Directed Network – Nitrogen Cycle
Nitrogen is the most abundant element on the earth. It is essential to all living things. Nitrogen cycles through both biotic and abiotic parts of the ecosystem. The image below shows the nitrogen cycle through a terrestrial ecosystem.
This is a directed network similar to the webpage network we discussed in lecture. According to the article, plants need to use nitrates to make organic compounds. Nitrogen goes into the soil. Some reacts with the nitrogen-fixing soil bacteria and goes through ammonification to make ammonia. The ammonia then react with nitrifying bacteria to make nitrites, which then react with nitrifying bacteria to make nitrates. Some of the nitrates react with denitrifying bacteria to produce nitrogen gas, and some are used by plants. Plants are then either decomposed after death by aerobic and anaerobic bacteria and fungi, or eaten by animals which are also decomposed after death.
This process includes a strongly connected component. Every node can reach every other node in this component, which includes nitrogen gas, nitrogen-fixing soil bacteria, ammonia, nitrifying bacteria, nitrites, nitrates, and denitrifying bacteria. In fact, these nodes form the component called nitrification, which is how nitrogen cycles in nature. Animals, plants, and decomposing bacteria and fungi are not part of this component because they cannot get back to nitrates.
http://science10.knowillage.com/HostedContent/s-html/401/401.html