Carbon limitation of heterotrophic dinitrogen fixation in the coastal Eastern Mediterranean Sea

Dinitrogen (N2) fixation by diazotrophs is an important source of new bioavailable nitrogen (N) in oligotrophic marine systems (Falkowski, 1997; Gruber, 2008). Due to the high energetic requirements of N2 fixation (Howarth et al.,1988; Postgate, 1998; Karl et al., 2002), most studies focused on photoautotrophic diazotrophs such as Trichodesmium spp. (Capone et al. 1997; 2005) or unicellular cyanobacteria (Zehr et al. 2001, Montoya et al. 2004; Langlois et al., 2005) that uses light as energy source. Recently it was found that heterotrophic proteobacteria diazotrophs are also important contributors to N2 fixation (Zehr et al., 2003; Halm et al., 2012; Rahav et al., 2013 frontiers) and are widely distributed throughout many marine environments (Riemann et al., 2010, Hamersley et al., 2011; Rahav et al., 2013 Meteor, 2014).