He majority of earth's atmosphere is nitrogen, n2. the percentage of nitrogen in earth's atmosphere remains constant as prescribed by the law of conservation of matter and because it is a reasonably non-reactive gas. like carbon, nitrogen is cycled through earth's spheres. however, nitrogen can be converted into forms usable by plants and animals, either by lightning or bacteria. once converted to usable forms, nitrogen is able to cycle the rest of the way through the ecosystem. much like carbon, the recycling of nitrogen through earth's spheres relies heavily on what type of organism? a) autotrophs b) decomposers c) parasites d) producers