Simulated effects of elevated CO2 on nitrogen cycling using the NuCM model

摘要

The interactions between elevated CO(sub 2) and N cycling were explored using211u001esimulations generated by the Nutrient Cycling Model (NuCM) for a Pinus taeda site 211u001eat Duke, North Carolina and a mixed deciduous site at Walker Branch, Tennessee. 211u001eThe simulations tested whether N limitation would prevent growth increase in 211u001eresponse to elevated CO(sub 2) and whether growth response to CO(sub 2) in N-211u001elimited systems could be facilitated by increased biomass/N (reduced 211u001econcentration) and/or increased litter N mineralization. Nitrogen limitation 211u001eprecluded additional growth when target growth rates and litterfall were 211u001eincreased (simulating potential response to elevated CO(sub 2)) at the Duke site. 211u001eAt the Walker Branch site, increasing target growth and litterfall caused a 211u001eslight (790) increases in growth. Reducing foliar N concentrations caused reduced 211u001egrowth because of N limitation created by reduced litter quality (C/N ratio), 211u001ereduced decomposition and N accumulation in forest floor. These effects were most 211u001epronounced at the Duke site, where the forest floor N turnover rate was lower 211u001ethan at the Walker Branch site. Reducing wood N concentration allowed prolonged 211u001eincreases in growth because of greater biomass/N; however, N uptake was reduced, 211u001eallowing greater N immobilization in the forest floor and soil. Increased N 211u001emineralization caused increased growth at the Duke site but not at Walker Branch.