Comparison of methods for extracting intracellular pools of inorganic nitrogen from marine phytoplankton

Concentration profiles of NH., and NO? in pore water and particulate matter were determined at high spatial resolution (mm bcale) in surface sediment from a coastal bay area (Aarhus Bight, Denmark) at 15 m depth during an annual cycle. Pore water pools of NH: and NO; were always considerably lower than particulate pools in the surface sediment. Particulate NH: and NO; were apparently intracellular pools in deposited microalgae and were extracted after freezing sedlment samples in liquid NZ (-196 "C). Pore water NH: and most of the adsorbed (KCI-extractable) NH: were also extracted by the freezing technique, and an estimate of the intracellular NH: pool was obtained by difference. In the absence of an adsorbed NOS pool, intracellular NO? was determined by subtraction of the pore water pool from the liquid NZ-extractable pool. Highest concentrations of intracellular NH: and NO; were always observed in the upper 2 mm of sediment, declining sharply with depth. A distinct seasonal maximum for both pools, ca 200 nmol cm-3 at 0 to 2 mm depth, appeared after sedimentation of a phytoplankton bloom in early spring, and should be compared to a minimum of only 25 nmol or less in fall and winter. The freeze-extraction technique is proposed for a reliable estimate of intracellular NH: and NO; pools in surface sediments r~c h In microalgae, and may thus be used as an indicator of sedimentation of phytoplankton blooms. The signiflcance of intracellular pools for sediment nitrogen cycling is discussed.

Section: Nh; and N O Pools In The Sedimentmentioning

confidence: 97%

Section: Nh; and N O Pools In The Sedimentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Intracellular NH4 and NO5 pools associated with deposited phytoplankton in a marine sediment (Aarhus Bight, Denmark)

Lomstein¹,

Jensen²,

Sørensen³

1990

“…Intracellular NH4+ concentrations were measured on a number of occasions by rupturing cells with a combination of heat and osmotic shock (Thoresen et al 1982). Interfilamental nutrient concentrations were approximated by placing 30 colonies into 30 m1 nutrient-free filtered seawater, gently agitating them to disperse trichomes without disrupting cells, and then collecting the resultant filtrate for nutrient analysis, as described in Capone et al (1994).…”

Section: N Uptakementioning

confidence: 99%

Nitrogen fixation, uptake and metabolism in natural and cultured populations of Trichodesmium spp.

Mulholland¹,

Capone²

1999

Uptake rates of several combined N sources, NZ fixation, intracellular glutamate (glu) and glutamine (gln) pools, and glutamine synthetase (GS) activity were measured in natural populations and a culture of Trichodesmium IMSlOl grown on seawater medium without added N. In cultured populations, the ratio of GS transferase/biosynthetic activity (an index of the proportion of the GS pool that is active) was lower, and intracellular pools of glu and gln and the ratios of gldglu and glnlaketoglutarate (glnlakg) ratios were higher when NZ fixation was highest (mid-day). There was an excess capacity for NH,' assimilation via GS, indicating that this was not the rate-limiting step in N utilization. In natural populations of Trichodesmium spp., the gldglu ratio closely approximated the glnlakg ratio over the die1 cycle. High gln/glu and gln/akg ratios were noted in near-surface populat i o n~. These ratios decreased in samples collected from greater depths. Natural populations of Tnchodesmium spp. showed a high capacity for the uptake of NH4+, glu, and mixed amino acids (AA).Rates of NO3-and urea uptake were low. NH,+ accumulated in the culture medium during growth and rates of NH4+ uptake showed a positive relationship with the NH4+ concentration in the medium. Although rates of NZ fixation were highest and accounted for the majority of the total measured N utilization during mid-day, rates of NH4+ uptake exceeded rates of NZ fixation throughout much of the die1 cycle. In exponentially growing cultures, only 23% of the total daily N utilization was due to N, fixation while NH,+ uptake accounted for more than 70%. Based on N2 fixation alone, the N turnover time for this culture during exponential growth was on the order of 9 d. This is consistent with the observed chlorophyll-based growth rates for these cultures suggesting that N, fixation was responsible for net growth. Our results contrast with the view that natural populations of Trichodesmium spp. acquire their cell N exclusively through N, fixation. C productivity may overestimate N demand for net production if regenerated production is significant in these populations.

“…Goldman & Glibert (1982) disregarded such a possibility, but it must be recognized that such a relation has the advantage of liberating us from the paradox which is apparent in the hypothesis of McCarthy & Goldman (1979) VmaxNH, :GROWTH RATE Berland et al (1973). Thoresen et al (1982), Dortch et al (1984). For A and Tp, growth lag values are minimum values involving an inverse relation between p and V: either the phytoplankton grows fast and has low uptake rates, or it grows slowly, and exhibits high uptake rates.…”

Section: Uptake-growth Uncoupling Internal Nutrient Pools and Growthmentioning

confidence: 99%

Time-lag algal growth dynamics: biological constraints on primary production in aquatic environments

Collos¹

1986

105

Changes in the nutrient regime of phytoplankton cells induce variable time lags before the onset of cell division (quasi-instantaneous response to more than 24 h lags), dependent mainly on the algal species and the magnitude of the nutrient pulse. The latter parameter appears to be a main controlling factor in algal growth dynamics under transient conditions, overriding other variables such as temperature, irradiance and nutritional state. The presence of such phenomena puts intrinsic limits on primary production in a variable nutrient environment because algal cells are not made up of synthetic components only (sensu Williams 1971), but also of structural and genetic material. Under these conditions, high nutrient uptake rates over short time periods do not necessarily lead to high growth rates (defined as increase in cell numbers) over comparable time scales, even ~f cell quota increase very rapidly follow~ng nutrient resupply. Data from different groups of investigators on uptake-growth coupling, internal nutrient pools, growth lag, and carbon-nitrogen uptake interactions show consistent patterns as follows. for phytoplankton in a vanable nutrient environment, 2 essential strategies emerge at the genus level. One is the 'growth' response, exhibited by the genera Durialiella and Chaetoceros, which do not accumulate internal pools of inorganic nutrients, whose uptake and growth are closely coupled, and which therefore process nutrient pulses very rapidly into new cells. The other is the 'storage' response, found in genera such as Thalassiosira or Amphidinium, which have the capability of accumulating large internal nutrient pools, present extensive uncoupling between uptake and growth, and exhibit lags in cell &vision of up to 24 h following a single addition of the Limiting nutrient. The latter response type presents an ecological advantage when nutrient pulsing frequency is lower than cell dlvision rate; the first response type would provide a competitive advantage at high frequency pulses.