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.