Effects of elevated atmospheric CO2 concentration on C and N pools and rhizosphere processes in a Florida scrub oak community

The effect of elevated atmospheric CO2 concentration (C-a) on soil carbon a nd nitrogen accumulation and soil microbial biomass and activity in a nativ e Florida scrub oak community was studied. The plant community, dominated b y Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated C-a in open-top chambers. Buried subsoil bags were retrieved af ter 1 year of exposure to elevated C-a. In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the first after a lo ng dry spell and the second after 25 mm of rainfall) and divided into rhizo sphere and bulk soil. Soil organic matter accumulation (excluding roots) in to the buried subsoil bags was lower in elevated than in ambient C-a. Conce ntrations of soluble carbon and ninhydrin-reactive nitrogen (N-ninh) in the rhizosphere soil were reduced by elevated C-a for the first sampling date and unaffected for the second sampling date. Microbial activity, measured a s fluorescein diacetate (FDA) hydrolysis, decreased in elevated C-a for the first sampling date. Microbial biomass carbon and nitrogen in the bulk soi l were unaffected by elevated C-a. There was no effect of elevated C-a on b acterial numbers in the rhizosphere.