Document: JAV-3-33-25

Tree species of the southeastern US sandhills differ in root proliferation responses to resource availability.

ESPELETA, J.F.* and L.A.DONOVAN

University of Georgia, Athens, GA 30602, USA ¹

Abstract:
The sandhills of the southeastern US present deep sandy soils with poor water and nutrient retention capacity. Longleaf pine (Pinus palustris) is the dominant overstory tree in xeric and mesic areas. Two oak species, Quercus laevis and Q. marilandica, are co-dominants that are distributed differentially in xeric and mesic sites, respectively. Based on resource economy theory, we predicted that the species from more infertile habitats (Q. laevis) would exhibit lower growth rates, higher tissue retention rates and lower response to changes in resource availability than the species from more fertile habitats (Q. marilandica) or the more generalist species (P. palustris). We investigated these predictions in a six-month greenhouse study by exposing seedlings in sand culture to four regimes of resource supply (water and nutrients): 1) consistently low resources, 2) consistently high resources, 3) shifting from high to low resources, and, 4) shifting from low to high resources. The shift in resource regimes occurred at four months after the start of the experiment. Maximum leaf photosynthesis (Amax) was measured at four months. For the four to six month interval, root growth was measured as the length of the roots visible in transparent windows in the culture pots. Leaf turnover rates and root death were recorded throughout the experiment. Analysis of root growth data by a two-way ANOVA indicated significant species, treatment, and species by treatment effects. The data suggest that root growth in all species was lower under low resource supply, and that proliferation was lowest for Q. laevis when comparing among species in the high resource treatment. Q. laevis also appeared to have the least reduction in root growth in response to decline in resource supply. For the oaks, Q. laevis also exhibited the lowest Amax and leaf turnover rate and the highest leaf longevity. Root death was not observed in significant amounts. Our results are consistent with the resource economy theory and confirm the existence of different strategies of resource use, and of analogies between aboveground traits (leaf turnover) and belowground traits (root proliferation).

Keywords: belowground dynamics, leaf lifespan, nutrients, Pinus palustris , Quercus laevis, Quercus marilandica, resource economy, resource use, root death, root growth, root proliferation, water

This abstract is being presented at: 3:30 PM in session:
ROOT PROCESSES