Utilization of DOC from seagrass rhizomes by sediment bacteria: 13C-tracer experiments and modeling

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 317:41-55 (2006) - doi:10.3354/meps317041 Utilization of DOC from seagrass rhizomes by sediment bacteria: 13C-tracer experiments and modeling James E. Kaldy1,2,*, Peter M. Eldridge2, Luis A. Cifuentes1, W. Brian Jones1 1Department of Oceanography, Texas A&M University, MS 3146, College Station, Texas 77843, USA 2US EPA—Western Ecology Division, Pacific Coastal Ecology Branch, 2111 SE Marine Science Center Drive, Newport, Oregon 97365, USA *Address for correspondence: Newport.Email: kaldy.jim@epa.gov ABSTRACT: Seagrasses are widely recognized as contributing to net ecosystem primary production and to supporting heterotrophy in estuarine systems. We investigated the linkage between seagrass (Thalassia testudinum) rhizosphere carbon exudation and sediment bacteria. In microcosms, we simulated summer conditions and enriched the water column DIC (dissolved inorganic carbon) pool with 13C, then followed the tracer into the sediment porewater DOC (dissolved organic carbon) and the bacterial biomarkers (phospholipid fatty acids, PLFAs). Subsequently, we developed an inverse analysis of the seagrass microcosm system and calculated the flux of carbon between biological and geochemical compartments. After 18 d, the bacterial pool was enriched by about Δ +4‰, while the DOC pool was enriched by about Δ +50 to +60‰. We estimate that about 15 to 30% of gross primary production was exuded from the root/rhizome and that this accounts for about 41 to 61% of the carbon required by sediment bacteria. Mineralization of detrital seagrass leaf material or refractory seagrass DOC rhizodeposition may account for the other 38 to 59% of the bacterial carbon demand. We suggest that the sediment bacteria in the seagrass rhizosphere rapidly utilize labile DOC and, consequently, build up 13C label in the refractory DOC pool. Our results conclusively show a direct linkage between seagrass carbon exudation and sediment biogeochemical processes. KEY WORDS: Thalassia testudinum · Stable isotope · DOC · Tracer · Phospholipid fatty acid · Rhizodeposition · Carbon flux Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 317. Online publication date: July 18, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.