Document: MAT-3-66-14

How long do roots live? A ¹³C tracer technique for assessing fine root longevity in a North Carolina pine forest.

MATAMALA, R.*, M.A.GONZALEZ-MELER and W.H.SCHLESINGER

Duke University, Durham, NC 27708 USA ¹

Abstract:
Quantifying root lifespan and root turnover are two of the most intractable problems in studies of belowground processes in terrestrial ecosystems. The lack of information on the root mean residence time creates uncertainty in estimates of fine root production that affects estimates of forest net primary production. We have developed a method to assess root turnover using changes in the ¹³C signature of roots exposed to a depleted ¹³C air in a forest FACE experiment. The progressive change in ¹³C of the vegetation C allows a quantitative estimate of parameters such as the turnover time and biomass of roots. The experimental site is a loblolly pine (Pinus taeda) plantation located in the Duke Forest in North Carolina. The experimental plots receive a continuous supplement of CO₂ to maintain an atmospheric concentration 200 L L^-1 above ambient. The CO₂ used in the elevated plots is depleted in ¹³C ¹³C = -44 vs. PDB). Using this CO₂ to elevate the atmospheric concentration changes the ¹³C of CO₂ in the FACE plots from -8 to -21 . We found that roots growing in in-growth cores, after one year of fumigation, had the same ¹³C signature as leaves, indicating that root growth was derived from newly fixed C. The isotopic ratio, ¹³C of roots of the pines in the elevated CO₂ treatment is -39.5 compared to -28 in the ambient treatment. The replacement of the fine root population with new fine roots grown since the beginning of fumigation of the experimental plots is gradual and can be fitted to an exponential regression. This regression estimates that the lifespan of fine roots, (1 mm diameter), is 4.3 years, the lifespan of roots between 1 and 2 mm in diameter is 7.2 years and the lifespan of thicker roots, those larger than 2 mm but less than 5 mm, is 7.6 years. This technique can be applied to estimate root turnover in various existing FACE experiments and in other Global Change experiments using elevated CO₂ with a constant ¹³C to fumigate vegetation.

Keywords: root turnover, forests, 13C, elevated CO2

This abstract is being presented at: 1:45 PM in session:
Oral Session #12: Roots.