Practice question

Wood yields low assimilation efficiency because most of its mass consists of cellulose embedded in hemicellulose and lignin. Vertebrate digestive enzymes cannot cleave cellulose, and lignin physically shields polysaccharides while resisting hydrolysis. Even consumers with symbiotic microbes recover energy slowly and incompletely, losing much material in feces. Seeds and fruits generally contain concentrated starches, oils, or sugars, while leaves, though fibrous and defended, usually contain more accessible cellular contents than secondary xylem. Carbon and mineral nutrients follow different accounting paths: energy is dissipated, whereas atoms may be retained, exported, or recycled into new biomass. Decomposition rate therefore emerges from interactions among substrate chemistry, decomposer traits, temperature, water, oxygen, and nutrient balance rather than from a single universal control. 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.