The flower structure depends on the specific type. There are 10 stamens that are fused together. The flowers are designed for bee pollination. The latter three are mostly dissolved in water. Favored by warm temperature and neutral pH. Wastes and decayed organic materials decomposed by another set of bacteria into ammonia - called ammonification.
Various microbes are responsible, favored by cool temperatures, all pH's.
Denitrification - closes the cycle. Returns nitrogen to the atmosphere. Note the heavy reliance on microbes for the function of this cycle. Legumes are excellent green manure because they have high levels of nitrogen. Nitrogen in many systems is usually in short supply so legumes are valuable soil enhancers.