Morphological and anatomical relationships of loblolly pine fine roots
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Suberized or brown roots have been traditionally considered secondary or woody tissues. The validity of using morphological features such as color to infer root anatomy for southern pines is questionable and unproven. The objectives of this study were (i) to establish relationships between root color, diameter, and developmental stage (i.e., primary or secondary tissues) for loblolly pine, (ii) to determine the percentages of primary and secondary brown roots by diameter class, and (iii) to use these percentages to make first order estimates of the amount of brown root length and surface area that is in the primary and secondary developmental stages for sampled roots of a semi-mature loblolly pine stand. ”Unsectioned” roots were collected by coring to a 25-cm depth 3 times a year and measuring roots for length and surface area by diameter class. ”Sectioned” roots were sampled from a one-time core and from periodic grab samples. These roots were sectioned and characterized by their color, diameter and developmental stage. Diameters of sectioned roots (n=353) ranged from 0.21 to 8.24 mm. White and orange roots ranged from 0.23 to 2.50 mm, while brown roots spanned the range. White roots were developmentally primary, whereas orange/brown roots were either primary (from 0.21 to 2.50 mm), secondary (from 0.33 to 8.24 mm), or in transition (from 0.27 to 0.76). Total live root length of the sampled stands was estimated to be composed of 38% primary tissue, 58% secondary tissue, and 4% transition tissue. Lastly, neither root color nor diameter was a reliable predictor of developmental stage unless roots were white (primary), or orange/brown and >2.5 mm in diameter (secondary).
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