HR: 1340h
AN: B23C-1506    [Abstracts]
TI: Patterns and Implications of Plant-Soil C and N Isotopic Compositions in African Savanna Ecosystems
AU: * Wang, L
EM: Lixin@virginia.edu
AF: University of Virginia, 291 McCormick Rd, Department of Environmental Sciences, Charlottesville, VA 22904, United States
AU: Macko, S A
EM: sam8f@virginia.edu
AF: University of Virginia, 291 McCormick Rd, Department of Environmental Sciences, Charlottesville, VA 22904, United States
AU: D'Odorico, P
EM: paolo@virginia.edu
AF: University of Virginia, 291 McCormick Rd, Department of Environmental Sciences, Charlottesville, VA 22904, United States
AU: Ries, L
EM: lries@bren.ucsb.edu
AF: University of California, Santa Barbara, Bren School of Environmental Science and Management, Santa Barbara, CA 93103, United States
AB: Southern African savannas are mixed plant communities where C₃ trees co-exist with C₄ grasses. Owing to differences in their morphology and physiology, trees and grasses have different access to nutrients and water and different efficiency in the use of these resources. It is still unclear how climate variables such as the mean annual precipitation may affect the relative efficiency of grasses and trees in the use of water and soil nutrients such as nitrogen. In this study, the foliar δ¹⁵N and δ¹³C were used as indicators of nitrogen uptake and of water use efficiency, respectively, to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants. To this end, patterns of foliar δ¹⁵N and δ¹³C for both C₃ and C₄ plants as well as patterns of soil δ¹⁵N and δ¹³C in canopy and intercanopy areas were investigated both in the dry and in the wet season along the Kalahari megatransect, where a distinct rainfall gradient exists on a homogeneous soil substrate. Foliar δ¹⁵N signatures increased as aridity heightened for both C₃ and C₄ plants in both seasons, although the magnitude of the increase was different for these two plant functional types. Soil δ¹⁵N also significantly increased with aridity. Foliar δ¹³C signatures increased with aridity for C₃ plants in the wet season but not in the dry season, while in C₄ plants the relation between foliar δ¹³C signatures and aridity was more complex and non-linear in both seasons. The consistent higher foliar δ¹⁵N for C₃ plants suggests that C₄ plants are superior competitor for N. The different foliar δ¹³C relationships with rainfall for the C₃ plants and C₄ plants may indicate that the C₃ plants have an advantage over C₄ plants when competing for water resources. The differences in water and nitrogen use between C₃ and C₄ plants likely collectively contribute to the tree-grass coexistence in savannas.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0476 Plant ecology (1851)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting