Question

nitrogen gas makes up 78% of earths atmosphere. why are so many ecosystems limited by nitrogen even though it is so abundant?
your answer

Explanation:

Nitrogen gas (\(N_2\)) in the atmosphere has a strong triple bond (\(N\equiv N\)). Most organisms (except nitrogen - fixing bacteria) cannot directly use \(N_2\). Nitrogen - fixing bacteria convert \(N_2\) to ammonia (\(NH_3\)) through nitrogen fixation. Then, nitrification (conversion of \(NH_3\) to nitrites \(NO_2^-\) and nitrates \(NO_3^-\)) occurs. Plants can take up \(NO_3^-\) (and some \(NH_3\)). The processes of nitrogen fixation, nitrification, and the limited number of nitrogen - fixing organisms make the conversion of atmospheric \(N_2\) to a usable form (for most organisms) slow and rate - limiting.

Answer:

Most organisms cannot use atmospheric nitrogen gas (\(N_2\)) directly. Only through nitrogen - fixing bacteria (and subsequent nitrification) is \(N_2\) converted to a usable form (like \(NO_3^-\)). The slow rate of these conversion processes (due to the strong \(N\equiv N\) bond and limited nitrogen - fixing organisms) limits the availability of nitrogen in ecosystems, even though \(N_2\) is abundant in the atmosphere.