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).
Needlefall, aboveground net primary production (ANPP), canopy light interception and attenuation, and "radiation use efficiency" of five open-pollinated loblolly pine (Pinus taeda L.) families were investigated using 100-tree family block plots near Summerville, SC. Family variation in annual needlefall amounts was significant during the fourth (from 4796 to 6191 kg ha-1) and fifth growing seasons (from 4717 to 5721 kg ha-1); needlefall patterns for the poorest performing family were asynchronous from those of the others, with notably higher needlefall rates from April to July. Estimates of ANPP at age 4 yr varied by 16% (from 32.9 to 38.2 Mg ha-1) among families, and were generally commensurate with progeny test rankings based on height growth. The relationship between ANPP and leaf area index (LAI) was both significant and curvilinear, with an apparent optimum level of production (42.6 Mg ha-1) achieved at a LAI of about 13 (all-sided; February). The least productive families had the lowest mean LAI (e.g., 7.9), while the most productive families generally had higher levels of LAI (e.g., 13.6). Significant family differences in canopy light interception were present in every month sampled except June, when photosynthetically active radiation (PAR) interception exceeded 90% for all families. Light extinction coefficients (k) for February differed significantly among the five families, and ranged from 0.28 to 0.38; families with the largest LAIs generally had the lowest values of k and the highest levels of PAR interception. A strong linear relationship (r² = 0.74) was found between ANPP and intercepted PAR. Estimates of the dry matter:radiation quotient (ε "radiation use efficiency") differed significantly among families, and ranged from 1.33 g MJ-1 to 1.48 g MJ-1. Results of this study suggest that fundamental differences exist in production ecology among loblolly pine families, and that canopy-level characteristics such as LAI, PAR interception, and "radiation use efficiency" are important in conferring differential family performance. For. Sci. 44(1):64-72.
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