Mission impossible? Criteria for judging dead fine roots in forest field studies

The determination of dead roots is important for clarifying the roles of fine tree roots in carbon (C) and nutrient cycling in forest ecosystems. However, the various methods proposed for determining dead roots and the variation in terminology expressing fine-root mortality can cause significant errors in quantifying dead roots. In this study, we aimed to clarify the various criteria used for sorting dead fine roots using published papers. The second aim was to identify problems in defining fine-root mortality and to clarify the border between defining dead roots and root litter. Finally, we propose future challenges in determining dead fine roots to collect data with the same standards. We collected 95 papers published in the last 50 years and found that visual- and touch-based judgments are most commonly used for sorting dead roots. We found many different terms representing the state of fine-root shedding and mortality. In this study, we proposed that the terminology for dead fine roots needs to be based on the process from root death to decomposition. The accuracy of dead root determination can be improved by experimentally elucidating the fine-root decomposition process. It is also important to increase objectivity in the description of the criteria when judging dead roots in a field. Then, if we combine multiple methods and introducing new tools such as Automatic Intelligence, the mission of identifying dead roots would be possible in future.