Uptake and Recycling of Soluble Reactive Phosphorus by Marine Microplankton

Bacterial 5'-nucleotidase activity was studied during a mesocosm enrichment experiment on the SW coast of Finland, Baltlc Sea. 5'-nucleotidase activlty and uptake of 3 2~0 4 hydrolyzed from 5'-nucleotide was compared to direct 3 2~0 4 uptake measurements and other nutrient data. The enzyme was not repressed by elevated PO, concentrations, and it hydrolyzed orthophosphate from dissolved organic phosphorus in amounts which were quantitatively significant in the phosphorus dynamics of the community. Bacteria partly assimilated the hydrolyzed PO,, but depending on nutritional conditions, 0 to 80 YO of the hydrolyzed PO4 was released to the environment. Temporal uncoupling between nutrient assimilation and growth was evident for both bacteria and algae. 5'-nucleotidase represented a mechanism of phosphorus regeneration which supports the concept of closely integrated microaggregates having an important role in nutrient cycles of nutrient-depleted surface waters

Section: Introductionmentioning

confidence: 82%

Dissolved organic phosphorus regeneration by bacterioplankton: 5'-nucleotid-ase activity and subsequent phosphate uptake in a mesocosm enrichment experiment

Tamminen¹

1989

“…Taft et al 1975, Harrison et al 1977, Krempin et al 1981, Lebo 1990, Thingstad et al 1993, Bjijrkman & Karl 1994, whereas studies of oceanlc communit~es are still few and largely focused on the Pacific Ocean (Perry 1976, Perry & Eppley 1981, Harrison 1983, Laws et al 1984) and the Sargasso Sea (Cotner et al 1997) The available information suggests that P limitation is particularly important in warm, oligotrophic waters, but the empirical basis on the rates of P uptake and P requirements by oceanic plankton communities is still too meager to test this notion. Moreover, most studies report the incorporation of P into the particulate organic pool, but do not address its possible release to the dissolved organic pool.…”

Section: Introductionmentioning

confidence: 99%

Latitudinal variability in phosphate uptake in the Central Atlantic

Cañellas¹,

Agustı́²,

Duarte³

2000

The role of P in regulating planktonic production in Atlantlc waters was assessed by the examination of the phosphate turnover time and uptake rate along a latitudinal transect across the Central Atlantic Ocean ( 2 f 0 N to 36"s). Phosphate uptake rates and the affinity for phosphate were higher for small (<0.8 pm) organisms, compared with those >0.8 pm. Phosphate uptake rates were relatively low, resulting in long phosphate turnover times (days), except in the surface waters south of 25"S, which were also characterized by the highest uptake rates and affinlty for phosphate, and the smallest total P pools observed along the transect The organisms were found to realize their maximal phosphate uptake rates at ambient phosphate concentrations, suggesting the adequacy of the P supply to support the requirements of organisms. These findings suggest that inorganic P was not Limiting community production in most of the Central Atlantic, except for the area south of 25" S, where P uptake could possibly be limited by P supply. The long turnover times generally observed in the Central Atlantic Ocean are in agreement with previous observations in oceanic systems elsewhere, suggesting that the observation that P is unllkely to be a limlting resource for planktonic growth can be extrapolated to most of the open ocean. The combined rate of P excretion from planktonic organisms and their microbial grazers as dissolved organic phosphorus (DOP) represented 75% of the total phosphate uptake. This DOP does not reach a sufficient accumulation as to drive an important downward flux of DOP, which represents a loss of only 9% of the P inputs into the biogenic layer. Hence, the high P uptake rate of the planktonic community in the Central Atlantic provides P in excess to support primary production, leading to a release as DOP, which appears to be rapidly recycled in the biogenic layer, thereby maintaining an adequate P supply to fuel primary production.

“…This may be due to recycled nitrogen (Paasche & Kristiansen 1982~1, Furnas et al 1986). Furnas et al (1986) contend that microheterotrophs supply most of the recycled nitrogen in coastal waters (and probably most of the recycled phosphorus; Harrison 1983). Ammonium becomes the dominant dissolved nitrogen form in summer (Paasche & Kristiansen 1982b).…”

Section: Spring Bloommentioning

confidence: 99%

Phytoplankton ecology of Sechelt Inlet, a fjord system on the British Columbia coast. I. General features of the nano- and microplankton

Haigh¹,

Taylor²,

Sutherland³

1992

The Sechelt Inlet complex (British Columbia, Canada), Including Narrows and Salmon Inlets, was sampled from h4ay 1988 to September 1990 in order to d e s c r~b e the nutrient and plankton regimes. Species succession w i t h~n the inlet was typical for temperate unpolluted waters despite aquaculture activity and nutrient-loading from the town of Sechelt at the southern end. The N : P ratio in the upper 21 m of 8.3, which is well below the Redfield ratio of 16, suggests an N-limited system. The ratio is also lower than those found in adjacent systems, and supports the a s s u~n p t~o n that Sechelt Inlet is the least influenced by oceanic waters. The N : P ratio also c o~n c~d e s with the optimum ratio for Skeletonerna costaturn of 8.1 which suggests that either the system provided an optimal nutrient regime for this diatom or the dominance of S. costatum determined ambient N:P ratios. The spring bloom, dominated by S. costatum and ThalaSS~~Sira nordenskioeldii, occurred early (in March) due to the combined influence of stratification, created by runoff from Salmon Inlet, and shelter from wind exposure. By summer the waters became depleted of nitrate down to 5 m, and nanoplankton, composed chiefly of cryptomonads and Chrysochrornulina spp., prevailed. Bimodal peaks in nanoflagellate biomass occurred each summer, with the cryptomonads remaining regular components. Under normal meteorological conditions Chrysochromulina spp. \vould codominate but during 1989, storm activity in May somehow caused the replacement of the prymnesiomonads by the silicoflagellate Dictyocha speculurn. The latter occurred In ~t s askeletal form during the late summer nanoflagellate peak. The water injected through the mouth of Sechelt Inlet by a tidal jet combined with water overlying the anoxic bottom of inner Narrows Inlet and caused stimulation of plankton growth at the confluence of these 2 inlets. There was also h~g h biomass at the shallow southern end possibly due to increased mixing over a sill and m~l d eutrophication.