THE GROWTH, REPRODUCTION, AND NUTRIENT DYNAMICS OF TWO POCOSIN SHRUBS, THE EVERGREEN LYONIA LUCIDA AND THE DECIDUOUS ZENOBIA PULVERULENTA (PROFILE-ANALYSIS, WETLANDS, FIRE)

Evergreenness is one of several characters common to plants adapted to nutrient-poor soils; others include low growth and reproductive rates and high efficiency of nutrient use. In the nutrient-deficient pocosins of the southeastern United States coastal plain, evergreen and deciduous shrubs co-occur, although each dominate at different times in the 20 - 40 year fire-cycle which controls nutrient availability. Despite their difference in growth form, the evergreen Lyonia lucida and the deciduous Zenobia pulverulenta both exhibited no sexual reproduction, unusually high efficiency of nutrient use, and similar rates of growth, in a 30-year-old stand.; The two species responded differently, over two years, to a single application of three levels each of nitrogen and phosphorus in a factorial design. Nitrogen addition increased Zenobia growth in the first season but did not affect Lyonia growth. It did not induce flowering in either species. Foliar nitrogen content, expressed on a leaf area basis, remained remarkably constant over all treatments and species. Phosphorus addition increased growth in Zenobia during the first season and triggered flowering and branch production in the second, suggesting an effect of phosphorus meristem activity, whereas Lyonia exhibited no growth or reproductive response. Phosphorus addition increased foliar phosphorus content in both species to the same extent.; Compensatory growth response to fire in plants resprouting from underground rhizomes may be due to destruction of aboveground parts, to fertilization, or both. A clipping and fertilization experiment demonstrated no compensatory growth in response to artificial defoliation in either species after one season. Both species produced more, larger stems when fertilized.; I conclude that, rather than being adapted to different nutrient regimes, both species are adapted to highly competitive conditions in which fire occasionally destroys aboveground parts, increases the likelihood of seedling establishment, and enhances the availability of the limiting nutrient phosphorus.; Profile analysis of variance was used in the two experiments reported here, to compare treatment-responses between species because both species occurred within each plot and may have interacted differently under each treatment. The utility, assumptions, and method of calculating this statistical analysis are discussed.