Christina Richards,
PhD student
Department of Botany
The University of Georgia
richards@dogwood.botany.uga.edu
 Salt marsh habitats are important for the health of fisheries, protection against storm damage and potential filters against toxins entering marine and ground water. Many salt marsh ecology studies have experimentally identified a strong response of salt marsh plants to gradients of soil water content and salinity (reviewed in Pennings and Bertness 1999). However, we still lack an understanding of how plants respond morphologically and physiologically to these gradients and the genetic basis of their responses. Classic and recent studies have documented that populations of plants within a few meters of each other can diverge remarkably in response to severe selection along stressful environmental gradients (Antonovics and Bradshaw 1970, Antlfinger 1981, Dyer and Rice 1997, Nagy and Rice 1997). The broad objective of my studies is to describe the physiological traits and genetic patterns underlying salt marsh plant distribution across steep environmental gradients.
The Garden Club of America has funded these specific objectives, essential to my dissertation program:
Objective 1. Examine morphological variability in salt marsh plants and determine if this variability correlates with environmental factors (salinity, flooding, nutrients).
The GCA has funded and continues to fund my analysis, presentation and submission for publication of the morphological data I collected on the twelve marsh species on Sapelo Island, GA in the summer of 1999. To summarize, there was significant correlation between soil parameters and morphological characteristics in the 12 marsh species. Specifically, salinity significantly predicts height in 8 of 11 species and leaf area in 6 of 12 species. Water content predicts height in 6 of 11 species and leaf area in 2 of 12. Ash content predicts height in 3 of 11 species and leaf area in 2 of 12. I also found that between species, comparisons of CVs of plant traits and soil parameters do not support the hypothesis that species that occupy the broadest range in soil parameters have the broadest range in phenotype . This data was presented at the Ecological Society of America's annual meeting in Snowbird, UT this summer and is currently being prepared for publication.
Objective 2. Determine if intraspecific phenotypic differences are heritable.
The GCA is funding the harvest and analysis of a greenhouse project with Borrichia frutescens. I grew Borrichia in a full factorial design 2 purported ecotypes (short and tall) * 2 salinity treatments * 7 families/ ecotype * 16 individuals/ family (8 individuals/ family/ salinity). The results of this study will determine if the morphological and physiological phenotypic differences of these purported ecotypes are heritable or induced by environment.
Objective 3. Determine if genetic differences among marsh plants correspond to environmental gradients.
The GCA funded my work this summer to isolate allozyme markers for 3 dominant marsh plants: Spartina alterniflora, Borrichia frutescens, and Distichlis spicata . I found 12-14 polymorphic loci for each of these species which will allow me to identify the clonal size of these species as well as standard population genetics statistics. I will then determine if there is a correlation between the level of genetic differentiation within and among populations and the same edaphic factors from Objective 1
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