Assessing N2 fixation in estuarine mangrove soils

- We measured the magnitude of nitrogenase activity (NA) of mangrove soils.
- The NA was affected by the available soil C but not salinity.
- The diazotrophs in these mangrove soils were mostly heterotrophs.
- More than 51% of the NA was attributed by sulfate-reducing bacteria.
- The NA was attributed by the microbial activity rather than their cell reproduction.

Nitrogen (N) limited mangrove forest may have a high potential for microbial N2 fixation. Previous research has focused on soil nitrogenase activity in pristine mangrove forests with little anthropogenic impact. This research was designed to evaluate the magnitude of nitrogenase activity of mangrove soils in a high anthropogenic N-loading environment and the way in which soil N2 fixation in mangrove forest may be related to organic carbon and salinity. The test involved an acetylene reduction method under controlled laboratory conditions. The mangrove forests with high anthropogenic N loading may have high nitrogenase activity in the soils. The diazotrophs in these mangrove soils were mostly heterotrophs and the sulfate-reducing bacteria were the major N2-fixing bacteria. The nitrogenase activity was little affected by the soil salinity, which suggests that these groups of N2 fixation bacteria adapted well to saline conditions in the estuary.