Microbial colonization in the seagrass Posidonia spp. roots

Abstract

The pattern of colonization by microorganisms on root surfaces from three species of seagrass belonging to the genus Posidonia was assessed. Microbial abundance on roots was measured by two electronic microscope techniques. Trends in microbial colonization between species and root order were defined. In addition, eutrophication status of the sampling sites and physiological status of Posidonia oceanica (L.) Delile roots have been taken into account. Our results show high microbial abundance in the Mediterranean species P. oceanica, in comparison with the low rates of colonization found in the Australian species P. australis Hook f. and P. sinuosa Cambridge et Kuo. Microbial density tended to decrease as root order increased, and living roots always showed higher microbial abundance than dead ones. Colonization of P. oceanica roots at the three sites with different environmental status follows different trends according to root order. It is suggested that root age influences the rate of microbial colonization of seagrass roots and that colonization of root surface by microorganisms is associated with organic exudates from the roots rather than with decaying root tissues.

Keywords:

• Posidonia spp.
• microbial colonization
• roots
• seagrasses
• Scanning Electron Microscopy (SEM)

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

This work was funded by a grant from the Fundación BBVA and by the grant VEM2003-200075-C02-01 from the Spanish Ministerio de Educación y Ciencia. We thank Geoff Bastyan and Tom Davis for their support with the field work, and Javier Rodriguez, Elena Díaz-Almela and Miquel Palmer for useful comments. We also thank all members of the laboratory of Microbiology (University of Balearic Islands) for access to their facilities. M.G. was supported by a FPU grant from the Spanish Ministerio de Educación y Ciencia.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark