Abstract
The aims of this study are (i) to assess the function of diversity of N2-fixing microorganisms in a coastal microbial mat, (ii) to identify the niches of the different N2-fixing organisms, and (iii) to determine the controlling factors of N2 fixation at the ecosystem level. In order to achieve these aims a molecular biological approach will be combined with detailed measurements of N2 fixation, among others with the aid of stabile isotopes. Microbial mats are complex, vertical stratified ecosystems in which cyanobacteria play a key role. The most important source of nitrogen in coastal microbial mats is N2 and the N2 fixation rates in these ecosystems are therefore high. There are several functional groups of microorganisms in the mats that are potentially capable of N2 fixation but it is not known whether they are all actively fixing. Many species of cyanobacteria fix N2. Some microbial mats display a high diversity of cyanobacteria while others do not. The reason for this is not precisely known but is likely due to differences in environmental conditions, particularly with the inhibiting effect of O2 on nitrogenase. Microbial mats are found on the green beaches of the barrier islands of the southern North Sea. Because of their diversity these microbial mats are excellent systems to study the niches of the different N2-fixing microorganisms.
Netherlands