Plant-soil Interactions in Coastal Systems

Relatively little is known about plant-soil interactions in marine ecosystems compared to terrestrial ecosystems, yet there is compelling evidence from multiple coastal habitats to suggest that linkages between plants and associated bacteria and fungi may play a key role in species interactions and community dynamics. Further, a better understanding of plant-soil linkages in marine ecosystems may inform and improve future restoration efforts and practices, as well as providing a unique opportunity to explore the importance of intraspecific variation in plant-soil interactions given that many coastal systems are dominated by a single species.

In collaboration with Dr. Catherine Gehring at Northern Arizona University and Dr. Christina Richards at the University of South Florida, we conducted a series of studies focusing on the foundational plant Spartina alterniflora and associated fungal and microbial species with funding from NSF IOS. In a greenhouse experiment assessing fungal effects on host plants, we explored how Spartina genotypic identity affected plant response (e.g., survival, stem density, stem height) to inoculation with Lulwoana, a common root-associated dark septate endophytic (DSE) fungi (Hughes et al. in review). We have also examined plant effects on microbial communities, comparing the effects of Spartina genotypic identity and population history on soil microbial community structure and composition in a greenhouse common garden study (Hanley et al. in review).

In addition, we have explored how the relationship between Spartina and its root-associated fungi (RAF) varies within a population and across environmental and stress gradients using a combination of field reciprocal transplants and greenhouse experimental manipulations. For this, we focused on comparisons between short- and tall-form Spartina (the former being located in the high marsh, and the latter being located in the low marsh adjacent to tidal creeks) and RAF found in the low and high marsh to assess how saltmarsh plant-fungal interactions vary across salinity and stress gradients at relatively small spatial scales

Currently, we are also exploring similar questions about plant-soil interactions in seagrass beds (focusing on Zostera marina) with new funding from NSF BIO-OCE.

Past Work in Marsh Systems

With funding from the National Science Foundation, I investigated interactions among plant (Spartina alterniflora) genetic diversity and the species diversity of associated plants and animals in salt marsh systems in the Gulf of Mexico. We experimentally examined the independent and interactive effects of two Spartina facilitators - fiddler crabs (Uca sp.) and the ribbed mussel (eukensia demissa) - see Hughes et al. 2014 Oikos. We also discovered trait variation within the key consumer species Littoraria (Hughes et al. 2015 Ecology and Evolution).

Plant species diversity can also play an important role in marsh systems. Field and laboratory experiments in our lab demonstrate that the presence of a neighboring plant species, Juncus roemerianus, can mediate the relationship between Spartina and its primary consumer, the marsh snail Littoraria (Hughes 2012, Ecology). Current experiments are testing how Spartina genetic identity further modulates these relationships. Given that snails can cause widespread declines of Spartina, these results have important restoration implications.

Conventional wisdom holds that genetic diversity is low within salt marsh plants. However, we find high numbers of unique genotypes of Spartina alterniflora in natural marshes, even at small spatial scales (Hughes and Lotteries 2014 MEPS). The number and traits of these genotypes can have important effects on marshes both above and below ground (Hughes 2014 J. Ecology).

Chronic nutrient enrichment as a result of human activities has contributed to the loss of salt marsh ecosystems. Current experiments in the Hughes Lab are testing how long-term nutrient addition effects Spartina genetic diversity and phenotypic trait variation. This work is in collaboration with the TIDE project, a long-term, ecosystem-level fertilization experiment at the Plum Island Estuary in Rowley, MA. Understanding how coastal eutrophication affects genetic diversity and trait variation of this marsh foundation species has important implications for primary production, species interactions, and ecosystem processes.