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Dynamics of fine root carbon in Amazonian tropical ecosystems and the contribution of roots to soil respiration

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Citation

Trumbore, S. E., Da Costa, E. S., Nepstad, D. C., De Camargo, P. B., Martinelli, L., Ray, D., et al. (2006). Dynamics of fine root carbon in Amazonian tropical ecosystems and the contribution of roots to soil respiration. Global Change Biology, 12(2), 217-229. doi:10.1111/j.1365-2486.2005.001063.x.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0027-C3CC-4
Abstract
Radiocarbon (C-14) 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 C-14 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 Delta C-14 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 C-14) from the rate of C flow through the live root pool, and resolve these apparently disparate estimates of root C dynamics. Explaining the C-14 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.