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Automated Image Analysis of Annual Rings in the Roots of Perennial Forbs

2005; University of Chicago Press; Volume: 166; Issue: 5 Linguagem: Inglês

10.1086/431230

1537-5315

Georg von Arx, Hansjoerg Dietz,

Tree Root and Stability Studies

Analysis of annual rings in the secondary root xylem is a relatively new approach to gain a posteriori insight into individual and population life history of perennial dicotyledonous herbs (herb‐chronology). Until now, herb‐chronology has involved manual analysis, which is limited by low reproducibility and comparability and which requires considerable time and expertise from the researcher. We have therefore developed an automated image analysis system (Root Xylem Analysis System [ROXAS]) to improve the standardization and efficiency of conventional herb‐chronological analysis. Digital images of stained root cross sections are used by ROXAS to automatically extract xylem vessels according to morphometric criteria. Annual rings are detected by pattern algorithms that analyze the local anatomical context of each vessel. Besides growth parameters, such as annual ring width and area, parameters related to functional root anatomy, such as vessel area or vessel density, are automatically calculated. We evaluated the results produced by ROXAS, using six individuals from each of five perennial plant species representing a variety of taxonomic groups and anatomical root patterns. All species were conducive to automated analysis, which was six times faster than the manual method. Overall, 95% of all annual rings and 98% of all vessels were correctly identified. Accuracy of automated ring width measurements tended to be slightly higher than that of manual analysis, ranging from 2.1% to 5.3% deviation from reference data for all species. Further anatomical parameters, such as vessel area or vessel density, varied substantially between species, indicating anatomical adaptations of these perennial forbs to the constraints of their specific habitats. Automated herb‐chronology using ROXAS may therefore prove to be useful for efficient and reproducible analysis of annual growth increments in the roots of forbs and for investigations into their functional root anatomy.