Soil microbial activity in a Liquidambar plantation unresponsive to CO2-driven increases in primary production

The indirect responses of soil microbiota to changes in plant physiology effected by elevated atmospheric carbon dioxide have the potential to alter nutrient availability and soil carbon storage. We measured fine root density, microbial biomass nitrogen, rates of nitrogen mineralization and nitrification, substrate utilization by soil bacteria and extracellular enzyme activities (EEA) associated with bulk soil and fine root rhizoplanes within a 3-year period at the Oak Ridge National Laboratory (ORNL) Free Air Carbon Enrichment (FACE) experiment, situated in a Liquidambar styraciflua plantation. Rhizoplane EEA was similar to that of bulk soil. Prior studies have reported a 21% increase in net primary production (NPP) in the enrichment plots and evidence that additional carbon is reaching the soil system, however we observed no response in any of the variables we measured. These results, which contrast with those from other temperate forest FACE sites, suggest that soil characteristics can influence the magnitude and timing of belowground responses. (C) 2003 Elsevier B.V. All rights reserved.