LEAF-AREA AND ABOVE-GROUND AND BELOW-GROUND GROWTH-RESPONSES OF LOBLOLLY-PINE TO NUTRIENT AND WATER ADDITIONS

A 2 x 2 nutrient and water factorial experiment with four replications was installed in an 8-yr-old stand of loblolly pine (Pinus taeda L.) growing on an infertile, excessively drained sandy site in Scotland Co unty, North Carolina. After the fourth year of treatment, estimated st em volume increment, total biomass production, and peak leaf area inde x (LAI) increased 152%, 99%, and 101%, respectively, with fertilizatio n and 25%, 23%, 16%, respectively, with irrigation. Stem volume growth efficiency (growth per unit LAI) increased 21% with fertilization, 9% with irrigation, and 30% with both fertilization and irrigation, Tota l biomass production efficiency increased 91% with fertilization, 29% with irrigation, and 120% with both fertilization and irrigation. The observed increase in stem volume growth efficiency may have been due, in part, to changes in biomass partitioning, However, altered partitio ning patterns alone did not explain the observed increase in total bio mass production efficiency, We hypothesized that the change in total b iomass production efficiency may have been a result of greater allocat ion to foliage (photosynthesizing tissue) and less allocation to fine roots (a high maintenance respiration tissue) under fertilization and irrigation treatments.