For example, bacteria in soil release nitrogen and phosphorus as they break down dead plants, and so these microbes could increase the amount of available nitrogen and phosphorus. (sciencemag.org)
In the nitrogen cycle, some microbes perform an especially important step: the oxidation of nitrite (NO2 −) to nitrate (NO3 −), the dominant form of biologically available nitrogen in the ocean. (eos.org)
In fact, astonishingly, humans have doubled the amount of available nitrogen in the biosphere. (sciencedaily.com)