Planta

, Volume 213, Issue 1, pp 64–70

Non-photosynthetic enhancement of growth by high CO2 level in the nitrophilic seaweed Ulva rigida C. Agardh (Chlorophyta)

  • Francisco J. L. Gordillo
  • F. Xavier Niell
  • Félix L. Figueroa

DOI: 10.1007/s004250000468

Cite this article as:
Gordillo, F., Niell, F. & Figueroa, F. Planta (2001) 213: 64. doi:10.1007/s004250000468
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Abstract.

The effects of increased CO2 levels (10,000 μl l−1) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO2 enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO2, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO2 levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO2 levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO2 was entirely dependent on the enhancement effect of CO2 on N-assimilation rates. The increase in nitrate reductase activity at high CO2 was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO2 in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO2 levels is discussed.

Key words: Carbon Carbon dioxide Nitrate reductase Nitrogen Organic carbon release Ulva (C: N balance) 

Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • Francisco J. L. Gordillo
    • 1
  • F. Xavier Niell
    • 1
  • Félix L. Figueroa
    • 1
  1. 1.Departamento de Ecología, Facultad de Ciencias, Universidad de Málaga, Campus de Teatinos, 29071 Málaga, SpainES