Quantifying root lateral distribution and turnover using pine trees with a distinct stable carbon isotope signature
- In order to help assess spatial competition for below-ground resources, we quantified the effects of fertilization on root biomass quantity and lateral root distribution of midrotation Pinus taeda trees. Open-top chambers exposed trees to ambient or ambient plus 200 µmol mol-1 atmospheric CO2 for 31 months.
- Tank CO2 was depleted in atmospheric 13C; foliage of elevated CO2 trees had δ13C of - 42·9%, compared with - 29·1% for ambient CO2 trees.
- Roots 1 m from the base of elevated CO2-grown trees had more negative δ13C relative to control trees, and this difference was detected, on average, up to 5·8, 3·7 and 3·7 m away from the trees for 0-2, 2-5 and >5 mm root-size classes, respectively. Non-fertilized tree roots extended as far as fertilized trees despite the fact that their above-ground biomass was less than half that of fertilized trees.
- These results are informative with respect to root sampling intensity and protocol, and the distances required between experimental manipulations to evaluate belowground processes of independent treatments.
- Fine-root turnover has usually been estimated to range from weeks to 3 years, representing a major avenue of carbon flux. Using a mixing model we calculated that 0-2 mm roots had a mean residence time of 4·5 years indicating relatively slow fineroot turnover, a result that has major implications in modelling C cycling.