HR: 15:25h
AN: B13B-08    [Abstracts]
TI: Spatial Patterns of Plant δ¹³C and δ¹⁵N Along a Topoedaphic Gradient in a Subtropical Savanna Landscape
AU: * Bai, E
EM: ebai@tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Boutton, T W
EM: boutton@neo.tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Liu, F
EM: asherliu@tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Wu, B
EM: xbw@tamu.edu
AF: Texas A&M University, Department of Rangeland Ecology and Management, College Station, TX 77843-2126 United States
AU: Archer, S R
EM: sarcher@ag.arizona.edu
AF: University of Arizona, School of Renewable Natural Resources, Tucson, AZ 85721-0043 United States
AB: δ¹³C and δ¹⁵N values of plants are powerful tools in physiological ecology, ecosystem science, and global biogeochemistry, yet we know relatively little about their variation and controls at the landscape scale. In this study, we investigated landscape-scale spatial variations in the foliar isotopic composition of 3 woody plant species across a 308 m topoedaphic gradient, along which soil texture and plant resources (water and nitrogen availability) varied from upland (86 m) to lowland (84 m) portions of the landscape. The study was conducted in a subtropical savanna at the La Copita Research Area, approximately 60 km west of Corpus Christi, TX. Foliar δ¹³C, δ¹⁵N, leaf nitrogen concentration ([N]), and specific leaf area (SLA) were measured on all individuals of Prosopis glandulosa, Condalia hookeri, and Zanthoxylum fagara present within a belt transect 308 m long x 12 m wide. Soil texture, available soil moisture, and total N were measured at 1 m intervals along the center-line of the belt transect. Clay content, available soil moisture, and soil total N were all negatively correlated with elevation along the transect. Leaf δ¹³C and δ¹⁵N values for all 3 species increased by 1-4 o/oo with decreasing elevation along the transect. Contrary to theory and previous studies, δ¹³C values were highest where soil water was most available, suggesting that some other variable could be overriding or interacting with water availability. Foliar [N] appeared to exert the strongest control over landscape-level variation, and was positively correlated with δ¹³C of all species (R ² = 0.58, p<0.0001). Since leaf [N] is positively related to photosynthetic capacity, plants with high [N] are likely to have low Ci/Ca ratios and therefore higher δ¹³C values. δ¹⁵N values of Zanthoxylum and Condalia were positively correlated with leaf [N] and soil water availability; however, these relationships were absent for Prosopis, an N-fixing tree legume. We speculate that the relationship between δ¹⁵N and leaf [N] and soil water may reflect the fact that plants with high δ¹⁵N values occurred on lower-lying portions of the landscape with relatively high N-transformation rates where soil mineral N was both relatively available and ¹⁵N-enriched. The lack of variation in δ¹⁵N values of Prosopis suggests that it may be somewhat uncoupled from these processes because it is an N-fixer. Results of this study indicate that N-availability plays an important role in landscale scale variation in plant δ¹³C and δ¹⁵N.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005