Janssens, I.A., Crookshanks, M., Taylor, G. and Ceulemans, R. 1998. Elevated atmospheric CO2 increases fine root production, respiration, rhizosphere respiration and soil CO2 efflux in Scots pine seedlings. Global Change Biology 4: 871-878.
What was done
Three-year-old Scots pine seedlings were grown in open-top chambers located in Belgium at ambient and 700 ppm atmospheric CO2 for six months to study the effects of elevated CO2 on root growth and respiration. In addition, rhizosphere respiration and soil CO2 efflux were examined to quantify belowground carbon losses from the entire root system. During the experiment, no irrigation or fertilization was applied.
What was learned
Elevated CO2 significantly increased total root length (sum of all roots) by 122% and total root dry mass by 135% relative to roots of seedlings grown in ambient CO2. Although starch accumulation in CO2-enriched roots was nearly 90% greater than that observed in roots produced in ambient CO2, the carbon to nitrogen ratio of CO2-enriched roots was significantly lower than that of roots from control plants, indicating that roots in the elevated CO2 treatment had significantly higher nitrogen concentrations.
When expressed on a per unit nitrogen basis, no significant differences in root respiration were observed between CO2 treatments. However, because rhizosphere respiration was significantly enhanced in elevated CO2, probably due to increased microbial and fungal activities resulting from increased root turnover and/or exudation, the overall CO2 efflux from the soil was about 25% greater with atmospheric CO2 enrichment.
What it means
As the CO2 content of the air rises, Scots pine seedlings will likely produce more extensive root systems that can search greater soil volumes for water and nutrients. Because nitrogen is a limiting element required for plant growth, and as the current study indicates that roots of seedlings grown in elevated CO2 contained significantly more nitrogen than roots of seedlings grown in ambient CO2, Scots pine seedlings, with their expanded root systems, will probably find the necessary resources to exhibit significant growth responses in a future world of higher atmospheric CO2.
Reviewed 1 April 1999