Practice question

Mineralization releases inorganic nutrients when decomposers convert organically bound elements into forms such as ammonium, phosphate, and sulfate. Immobilization runs in the opposite direction: microbes absorb inorganic ions and incorporate them into cellular biomass because detritus does not supply nutrients in the proportions required for growth. Whether net mineralization or net immobilization occurs depends strongly on substrate stoichiometry, especially carbon-to-nitrogen and carbon-to-phosphorus ratios, and on microbial demand rather than on decomposition alone. 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.