Abstract
Temporal variability in dissolved inorganic, organic phosphate (Pi, DOP) and particulate phosphorus (PPO4) concentrations, and microbial utilization of Pi and dissolved adenosine-5’-triphosphate (DATP) was studied at Station ALOHA (22.75˚N, 158˚W) in the North Pacific Subtropical Gyre (NPSG) over a multi-year period. Spatial variability of the same properties was investigated along two transects, to and from Hawaii, that traversed the NPSG boundaries to the east (2014) and north (2016). Radiotracer techniques were employed to measure the turnover time of Pi and DATP pools to calculate Pi uptake rates and the Pi hydrolysis rates of DATP. Pi concentrations were more variable, both in time and space, than DOP, ranging two orders of magnitude compared to a factor of two for DOP. The DATP pool, while constituting on average 0.2 µm size class dominating the DATP uptake. Our results indicate that during Pi limiting conditions, regenerated P is rapidly consumed, and that Pi limitation occurs locally and transiently but does not appear to be the predominant condition in the upper water column of the NPSG.
Highlights
Phosphorus (P) is essential for all life and is a key component of nucleic acids, cell membrane lipids and in biological energetic processes via e.g., adenosine-5′-triphosphate (ATP)
Time-series data from Station ALOHA have only rarely recorded such high temperatures, and in September 2014 was the first time in a decade to do so
The majority of the work presented here was conducted within the North Pacific Subtropical Gyre (NPSG), an environment characterized by its oligotrophic nature with perennially low inorganic nutrients, low standing stocks of chlorophyll and biomass, and typically low primary productivity, with Station ALOHA serving as a representative for the biome (Karl and Lukas, 1996; Karl and Church, 2014)
Summary
Phosphorus (P) is essential for all life and is a key component of nucleic acids, cell membrane lipids and in biological energetic processes via e.g., adenosine-5′-triphosphate (ATP). ATP has several advantages as a “model” compound, among them that it is available in different radiolabeled forms. This makes it possible to discern preferential uptake of subcomponents of the molecule, and importantly, it is possible to measure its ambient particulate and dissolved concentrations (Bossard and Karl, 1986; Ammerman and Azam, 1991a; Björkman and Karl, 2001) and to follow its utilization by the microbial community (Casey et al, 2009; Björkman et al, 2012). ATP may only be a small portion, and not necessarily representative of the average DOP pool constituents, getting a clearer assessment of its flux through the different P-pools will aid in elucidating the behavior of the bioavailable DOP
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