Extreme drought exacerbates light-mediated microbial mineralization of organic phosphorus in shallow lake sediments

Climate change intensifies hydrological extremes, threatening freshwater ecosystem stability by altering nutrient cycling. Here we conducted a field investigation and indoor simulation experiments to reveal the transformation and mineralization mechanisms of sediment organic phosphorus (OP) under extreme drought. Using sequential extraction, Fourier transform ion cyclotron resonance mass spectrometry, and molecular biological methods, we demonstrated that extreme drought significantly exacerbated mineralizations of sediment OP, increasing the accumulation of labile inorganic phosphorus. OP molecular structure was reshaped, with high-molecular-weight, complex compounds (lipid- and protein-like) converted into low-molecular-weight, readily degradable forms, while aromatic compounds (lignin-like) accumulated. The photochemical processes of sediment dissolved organic matter (SDOM) generated aliphatic-like compounds that provide bioavailable substrates for microbes. Although extreme drought simplified microbial community structure, light selectively enriched phosphorus-cycling bacteria, notably Acinetobacter (47.9 %), and upregulated functional genes for OP mineralization and inorganic phosphorus solubilization. The strong correlation between phosphorus-cycling microbial abundance, functional gene expression, and OP degradation suggested a potential process that light modified SDOM to produce bioavailable substrates, which stimulated phosphorus-cycling microbes to enhance OP mineralization. These findings highlight an internal phosphorus release pathway in shallow lakes under drought, providing key insights for eutrophication management under climate change. • Extreme drought exacerbates sediment organic phosphorus mineralization. • Drought reshapes organic phosphorus structure and increases bioavailability. • High-molecular-weight phosphorus compounds degrade; aromatic compounds accumulate. • Light selectively enriches phosphorus-cycling bacteria. • Light-modified dissolved organic matter stimulates bacterial phosphorus metabolism.