Hongbin Yin

Marine heterotrophic bacteria produce polyphosphate (polyP) ubiquitously, yet their polyP functions and ecological significance are rarely studied. We investigated polyP dynamics of three common marine bacteria under phosphorus (P) and organic carbon limitations. Our results show that these bacteria accumulate varying levels of polyP: Alteromonas sp. accumulates up to 87% of polyP in total biomass P, Photobacterium ganghwense accumulates up to 35%, and Vibrio sp. accumulates less than 16%. This variability appears linked to differences in polyP functions. Under P limitation, polyP supports the growth of the two high‐polyP‐accumulating species, but not in Vibrio sp. with a low polyP level. Under organic carbon limitation, P. ganghwense uniquely degrades polyP for energy and survival. However, this mechanism is not observed under P limitation, despite similar levels of polyP accumulation in the bacteria. The phosphate produced from polyP degradation in P. ganghwense under organic carbon limitation is recycled within cells rather than released into the environment. Overall, our findings suggest that polyP enables some marine heterotrophic bacteria to cope with P and organic carbon limitations, potentially enhancing their competitiveness against phytoplankton for the common limiting nutrient phosphorus in marine ecosystems.

Algal decomposition plays an important role in affecting phosphorus (P) release from sediments in eutrophic lakes under global warming. Yet how rising air temperature affect endogenous P release from sediments during the algal decomposition is poorly understood. In this study, effect of increasing air temperature on endogenous P release was investigated. A 22-day laboratory warming simulation experiment was conducted, with the overlying water and sediments collected from Lake Chaohu incubated in microcosms at three temperatures (21, 28 and 37°C). Dynamics of P fractions and related physiochemical properties in water and sediments were measured, and P release rate from sediments was calculated. Rising air temperature significantly reduced redox potential, but elevated pH, dissolved organic carbon (C) and alkaline phosphatase activity in water. For the average value during incubation, rising temperature significantly elevated P release rate and soluble reactive P by 3 times in overlying water, and greatly reduced total organic P (by 19.0%) in sediments, while did not affect total inorganic P in sediments. The NH₄Cl-Po and NaHCO₃-Po concentrations in sediments showed the greatest decrease (accounting for 97.6% of total decrease) during the experiment. Dynamics of P release rate, soluble reactive P, dissolved organic C in water and organic P, total organic C in sediments during incubation were also differed among different temperatures. The P release rate was significantly and negatively correlated with dissolved organic C and redox potential at all temperatures, negatively correlated with sediment inorganic P at 21°C, while negatively correlated with sediment organic P at 37°C. The results revealed that rising temperature strongly stimulated endogenous P release from sediments during the decay of algal residues, which was mainly due to the acceleration of organic P mineralization Warming-induced changes in the amount and dynamics of dissolved organic C played the dominant role in accelerating P release from sediments.

Polyphosphate (polyP) is found in plankton of diverse aquatic ecosystems and is important for plankton ecology and biogeochemical cycling. However, our knowledge of polyP in aquatic environments is hindered by a lack of data due to the limitations of quantification methods. The estimate of polyP in model organisms using phenol-chloroform extraction followed by enzymatic hydrolysis is complicated and fails for environmental samples. The commonly used 4',6-diamidino-2-phenylindole (DAPI) fluorescence method for environmental studies, on the contrary, severely overestimates polyP due to interference. In this paper, we develop a plankton lysis buffer to extract polyP and a quantification method using a novel polyP-specific fluorescence dye JC-D7. We test the methods using cultured algae and bacteria, as well as natural samples from marine and freshwater environments. We show that our plankton lysis extracts polyP with high recovery while requiring substantially less time and effort. Subsequent polyP quantification using JC-D7 fluorescence overcomes the interference encountered by the DAPI method and provides an accurate measurement of polyP down to -1. This novel method enables more accurate quantification of polyP in aquatic environments and will profoundly enhance our knowledge of polyP, plankton ecology, and biogeochemistry.