PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Water relations of Populus deltoides in response to varying nutrient and water availability.

Stokes, Thomas^*,1, Samuelson, Lisa¹, Coleman, Mark², Stanturf, John³, Leininger, Ted⁴, ¹ Auburn University, Auburn, AL, USA² USDA Forest Service, Aiken, SC, USA³ USDA Forest Service, Athens, GA, USA⁴ USDA Forest Service, Stoneville, MS, USA

ABSTRACT- We tested the hypothesis that increased nutrient and water availability would increase total plant hydraulic conductance in three-year-old Populus deltoides clones. Sap flux density and leaf water potential were studied in response to resource availability and clonal source (MS clone and east TX clone) at two different research installations: one in Aiken, SC and the other in Stoneville, MS. Resource availability was manipulated by irrigation and fertilization and the same clones were planted at each site. Aboveground primary productivity and LAI were increased by increasing resource availability at both sites, and production and LAI were two times greater at the MS site than the SC site. Height and diameter averaged 5.5 m and 5.75 cm, respectfully, for the SC site while for the MS site average height and diameter were 10 m and 9.4 cm, respectfully. Average maximum seasonal LAI was 2 m² m^-2 at SC and 4 m² m^-2 at MS. Although stand development differed between sites, sap flux density by clone and treatment were similar between sites and ranged between 60 and 100 g m^-2 s^-1. Predawn and midday leaf water potentials were similar between clones, treatments and sites, and midday water potential averaged -1.5 MPa. Cumulative stand-level transpiration was 225 mm in SC stands versus 500 mm in MS stands. Total plant hydraulic conductance did not vary with resource availability and was on average 3 mol m^-2 s^-1 MPa^-1 in SC trees and 7 mol m^-2 s^-1 MPa^-1 in MS trees. These results indicate that resource availability had a greater influence on growth than whole tree water relations and that total plant hydraulic conductance may increase with increasing plant size in Populus deltoides.

Key words: hydraulic conductance, sap flux density, cottonwood, water potential