Abstract
The dissolved organic phosphorus (DOP) pool in marine waters contains a variety of different compounds. Knowledge of the distribution and utilization of DOP by phyto- and bacterioplankton is limited, but critical to our understanding of the marine phosphorus cycle. In the Baltic Sea, detailed information about the composition of DOP and its turnover is lacking. This study reports the concentrations and uptake rates of DOP compounds, namely, adenosine triphosphate (dATP), deoxyribonucleic acid (dDNA), and phospholipids (dPL), in the Baltic Proper and in Finnish coastal waters in the summers of 2011 and 2012. Both areas differed in their dissolved inorganic phosphorus (DIP) concentrations (0.16 and 0.02–0.04 μM), in the C:P (123–178) and N:P (18–27) ratios, and in abundances of filamentous cyanobacteria and of autotrophic and heterotrophic picoplankton. The mean concentrations of dATP-P, dDNA-P, and dPL-P were 4.3–6.4, 0.05–0.12, and 1.9–6.8 nM, respectively, together contributing between 2.4 and 5.2% of the total DOP concentration. The concentrations of the compounds varied between and within the investigated regions and the distribution patterns of the individual components are not linked to each other. DIP was taken up at rates of 10.1–380.8 nM d-1. dATP-P and dDNA-P were consumed simultaneously with DIP at rates of 6.9–24.1 and 0.09–0.19 nM d-1, respectively, with the main proportion taken up by the size fraction <3 μm and with DIP to be the dominant source. Groups of hydrographical and biological parameters were identified in the multiple regression analysis to impact the concentrations and uptake rates. It points to the complexity of the regulation. Our results indicate that the investigated DOP compounds, particularly dATP-P, can make significant contributions to the P nutrition of microorganisms and their use seems to be not intertwined. Therefore, more detailed knowledge of all DOP components including variation of concentrations and the utilization is required to understand the roles of DOP in marine ecosystems.
Highlights
In the marine phosphorus (P) cycle, dissolved inorganic phosphorus (DIP), particulate inorganic (PIP) and organic phosphorus (POP) and dissolved organic phosphorus (DOP) are the main P pools
DOP Concentrations and Compounds There were no significant differences in the Total phosphorus (TP), DOP, and DIP concentrations between the southern and the northern stations of the transect through the central Baltic Sea (Tables 2, 3)
Our study shows that DOP compounds, namely, Dissolved adenosine triphosphate (dATP), Dissolved DNA (dDNA) and Dissolved phospholipids (dPL), comprised a small share of the total DOP pool in the Baltic Sea
Summary
In the marine phosphorus (P) cycle, dissolved inorganic phosphorus (DIP), particulate inorganic (PIP) and organic phosphorus (POP) and dissolved organic phosphorus (DOP) are the main P pools. The majority of the DOP pool consists of phosphoesters (Young and Ingall, 2010) including sugar phosphates, vitamins, nucleotides such as adenosine mono- and tri-phosphate (AMP, ATP) and nucleic acids, i.e., deoxyribonucleic (DNA) and ribonucleic acid (RNA) (Karl and Björkman, 2015). All these substrates are assumed to be bioavailable to the microbial community after enzymatic degradation. Several bacteria and cyanobacteria are reported to be genetically equipped for phosphonate utilization (Dyhrman et al, 2006; Feingersch et al, 2012; Repeta et al, 2016). Siuda and Chrost (2001) showed that P is hydrolyzed through enzymatic processes from DOP compounds to various degrees, with the highest proportion of P released from nucleotides
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