Elevated CO2 influences nutrient availability in young beech-spruce communities on two soil types

Abstract

The objectives of this study were to investigate how different soil types and elevated N deposition (0.7 vs 7gNm-2a-1) influence the effects of elevated CO2 (370 vs 570µmol CO2 mol-1) on soil nutrients and net accumulation of N, P, K, S, Ca, Mg, Fe, Mn, and Zn in spruce (Picea abies) and beech (Fagus sylvatica). Model ecosystems were established in large open-top chambers on two different forest soils: a nutrient-poor acidic loam and a nutrient-rich calcareous sand. The response of net nutrient accumulation to elevated atmospheric CO2 depended upon soil type (interaction soil × CO2, P<0.05 for N, P, K, S, Ca, Mg, Zn) and differed between spruce and beech. On the acidic loam, CO2 enrichment suppressed net accumulation of all nutrients in beech (P<0.05 for P, S, Zn), but stimulated it for spruce (P<0.05 for Fe, Zn) On the nutrient-rich calcareous sand, increased atmospheric CO2 enhanced nutrient accumulation in both species significantly. Increasing the N deposition did not influence the CO2 effects on net nutrient accumulation with either soil. Under elevated atmospheric CO2, the accumulation of N declined relative to other nutrients, as indicated by decreasing ratios of N to other nutrients in tree biomass (all ratios: P<0.001, except the N to S ratio). In both the soil and soil solution, elevated CO2 did not influence concentrations of base cations and available P. Under CO2 enrichment, concentrations of exchangeable NH4+ decreased by 22% in the acidic loam and increased by 50% in the calcareous sand (soil × CO2, P<0.001). NO3- concentrations decreased by 10-70% at elevated CO2 in both soils (P<0.01).