Morphological and anatomical relationships of loblolly pine fine roots

Abstract

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).

Root anatomy of Pinus taeda L.: seasonal and environmental effects on development in seedlings

“…15d), close to values for older stands (2.7-5.3%, Kramer and Bullock 1966;McCrady and Comerford 1998). The relatively late production of mycorrhizae was probably a result of sterilizing the soil with methyl bromide the fall prior to planting.…”

“…The small percentage of white zone (\5%) at the end of the first year is consistent with earlier field studies where white roots of much older trees constituted a small part of the root system (Reed 1939;Kramer and Bullock 1966;Wilcox 1968;McCrady and Comerford 1998). The amount of white zone was determined by the number of white root tips, their rate of elongation, and the rate of their maturation to CT zones or mycorrhizal roots.…”

“…2-15 m 2 m -2 for trees 10-35 years old; Kramer and Bullock 1966;McCrady and Comerford 1998;Hacke et al 2000).…”

“…The cork zone had significant secondary xylem and phloem growth to facilitate axial transport, and a complete ring of mature cork cells. The above-described system of dividing roots into three zones has distinct advantages over earlier studies where roots were considered to have two zones, i.e., non-suberized and suberized (Addoms 1946;Kramer and Bullock 1966), white and brown (Sands et al 1982), non-woody and woody (Van Rees and Comerford 1990;Escamilla and Comerford 2000), or primary and secondary (McCrady and Comerford 1998). The large cortical plasmalemma surface area (CPSA) of the white root zone provides a great potential for ion uptake, as it is in direct contact with the modified soil solution (MSS) in the apoplast of the cortex.…”

The Efficiency of Nutrient Acquisition over the Life of a Root

“…As new, white roots begin to turn yellow and brown (associated with the accumulation of condensed tannins; McKenzie and Peterson 1995), much of the cortex dies in some species (grape, Richards and Considine 1981;apple, Head 1967;spruce, Downes et al 1992;pine, Peterson et al 1999, but see McCrady andComerford 1998). In other species, especially those with a heavily suberized epidermis and exodermis, the cortex may remain viable for the entire life span of the root (e.g., citrus, Eissenstat and Achor 1999; sugar maple, Brundrett and Kendrick 1988).…”