Which of the followings statements about the cycling of Nitrogen in the biosphere are essentially correct? A) The atmosphere is the most important nonliving reservoir of Nitrogen. B) Changes in the concentration of atmospheric Nitrogen exhibit a profound effect on the climate. C) Nitrogen fixation is limited to a few species of organisms, including members of the genus Rhizobium, Anabaena, and Bradyrhyzobium. D) A and C E) All of the above.