Effects of elevated carbon dioxide on soils in a Florida scrub oak ecosystem

The results of a 3-yr study on the effects of elevated CO2 on soil N and P, soil pCO2, and calculated CO2 efflux in a fire-regenerated Florida scrub oak ecosystem are summarized. We hypothesized that elevated CO2 would cause (i) increases in soil pCO2 and soil respiration and (ii) reduced levels of soil-available N and P. The effects of elevated CO2 on soil N availability differed according to the method used. Results of resin lysimeter collections and anion exchange membrane tests in the field showed reduced NO3- in soils in Years 1 and 3. On the other hand, re-analysis of homogenized, buried soil bags after 1 yr suggested a relative increase in N availability (lower C to N ratio) under elevated CO2. In the case of P, the buried bags and membranes suggested a negative effect of CO2 on P during the first year; this faded over time, however, as P availability declined overall, probably in response to P uptake. Elevated CO2 had no effect on soil pCO2 or calculated soil respiration at any time, further suggesting that plant rather than microbial uptake was the primary factor responsible for the observed changes in N and P availability with elevated CO2.