Considerations in the study of tree fine-root turnover with minirhizotrons

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Fine-root turnover is an important component of forest carbon dynamics. We detail the characteristics of the minirhizotron method of measuring fine-root turnover and discuss its methodological implications. Minirhizotron data are relative values proportional to the data taken from the bulk, in situ soil, since they are taken at the soil-tube interface, so we propose several ways to validate minirhizotron data. Most short-term studies show fine-root production to be higher than fine-root mortality, suggesting that disturbance resulting from minirhizotron installation continues for several years. Initial-years results tend to lead to overestimates of fine-root dynamics, although these results define the maximal limits of fine-root production and mortality. We compare the definitions of fine-root turnover and methods of calculation used in different studies. We find that values of fine-root turnover depend on the definition of fine roots, methods of measurement, definition of turnover, and methods of calculation, so these factors must be taken into account when turnover values are discussed. In addition, soil depth is a key factor in the study of fine-root turnover, as is variation in the physical qualities, form and function, of the fine roots. Further long-term research into these key factors in relation to biotic and abiotic parameters will improve our knowledge of forest carbon dynamics.
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