Date of Award


Document Type

Campus Access Dissertation


Biological Sciences

First Advisor

Charles R. Lovell

Second Advisor

James L Pinckney


Many Spartina alterniflora dominated coastal salt marshes of the southeastern US are nitrogen-limited despite being among the most productive ecosystems known. Nitrogen fixation (diazotrophy) by the nitrogen-fixing microorganisms in these ecosystems is one of the primary sources of `new' nitrogen and is therefore ecologically significant. The diazotroph assemblages associated with the rhizosphere of S. alterniflora have been found to be highly diverse, mostly consisting of novel taxa, and relatively stable. The culturable O2 utilizing diazotrophs associated with other wetland plants have also been studied and found to be plant host specific and diverse. Coastal salt marshes along the eastern coast of the US typically occur along an elevation gradient that results in a distinctive pattern of plant zonation. This study examined the diazotroph assemblages associated with salt marsh plants in discrete zones along this elevation gradient in Crab Haul Creek Basin, North Inlet, SC, and their responses to environmental conditions and plant host species. The compositions of the assemblages associated with the rhizospheres and rhizoplanes of these plants were identified and the effect of a short but severe drought event on the rhizosphere assemblages was also determined. Ecologically significant diazotrophs in this system were identified. The diazotroph assemblages in all zones were found to be immensely diverse and novel and their members included host specific diazotrophs, as well as ubiquitous and functionally versatile species. The assemblages were responsive to seasonal changes as well as plant host species and therefore elevation gradient and edaphic conditions. A severe drought event resulted in a delayed but significant change in the structure of the assemblage, reducing all but a few species to levels below the threshold of detection. Diazotrophs that maintained detectable populations were mostly presumed oxygen-utilizers, photoautrophs and halophilic photoautotrophs. While the majority of the members of the assemblages remain unknown, undescribed species, the versatility and functional diversity of these assemblages indicate their ecological influence in these highly productive ecosystems.


© 2010, Debra Aline Davis