HR: 1340h
AN: B43D-0300    [Abstracts]
TI: Nitrogen Uptake Preferences by Plants in Arid and Semiarid Ecosystems
AU: * Macko, S
EM: sam8f@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Charlottesville, VA 22904
AU: Wang, L
EM: lw6t@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Charlottesville, VA 22904
AU: D'Odorico, P
EM: paolo@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Charlottesville, VA 22904
AB: In arid and semiarid ecosystems like African savannas, nutrient availability varies spatially and temporally and nutrients are considered to be a major limiting factor for growth in addition to water availability. Preference for different nitrogen forms presumably enhances the survivorship and fitness of plants since the relative abundances of nitrate and ammonium varies between drier and wetter areas. To test the hypothesis that species developing in dry areas will prefer nitrate whereas species growing in wet areas will prefer ammonium, a controlled experiment using a greenhouse was undertaken. Six native African grass species from different precipitation regimes were used in this study. Two species were from relatively wet areas (Pandamatenga, Botswana, precipitation = 698 mm/year), two were from relatively dry areas (Tshane, Botswana, precipitation = 232 mm/year) and other two were from intermediate environments (Ghanzi, Botswana, precipitation = 400 mm/year). The grass seeds were collected in the field during the dry season of 2004 and using germination pans, were grown in a greenhouse. When individuals were mature, they were transferred into plastic pots (one individual per pot) containing commercial sand. After one week period of adjustment, a ¹⁵N labeled fertilizer (NH₄NO₃) was applied. The total N applied as fertilizer was comparable to the mineralized field N based on a calculated rate for the top 15 cm of soil. A pair of individual plants was treated as an experimental unit. Each plant received the same amount of total N fertilizer, but one was ¹⁵NO3 labeled and another was ¹⁵NH₄ labeled. Nutrient uptake preference was determined by the ¹⁵N difference between pairs. The preliminary results with three species shows that, the individuals from dry area ( Enneapogon cenchroides from Tshane) has significantly higher foliar ¹⁵N signatures in the ¹⁵NO₃ labeling treatment (p = 0.0103) and no difference in root ¹⁵N signatures. Whereas individuals from the wet area ( Schmidtia pappophoroides and Leptocarydion vulpiastrum from Pandamatenga) showed significantly higher root ¹⁵N signatures in the ¹⁵NH₄ labeling treatment (p = 0.0248 and p = 0.0025, respectively) but no difference in foliar ¹⁵N signatures. Our results provide direct evidence of plant nitrogen uptake preference and suggest the possibility that this preference is associated with the abundance of the different forms of nitrogen in the different habitats. Furthermore, savanna plants along precipitation gradients, as seen in the Kalahari Transect in southern Africa, may have developed mechanisms to more fully utilize the types of nitrogen typically available in the associated soils.
DE: 0400 BIOGEOSCIENCES
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1851 Plant ecology (0476)
SC: Biogeosciences [B]
MN: Fall Meeting 2005