What are nitrogen sinks? Examples?

Nitrogen sinks:

Nitrogen gas in the atmosphere is the primary sink. As we know that in living beings, nitrogen is the part of the protein. It can easily get dissolved in the water, that's why sedimentary rock when exposed to water gets dissolved. For plant growth it may also be act as a limiting factor. Some of the most common examples are nitrogen fixing bacteria like azotobacter, cyanobacteria, anabaena and nostoc, rhizobium etc.