Incorporation of Different N Sources and Light Response Curves of Nitrogenase and Photosynthesis by Cyanobacterial Blooms from Rice Fields
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[1] Universidad Autónoma de Madrid
Universidad Autónoma de Madrid
Madrid, España
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- Localización: Microbial ecology, ISSN-e 1432-184X, ISSN 0095-3628, Vol. 51, Nº. 3, 2006, págs. 394-403
- Idioma: inglés
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Resumen
In this work, we estimate the contributions of the different sources of N incorporated by two N2-fixing cyanobacterial blooms (Anabaena sp. and Microchaete sp.) in the rice fields of Valencia (Spain) during the crop cycles of 1999 and 2000, and evaluate the response of nitrogenase and C assimilation activities to changing irradiances. Our results show that, far from the generally assumed idea that the largest part of the N incorporated by N2-fixing cyanobacterial blooms in rice fields comes from N2 fixation, both cyanobacterial blooms incorporated about three times more N from dissolved combined compounds than from N2 fixation (only about 33–41% of the N incorporated came from N2 fixation). Our results on the photodependence of C and N2 fixation indicate that in both cyanobacterial blooms, N2 fixation showed a steeper initial slope (α) and was saturated with less irradiance than C fixation, suggesting that N2 fixation was more efficient than photosynthesis under conditions of light limitation. At saturating light, N2 fixation and C fixation differed depending on the bloom and on the environmental conditions created by rice plant growth. Carbon assimilation but not nitrogenase activity appeared photoinhibited in the Anabaena but not in the Microchaete bloom in August 1999, when the plants were tall and the canopy was important, and there was no limitation of dissolved inorganic carbon. The opposite was found in the Microchaete bloom of June 2000, when plants were small and produced little shade, and dissolved inorganic carbon was very low.
