ENV234H1 Lecture Notes - Lecture 21: Carl Bosch, Estuary, Diazotroph
Document Summary
N2 (stable gas, triple bond) + 3 h2 -> 2 nh3 (ammonia) Some chemical fixation in atmosphere (by lightning) 85% n2 fixation is biological (by diazotrophs) Suppressed when other forms of n available. If there is available nitrogen, other organisms will outcompete nitrogen fixers. Need anaerobic conditions: e. g. , the enzyme nitrogenase is very sensitive to oxygen, e. g. , heterocysts: special structure that is anoxic and can be used for n2 fixation. N2 can do better in terms of activity. Having nitrogen fixers is not because n is limiting, but rather gives them advantage to use other elements that are limiting: spatial patchiness large parts of tropical ecosystems are n-poor and n2 fixation occurs in n-poor layers. Nitrogen is high in leaves and litter (patchy where there is high n) due to patchiness, there is more nitrogen for plants, but patchiness is deduced to be more fixation.
