PARENT SESSION
Poster Session 32: Biogeochemistry
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of time since fire on ¹⁵N natural abundance of Florida scrub vegetation.

Schafer, Jennifer^*,1, Mack, Michelle¹, ¹ University of Florida, Gainesville, Florida

ABSTRACT- Partitioning of nitrogen (N) resources may allow for the coexistence of plant species in N-poor ecosystems, and plant N sources are often inferred from measurements of the natural abundance of ¹⁵N in plant tissues. Disturbances such as fire can change N availability, which may alter N partitioning. Little is known about N partitioning in the fire-adapted scrubby flatwood communities of Florida, which occur on sandy, nutrient-poor soils. We collected leaves of eleven common scrubby flatwood species from sites burned 3 and 12 years previously and measured foliar ¹⁵N and %N. Mean ¹⁵N values ranged from -4.95 to 2 ‰, suggesting that plants are partitioning N spatially or by form (e.g. ammonium vs. nitrate). Oak species (Quercus chapmanii, Quercus geminata, and Quercus inopina) had the lowest mean ¹⁵N (-4.15 ‰), which may be related to their associations with ectomycorrhizae, while the sedge Rhynchospora megalocarpa had the highest ¹⁵N (1.99 ‰). Mean foliar %N was lowest in R. megalocarpa (0.95 %) and highest in Palafoxia feayi (1.95 %). Overall, plants had higher ¹⁵N and lower foliar %N three years compared to 12 years post-fire; however, only a few species differed significantly in either ¹⁵N or %N with time since fire. Rhynchospora megalocarpa was more enriched in ¹⁵N three years post-fire, but did not differ in %N. Three of the four ericaceous species studied (Gaylussacia dumosa, Lyonia lucida, and Vaccinium myrsinities) had higher foliar %N 12 years post-fire, but did not differ in ¹⁵N. Our results suggest that partitioning of N sources may contribute to coexistence of scrubby flatwood species and that time since fire may affect N partitioning and plant N nutrition in these fire-adapted plant communities.

Key words: fire, Florida scrub, ¹⁵N natural abundance, nitrogen partitioning