Extended phenotype of an ecosystem engineer: Variation across cultivated and wildtype clones influences processes of erosion

Background/Question/Methods

Functional traits represent underlying mechanisms that permit biota to influence ecosystem attributes, thus functional composition and diversity can be strong predictors of ecosystem properties. While the species comprising a community are often treated as its units of functional variation, this fails to capture large effects that can arise from trait variation among individuals within numerically dominant or keystone species.

One such dominant plant found in coastal salt marshes is the grass species Spartina alterniflora—a well-recognized ecosystem engineer that interacts with its environment in diverse ways.  Transplantion studies have demonstrated that S. alterniflora ecotypes can regulate ecosystems independently of the local environment, and the geographic distribution of genetic variation largely parallels variation in plant performance attributable to heritable functional traits.

Changes in hydrology and water quality have contributed to extensive wetland loss along the Atlantic and Gulf coasts of North America, and have generated highly erosional environments. To examine the influence of S. alterniflora genotypic identity on processes of erosion, field transplantation studies and controlled greenhouse experiments were conducted. Plant traits, soil properties, accretion/subsidence, and rates of land loss were compared for a number different wildtype and cultivated clones.

Results/Conclusions

We found significant differences in rates of erosion for wildtype and cultivated S. alterniflora genotypes. Differences in erosion corresponded to variation in soil properties including shear strength, decomposition, compaction, and subsidence. These properties in turn were correlated with differences in plant traits such as belowground biomass, root elasticity and tensile strength. Genetic and phenotypic variation in S. alterniflora thereby establishes the functional basis an extended phenotype in coastal salt marshes. These results elucidate the importance of genetic variation to salt marsh functioning, help to understand the relationship between evolutionary and ecological processes in these systems, and suggest appropriate actions regarding marsh restoration and management decisions.