Practice question

During nitrogen mineralization, decomposers convert nitrogen in proteins, nucleic acids, and other organic compounds into ammonium. Ammonification can be followed by nitrification, in which specialized microorganisms oxidize ammonium to nitrite and nitrate under oxic conditions. Plants and microbes can then take up these inorganic forms, while some nitrogen may be lost by leaching or denitrification. Net release occurs only when substrate nitrogen exceeds microbial requirements; carbon-rich litter can instead cause temporary nitrogen immobilization. At ecosystem scale, these reactions regulate soil fertility, atmospheric carbon exchange, detrital food webs, and the residence time of organic matter. Mass loss alone cannot identify mechanism, because leaching, fragmentation, respiration, assimilation, and stabilization can produce different fates for carbon and nutrients. The distinction between gross transformation and net nutrient release is important: simultaneous microbial uptake can conceal substantial biochemical turnover. Environmental effects are often nonlinear; drought suppresses microbial access to substrates, waterlogging restricts oxygen, and extreme heat can reduce activity despite faster kinetics.