Bacterially mediated phosphorus cycling favors resource use efficiency of phytoplankton communities in a eutrophic...

Resource use efficiency has garnered much attention globally owing to its linkage with phytoplankton growth and extinction. However, little is known about how microbially mediated phosphorus (P) cycling affects phytoplankton P resource use efficiency (RUE_P), especially in eutrophic plateau lakes. Here, we studied the vertical relationship between bacterial communities and phytoplankton RUE_P in water profiles from Hongfeng Lake, a eutrophic lake located in the Guizhou Plateau, and further revealed the influence of bacterially mediated endogenous P release on phytoplankton RUE_P. Generally, phytoplankton RUE_P increased slightly and then decreased toward deep water layers. Compared to dormancy and recovery periods, outbreak period showed higher RUE_P in water profiles and bottom waters. The importance of phytoplankton RUE_P in the co-occurrence networks progressively increased from dormancy to outbreak periods. Rhodococcus may affect phytoplankton RUE_P in water profiles by dissolving Ca-P or polymerizing excess phosphate. Functional composition of P-related genes was largely affected by NH₄Cl-Po, BD-TP and BD-Pi in recovery period, and by NaOH-Po in outbreak period. During phytoplankton growth, bacterial P functional genes promote phytoplankton RUE_P mainly by regulating Pi solubilization and Po mineralization in surface sediments. Note that ppk could regulate the formation of polyphosphates and thus reduce phytoplankton RUE_P. Taken together, our study revealed the relationship between bacterially mediated P cycling and phytoplankton RUE_P, which can effectively monitor the potential risk of phytoplankton blooms and improve eutrophication management.