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MEPS 239:45-55 (2002)
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Abstract
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Phosphorus dynamics in cultures and natural populations of Trichodesmium spp.
Margaret R. Mulholland1,*, Sheri Floge2, Edward J. Carpenter3, Douglas G. Capone4
1Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, Virginia 23529-0276, USA
2School of Marine Sciences, University of Maine, Darling Marine Center, Walpole, Maine 04573, USA
3Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, California 94920, USA
4Wrigley Institute of Environmental Studies and Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
*E-mail: mmulholl@odu.edu
ABSTRACT: Trichodesmium spp. fix atmospheric N2 and so an element other than N limits production by these species in the oligotrophic ocean. Because dissolved inorganic phosphorus (DIP) is in short supply in many marine systems, it has
been hypothesized that P is a growth-limiting nutrient for these species in nature. However, Trichodesmium is capable of hydrolyzing dissolved organic P (DOP) compounds and the inorganic products from hydrolysis may provide an additional source of
P for growth. We investigated P dynamics and alkaline phosphatase activity in cultures and natural populations of Trichodesmium from the Atlantic Ocean and the north coast of Australia to determine whether hydrolysis of DOP could supply enough P to
fuel growth. During the Atlantic cruise, concentrations of DIP were lower and chlorophyll (chl a)-specific rates of alkaline phosphatase activity by Trichodesmium were higher than during the Australian transect. However, because
Trichodesmium were much more abundant during the Australian transect, where they represented the bulk of the surface chl a biomass, total water column rates of alkaline phosphatase activity were higher along the Australian transect than in
the Atlantic. In both systems, DOP could potentially supply a significant portion of the cellular P necessary for growth. In cultures and natural populations, alkaline phosphatase activity was inhibited when DIP was present and increased in the presence
of DOP. Cultures of Trichodesmium IMS101 grew equally well on media enriched with DOP or DIP at all but the highest enrichment levels. From these studies, we conclude that if the supply of appropriate DOP substrates is adequate, DOP can represent
an important P source for Trichodesmium growth which should be included in estimates of P availability in surface waters.
KEY WORDS: Trichodesmium · Alkaline phosphatase activity · P dynamics · Dissolved organic phosphorus
Full text in pdf format
Published in MEPS Vol.
239
(2002) on August 23
Print ISSN: 0171-8630; Online ISSN: 1616-1599.
Copyright © Inter-Research, Oldendorf/Luhe, 2002
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