivity T his study also highlights the significance of DNRA in buffering the climate by modulating the production of the greenhouse gas nitrous oxide.