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

Abstract

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.