Regime difference trigger the regulation of mineralization progress of organic phosphorus in lake sediments

Regime difference induced by nutrient load regulation can alter microbial community structure and interaction in the sediments of lakes. However, the mechanism, processes and effect of bacterial community regulation on organic phosphorus (Po) mineralization in different regimes remains highly uncertain. Different Po pools in the sediments from Cyanophyta-dominated and macrophyte-dominated regimes of Taihu Lake, China were obtained using multiple extraction procedures. Alkaline phosphatase activities (APA) and three-dimensional fluorescence spectra for Po fractions were obtained. The abundances of functional gene phoD and diversity of bacterial communities encoding Po mineralization in the sediments were also assessed using high throughput sequencing. The results showed that different P fractions including Po compounds in the sediments had higher concentrations in Cyanophyta-dominated regime than macrophyte-dominated regime, indicating higher mineralization potential of sedimentary P. Higher APA values detected in macrophyte-dominated regime indicated noteworthy mineralization efficiency of Po into bioavailable P. However, the accumulation of bioavailable P via Po mineralization due to extensive Po stock especially Mono-Po contributed to the higher reactive P load in Cyanophyta-dominated regime. Higher phoD gene abundance (2.38-6.74 × 10⁶ Copies/g) and community structure diversity were found in Cyanophyta-dominated regime, suggesting that regime difference differentiated the aggregation of phoD-encoding bacteria in Cyanophyta-dominated regime (1.6-5.90 × 10⁶ Copies/g). Community structure regulation triggered by abundant and rare taxa demonstrated that regime difference regulated the phoD gene abundance and subsequent Po mineralization pathway and effects in the lake ecosystems. Generally, abundant and rare microflora responded to the regime regulation and synchronously contributed to the phoD gene abundance and mineralization effect. Our findings implied that Cyanophyta-dominated regime had higher Po mineralization potential via microbial activities and eutrophication risk activated by extensive P accumulation relative to macrophyte-dominated regime.