Lightning breaks apart nitrogen molecules. This allows the molecules to combine with oxygen and, together, they form nitrogen oxides. The nitrogen oxides dissolve in rain and form nitrates.
Nitrogen only reacts with oxygen at high temperatures and pressures associated with lightning. During a lightning storm, NO2, nitrogen dioxide and nitric oxide form and nitrogen oxide reacts with water to form nitric acid. Nitric acid makes water suitable as a nutrient for plants.
There are four processes in the cycling of nitrogen through the atmosphere and microorganisms play a part in each process. The processes are nitrogen fixation, decay, nitrification and denitrification.
Nitrogen fixation is the breaking apart of nitrogen atoms by lightning. This nitrogen fixation accounts for up to 8 percent of the total nitrogen fixed.
The next phase in the nitrogen cycle is decay. As the nitrogen rich water is used by plants, the plants' metabolism release nitrogen compounds that are eventually returned to the environment. Small organisms break down these nitrogen compounds and turn them into ammonia.
Ammonia is often used by plants but much of it is converted to nitrates. This is the third process of the nitrogen cycle. These nitrates are available for plants to use and are absorbed through their roots.
The final step in the nitrogen cycle is denitrification. Denitrification turns nitrates into nitrogen gas and this gas gets released back into the atmosphere.