Reference
Wiemken, V., Ineichen, K. and Boller, T. 2001. Development of ectomycorrhizas in model beech-spruce ecosystems on siliceous and calcareous soil: a 4-year experiment with atmospheric CO2 enrichment and nitrogen fertilization. Plant and Soil 234: 99-108.
What was done
The authors grew seedlings of beech (Fagus sylvatica L.) and spruce (Picea abies L.) in model ecosystems on nutrient rich and poor soils within open-top chambers exposed to ambient and elevated (560 ppm) atmospheric CO2 concentrations for four years to study the development of ectomycorrhizal fungi in these forest communities. In addition, for each of the two soil types investiagated, nitrogen fertilization was conducted at both low and high rates to determine if soil nitrogen status plays any role in eliciting CO2- or nutrient-mediated growth responses.
What was learned
On nutrient poor soils, elevated CO2 and high nitrogen input individually caused 30 and 25% increases in fine root biomass, respectively, while they collectively increased it by about 50%. On nutrient rich soils, however, high nitrogen input had no effect on fine root biomass, while elevated CO2 enhanced it by 75 and 78% alone and in combination with high nitrogen, respectively.
On nutrient poor soils, elevated CO2 and high nitrogen increased the amount of fungal biomass associated with fine roots by 31 and 97%, respectively. In combination, these two variables enhanced fungal biomass by about 116%. On nutrient rich soils, however, high nitrogen input had no effect on fungal biomass, while elevated CO2 enhanced it by about 100%. Together, high nitrogen and elevated CO2 increased fungal biomass on nutrient rich soils by almost 200%.
What it means
As the CO2 content of the air continues to rise, it is likely that regenerating forest communities of beech and spruce will exhibit enhanced fine root production and ectomycorrhizal fungal growth, regardless of soil nutritional characteristics. However, with additional soil nitrogen, these growth increases will likely become even more robust, allowing greater nutrient acquisition and transfer from the fungal symbionts to their host seedlings. Thus, in a future CO2-enriched world, these forest communities will likely sequester much greater amounts of atmospheric carbon belowground in fine root and ectomycorrhizal biomass.