The nutrients in dead organic matter are broken down by a group of processes known as decomposition, which also return carbon dioxide or water to the atmosphere, where it can be reused by autotrophs for photosynthesis. → Substances such as amino acids and sugars decompose readily and are considered labile. → Cellulose and hemicellulose, which are broken down more slowly, are “moderately labile”. → Compounds which are more resistant to decay, like lignin or chitin, are considered “recalcitrant”. Thus, rate of decomposition is slower if detritus is rich in lignin and chitin and faster if detritus is rich in nitrogen and water-soluble substances like sugars.