Biological nitrogen (N2) fixation represents the major source of new nitrogen input to the ocean. Diazotrophic activity has thus great implications in the biogeochemical cycling of nitrogen and plays an important role in marine primary productivity. A better understanding of the major environmental factors as well as the nutrient status governing the extent of N2 fixation is highly required. Iron (Fe) and phosphorus (P) are considered to be co-limiting factors in most regions and the deposition of mineral dust is believed to promote N2 fixation through increasing availability of both Fe and P. Laboratory bioassays (+Fe, +P, +Dust) via incubation experiments performed on Trichodesmium IMS101, show that the addition of Fe, P or desert particles could stimulate the growth and N2 fixation of this cyanobacteria. In addition, during a field study using natural phytoplankton assemblages from the temperate Northeast Atlantic Ocean the key role of dissolved Fe (DFe) has been furthermore highlighted by the remarkably enhanced N2 fixation rate observed after the addition of DFe under low temperature and P-depleted conditions.

Recently, the effects of ongoing climate change (ocean warming and acidification) on N2 fixation has been intensively studied but controversial conclusions have been reached. Semi-continuous dilution growth experiments were conducted on Trichodesmium IMS101 under two pCO2 (400 and 800 μatm) and temperature (24 and 28 °C) conditions. The results indicate that higher pCO2 and therefore ocean acidification may be beneficial for Trichodesmium growth and N2 fixation. However, Fe or P limitation in oligotrophic seawaters may offset the stimulation induced on Trichodesmium IMS101 resulting from ocean acidification. In contrast, ocean warming may not play a crucial role in Trichodesmium growth and N2 fixation with a 4 °C increase from 24 °C to 28 °C. Nevertheless, ocean warming is predicted to cause a shift in the geographical distribution of Trichodesmium species towards higher latitudes, extending its niche to subtropical ocean regions and potentially reducing its coverage in tropical ocean basins.