Global nitrogen budget revisited.

Nitrogen is essential for the growth of all organisms. Although it is the most abundant element in Earth's atmosphere, most organisms cannot use atmospheric nitrogen gas (N2) directly. It must be converted to usable forms, such as ammonium. Certain microorganisms perform this conversion using enzymes through the process of biological nitrogen fixation. This process is also important for Earth's carbon budget because faster plant growth leads to more carbon sequestration. On page 1205 of this issue, Fulweiler et al. (1) report that coastal and inland water habitats are important in the global nitrogen budget, despite their relatively small areal coverage compared with that of the oceans. This finding could stimulate further studies of biological nitrogen fixation in coastal and inland waters, particularly in habitat types that have been poorly studied. [ABSTRACT FROM AUTHOR]