Dynamics of fine root carbon in Amazonian tropical ecosystems

TitleDynamics of fine root carbon in Amazonian tropical ecosystems
Publication TypeJournal Article
Year of Publication2006
AuthorsTrumbore, SE, Restom, T, E. da Costa, S-, Barbosa-deCamargo, P, Martinelli, LA, Nepstad, D, Ray, D, Silver, WL
JournalGlobal Change Biology
Accession NumberLUQ.661

Radiocarbon (14C) provides a measure of the mean age of carbon (C) in roots, or the time elapsed since the C making up root tissues was fixed from the atmosphere. Radiocarbon signatures of live and dead fine (<2 mm diameter) roots in two mature Amazon tropical forests are consistent with average ages of 4–11 years (ranging from <1 to >40 years). Measurements of 14C in the structural tissues of roots known to have grown during 2002 demonstrate that new roots are constructed from recent (<2-year-old) photosynthetic products. High Δ14C values in live roots most likely indicate the mean lifetime of the root rather than the isotopic signature of inherited C or C taken up from the soil. Estimates of the mean residence time of C in forest fine roots (inventory divided by loss rate) are substantially shorter (1–3 years) than the age of standing fine root C stocks obtained from radiocarbon (4–11 years). By assuming positively skewed distributions for root ages, we can effectively decouple the mean age of C in live fine roots (measured using 14C) from the rate of C flow through the live root pool, and resolve these apparently disparate estimates of root C dynamics. Explaining the 14C values in soil pore space CO2, in addition, requires that a portion of the decomposing roots be cycled through soil organic matter pools with decadal turnover time.