Carbon loss by photosynthesis is balanced by carbon release during respiration . Some carbon is diverted from cycling for longer periods of time, as when it accumulates in wood or other durable organic material. Decomposition eventually recycles this carbon to the atmosphere. Can be diverted for millions of years, such as in the formation of coal and petroleum . The amount of atmospheric CO2 decreases in the Northern Hemisphere in summer due to increased photosynthetic activity.
Amounts increase in the winter when respiration exceeds photosynthesis.
Atmospheric CO2 is increased by combustion of fossil fuels by humans, disturbing the balance. The nitrogen cycle Nitrogen is a key chemical in ecosystems as it is found in all amino acids which comprise the proteins of organisms. Only certain prokaryotes can fix nitrogen. Cyanobacteria fix nitrogen in aquatic ecosystems. Nitrogen fixing prokaryotes are fulfilling their own metabolic needs, but other organisms benefit since excess ammonia is released into the soil or water.