ABOVE-GROUND AND BELOWGROUND EMERGENT MACROPHYTE PRODUCTION AND TURNOVER IN A COASTAL MARSH ECOSYSTEM, GEORGIA

Seasonal patterns of aboveground plant mass and the depth distribution of live roots, rhizomes and dead belowground organic matter were measured for Spartina alterniflora and Spartina cynosuroides in Georgia tidal marshes. Peak live aboveground biomass was 1.6.times. higher for S. cynosuroides than for S. alterniflora. Live biomass was 2.4.times. more belowground than aboveground for S. cynosuroides and 1.7.times. for S. alterniflora. Rhizomes made up 76 and 87% of live belowground biomass during the year. Mirrored patterns of biomass accumulation and loss in above- and belowground tissues during the year suggest the importance of seasonal storage and redistribution of organic matter. Belowground production was measured with a technique that partially accounts for midseason decomposition. Total plant production was estimated to be 7620 g dry mass .cntdot. m-2 .cntdot. yr-1 for S. alterniflora and 7708 for S. cynosuroides. Belowground production was roughly 1.6.times. aboveground production. Turnover rates for belowground live material were 1.42/yr for S. cynosuroides and 3.22/yr for S. alterniflora. The fate of root and rhizome material, including the extent to which such material enters the estuarine or nearshore food webs, is not clear.