PARENT SESSION
Poster Session #40: Water Relations I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Source water use by Loblolly (Pinus taeda L.) and Virginia (Pinus virginiana Miller) pines.

Martin, Allison^*,1, Jackson, Paula¹, Sutton, Heather¹, ¹ Kennesaw State University, Kennesaw, GA

ABSTRACT- We used stable hydrogen isotope compositions (D) to determine the water acquisition patterns of Loblolly and Virginia pines of various ages growing in a mixed deciduous forest in Northwest Georgia. We compared D signatures of tree xylem samples with the D signatures of various potential water sources on the site (e.g. soil samples at various depths and rain, well, and lake water samples). Samples were collected during wet and dry soil conditions to determine if the pines switch water sources depending on water availability. Concurrent measurements of pre-dawn and mid-day leaf water potentials were also determined. Xylem D-values of Pinus taeda (M = -44.50 ^o/oo, SD = 6.07) and Pinus virginiana Miller (M = -49.07 ^o/oo, SD = 11.28) were similar during wet conditions. However, the average D-values for each species differed under dry conditions, with xylem water in Pinus taeda (M = -63.56 ^o/oo, SD = .03) displaying a trend towards more negative average values than those of Pinus virginiana Miller(M = -37.39 ^o/oo, SD = 9.96). In addition, our results indicated a relationship between tree size and xylem isotope ratio. For the Loblolly pine, D-values became more negative as tree circumference increased (r = -.87, p = .13). In contrast, the larger circumferences of the Virginia pine were correlated with less negative D-values (r = .92, p <.05). In support of this trend, average midday water potentials taken during dry conditions indicate that young Virginia Pines presented a slightly more favorable water status (-5.5bars) compared to that of young loblolly pines (-8.5bars). Taken together, these results suggest that the two pine species alter their water acquisition patterns depending on soil moisture and use different growth strategies that may allow them to partition resources.

KEY WORDS: Pinus virginiana , Pinus taeda, stable-isotopes, water