Leaf litter is processed by a hierarchy of decomposers: fungi break down lignin and cellulose, bacteria mineralize organic compounds, and invertebrates (millipedes, isopods, earthworms) fragment material, increasing surface area. Temperature and moisture are key rate controllers — decomposition roughly doubles per 10°C rise (Q10 ≈ 2). The immobilization-mineralization ratio determines whether nutrients are locked in microbial biomass or released as plant-available forms. A single gram of forest soil contains ~10⁸ bacterial cells from thousands of species.