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Effects of nitrogen and phosphorus availability on Dicerandra (Lamiaceae) congeners with different life-histories.
Merchant, Amethyst*,1, Mulkey, Stephen1, 1 University of Florida, Gainesville, Florida
ABSTRACT- Endemic to the southeastern United States, the genus Dicerandra consists of nine species displaying different growth habits in specific ecosystems. Annuals range throughout recently disturbed sandhill habitats of Georgia and northern Florida. Perennials are limited to small, geographically isolated scrub habitats along relict beach ridges and dunes within Florida's peninsula. Scrub has been described as nutrient deficient, notably in phosphorus, relative to other habitats. We applied a factorial experiment crossing three levels of nitrogen and phosphorus within two blocks to individuals of D. densiflora (herbaceous annual) and D. cornutissima (semi-woody evergreen perennial) to determine how variation in nutrient availability affects growth, biomass allocation, gas exchange, and nutrient concentration of tissues. Annuals were expected to increase growth and fruit production with changes in biomass allocation while perennials exhibit greater nutrient accumulation and little change in growth and biomass allocation as nutrients increase. Total dry weight increased with nutrient availability for both. Biomass allocation to floral structures (including seeds) in D. densiflora was relatively consistent throughout treatments. Stem, leaf, and root weight ratios were also similar throughout treatments for this annual. Root : shoot ratio decreased significantly for D. cornutissima as nitrogen availability increased. Root : shoot ratio was significantly higher in D. cornutissima. Significant differences in maximum photosynthetic rates (area-based) were not apparent due to great variability within treatments although larger rates were expected as phosphorus availability increased. Specific leaf area, branch production, and tissue nutrient concentrations will be discussed in reference to interactions between nitrogen and phosphorus availability.
Key words: perennial, biomass allocation, annual, nutrient availability