Roles of bacterial biomass, physiology and community in sediment phosphorus solubilizing at varying hydrostatic pressures

Abstract

In this study, the mechanism behind the effect of hydrostatic pressure on phosphorus solubilization from sediment to water was studied in culture experiments using reactors pressurized at 0.1, 0.2, 0.5, and 1.0 MPa. In the sterilized group, the phosphorus content in the sediment was not affected by the hydrostatic pressure. In the unsterilized group, the phosphorus release values were 162, 198, 253, and 289 mg kg−1 at 0.1, 0.2, 0.5, and 1.0 MPa, respectively. In addition, when the hydrostatic pressure was increased from 0.1 to 1 MPa, the activity of alkaline phosphatase increased from 210 to 357 mg kg−1 h−1. The abundance of inorganic phosphorus-solubilizing bacteria increased with rising hydrostatic pressure, but the abundance of organic phosphorus-solubilizing bacteria was highest when the hydrostatic pressure was 0.5 MPa. Pearson regression analysis indicated that the maximum organic phosphorus-solubilizing capacity was positively correlated with the alkaline phosphatase activity (R = 0.97, p < 0.05), but not to the biomass of the organic phosphorus-solubilizing bacteria. Conversely, the maximum inorganic phosphorus-solubilizing capacity was positively correlated to the biomass of the inorganic phosphorus-solubilizing bacteria (R = 0.974, p < 0.05), but not to the alkaline phosphatase activity. The makeup of the bacterial community varied as the hydrostatic pressure increased, but the major bacterial phyla did not change. This implies that changes in the bacterial community did not contribute to variations in phosphorus release. Our results suggest that bacteria are the main factor influencing phosphorus release at various hydrostatic pressures. For organic phosphorus release, the physiology of the organic phosphorus-solubilizing bacteria was more important than biomass, while for inorganic phosphorus release, the biomass of the inorganic phosphorus-solubilizing bacteria was more important than cell physiology.