How do nitrogen-fixing bacteria die…?
Bacteria are pH sensitive. Acid soils are not habitable by some soil bacteria they favor alkaline or neutral soil pH. They also have oxygen & moisture requirements. Only anaerobic bacteria grow without oxygen but the Rhizobium occupy the root nodules that cater to their exact oxygen needs that are fairly restricted. Azobacter are free living as are actinomycetes that also fix nitrogen. Actinomycetes do not tolerate the wet so are usually found in associations with plants like bitterbrush, mountain mahogany, alder, and ceanothus. In the desert the cryptobiotic crust forms where cyanobacteria in lichen fix nitrogen. http://www.biology.ed.ac.
