SOIL PCO(2), SOIL RESPIRATION, AND ROOT ACTIVITY IN CO2-FUMIGATED AND NITROGEN-FERTILIZED PONDEROSA PINE

The purpose of this paper is to describe the effects of CO2 and N treatments on soil pCO(2), calculated CO2 efflux, root biomass and soil carbon in open-top chambers planted with Pinus ponderosa seedlings. Based upon the literature, it was hypothesized that both elevated CO2 and N would cause increased foot biomass which would in turn cause increases in both total soil CO2 efflux and microbial respiration. This hypothesis was only supported in part: both CO2 and N treatments caused significant increases in root biomass, soil pCO(2), and calculated CO2 efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO2 efflux rates indicated that microbial respiration contributes little to total soil CO2 efflux in the field. Measurements of soil pCO(2) and calculated CO2 efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO2 and N treatments.