The CO2 dependence of photosynthesis, plant growth responses to elevated CO2 concentrations and their interaction with soil nutrient status, II. Temperate and boreal forest productivity and the combined effects of increasing CO2 concentrations and in

摘要

Appropriate rates of carbon acquisition by temperate and boreal forests were re-evaluated. Based on continental-scale forestry data it was suggested that the productivity of temperate and boreal forests had been previously overestimated. Using thesevalues, a model of the integrated response of ecosystems to carbon dioxide concentration and soil nitrogen availability is presented. The model did not assume constant C:N ratios in plant or soil and considered the effect of increases in atmospheric CO2concentrations and nitrogen deposition separately or together. For temperate-zone forests a co-occurrence of a CO2 increase and N deposition doubled the increase in net primary productivity and carbon sequestration. Considered separately, the effect ofthe atmospheric CO2 increase was less than even moderate rates of anthropogenic N deposition for temperate or boreal forests. By contrast, for tropical forests, the atmospheric CO2 increase was sufficient to induce large rates of carbon accumulation in plants and soil. Application of the model at the global scale suggests large localized sinks for CO2 in either tropical rain forests or in forested or grassland areas of Europe and North America where appreciable N deposition occurs. Overall, the model suggests a terrestrial sink owing to CO2 fertilization and N deposition of about 0.2 Pmol C per year. Approximately half of this was in the mid-latitudes of the northern hemisphere and half in the tropics.