Thursday, 9 October 2008: 9:00 AM
George R. Brown Convention Center, 371D
A range of growth responses to fertilization have been observed among clones of Pinus taeda in field conditions. Increased leaf area is widely accepted as the long-term mechanism leading to increased carbon (C) fixation and thus volume response as a result of fertilization. However, clonal variability with respect to short-term changes in C allocation and photosynthetic rates (Asat) as a result of fertilization is less well-understood. Increased C allocation to above-ground portions of the tree may be due to short-term increases in Asat or reductions in C allocation below-ground. The objective of this research was to determine if short-term fine root and root exudate C allocation or Asat may be altered by fertilizer application. Our hypotheses were (1) fertilization and water stress decrease C allocation to root exudates and fine roots, (2) fertilization increases and drought decreases Asat, and (3) specific C allocation patterns and changes in Asat vary between clones. To test these hypotheses a 2 x 2 x 2 factorial experiment with clone, fertilizer, and drought treatments was replicated in five large growth rooms. Seedlings were planted in pots containing 120,000 cm3 of coarse, nutrient and organic matter deficient sand. Root exudates were quantified with XAD-7 resin capsules placed in situ sequentially throughout the experiment. Capsules were extracted with deionized water and a 50 % methanol solution to partition anthrone reactive C and phenols. Fine roots were quantified with root cores and the destructive harvest of all trees at the conclusion of the experiment. Asat was quantified with a LI-6400 portable photosynthesis system. Our results will quantify changes in carbon allocation patterns between the clones due to changes in nutrient and water availability.