Effects of CO{sub 2} and nitrogen fertilization on soils planted with ponderosa pine

The effects of elevated CO{sub 2} (ambient, 525, and 700 {micro}l l{sup -1})and N fertilization (0, 10, and 20 g N m{sup 2} yr{sup -1}) on soil pCO{sub 2}, CO{sub 2} efflux, soil solution chemistry, and soil C and nutrients in an open-top chamber study with Pinus ponderosa are described. Soil pCO{sub 2} and CO{sub 2} efflux were significantly greater with elevated CO{sub 2}, at first (second growing season) in the 525 {micro}l l{sup -1} and later (fourth and fifth growing seasons) in the 700 {micro}l l{sup -1} CO{sub 2} treatments. Soil solution HCO{sub 3}{sup -} concentrations were temporarily elevated in the 525 {micro}l l{sup -1} CO{sub 2} treatment during the second growing season, consistent with the elevated pCO{sub 2}. Nitrogen fertilization had no consistent effect on soil pCO{sub 2} or CO{sub 2} efflux, but did have the expected negative effect on exchangeable Ca{sup 2+}, K{sup +}, and Mg{sup 2+}, presumed to be caused by increased nitrate leaching. Elevated CO{sub 2} had no consistent effects on exchangeable Ca{sup 2+}, K{sup +}, and Mg{sup 2+}, but did cause temporary reductions in soil NO{sup 3{sup -}} (second growing season). Statistically significant negative effects of elevated CO{sub 2} on soil extractable P were noted in the third and sixth growing seasons. However, these patterns in extractable P reflected pre-treatment differences, which, while not statistically significant, followed the same pattern. Statistically significant effects of elevated CO{sub 2} on total C and N in soils were noted in the third and sixth growing seasons, but these effects were inconsistent among N treatments and years. The clearest effect of elevated CO{sub 2} was in the case of C/N ratio in year 6, where there was a consistent, positive effect. The increases in C/N ratio with elevated CO{sub 2} in year six were largely a result of reductions in soil N rather than increases in soil C. Future papers will assess whether this apparent reduction in soil N could have been accounted for by plant uptake