Journal of Applied Phycology

, Volume 8, Issue 1, pp 41–49 | Cite as

Effects of phosphate and nitrate supply on productivity, agar content and physical properties of agar ofGracilaria strain G-16S

  • Raymond J. Lewis
  • M. Denni Hanisak


Gracilaria strain G-16S was cultured in various phosphorus (P) supply rates with low or high nitrogen (N) supply to determine the effects of nutrient supply on its productivity, agar content and physical properties of the agar. Productivity was reduced after four weeks of growth in zero P supply as plants reached 0.07% P tissue content (critical level), with fragmentation of these plants by six weeks (0.05% P; minimum viable level). Native agar content was higher in low P and high N, or low N conditions. Agar content appeared to increase with decreasing P under high N supply. This increase was not apparent with alkali treatment prior to extraction. Agar gel strength was greatly increased by alkali treatment. The highest gel strengths were obtained under high N supply at all P supply rates except zero P, and under low N supply at 12 μM P week−1. Native agar gel strengths showed a similar pattern on a lower scale. Melting temperatures were higher in agars with higher gel strengths. Dynamic gelling temperatures were generally high for alkali-treated agar, with agar from plants grown in zero P supply showing a slightly elevated gelling temperature. Melting and gelling temperatures of native agars with the highest gel strengths were in the same range as bacteriological agar. These results show that P and N supply affects productivity, agar content and agar physical properties, but the tradeoffs between a slightly higher agar quantity under nutrient limitation and higher agar quality under nutrient-replete conditions seem to favor the latter.

Key words

agar agar gel strength agar gelling temperature agar melting temperature cultivation Gracilaria phosphorus nutrition productivity 


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Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • Raymond J. Lewis
    • 1
  • M. Denni Hanisak
    • 1
  1. 1.Harbor Branch Oceanographic InstitutionFort PierceUSA

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