Effect of phytoplankton cell size on transient-state nitrate and ammonium uptake kinetics.

SUMMARYThe uptake of nitrate or ammonium (at a concentration of 10 mol I-1) by marine phytoplankton was studied in relation to cell size. Initial specific nitrate uptake rates by small (35000 m3) and large (130000 m3) cells of the diatom Ditylum brightwellii did not differ significantly. However, the larger cells maintained a high uptake rate for a longer time. Therefore, they accumulated nitrate in a higher biomass-specific pool than the smaller cells. In the dark, this effect was even more pronounced. Two smaller diatom species, Lauderia borealis (7474 m3) and Thalassiosira pseudonana (98 (m3), had lower initial specific nitrate uptake rates and lower intracellular pools. Transient-state ammonium uptake did not result in accumulation of large intracellular pools of ammonium. Theoretically, and on the basis of the presented results, we stress the dualistic functional role of the vacuole. A large vacuole is an effective way for larger algal species to possess a minimum cell nutrient quota/cell surface ratio which is in the range of smaller species. Furthermore, by functioning as a storage reservoir it reduces inhibition of the uptake rate by cytoplasmic accumulated nutrients. The effect of the latter mechanism is that larger algal species are better at nitrate uptake under fluctuating conditions. These results imply that, in nitrogen-controlled marine systems, resource competition under fluctuating nutrient concentrations can only lead to a shift towards larger phytoplankton species if nitrate rather than ammonium is the main nitrogen source. From theoretical considerations it is argued that the maximum growth rate of algae is determined by nutrient assimilation properties rather than by photosynthetic capacity.

[1]  J. Hobbie,et al.  Use of nuclepore filters for counting bacteria by fluorescence microscopy , 1977, Applied and environmental microbiology.

[2]  K. Banse.  Cell volumes, maximal growth rates of unicellular algae and ciliates, and the role of ciliates in the marine pelagial1,2 , 1982 .

[3]  J. Kalff,et al.  SIZE‐DEPENDENT PHOSPHORUS UPTAKE KINETICS AND CELL QUOTA IN PHYTOPLANKTON 1 , 1982 .

[4]  James J. McCarthy,et al.  HALF‐SATURATION CONSTANTS FOR UPTAKE OF NITRATE AND AMMONIUM BY MARINE PHYTOPLANKTON1 , 1969 .

[5]  M. Whitehouse,et al.  Variations in phytoplanktonic nitrogen assimilation around South Georgia and in the Bransfield Strait (Southern Ocean) , 1991 .

[6]  Q. Dortch.  Effect of growth conditions on accumulation of internal nitrate, ammonium, amino acids, and protein in three marine diatoms , 1982 .

[7]  R. Riegman,et al.  Effect of nitrogen source on the size distribution within marine phytoplankton populations , 1994 .

[8]  K. Banse.  RATES OF GROWTH, RESPIRATION AND PHOTOSYNTHESIS OF UNICELLULAR ALGAE AS RELATED TO CELL SIZE—A REVIEW 1, 2 , 1976 .

[9]  R. Riegman,et al.  Size-differential control of phytoplankton and the structure of plankton communities , 1993 .

[10]  J. Gavis,et al.  Transport limitation of nutrient uptake in phytoplankton1 , 1974 .

[11]  F. Ramos,et al.  Automated chemical analysis in fish health assessment. , 1980 .

[12]  W. Admiraal,et al.  Influence of phosphate depletion on the growth and colony formation of Phaeocystis pouchetii , 1987 .

[13]  I. Valiela,et al.  The effects of ammonium and phosphate enrichments on clorophyll a, pigment ratio and species composition of phytoplankton of Vineyard Sound , 1973 .

[14]  K. Timmermans,et al.  Iron-mediated effects on nitrate reductase in marine phytoplankton , 1994 .

[15]  T. Parsons,et al.  ENVIRONMENTAL CONTROL OF PHYTOPLANKTON CELL SIZE , 1973 .

[16]  T. Malone.  Environmental control of phytoplankton cell size , 1975 .

[17]  J. Aiken,et al.  Primary production and nitrogen assimilation in the North sea during July 1987 , 1990 .

[18]  J. Grover.  INFLUENCE OF CELL SHAPE AND SIZE ON ALGAL COMPETITIVE ABILITY 1 , 1989 .

[19]  J. Grover.  Phosphorus-dependent growth kinetics of 11 species of freshwater algae , 1989 .

[20]  Paul J. Harrison,et al.  Limiting nutrient patchiness and its rôle in phytoplankton ecology , 1979 .

[21]  U. Sommer.  Maximal growth rates of Antarctic phytoplankton: Only weak dependence on cell size , 1989 .

[22]  M. Perry,et al.  Phytoplankton rate processes in the oligotrophic waters of the central North Pacific Ocean , 1980 .

[23]  S. Fitzwater,et al.  Iron deficiency limits phytoplankton growth in the north-east Pacific subarctic , 1988, Nature.

[24]  G. Riley,et al.  Absorption of nutrients by aquatic plants , 1952 .

[25]  F. Morel,et al.  Iron and nitrogen nutrition of equatorial Pacific plankton , 1991 .

[26]  P. Donaghay,et al.  The rapid response of the marine diatom Skeletonema costatum to changes in external and internal nutrient concentration , 1979 .

[27]  B. Shuter.  Size dependence of phosphorus and nitrogen subsistence quotas in unicellular microorganisms 1 , 1978 .

[28]  E. Laws,et al.  Effect of Sewage Enrichment on the Phytoplankton Population of a Subtropical Estuary , 1979 .

[29]  D. Blasco,et al.  SIZE DEPENDENCE OF GROWTH RATE, RESPIRATORY ELECTRON TRANSPORT SYSTEM ACTIVITY, AND CHEMICAL COMPOSITION IN MARINE DIATOMS IN THE LABORATORY 1 , 1982 .

[30]  R. Margalef.  Life-forms of phytoplankton as survival alternatives in an unstable environment , 1978 .

[31]  T. Parsons,et al.  A rebuttal to the comment by Hecky and Kilham , 1974 .

[32]  T. Probyn.  Nitrogen uptake by size-fractionated phytoplankton populations in the southern Benguela upwelling system , 1985 .

[33]  A. T. Chan.  COMPARATIVE PHYSIOLOGICAL STUDY OF MARINE DIATOMS AND DINOFLAGELLATES IN RELATION TO IRRADIANCE AND CELL SIZE. I. GROWTH UNDER CONTINUOUS LIGHT 1, 2 , 1978 .

[34]  A. T. Chan.  COMPARATIVE PHYSIOLOGICAL STUDY OF MARINE DIATOMS AND DINOFLAGELLATES IN RELATION TO IRRADIANCE AND CELL SIZE. II. RELATIONSHIP BETWEEN PHOTOSYNTHESIS, GROWTH, AND CARBON/CHLOROPHYLL a RATIO 1, 2 , 1980 .