Ecologists have a longstanding interest in the relationship between biodiversity and ecosystem processes. More recently, it has been proposed that intraspecific richness can act as a functional surrogate for interspecific richness in species-depauperate systems. Salt marshes provide a model system for exploring the effects of genotypic richness on ecosystem processes, given that they are dominated by relatively few, small, clonally-spreading plants, and are highly amenable to experimental manipulation. They are also an excellent environment in which to examine how intraspecific diversity might modulate ecosystem response to global change. The persistence of salt marshes in the face of anthropogenic sea-level rise will be determined in part by plant response to increased tidal inundation, as plant productivity contributes to marsh accretion directly via organic matter inputs and indirectly by trapping inorganic sediment. Because of extensive intraspecific quantitative trait variation among genotypes of Spartina alterniflora, the foundational species in low elevation marshes, as well as limited evidence that clonal productivity is dependent on elevation, we hypothesized that productivity would vary among clones in response to tidal inundation. To test this hypothesis we collected stems from eight different clones in a New England salt marsh and grew them for sixteen weeks in flow-through seawater tanks, simulating a natural tidal regime or sea level rise.
Results/Conclusions
We found a significant effect of hydrology on aboveground biomass production, with the specific nature of the effect varying by genotype (i.e., a significant genotype x hydrology interaction). In about half of our experimental genotypes, increased tidal inundation reduced productivity, whereas the remaining genotypes showed the reverse trend. We found similar results for plant stem height and number of stems. However, high mortality dramatically reduced replication in our study and these results will need to be confirmed in a future experiment. Nonetheless, our data suggest that clones vary in their response to increased tidal inundation. We are also examining clonal patterning at our study site – in order to provide a spatially-explicit framework within which to consider the mechanistic responses of plants gleaned from our experimental work. Because genotypic diversity can be critical in determining community resistance to, or recovery following, disturbance (e.g., as has been shown for eel grass, Zosteria marina, communities), understanding variation in the clonal response of marsh plants to flooding may be important in predicting marsh response to anticipated rises in sea level.
