[49] Nitrogen fixation in cyanobacterial mats

TLDR: This chapter focuses on nitrogen fixation in cyanobacterial mats, where the availability of combined nitrogen alone is too low to allow development of the mat, and it is assumed that in many mats nitrogen fixation is performed by nonheterocystous organisms.

Abstract: Publisher Summary This chapter focuses on nitrogen fixation in cyanobacterial mats. Intertidal sediments, hot springs, salt ponds, salt marshes, and mangrove forest sediments are often characterized by dense populations of cyanobacteria. Benthic filamentous cyanobacteria may form rigid structures, called cyanobacterial mats. Cyanobacterial mats usually contain a very high biomass, and in many environments, especially intertidal sediments, the availability of combined nitrogen alone is too low to allow development of the mat. Therefore, biological nitrogen fixation in many mats will be of paramount importance. Many cyanobacteria are known to fix nitrogen. Not only cyanobacteria that differentiate heterocysts, but also several unicellular and filamentous cyanobacteria without heterocysts have been shown to fix nitrogen. The majority of cyanobacterial mats are built by filamentous, nonheterocystous cyanobacteria. Therefore, it can be assumed that in many mats nitrogen fixation is performed by nonheterocystous organisms. In cyanobacterial mats, two different methods of nitrogenase measurement can be used. These are the bell-jar method for in situ measurements and the cork-borer sampling technique.