Final answer:
Azotobacter is an example of non-symbiotic nitrogen-fixing bacteria in terrestrial ecosystems, as it does not form a symbiotic relationship with plants to fix nitrogen.
Step-by-step explanation:
The subject of non-symbiotic nitrogen fixation in terrestrial ecosystems relates to the process by which some bacteria convert atmospheric nitrogen into a form that is usable by plants, without forming a symbiotic relationship with other organisms. In this context, Azotobacter is an example of a free-living, non-symbiotic nitrogen-fixing bacterium. Unlike Rhizobium and Frankia, which form symbiotic relationships with plants, and Mycorrhizae, which are fungi that form symbiotic relationships with plant roots, Azotobacter does not rely on a host organism to fix nitrogen.