Nitrogen-fixing bacteria in the soil and within the root nodules of some plants convert nitrogen gas in the atmosphere to ammonia. Nitrifying bacteria convert ammonia to nitrites or nitrates. Ammonia, nitrites, and nitrates are all fixed nitrogen and can be absorbed by plants.
A nutrient cycle is the movement and exchange of organic and inorganic matter back into the production of matter. Energy flow is an unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cyclic. Mineral cycles include carbon cycle, sulfur cycle, nitrogen cycle, water cycle, phosphorus cycle, oxygen cycle, among others that continually recycle along with other mineral nutrients into productive ecological nutrition.
The oxygen cycle is the biogeochemical cycle of oxygen within its four main reservoirs: the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all ecosystems), the hydrosphere (the combined mass of water found on, under, and over the surface of planet Earth), and the lithosphere/Earth's crust.
Sulfur Cycle Sulfur (S), the tenth most abundant element in the universe, is a brittle, yellow, tasteless, and odorless non-metallic element. It comprises many vitamins, proteins, and hormones that play critical roles in both climate and in the health of various ecosystems.
Water found at the Earth's surface can cycle rapidly, but much of Earth's water lies in ice, oceans, and underground reservoirs; this water cycles slowly. The water cycle is complex and involves state changes in water as well as the physical movement of water through and between ecosystems.