Why does plant material decay differently under water without oxygen?

Plant material decays differently under water because the environment becomes oxygen-depleted, or anaerobic, which significantly inhibits the activity of microorganisms responsible for decomposition.123

In environments where oxygen is readily available, aerobic microorganisms break down organic matter into gaseous and liquid products, leading to complete decomposition. However, in waterlogged conditions such as swamps, the limited access to oxygen prevents this process. While some microbial activity still occurs, it is restricted to anaerobic pathways, which are much less efficient at breaking down complex organic structures.124

Because these anaerobic conditions halt or slow the rate of decomposition, organic matter—primarily plant material—accumulates rather than being fully consumed. This buildup of partially decomposed organic matter is known as peat, which serves as the essential precursor to the formation of coal.2351