Site and Silvicultural Effects On Root Growth and Nutrient Content of 4 Loblolly Pine (Pinus taeda L.) Clones.

Four loblolly pine clones representing 2 moderate and 2 broad crown ideotypes were planted on a clayey Virginia Piedmont site and a loamy North Carolina Coastal Plain site in order to investigate growth with low (control) and high (competing vegetation control + fertilization) silvicultural regimes. Two years after establishment, no differences in aboveground growth were observed. We hypothesized that in the initial growth stages, silvicultural treatments may instead be affecting belowground growth. Investigating these effects on the fine root system may provide insight into the future aboveground growth strategies of these loblolly pine clones. Root development over time was determined with in-growth root cores. At each site, 2 trees of average plot height for each clone were selected for height, diameter, and root growth measurements in April, June, and November 2011. In February 2011, six in-growth root cores were installed 80 cm from the base of each selected tree by taking a 0.009558 m³ core sample to 20 cm in depth, sieving the soil to remove roots, and re-filling the hole with the sieved soil. The six in-growth root cores were sampled in April (1), June (2), and November (3) 2011 using the 0.009558 m³ core sampler. Fine roots were separated from the soil using a hydro-pneumatic elutriation system and scanned to obtain root length and root diameter distribution using WinRhizo® Software. Root mass and nitrogen (N) and phosphorus (P) content were also determined. Initial results from the April 2011 sampling indicate site, silviculture, and clonal variation in root length. In addition, root length was negatively correlated to tree height growth and slopes varied by clone. These differences in root system development indicate a strong potential for future variation in aboveground growth. We anticipate N and P contents to exhibit similar clonal variation indicating differences in nutrient capture.