Biological N2 fixation is the dominant supply of new nitrogen (N) to the oceans, but is often inhibited in the presence of fixed N sources such as nitrate (NO3-). Anthropogenic fixed N inputs to the ocean are increasing, but their effect on marine N2 fixation is uncertain. Thus, global estimates of new oceanic N depend on a fundamental understanding of factors that modulate N source preferences...

The biological fixation of atmospheric nitrogen (N) is a major pathway for available N entering ecosystems. In N-limited boreal forests, a significant amount of N2 is fixed by cyanobacteria living in association with mosses, contributing up to 50% to the total N input. In this review, we synthesize reports on the drivers of N2 fixation in feather moss-cyanobacteria associations to gain a deeper...

Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at ...

A variety of N2-fixers occur in oligotrophic waters and these diazotrophs make a substantial contribution to the nitrogen budget of the upper water column. A synthesis of previously published and new rate measurements for the North Atlantic provides insight into the role of two different groups of N2-fixers (Trichodesmium and small diazotrophs) in supporting N2 fixation in the tropical Atlantic...

Annual rates of N2 fixation were measured over 3 yr (1998–2000) at an open water station (BY31) and 2 coastal stations (H4 and X1) in the Baltic Sea. This is the first report on depthintegrated rates of N2 fixation from more than one complete growth season in the Baltic Sea. Annual estimates of N2 fixation ranged from 56 000 to 125 000 t N in the Baltic Proper, and 18 000 to 162 000 t N at the ...

The response of N2 fixation and [Formula: see text] uptake to environmental conditions and nutrient enrichment experiments in three western U.S. lake systems was studied (eutrophic Clear Lake; mesotrophic Walker Lake; oligotrophic Lake Tahoe). We tested the effect of additions of bioactive trace metals molybdenum as Mo(V) and iron (Fe) as well as phosphate (P), N2 fixation, [Formula: see text],...

Nitrogen (N) accumulation rates in peatland ecosystems indicate significant biological atmospheric N2 fixation associated with Sphagnum mosses. Here, we show that the linkage between methanotrophic carbon cycling and N2 fixation may constitute an important mechanism in the rapid accumulation of N during the primary succession of peatlands. In our experimental stable isotope enrichment study, pr...

The potential coupling of nitrogen (N2) fixation and sulfate reduction (SR) was explored in sediments of the Peruvian oxygen minimum zone (OMZ). Sediment samples were retrieved by a multiple corer at six stations along a depth transect (70–1025 m water depth) at 12 S, covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation, determined by the acetylene reduction assay, was detec...

12 The potential coupling of nitrogen (N2) fixation and sulfate reduction (SR) was explored in 13 sediments of the Peruvian oxygen minimum zone (OMZ). Sediment samples were retrieved 14 by a multiple corer at six stations along a depth transect (70 1025 m water depth) at 12°S, 15 covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation, determined by 16 the acetylene reduction a...

Tropical coral reefs are among the most productive and diverse ecosystems, despite being surrounded by ocean waters where nutrients are in short supply. Benthic dinitrogen (N2) fixation is a significant internal source of "new" nitrogen (N) in reef ecosystems, but related information appears to be sparse. Here, we review the current state (and gaps) of knowledge on N2 fixation associated with c...