MORPHOLOGICAL AND ANATOMICAL RELATIONSHIPS OF LOBLOLLY-PINE FINE ROOTS

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 un proven. The objectives of this study were (i) to establish relationshi ps between root color, diameter, and developmental stage (i.e., primar y or secondary tissues) for loblolly pine, (ii) to determine the perce ntages of primary and secondary brown roots by diameter class, and (ii i) to use these percentages to make first order estimates of the amoun t of brown root length and surface area that is in the primary and sec ondary developmental stages for sampled roots of a semi-mature lobloll y pine stand. ''Unsectioned'' roots were collected by coring to a 25-c m depth 3 times a year and measuring roots for length and surface area by diameter class. ''Sectioned'' roots were sampled from a one-time c ore and from periodic grab samples. These roots were sectioned and cha racterized by their color, diameter and developmental stage. Diameters of sectioned roots (n=353) ranged from 0.21 to 8.24 mm. White and ora nge roots ranged from 0.23 to 2.50 mm, while brown roots spanned the r ange. White roots were developmentally primary, whereas orange/brown r oots 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 len gth of the sampled stands was estimated to be composed of 38% primary tissue, 58% secondary tissue, and 4% transition tissue. Lastly, neithe r root color nor diameter was a reliable predictor of developmental st age unless roots were white (primary), or orange/brown and >2.5 mm in diameter (secondary).