Fine roots support the water and nutrient demands of plants and supply carbon to soils.
Quantifying turnover times of fine roots is crucial for modeling soil organic matter dynamics
and constraining carbon cycle–climate feedbacks. Here we challenge widely used isotopebased
estimates suggesting the turnover of fine roots of trees to be as slow as a decade. By
recording annual growth rings of roots from woody plant species, we show that mean
chronological ages of fine roots vary from <1 to 12 years in temperate, boreal and sub-arctic
forests. Radiocarbon dating reveals the same roots to be constructed from 10 ± 1 year (mean
± 1 SE) older carbon. This dramatic difference provides evidence for a time lag between plant
carbon assimilation and production of fine roots, most likely due to internal carbon storage.
The high root turnover documented here implies greater carbon inputs into soils than previously
thought which has wide-ranging implications for quantifying ecosystem carbon