Changes in chemical composition of a decomposing aquatic macrophyte,Lemna paucicostata.

To understand the changes in chemical composition which may occur as an individual aquatic macrophyte decays, a species of tropical duckweed (Lemna paucicostata) was decomposed (aerobically and anaerobically) by its associated microbial population. Under anaerobic conditions, decomposition of the plant and microbial growth were very rapid. Shortchain carboxylic acids (C2-C5) and ammonia were generated in considerable amounts (reaching a maximum of ca. 30% by weight of original dry weight ofLemna after 71 days). In contrast, free sugars decreased, and amino compounds initially increased slightly and then decreased to the original levels. There were no physical or chemical indications of decomposition occurring under aerobic conditions. The likely biochemical pathways involved in anaerobic decomposition are discussed, and the results are compared with other anaerobic systems such as the rumen, sludge digestion, and aquatic sediments.