The objectives of this study were to investigate how different soil types and elevated N deposition (0.7 vs 7 g N ma) influence the effects of elevated CO (370 vs 570 µmol CO mol) 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 CO depended upon soil type (interaction soil × CO, P<0.05 for N, P, K, S, Ca, Mg, Zn) and differed between spruce and beech. On the acidic loam, CO 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 CO enhanced nutrient accumulation in both species significantly. Increasing the N deposition did not influence the CO effects on net nutrient accumulation with either soil. Under elevated atmospheric CO, 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 CO did not influence concentrations of base cations and available P. Under CO enrichment, concentrations of exchangeable NH decreased by 22% in the acidic loam and increased by 50% in the calcareous sand (soil × CO, P<0.001). NO concentrations decreased by 10-70% at elevated CO in both soils (P<0.01).
A factorial experiment was used to evaluate light, a range of alternating temperatures, and stratification on germination of freshly collected current year's seed of Piceamariana (Mill.) B.S.P. Light was required for complete germination of unstratified seed at low (5–15 °C) and moderate (10–20 °C) temperatures. This light requirement was removed by moist chilling at 3 °C for 24 days.
The objectives of this study were to estimate how soil type, elevated N deposition (0.7 vs. 7 g N m −2 y −1) and tree species influenc the potential effects of elevated CO 2 (370 vs. 570 µmol CO 2 mol −1) on N pools and flu es in forest soils. Model spruce-beech forest ecosystems were established on a nutrient-rich calcareous sand and on a nutrient-poor acidic loam in large open-top chambers. In the fourth year of treatment, we measured N concentrations in the soil solution at different depths, estimated N accumulation by ion exchange resin (IER) bags, and quantif ed N export in drainage water, denitrif cation, and net N uptake by trees. Under elevated CO 2 , concentrations of N in the soil solution were signif cantly reduced. In the nutrient-rich calcareous sand, CO 2 enrichment decreased N concentrations in the soil solution at all depths (−45 to −100%). In the nutrient-poor acidic loam, the negative CO 2 effect was restricted to the uppermost 5 cm of the soil. Increasing the N deposition stimulated the negative impact of CO 2 enrichment on soil solution N in the acidic loam at 5 cm depth from −20% at low N inputs to −70% at high N inputs. In the nutrient-rich calcareous sand, N additions did not influenc the CO 2 effect on soil solution N. Accumulation of N by IER bags, which were installed under individual trees, was decreased at high CO 2 levels under spruce in both soil types. Under beech, this decrease occurred only in the calcareous sand. N accumulation by IER bags was negatively correlated with current-years foliage biomass, suggesting that the reduction of soil N availability indices was related to a CO 2-induced growth enhancement. However, the net N uptake by trees was not significantl increased by elevated CO 2. Thus, we suppose that the reduced N concentrations in the soil solution at elevated CO 2 concentrations were rather caused by an increased N immobilisation in the soil. Denitrificati n was not infl enced by atmospheric CO 2 concentrations. CO 2 enrichment decreased nitrate leaching in drainage by 65%, which suggests that rising atmospheric CO 2 potentially increases the N retention capacity of forest ecosystems.
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