Does ecotypic-based genetic diversity improve productivity? A mesocosm study with Spartina alterniflora

Background/Question/Methods

Increased genetic diversity of habitat-forming species correlates with high productivity and disturbance resiliency and recovery. Typically, salt marsh restoration utilizes grasses from a single donor site, yielding low genetic diversity because of clonal reproduction. Creating a marsh with ecotypes from multiple sites should be an inexpensive, efficient way to increase genetic diversity, which may increase productivity and resiliency of the restored plant canopy. To quantify the benefits of increased genetic diversity within a single plant species and understand response to disturbance, I performed a mesocosm experiment utilizing ecotypes of Spartina alterniflora from three locations on the northeastern Texas coast. I compared growth patterns among monoculture, diculture, and triculture treatments across a range of salinities (10, 20, 30 ppt) during June-October 2012. Plant morphological characteristics were recorded to compare monoculture and polycuture performance and response to salinity.

Results/Conclusions

Plants in both polycultures exhibited an increase in inflorescence density and root biomass relative to monocultures. Inflorescence produced by tricultures was at least 20% greater than monoculture inflorescence density across all salinities. As salinity increased, root biomass in monocultures decreased by 50% while both polycultures increased by 25%. Throughout the experiment, significant impacts of salinity stress were noted for all culture treatments. For example, after one hundred days stem production decreased by 40% at the highest salinity relative to 20 ppt (p-value= 0.04). Although both salinity and diversity affected the metrics, there was not a statistical interaction between these treatments so they were independent of each other. Based on these trends, plant canopy features might be enhanced, even in stressful events, if marsh planting utilizes multiple ecotypes.