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Substituting root numbers for length - Improving the use of minirhizotrons to study fine root dynamics.
CROCKER, TRACEY1, HENDRICK, RONALD1, 1
ABSTRACT- Minirhizotrons provide a unique means by which individual root segments can be continuously measured over time, while minimizing soil disturbance and the confounding of spatial-temporal variation. However, the difficulty associated with processing taped images limits the amount of data that can be realistically collected and extracted. We have found that this limitation can be ameliorated using a substitute parameter, root numbers, to estimated root lengths. Linear regression models were fit between root length vs. root number production and mortality for seven sample data sets of varying species and treatments. The resulting r2 values ranged from 0.79 to 0.99, indicating a strong predictive value of root numbers for root lengths. Slope values, representing the average length of a root segment, ranged from 2.34 to 8.38 mm per root for both production and mortality. Most treatments did not significantly alter mean root segment length, the exception being CO2 treatments and treatments that altered community structure which resulted in an alteration of root morphology. When all data were combined into one regression analysis the slope value for production was 3.54 mm per root with a r2 of 0.93 while the slope value for mortality was 4.29 mm per root with a r2 of 0.98. Use of an easily measured variable like root numbers instead of length, once a quantitative relationship between the two variables has been established for a particular species-treatment combination, should substantially minimize current analysis time of minirhizotron images.
KEY WORDS: minirhizotron, fine roots, production, mortality