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A MODEL FOR THE DISTRIBUTION OF BACTERIA IN THE SEAGRASS RHIZOSPHERE REDOX GRADIENT
Citation:
DEVEREUX, R. A MODEL FOR THE DISTRIBUTION OF BACTERIA IN THE SEAGRASS RHIZOSPHERE REDOX GRADIENT. Presented at Wetland and Estuary Scientists from the US Gulf Coast and SE Atlantic, Pensacola, FL, March 31 - April 02, 2005.
Description:
Abstract and Oral presentation for the meeting of Wetland and Estuary Scientists from the US Gulf Coast and S.E. Atlantic.
A conceptual model of seagrass bed sediments accounts for observations on the distribution and activities of bacteria associated with seagrass roots in relation to biogeochemistry. The model contains two compartments. The first is based on definition of the rhizosphere as the sediment zone that is directly influenced by the root. This compartment is scaled from recent studies that have shown oxygen diffuses from the roots at the onset of photosynthesis some 80 uM into the sediment, generates a sharp redox gradient, and then becomes depleted at night. High numbers of sulfate- reducing bacteria on and within seagrass roots, and the distribution of methanogenic, acetogenic and sulfate-reducing bacteria inside Halodule wrightii roots, are accounted for with the model suggesting the redox gradient recedes into the root at night. This rhizosphere compartment is further supported by studies that have shown root-associated bacteria, in comparison to bacteria in the surrounding sediment, respond more immediately to plant activity and root exudates, are higher in number, show different seasonal community dynamics, and differ taxonomically. The second compartment consists of seagrass bed sediments outside the rhizosphere. It is proposed that bacterial communities there are influenced more by inputs of carbon and solutes from the overlying water than by the roots. The model provides a framework for gaining a better understanding of interactions between seagrass roots and bacteria which may be useful for assessing seagrass condition.