Against the backdrop of global lake eutrophication, algal bloom decay is increasingly affecting ecosystems. Algal organic matter (AOM), a natural complex mixture, undergoes multiple release and transformation stages, yet its composition and pathways remain unclear. This study used spectroscopic, mass spectrometric, and metagenomic analyses to monitor a time-compressed algal decay experiment. Results showed that AOM release and transformation can be divided into three stages. Within 1 day, labile AOM consisting mainly of proteins (8.36%), lipids (8.22%), and unsaturated carbohydrates (7.72%) was rapidly released, reshaping nitrogen (N) cycling. Its high bioavailability promoted sediment mineralization and a positive priming effect, while anaerobic conditions reduced nitrification and denitrification rates by 88.7% and 34.5%. Within 3-7 days, semilabile AOM rich in tannins (19.2%) and carbohydrates (9.41%) was gradually decomposed, maintaining anaerobic conditions. The imbalance of excessive NH4+ and depleted NO3- led to the decoupling of nitrification-denitrification. After 7 days, humic-like AOM dominated by lignins (56.8%) prevailed, reducing oxygen consumption and enabling rapid recovery of nitrification and slow rebound of denitrification. These findings clarify the phased transformations of AOM and their microbial interactions, providing mechanistic insights into the short-term fluctuations of lake water quality and microbial processes during bloom decay.
Liu et al. (Sat,) studied this question.